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Purpose: To quantify the effects of three vision rehabilitation training approaches on improvements in reading performance., Methods: Thirty subjects with AMD participated in the training portion of the study. The median age of the subjects was 79 years (range, 54-89 years). The three training modules were: Visual Awareness and Eccentric Viewing (module 1), Control of Reading Eye Movements (module 2), and Reading Practice with Sequential Presentation of Lexical Information (module 3). Subjects were trained for 6 weekly sessions on each module, and the order of training was counterbalanced. All subjects underwent four assessments: at baseline and at three 6-week intervals. Reading performance was measured before and after each training module. A separate group of 6 subjects was randomly assigned to a control condition in which there was no training. These subjects underwent repeated assessments separated by 6 weeks., Results: Reading speeds decreased by an average of 8.4 words per minute (wpm) after training on module 1, increased by 27.3 wpm after module 2, and decreased by 9.8 wpm after module 3. Only the increase in reading speed after module 2 was significantly different from zero. Sentence reading speeds for the control group, who had no reading rehabilitation intervention, was essentially unchanged over the 18 weeks (0.96 ± 1.3 wpm)., Conclusions: A training curriculum that concentrates on eye movement control increased reading speed in subjects with AMD. This finding does not suggest that the other rehabilitation modules have no value; it suggests that they are simply not the most effective for reading rehabilitation.

To investigate the relationship between depression and quantitative measures of visual function, we recruited 18 subjects with central scotomas from macular degeneration who were enrolled in a reading rehabilitation program. Psychological batteries and reading assessments were administered prior to rehabilitation; reading assessments and a measure of adaptation to vision loss were administered following rehabilitation. We investigated relationships between reported levels of depressive symptoms and reading and adaptation outcome measures by using Pearson product moment correlation analysis. Results revealed a significant relationship between depression levels and reading acuity difference scores (r(16) = 0.54, p = 0.02) and changes in adaptation to vision loss levels (r(16) = 0.62, p = 0.01), suggesting that those who reported greater depressive symptoms did not respond as well functionally to reading rehabilitation but reported greater improvement in levels of adaptation to vision loss following rehabilitation. Future research should focus on defining standard methods to assess and remediate depression as part of the rehabilitation process.

Purpose: To examine if vision in subjects with macular heterotopia (MH) secondary to retinopathy of prematurity (ROP) is related to anatomical macular structure., Methods: Six subjects with MH who were between 18 years and 65 years of age and three age-matched subjects with normal vision were recruited for the study. Vision and macular structure of the better eye of the subjects with MH and the dominant eye of age-matched subjects with normal vision were assessed. High contrast visual acuity and contrast sensitivity were measured using Early Treatment of Diabetic Retinopathy Study and Pelli-Robson charts, respectively. The Micro Perimeter (Nidek Technologies MP-1) was used to assess macular sensitivity and fixation stability. Using optical coherence tomography, macular thickness and relative retinal thickness at fixation were measured., Results: Subjects with MH had significantly reduced visual acuity and macular sensitivity compared with age-matched subjects with normal vision. In comparison with their age-matched counterparts, subjects with MH had significantly increased macular thickness and increased relative retinal thickness at fixation. A normal foveal architecture was absent in three subjects with MH (50%)., Conclusion: Patients with MH secondary to ROP have increased macular thickness and reduced vision.

Purpose: To investigate the location and fixation stability of preferred retinal locations (PRLs) in patients with macular disease, and the relationship among areas of abnormal fundus autofluorescence, the PRL and visual sensitivity., Methods: Fifteen patients (15 eyes) were studied. Seven had Stargardt disease, 1 bull's eye maculopathy, 5 age-related macular degeneration, 1 Best disease, and 1 pattern dystrophy. All tested eyes had areas of abnormal fundus autofluorescence. The PRL was evaluated with fundus photography and the Nidek microperimeter. Visual field sensitivity was measured with the Nidek microperimeter., Results: Of the 15 eyes, 4 had foveal and 11 had eccentric fixation. Eccentric PRLs were above the atrophic lesion and their stability did not depend on the degree of eccentricity from the fovea. Visual sensitivity was markedly decreased in locations corresponding to hypofluorescent areas. Sensitivity was not decreased in hyperfluorescent areas corresponding to flecks but was decreased if hyperfluorescence was in the form of dense annuli., Conclusion: Eccentric PRLs were in the superior retina in regions of normal fundus autofluorescence. Fixation stability was not correlated with the degree of eccentricity from the fovea. To assess the outcomes of treatment trials it is important to use methods that relate retinal morphology to visual function.

Purpose: To test whether choroideremia carriers have a mosaic pattern of retinal dysfunction, as noted in carriers of X-linked recessive retinitis pigmentosa and X-linked retinoschisis., Design: Prospective observational case series., Participants: Seven obligate choroideremia carriers (age range, 18-72) with visual acuity (VA) of 20/25 or better were recruited into the study., Methods: The carriers underwent VA testing (Snellen chart), ophthalmic examination, Humphrey visual field (VF), and multifocal electroretinographic testing. The amplitude and implicit time scales were measured by the algorithm of Hood and Li. The amplitude measures (a scales) and implicit time measures (t scales) were reported abnormal when they were >2 standard deviations above the mean of age-similar normally sighted control subjects., Main Outcome Measures: Mapping of local 103 electroretinographic response amplitudes and implicit times., Results: Only 1 of the 7 carriers showed abnormal Humphrey VF thresholds, whereas 6 of the 7 carriers showed a mosaic pattern of retinal dysfunction measured by multifocal electroretinographic testing. All 6 carriers showed statistically significant implicit time delays, whereas 4 carriers showed statistically significant amplitude reductions and implicit time delays (P<0.05 to P<0.0006). One carrier with a normal-appearing macula and normal Humphrey VF showed a cluster of statistically significant implicit time delays within the macula (P<0.05 to P<0.0006). The overall extent of local electroretinographic abnormalities corresponded to the severity of ophthalmoscopically apparent pigmentary changes. The one carrier with mild threshold elevation on Humphrey VF testing showed the most ophthalmoscopically apparent extensive fundus pigmentary changes., Conclusions: We demonstrated a mosaic pattern of retinal cone dysfunction in carriers of choroideremia. Our findings are consistent with the Lyon hypothesis of random X-chromosome inactivation. Multifocal electroretinographic testing is potentially sensitive to detect local retinal dysfunction in choroideremia carriers even in those with a normal-appearing macula and good VA.

Purpose: To investigate possible adverse effects of a yellow-tinted intraocular lens (IOL) on scotopic sensitivity and hue discrimination., Setting: Departments of Ophthalmology, Columbia University and New York University School of Medicine, New York, New York, USA., Methods: Nine patients with a yellow-tinted IOL in 1 eye and a colorless ultraviolet IOL in the fellow eye and 9 young phakic subjects with and without a yellow-tinted clip-on lens were tested. Hue discrimination was measured with the Farnsworth-Munsell (FM) 100-hue test. Dark-adapted thresholds to 440 nm, 500 nm, and 650 nm lights were measured at 23 locations using a modified Humphrey perimeter, and dark-adapted thresholds to white light were measured at 15 degrees temporal retina., Results: In the 9 patients, there were no significant differences in dark-adapted sensitivities to 440, 500, 650 nm, or white-light stimuli and no differences in FM 100-hue error scores between eyes with yellow-tinted IOLs and those with colorless IOLs. Similarly, in young phakic subjects, there were no significant differences in FM 100-hue error scores or dark-adapted sensitivity to the white light with and without the yellow-tinted clip-on lens. However, with the clip-on lens, mean sensitivities to the 440 nm, 500 nm, and 650 nm stimuli were significantly decreased by 2.7 to 2.8 dB, 0.7 to 1.0 dB, and 0 to 1.2 dB, respectively., Conclusion: Results suggest that implantation of a yellow-tinted IOL has non-significant effect on scotopic sensitivity and hue discrimination.

Purpose: To determine whether retinal dysfunction in obligate carriers of X-linked retinoschisis (XLRS) could be observed in local electroretinographic responses obtained with the multifocal electroretinogram (mfERG)., Methods: Nine obligate carriers of XLRS (mean age, 46.2 years) were examined for the study. Examination of each carrier included an ocular examination and mfERG testing. For the mfERG, we used a 103-scaled hexagonal stimulus array that subtended a retinal area of approximately 40 degrees in diameter. The amplitudes and implicit times in each location for the mfERG were compared with the corresponding values determined for a group of 34 normally-sighted, age-similar control subjects., Results: Mapping of 103 local electroretinographic response amplitudes and implicit times within a central 40 degrees area with the mfERG showed regions of reduced mfERG amplitudes and delayed implicit times in two of nine carriers., Conclusions: The mfERG demonstrated areas of retinal dysfunction in two carriers of XLRS. When present, retinal dysfunction was evident in the presence of a normal-appearing fundus. Multifocal ERG testing can be useful for identifying some carriers of XLRS.

Purpose: To quantify the extent of visual function losses in patients with North Carolina Macular Dystrophy (NCMD) and to demonstrate the importance of accounting for eccentric fixation when making comparisons with normal data., Methods: Five patients with NCMD who were from a single family were examined. Multifocal electroretinograms (mfERGs) and psychophysical assessments of acuity and luminance visual field sensitivities were measured throughout the central retina. Comparisons of responses from equivalent retinal areas were accomplished by shifting normal templates to be centered at the locus of fixation for each patient., Results: Losses of psychophysically measured visual function in patients with NCMD extend to areas adjacent to the locations of visible lesions. The multifocal ERG amplitude was reduced only within the area of visible lesion. Multifocal ERG implicit times were delayed throughout the entire central retinal area assessed., Conclusions: ERG timing is a sensitive assay of retinal function, and our results indicate that NCMD has a widespread effect at the level of the mid and outer retina. The findings also demonstrated that it is necessary to account for fixation locus and to ensure that equivalent retinal areas are compared when testing patients with macular disease who have eccentric fixation.

Purpose: To evaluate the contrast response of the visual system in retinitis pigmentosa (RP) under conditions designed to emphasize the parvocellular (PC) and magnocellular (MC) pathways., Method: Visual evoked potentials (VEPs) were measured in 10 patients with RP and in 10 age-equivalent control subjects with normal visual acuity and color vision, by using an array of isolated checks that were presented against a steady yellow background. The checks were modulated sinusoidally, either in isoluminant chromatic contrast (5.6 Hz), to favor the chromatic PC pathway, or in luminance contrast (5.6 and 11.2 Hz), to favor the MC pathway. Response amplitude and phase at the stimulus (fundamental) frequency were derived from Fourier analysis, and contrast response functions were fit with a Michaelis-Menten equation to derive R(max), the maximum response amplitude, and sigma, the contrast necessary to produce R(max)/2., Results: In the control subjects, the mean amplitude function for chromatic modulation increased approximately linearly with increasing contrast, whereas the function for luminance modulation increased sharply at low contrasts and saturated at contrasts above approximately 30% for both temporal frequencies, as expected. The patients with RP showed primarily a reduction in R(max) with little change in sigma in all testing conditions. The reduction in R(max) was equivalent for chromatic modulation and luminance modulation at 5.6 Hz, but was substantially lower for luminance modulation at 11.2 Hz., Conclusion: Contrast processing was impaired within both the MC and PC pathways in these patients with RP, but the degree of impairment within the MC pathway depended on temporal frequency. These VEP results are in general agreement with recent psychophysical studies of contrast sensitivity losses in patients with RP, and further they characterize contrast processing deficits in these patients at suprathreshold levels.

Purpose: To determine whether training oculomotor control, without direct practice in reading sentences, could increase reading speed in patients with age-related macular degeneration (AMD)., Methods: Sixteen patients with AMD participated in the study (age range, 65-87 years; mean, 77). The training program consisted of a series of exercises that were designed to allow the patients to practice eye movements. At the beginning of training, the subjects practiced small horizontal saccades in response to cognitively easy stimuli (e.g., dots). The training then progressed to practicing larger eye movements and then to practicing saccades with single letters, pairs of letters, and three-letter words. Reading of sentences was practiced in only one exercise, during the last session of the 8-week training., Results: The difference between average reading speeds before and after training was 24.7 wpm (difference between medians, 17.9 wpm). The increase in speed was statistically significant (Wilcoxon signed rank test = 124.0, P < 0.001). There was no significant relationship between change in maximum reading speed and ETDRS (Early Treatment Diabetic Retinopathy Study) acuity (r = -0.14, P = 0.76) or between change in maximum reading speed and age (r = 0.25, P = 0.45)., Conclusions: The results indicate that a training curriculum that concentrates on eye-movement control can increase reading speed in patients with AMD. This finding is especially interesting, because the training involved little direct practice in reading sentences but instead concentrated on having subjects practice control of eye positions and eye movements.

Purpose: Previous studies indicated abnormal development of fixation toward the optic nerve head in patients with the inherited retinal disease North Carolina macular dystrophy (NCMD). The implication of this development on functional vision and structural characteristics has not been described., Methods: The anatomical characteristics of five NCMD-affected individuals were assessed by measuring the retinal thickness of the macula using optical coherence tomography. The underlying physiologic health of the retina was assessed using the multifocal ERG. Psychophysical assessment of remaining vision in the affected areas was done with a new microperimetry system that measures functional visual acuity at 27 discrete locations and the Humphrey visual field analyzer., Results: All patients had better areas of visual sensitivity toward the nasal macula. Follow-up examination showed no changes in the clinical appearance of the retina. Visual acuities ranged from -0.10 logMAR (Snellen equivalent, approximately 20/16) to 0.50 logMAR (Snellen equivalent, approximately 20/63) in the better eye. No significant changes in visual acuity were found over time. Local multifocal electroretinogram deficits were found in all patients. Patients with grade 2 or 3 disease had large patches of decreased amplitudes and delayed implicit times. Results of the anatomical, electrophysiological, and psychophysical tests were consistent., Conclusion: The electrophysiological and psychophysical deficits found in patients with more severe disease were consistent with an abnormal development of fixation from the anatomical fovea toward the optic nerve head with the placement of the lesion temporal to fixation (into the nasal visual field).

We examined the effects of inter-modal attention and mental arithmetic on Humphrey visual field sensitivity and multifocal visual evoked potential (mfVEP) amplitude. Four normally sighted subjects (ages ranging from 24 to 58 years) participated in this study. Monocular visual field sensitivity was measured under two conditions: (1) standard testing condition and (2) while the subject performed a Paced Auditory Serial Addition Task (PASAT). Monocular mfVEPs were recorded in response to a 60-sector stimulus. The checkerboard pattern in each sector was contrast reversed according to a binary m-sequence. mfVEPs were recorded under two conditions: (1) standard testing conditions and (2) while the subject performed a PASAT. We found that, when compared to the no-task condition, all subjects had locations of significantly reduced Humphrey visual field sensitivities when performing the PASAT. In contrast, there were no significant decreases in mfVEP amplitude in any sector for any of the subjects while performing the PASAT. Our findings indicate that divided attention and ongoing mental processes did not affect the mfVEP. Therefore, the mfVEP provides an objective measure of visual field function that may be useful for some patients with unreliable automated static perimetry results.

Purpose: To identify clinical vision measures that are associated with the driving performance of glaucoma patients who have visual field loss and visual acuity better than 20/100 and to compare the driving performance of glaucoma patients with the driving performance of a group of age- and sex-equivalent individuals without eye disease., Patients: Forty patients with glaucoma and 17 normally sighted control subjects participated in this study., Methods: Clinical vision data, consisting of visual acuity, letter contrast sensitivity, and visual fields, were collected. Driving performance was assessed by (1) an interactive driving simulator that measured 7 indices of performance (including number of accidents) and (2) the self-reported accident involvement for the past 5 years., Main Outcome Measures: Driving simulator performance and real-world, self-reported accident involvement., Results: The number of accidents as measured on the driving simulator in the glaucoma group was significantly correlated with three Goldmann visual field measures: combined horizontal extent (rho = -0.47, P = 0.01), total horizontal extent (rho = -0.49, P = 0.007), and total peripheral extent (rho = -0.55, P = 0.002). There were no statistically significant correlations between the driving performance of the glaucoma group and the visual acuity or contrast sensitivity measures. When compared with the control group, a significantly greater proportion of the glaucoma group reported having at least one real-world accident within the past 5 years (Fisher exact test, P = 0.005)., Conclusions: Visual field reduced to less than 100 degrees of horizontal extent may place patients with peripheral field loss at greater accident risk. A higher incidence of real-world and simulator accidents was found for the group with glaucoma.

Purpose: To evaluate acuity and multifocal electroretinogram (mfERG) responses from the macula in affected and unaffected fellow eyes of patients with macular holes., Methods: We tested 10 eyes with macular hole and 10 fellow eyes from 11 patients. We measured local visual acuity thresholds at 27 discrete locations within 21 degrees diameter using the Functional Fundus Imaging System (FFIS), a psychophysical system that measures visual acuity as a function of visual field location, and local ERG responses within 45 degrees diameter using the mfERG., Results: In the affected eyes, the mean FFIS visual acuity thresholds were significantly elevated within the central 21 degrees diameter area, compared to a group of control eyes. No significant differences were found between the acuities of the fellow eyes compared to those of the control group. The amplitudes of the first positive peak of the mfERG were reduced in the central 7.8 degrees in affected eyes. In the central 2 degrees , 4 out of 10 affected eyes showed non-measurable ERG signals. The remaining six eyes showed significantly reduced mean amplitudes, but not delayed implicit times, when compared to the control group. For the fellow eyes, the mean amplitudes of the mfERG and implicit times did not differ from the means of the control eyes., Conclusions: Both local psychophysical and electrophysiological testing demonstrated retinal dysfunction extending beyond the site of the macular holes in some patients (three of the patients had central mfERG amplitudes falling within the normal range).

Purpose: (1) To compare the outcomes of orientation and mobility and driving training with Fresnel prisms and the Gottlieb Visual Field Awareness System for patients with homonymous hemianopsia, and (2) To determine whether the patients continue to use the optical enhancement devices at a 2-year follow-up point., Methods: Patients with homonymous hemianopsia were provided with a rehabilitation program where they were fitted with prism lenses and trained to use them for navigation and driving. Telephone interviews were used to obtain information about device usage 2 years following the completion of the training program., Results: Patients' performance was compared with a test-retest criterion in the visual skills areas of recognition, mobility, peripheral detection, scanning, tracking, and visual memory. Patients with hemianopic loss showed improvements in all of the visual skills categories, ranging from the highest improvements of 26% of tasks improved in the mobility category to 13% in the recognition category. The majority of the hemianopic patients reported using the devices at the 2-year follow-up interview., Conclusions: The patients with homonymous hemianopsia showed improvements in visual functioning using prism lenses, although these improvements were smaller than those found in previous studies with central or bilateral peripheral vision loss groups who were trained to use other optical enhancement devices for navigation and driving using a similar curriculum. However, given the evidence of increased risk of accidents for patients with peripheral vision loss, the safety of peripheral enhancement devices for driving must be thoroughly evaluated before their impact on public safety is known.

We examined the reliability of Humphrey visual field thresholds and multifocal electroretinogram (mfERG) amplitudes and timing in a group of patients with Retinitis Pigmentosa (RP). Eight patients with RP and seven control subjects were tested five times: at baseline (visit #0), at three weekly follow-up visits (visits #1 - #3), and at three months (visit #4). For the Humphrey thresholds, differences between dB values on repeat visits were obtained. Differences between log values on repeat visits were calculated for mfERG amplitude and implicit time. We used the standard deviations of these difference scores as a measure of reliability and the means of the difference scores as a measure of progression. We found that the majority of the patients' repeat data were more variable than that of the control subjects for both the Humphrey and mfERG. We found no single factor that predicted the magnitude, or the variance, of the SD of differences scores for the patients. We recommend that each patient's reliability be assessed individually. Ultimately, the choice of an outcome measure must be guided by its reliability, as well as its ability to assess the visual function of interest.

Purpose: To determine the extent of rod and cone photoreceptor dysfunction in patients with cone dystrophy using psychophysical and electrophysiological tests., Methods: Ten patients with cone dystrophy participated. Rod and cone system psychophysical thresholds were measured as a function of retinal eccentricity. Bright-flash full-field electroretinograms were obtained under dark-adapted (rod-mediated) and light-adapted (cone-mediated) conditions. The a-wave data were fitted with a model based on photopigment transduction to obtain values for log Rmax (maximum response) and log S (sensitivity). b-Wave parameters were also examined by fitting a nonlinear, saturating function (the Naka-Rushton equation) to the rod-mediated responses. Oscillatory potentials were measured to the cone-mediated high-intensity flashes., Results: On average, the rod-mediated psychophysical thresholds were elevated by 0.5 log unit. These threshold elevations did not differ significantly with retinal eccentricity. In contrast, cone-mediated psychophysical thresholds were elevated up to 3.0 log units. Threshold elevation was greatest in the central retinal locations. For rod-mediated conditions, the a-wave Rmax parameter was significantly reduced in three patients; the a-wave log S parameter was within normal limits. The rod-mediated b-wave Rmax parameter was reduced in six patients; log k was abnormal in one patient. For cone-mediated conditions, the a-wave Rmax parameter was reduced in six patients and the a-wave log S parameter was reduced in two patients. The cone system oscillatory potentials were abnormal in nine patients., Conclusions: Patients with cone dystrophy show different patterns of psychophysical rod versus cone system sensitivity losses with retinal eccentricity. The full-field electrophysiological data indicate that most of the patients had abnormal cone photoreceptor function. Some patients also showed rod photoreceptor abnormalities. The rod system changes were smaller than the cone system changes.

Purpose: To determine the influence of age on local electroretinographic responses in humans., Methods: Multifocal electroretinograms (mfERGs) were obtained from 62 normally sighted subjects ranging in age from 21 to 81 years. A stimulus array of 103 scaled hexagons was used to measure electrical signals within a retinal area approximately 46 degrees in diameter. Commonly reported mfERG methods were used to quantify the responses: peak-to-peak amplitudes and implicit times, scalar product amplitude, and amplitude and time scales derived from the algorithm of Hood and Li, published in 1997., Results: Regression analysis showed significant linear relationships of amplitude and timing measures with age. The rates of losses were 10.5% per decade for peak-to-peak amplitude, 11.7% per decade for scalar product amplitude, and 9.5% per decade for a-scale. The rate of amplitude reduction was highest in the central 3 degrees. Age had less influence on implicit time measures. The rates of timing losses were 1.4% per decade for the N1 component and 1.0% per decade for both the P1 component and the t-scale measure. Using predicted interval ranges, the age was calculated at which 50% of the expected values would fall below the lower 95% prediction interval band of younger subjects., Conclusions: The age-associated mfERG alterations are presented to emphasize the importance of appropriate normative data in interpretation of mfERGs.

Purpose: To compare the patterns of local cone and rod system impairment in patients with progressive cone dystrophy (CD) using psychophysical and electrophysiological techniques., Methods: Local cone system function was assessed by measuring cone system thresholds (visual fields) and cone-mediated multifocal electroretinograms (mfERGs). Rod system function was assessed by measuring rod system thresholds (visual fields) and rod-mediated mfERGs. The results in a group of eight patients with CD were compared with those in an age-similar control group., Results: All the patients had abnormal cone system visual field thresholds and cone-mediated mfERGs. Cone system psychophysical thresholds were elevated for targets presented within the central 10 degrees, but were within normal limits for targets at peripheral locations. Cone-mediated mfERG measures of amplitude scale and time scale were abnormal for most of the hexagons tested. Most of the rod-mediated psychophysical thresholds and mfERGs were within normal limits. Rod system losses tended to be patchy and scattered throughout the area tested., Conclusions: There was poor correspondence among local measures of cone and rod system losses in these patients with CD. The results suggest that the spatial pattern of cone system losses in this disease differs from the spatial pattern of rod system losses.

Purpose: To determine the extent of electrophysiologic dysfunction in patients with central serous chorioretinopathy (CSC)., Design: Prospective observational case series., Participants: Six patients with unilateral CSC (mean age, 40 years) were recruited into the study., Methods: Six patients with CSC underwent multifocal electroretinogram (mfERG) testing on both their clinically affected and opposite uninvolved eyes using the VERIS System, with a stimulus array of 103 scaled hexagons. The first positive peak responses were analyzed within six concentric ring annuli centered on the fovea. Amplitudes and implicit times were compared with those of an age-similar control group., Main Outcome Measures: Local electroretinographic response amplitudes and implicit times within the central 40 degrees with the mfERG., Results: All the clinically uninvolved eyes showed mfERG amplitudes and implicit times within the normal range throughout the central 40 degrees of the retina. All six eyes with CSC showed reduced amplitudes and/or delayed implicit times that were limited to the regions of the macula in which clinical changes associated with CSC were apparent., Conclusions: We observed electroretinographic changes only in the clinically affected eyes, and these were limited to regions with ophthalmoscopically apparent fundus changes. Our findings do not support the conclusion that functional impairment, as measured by the mfERG, in eyes with CSC extends beyond clinically observed fundus changes. We did not observe abnormal mfERG responses in the clinically normal eyes of such patients.

To determine the manner in which attention is distributed among numerous locations in the visual space, we used a multifocal recording technique that allowed simultaneous recordings of evoked cortical activity from 12 visual field areas out to 23.6 degrees. We found that multifocal visual evoked potential (mfVEP) amplitude was larger when a region of visual space was attended than when it was not attended. The magnitude of this effect was inversely related to visual field eccentricity and there was no attention-related modulation of VEP amplitude for the most eccentric region. In addition, we found that mfVEP amplitudes in the regions contiguous to the attended region could also be larger, depending upon their spatial relationship to the attended region. Specifically, amplitudes in more central regions on the 'meridian of attention' were larger when the subject attended anywhere along that meridian.

Purpose: To examine whether a mosaic pattern of retinal dysfunction in obligate carriers of X-linked retinitis pigmentosa (XLRP) could be observed in local electroretinographic responses obtained with the multifocal electroretinogram (mfERG)., Design: Prospective observational case series., Participants: Five obligate carriers of XLRP (mean age, 53.2 years) were recruited into the study., Methods: Examination of each subject included a complete ocular examination, Humphrey visual field, standard full-field electroretinogram (ERG), and mfERG testing. For the mfERG, we used a 103-scaled hexagonal stimulus array that subtended a retinal area of approximately 40 in diameter. The amplitudes and implicit times in each location for the mfERG was compared with the corresponding value determined for a group of normally sighted, age-corrected control subjects., Main Outcome Measures: Mapping of 103 local electroretinographic response amplitudes and implicit times within the central 40 with the multifocal electroretinogram., Results: Localized regions of reduced mfERG amplitudes and/or delayed implicit times were found in four of five carriers. In one of these four carriers, a mosaic pattern of mfERG dysfunction was present even in the absence of any clinically apparent retinal changes, retinal sensitivity losses on Humphrey field testing, or abnormal full-field cone ERG responses. However, one carrier with a typical tapetal-like reflex demonstrated no deficit on any functional tests., Conclusions: The mfERG demonstrated patchy areas of retinal dysfunction in some carriers of XLRP. This mosaic pattern of dysfunction may be observed in some patients with a normal-appearing fundus, normal psychophysical thresholds, and normal amplitude and implicit time full-field ERG cone responses.

The multifocal electroretinogram (mfERG) has been commonly used as a method for obtaining objective visual fields. Although qualitative comparisons have been good, quantitative comparisons between the results from mfERG and the results from Humphrey Visual Field Analyser (HVFA) have found variable degrees of agreement depending upon the mfERG response parameter examined and/or the disease studied. Lack of agreement may be due to differences in methodology, differences in the sites of response generation, and/or differences derived from comparing suprathreshold versus threshold responses. In addition, the two procedures are performed at different levels of adaptation. We developed an approach for matching stimulus parameters and compared mfERG and psychophysical thresholds to assess the effects of technique and level of adaptation on the two responses. Psychophysical and mfERG thresholds were obtained as a function of the adaptation level (1.5-4.0 log td) and retinal location. The derived increment threshold-versus-intensity functions for both measures were fitted using the equation logT=logT(0)+log((A+A(0))/A(0))(n). We found that the values of A(0) for the mfERG data were one log unit higher than those for the psychophysical data. In addition, the value of the slope (n) for the mfERG data was shallower (0.8) than that of the psychophysical data (1.0). Predictions were made about comparisons of HVFA threshold and mfERG amplitude data in patients with retinal disease based upon a two-site model of adaptation. The data for some groups of patients could be best-fitted with a model of a disease acting at a site distal to all gain changes, whereas data from other patients were best fitted with a model of a disease acting at a site proximal to all retinal gain. The relationship between the Humphrey visual field threshold losses and mfERG amplitude reductions depends upon the site and mechanism of a particular disease process and the model of retinal gain assumed. In no case is a one-to-one relationship between the losses in the two measures predicted.

Objective: To test the hypothesis that the retinal pigment epithelial/photoreceptor complex is affected in patients with pigment dispersion syndrome and/or in patients with pigmentary glaucoma., Methods: Electro-oculograms were recorded from patients with pigment dispersion syndrome, pigmentary glaucoma, ocular hypertension, and primary open-angle glaucoma and from control subjects. Electro-oculograms were recorded during 15 minutes of dark adaptation followed by 15 minutes of light adaptation. For each subject, dark-trough amplitudes, dark-trough latencies, light-peak amplitudes, light-peak latencies, and ratios of the light-peak amplitude to the dark-trough amplitude (Arden ratios) were calculated., Results: A 1-way analysis of variance of the Arden ratios indicated significant differences among the groups of subjects. Results of a post hoc Newman-Keuls test revealed that the mean Arden ratios of patients with pigment dispersion syndrome and patients with pigmentary glaucoma were significantly lower than the mean ratios of the controls, the patients with primary open-angle glaucoma, and those with ocular hypertension., Conclusions: The results provide support for the hypothesis that the integrity of the retinal pigment epithelial/photoreceptor complex is affected in patients with pigment dispersion syndrome and in those with pigmentary glaucoma. Congenital and/or structural abnormalities of the retinal pigment epithelial/photoreceptor complex should be considered when models of the etiology of pigment dispersion syndrome are proposed.

We examined whether lateral spread of adaptation can be observed in the electroretinogram in humans. Specifically, we tested whether the luminance level of a surrounding, nonmodulated annulus affects the multifocal electroretinogram (ERG) response of a modulated central area. Multifocal electroretinograms were recorded in response to an array of 37 unscaled hexagons subtending a retinal area of 38 deg x 35 deg. Responses were recorded in six control subjects. In the first series of experiments, only the center hexagon was modulated, while the surrounding 36 hexagons were held constant at either 0.45, 172, or 340 cd/m2. In a subsequent series of control experiments, modulation depth of the center hexagon was varied and the proximity of the surrounding hexagon systematically altered. For the center-modulated condition, response amplitude and implicit time for the first-order kernel response significantly decreased as a function of increasing surround luminance. Control experiments demonstrated that the effect of the surround illumination was not due to scattered light but was influenced by the proximity of the surrounding annulus. These results demonstrate that lateral adaptation influences can be measured using the multifocal ERG.

Purpose: To determine the correlation between the aesthetics of lens tints preferred for cosmesis and lens tints preferred for viewing., Methods: Thirty-five subjects (mean age: 25; 49% male, 51% female) with no significant ocular pathology participated in the study. Median visual acuity was 20/20. Color vision testing was performed on each subject using Ishihara plates, and those with abnormal scores were excluded from the study. Subjects were shown nine pre-selected tinted lenses (50% transmittance) of variable wavelengths. These lenses were mounted on two separate color backgrounds, one white and the other approximating their skin tone. Subjects were asked to choose from each background which tinted lens they would most prefer to wear and which lens they would least prefer to wear. The subjects were then shown a series of eight pictures (four nature photographs and four paintings) with different dominant wavelengths. Subjects were asked to grade the aesthetic effect of a clear lens and each of the nine tinted lenses on the appearance of the pictures. Chromaticity coordinates were calculated for each lens and picture., Results: The blue lens was the most frequently chosen preferred lens to wear, followed by green, purple, and gray. The least preferred lenses were yellow, brown, and pink. For viewing the nature photographs, the clear lens was preferred over any of the tinted lenses. For viewing the paintings, the purple lens was most preferred. The yellow lens was least preferred for both photographs and paintings., Conclusions: Younger individuals with no significant ocular pathology preferred viewing both nature photographs and paintings through tinted lenses that did not, or only slightly, altered the chromaticity of the image. Whereas a clear lens was favored over the tinted lenses for viewing the photographs, some tinted lenses (purple and pink) were preferred for viewing paintings. There was no correlation between the most favored lens tint chosen based purely on cosmesis and the most favored lens tint based on viewing preference. However, the least preferred lens tint for cosmesis and viewing was yellow.

Purpose: To compare local cone and rod system function in patients with retinitis pigmentosa (RP) using electrophysiological and psychophysical techniques., Methods: Cone-mediated multifocal electroretinograms (M-ERGs), cone system threshold visual fields, rod-mediated M-ERGs, and rod system threshold visual fields were measured in seven patients with RP., Results: All the patients had normal cone system visual field thresholds and normal cone-mediated M-ERG implicit times within the central 5 degrees. Both cone-mediated responses were abnormal at some peripheral retinal locations. There were significant correlations among cone system amplitude, timing, and visual field loss. All the patients had some retinal areas where the rod-mediated M-ERG amplitudes were not measurable. In areas where they were measurable, these rod-mediated M-ERG responses were often within normal limits for amplitude and timing. In contrast to the cone system data, there were no significant relationships between rod-mediated M-ERG measures and rod system threshold elevations. The cone and rod system psychophysical thresholds showed regional correspondence; the amplitude-scale and time-scale measures of the M-ERG did not., Conclusions: The results indicate that there was better local correspondence between psychophysical and electrophysiological measures in the cone system than in the rod system in patients with RP. In addition, the psychophysical measures of cone and rod system function showed better correspondence than did the electrophysiological measures.

Purpose: To investigate the functioning in daily task performance of individuals with retinitis pigmentosa (RP). Goals were (1) to quantify the relationships among clinical tests of vision, self-reports, and evaluations of actual task performance to predict difficulty in these tasks; and (2) to validate self-report questionnaire data about daily task performance with observations and measurements of actual task performance conducted by a certified low-vision specialist., Design: A cross-sectional study and survey., Participants: Sixty-two individuals with RP (mean age, 37 years) participated in the study., Methods: We obtained data about task performance from subjects' reports about their daily performance as assessed by a 53-item questionnaire and from a specialist's rating about actual ability on a 64-item battery of tasks, including ones similar to those assessed with the questionnaire., Main Outcome Measures: Clinical measures of vision included visual acuity, visual fields using Goldmann perimetry, letter contrast sensitivity, and cone and rod electroretinogram (ERG) function. The questionnaire and functional tasks were clustered into three categories: "reading," "mobility," and "peripheral detection.", Results: Self-report was correlated significantly with actual task performance. Task performance was correlated significantly with clinical test performance. Moderate or worse difficulty in performance was observed only for visual acuity worse than 20/40; log contrast sensitivity less than 1.4; a visual field area smaller than 2000 deg(2) (area equivalent to a 50-degree diameter of visual field to the Goldmann II-4-e target); and ERG amplitudes less than 10 microvolts for 32-Hz light-adapted white flicker., Conclusions: Despite the significant correlations, there remains variability in task performance that is unaccounted for in some individuals with low levels of clinical test performance. The assessment of actual task performance validated the use of self-reports in individuals with RP.

Purpose: To assess the effects of focal photocoagulation on retinal function in the macular and perimacular areas in patients with diabetes who have clinically significant macular edema., Methods: Eleven patients were assessed after focal laser treatment. Multifocal electroretinogram (ERG) and full-field ERG techniques were used to evaluate the effects of treatment on macular, paramacular, and peripheral retinal function. A modified visual field technique was used to obtain local threshold fields. The posttreatment results were compared with pretreatment results. Changes in local ERG response amplitudes and implicit times were calculated for each patient and presented as difference fields. The changes in local ERG responses were compared with the changes in local field sensitivity., Results: After treatment, the results of the psychophysical tests suggested little or no change in visual function, but changes in retinal function were observed with the multifocal ERG technique. Local ERG responses showed increases in implicit time and decreases in amplitude, compared with pretreatment values. Timing was affected more than amplitude., Conclusions: The results suggest that focal treatment produces changes in retinal function, and these changes are not restricted to the treated macular area.

Purpose: To evaluate the nature and extent of retinal dysfunction in the macular and surrounding areas that occurs in patients with diabetes with clinically significant macular edema (CSME)., Methods: Eleven patients were evaluated before focal laser treatment. Multifocal electroretinogram (ERG) and full-field ERG techniques were used to assess the effects of diabetic retinopathy and CSME on macular, paramacular, and peripheral retinal function. A modified visual field technique was used to obtain local threshold fields. The relationship between local sensitivity changes and local ERG changes was determined., Results: Local ERG responses were significantly delayed and decreased in amplitude, and timing changes were observed in a larger area of the retina than amplitude changes. Visual field deficits were similarly widespread with marked sensitivity losses occurring in retinal areas with normal ERG amplitudes and in areas that appeared to be free of fundus abnormalities. Despite this similarity and the finding that retinal areas with elevated thresholds have timing delays, timing delays were not good predictors of the degree of threshold elevation., Conclusions: The results demonstrate the widespread nature of timing deficits and visual field deficits that are associated with CSME.

Purpose: Electroretinograms to high-intensity flashes were obtained to determine the extent of rod and cone photoreceptor and postreceptor dysfunction in patients with primary open-angle glaucoma., Methods: Full-field flash electroretinograms were obtained using brief high-intensity flashes. Dark-adapted (rod-dominated) and light-adapted (cone-dominated) electroretinogram responses were recorded to a "white" light as a function of flash intensity. The a-wave data were fitted with a model based on photopigment transduction to obtain values for the parameters of log Rmax (the maximum response) and log S (sensitivity). Oscillatory potentials were measured to the cone-dominated high-intensity flashes. Standard clinical 30 Hz flicker electroretinogram responses were recorded using a Grass photostimulator., Results: Analysis of rod and cone a-wave data showed that log Rmax and log S values were within the normal range in nearly all of the patients. For some patients, oscillatory potentials were delayed beyond the normal range., Conclusion: Our results provide little evidence for widespread photoreceptor abnormalities in primary open-angle glaucoma.

Contributions to the multifocal electroretinogram (ERG) from the inner retina (i.e. ganglion and amacrine cells) were identified by recording from monkeys before and after intravitreal injections of n-methyl DL aspartate (NMDLA) and/or tetrodotoxin (TTX). Components similar in waveform to those removed by the drugs were identified in the human multifocal ERG if the stimulus contrast was set at 50% rather than the typically employed 100% contrast. These components were found to be missing or diminished in the records from some patients with glaucoma and diabetes, diseases which affect the inner retina.

Purpose: To assess the feasibility of obtaining reliable multifocal rod electroretinograms (ERGS) and to compare them to full-field ERGs., Methods: Multifocal rod ERGs were recorded using a stimulus array of 61 hexagons. The minimum number of dark, blank frames between flashes was varied from 0 (a minimum of 13.3 msec between flashes) to 21 (a minimum of 293 msec between flashes). Full-field ERGs were obtained using trains of flashes designed to simulate the multifocal sequences. Flashes were blue (W47B), except in a few cases in which red (W26) was used to check for cone intrusion. Flash intensities varied from -1 to 1.7 log scot td-s., Results: Dark-adapted, multifocal ERGs to blue flashes had a small, early component followed by a larger, late component. The early component showed little change in amplitude with increasing intensity. Comparisons with the full-field ERGs indicated that the early component was the focal response. The larger, late component was the response to stray light, and it can be suppressed with the addition of a surround. The focal response was from a relatively circumscribed retinal region. This is shown by comparing the multifocal rod responses from a patient with retinitis pigmentosa to her behaviorally measured rod visual field., Conclusions: By choosing conditions (namely, flashes of moderate intensity with a surround) to minimize the effects of stray light, multifocal rod ERGs can be recorded with sufficient localization to be clinically useful. However, the signal-to-noise ratio of these multifocal rod ERGs was poorer than for multifocal cone responses for comparable recording periods because of the need for blank frames and the slower recovery of the rods to successive presentations.

To assess local retinal function in patients with retinitis pigmentosa (RP), multi-focal ERGs and local thresholds (static visual fields) were obtained on eight RP patients with visual acuities of 20/25 or better. All eight patients showed multi-focal responses with normal timing within the central 5 deg. However, there were few responses with normal timing in the areas outside the central 7.5 deg, except in the case of the only patient with a 30 Hz full-field response with normal timing. Since full-field ERGs are dominated by responses from the periphery, this finding supplies a foundation for the commonly observed delays in the full-field cone ERGs of patients with RP. With respect to amplitude, only two patients showed multi-focal responses with near normal amplitudes anywhere in the field. The loss of amplitude at any point was not a good predictor of visual sensitivity in the Humphrey visual field. On the other hand, all areas with normal timing had near normal sensitivity. Timing changes appear to be an early indication of local retinal damage to the cone system. Nearly all areas with sensitivity losses greater than 0.5 log unit, and some areas with near normal sensitivity, showed significantly delayed multi-focal ERGs. Finally areas with extreme sensitivity loss show multi-focal responses with a wide range of amplitudes and implicit times across patients, suggesting different mechanisms of disease action in different patients.

Purpose: To determine whether the rod and cone photoreceptors are affected in patients with diabetic retinopathy., Methods: Twelve patients with diabetes and varying levels of retinopathy and nine age-similar control observers participated in this study. Two-color (500 versus 650 nm) dark-adapted thresholds were measured as a function of retinal eccentricity. Full-field flash electroretinograms were obtained using brief, high-intensity flashes. Dark-adapted rod-isolated (Wratten 47B filter) and light-adapted cone-isolated (Wratten 26 filter) electroretinographic responses were measured as a function of flash intensity. The a-wave data were fitted with a model based on photopigment transduction to obtain values for the parameters of Rmax (the maximal response) and log S (sensitivity). Standard clinical 30-Hz flicker electroretinographic responses were also measured., Results: Psychophysically measured dark-adapted thresholds were elevated primarily at eccentricities of 5 degrees and 10 degrees from the fovea. Analysis of rod and cone a-wave data showed that Rmax was normal in most of the patients, but log S was reduced. Analysis of b-wave and oscillatory potential parameters showed rod and cone postreceptoral abnormalities, including changes in the rod-isolated semisaturation constant (log k), cone-mediated 30-Hz flicker, and cone-isolated oscillatory potentials. The electrophysiological results were not significantly correlated with blood glucose or glycosylated hemoglobin level., Conclusions: The results provide evidence for rod and cone receptoral and postreceptoral deficits in patients with diabetic retinopathy. The photoreceptor changes are primarily in the log S (sensitivity) parameter and are attributed to transduction abnormalities.

The multi-input technique of Sutter and Tran (1992) yields multiple focal ERGs. The purpose here was to compare the components of this multifocal ERG to the components of the standard, full-field ERG. To record multifocal ERGs, an array of 103 hexagons was displayed on a monitor. Full-field (Ganzfeld) ERGs were elicited by flashes presented upon steady background fields. The latencies of two prominent subcomponents of the full-field ERG were altered by varying the intensity of the incremental flash or the intensity of the background field. By showing that similar manipulations of the multi-input parameters produce similar changes in latency, we were able to relate the components of the multifocal ERG to the components of the full-field ERG. The biphasic responses of the multifocal ERG appear to be generated by the same cells generating the a-wave and positive peaks of the full-field cone ERG.

Purpose: The authors examined electrophysiologic and psychophysical measures of retinal function in patients infected with human immunodeficiency virus (HIV) at different stages of infection, including patients with cytomegalovirus retinitis (CMVR)., Methods: All patients had complete ophthalmologic examinations. Rod-mediated psychophysical thresholds were measured using a modified two-color dark-adapted perimetry technique. Rod-dominated full field flash electroretinograms (ERGs) were obtained as a function of flash intensity, followed by cone-dominated ERGs. The 26 patients infected with HIV (26 eyes) were categorized into three groups. Six patients were infected with HIV but had not progressed to acquired immunodeficiency syndrome (AIDS), and 14 had AIDS. Six patients had CMVR with less than 10% of the retina involved. The data were compared with results from age-similar control subjects., Results: Psychophysical thresholds as a function of retinal eccentricity were elevated for each of the three stages of HIV infection. The group of patients with CMVR had the greatest amount of threshold elevation and threshold elevation increased with retinal eccentricity. In addition, all three patient groups had abnormal electroretinographic findings. Patients with CMVR were affected more severely on all measures than were the other HIV-infected groups., Conclusions: Results reveal that a diffuse functional retinal pathology exists in eyes with the funduscopic appearance of localized peripheral CMVR. Additionally, patients infected with HIV, including those without cotton wool spots, may have abnormal retinal function.

Previous studies have found an increase in peripheral target localization errors in normally sighted older adults. These results have been interpreted as indicative of a constriction of the "useful field of view". In the present study, we parametrically manipulated masking, distractors and stimulus luminance and examined the relationships between peripheral target localization and age. We found that backward masking and/or flashed distractors increased error rates. This decrement in performance was larger for more peripherally located targets and largest for the older subjects at all stimulus locations. Stimulus luminance (either 2 or 78 cd/m2) had no effect on peripheral localization performance at any age. We also demonstrated that all subjects, regardless of age, had higher localization error rates to more peripherally located targets. In older subjects, error rates increased equally at all eccentricities; that is, there was an eccentricity independent increase in the number of target localization errors as a function of age. This finding does not support the interpretation of a selective constriction of the functional visual field in older subjects.

Rod-mediated electroretinograms (ERG's) were recorded from transgenic mice expressing a mouse opsin gene with three point mutations (V20G, P23H, and P27L; termed VPP mice) and from normal littermates. The leading edge of the alpha wave was analyzed in relation to a computational model of rod phototransduction [J. Physiol. 499, 719 (1992)], in which values for the maximum response (RmP3), transduction gain (S), and transduction delay (td) are derived from alpha-wave data. VPP mice exhibited an age-related decrease in RmP3. This decrease was consistent with reductions in the number of rod photoreceptors and in the length of rod outer segments observed in previous histological studies of the VPP retina. Values of S determined for the VPP mice were within the normal range, consistent with a normal amplification of the visual signal in VPP rods. At high stimulus intensities, both normal and VPP mice exhibited a decrease in S, which may reflect depletion of a phototransduction substrate at these stimulus levels. We examined the recovery of the alpha wave after a bright conditioning flash by measuring the rod alpha-wave response to a probe flash presented at varying times after the conditioning stimulus. In both normal and VPP mice a fourfold (0.6-log-unit) increase in conditioning stimulus intensity increased both T50%, the period required for half-maximal recovery, and tau, the exponential time constant describing recovery. However, the increases in T50% and tau were significantly greater in VPP mice, indicating an abnormally slow recovery of the flash response in VPP rods.

We tested alternative hypotheses concerning the locus of enhanced flicker sensitivity observed in response to stimuli presented to the peripheral retina. The first hypothesis attributes increased temporal frequency sensitivity to ganglion cell and higher-order neural processing, whereas the second hypothesis states that the locus of these temporal effects is at the cone photoreceptors. To test these alternative hypotheses we measured retinal electrophysiological and psychophysical temporal modulation thresholds. We found that sensitivity for temporal frequencies < 30 Hz did not vary as a function of retinal location for either the focal electroretinogram (ERG) or the psychophysical measure. However, for both measures, sensitivity for temporal frequencies > or = 30 Hz was greater in the peripheral retina than in the central retina. In addition, critical flicker frequency for the central retina was linear as a function of retinal illuminance for both the psychophysical and the electrophysiological measures. For the peripheral retina the slopes of critical flicker frequency versus log illuminance functions were steeper than the central slopes for both threshold measures. Eccentrically measured focal ERG and psychophysical critical flicker frequency values showed a relative saturation, deviating from the linear slope above 3.5 log Td. The findings of similar focal ERG and psychophysical temporal sensitivity changes with eccentricity support an outer retinal origin of this phenomenon.

Purpose: To assess changes in measures of visual function in patients with retinitis pigmentosa (RP) over time., Methods: Patients with RP and visual acuity of 20/40 or better and central visual fields of 10 degrees or larger were enrolled in a 9-year prospective study. The following measures of visual function were obtained annually over the follow-up period: visual acuity, Goldmann visual fields (V4e target), focal electroretinograms, and hue discrimination., Results: Over the follow-up period, the averaged group data showed changes in all measures of visual function. The smallest amount of change occurred for visual acuity and hue discrimination, and the greatest amount of change occurred for visual field area. Examination of individual patient data over the follow-up period indicated that the rates of change varied among patients and that losses in function for one measure did not correlate well with losses on other measures., Conclusions: These results stress that although visual function deteriorated over time for this group of patients with RP, there were differences among our measures of visual function. Measures that primarily assess central retinal function change relatively slowly compared with measures that assess more peripheral retinal function.

The hypothesis that reductions in Snellen acuities in patients with retinitis pigmentosa are due solely to losses of photoreceptors was tested by measuring the effects of random losses of sampling elements on letter identification. Sampling element losses were mimicked by setting the luminance of randomly selected pixels equal to the luminance of the surround. The amount of pixel blanking ranged from 0 to 90%. Letters varying in retinal subtense from 5 to 17 min arc were presented for 500 msec. Although letter identification accuracy decreased with increasing pixel blanking for all letter sizes, performance remained relatively high even when a majority of the pixels was blanked. The data suggest that unless the loss of cone photoreceptors in greater than 80%, loss of sampling elements alone can not account for letter acuities poorer than 20/40. In addition to loss of cone photoreceptors in patients with RP, there are histological reports of photoreceptor abnormalities and psychophysical studies of visual sensory deficits. It is conceivable that these alone, or in combination with losses of photoreceptors, could account for decreased visual acuity. In a series of experiments, stimulus parameters were manipulated in order to mimic the effects of some of these abnormalities and deficits and the effects on letter identification were examined. The results of these experiments demonstrated that sampling element loss interacts with sensory factors (e.g. luminance and contrast sensitivity) and perceptual factors (e.g. set size and letter orientation) to reduce letter identification accuracy. The implication of these results is that decreases in letter acuity observed in patients with retinitis pigmentosa cannot be attributed solely to a random loss of sampling elements in the underlying retina, but may be due to the combination of photoreceptor degeneration and other sensory and perceptual factors.

The aim of this study was to determine the relative effects of age and compromised vision on driving-related skills and on-road accidents. A total of 107 subjects were tested. They represented four groups that varied in age and visual status, as follows: (1) a younger, normally sighted group; (2) an older, normally sighted group; (3) a younger, visually compromised group; and (4) an older, visually compromised group. Driving performance was assessed by self-reported and state-recorded accident frequency and by an evaluation of performance on an interactive driving simulator. The older groups had poorer driving-related skills, as measured with our interactive driving simulator, than had the younger groups, but they did not have significantly higher on-road accident rates than the younger groups. The older subjects and those with compromised vision had reduced risk-taking scores, as measured with a self-report questionnaire. In addition, all older drivers had increased eye movements and had slower simulator driving speeds, which suggests that behavioral compensation is made for visuocognitive/motor deficits. Regression analyses showed that compromised vision and visual field loss predicted real-world accidents in our study population.

To investigate the relative sensory and perceptual contributions to central visual function of patients with retinitis pigmentosa (RP), we tested symmetry discrimination using block patterns with varying types of symmetric organization. Eleven control subjects with normal vision and 11 patients with RP with 20/30 visual acuity or better, viewed patterns presented for 255 msec. The patterns differed in the type of symmetric organization and the subjects were required to identify the type. The control subjects performed significantly better (89.2%) than the patients (74.5%). Four hypotheses to account for these findings were tested and the results were as follows, (1) A reduction in pattern luminance did not change symmetry discrimination performance in the control subjects. (2) Large reductions in pattern contrast did not alter symmetry discrimination in the control subjects. (3) Reductions in stimulus duration, likewise, did not produce similar error patterns in the control subjects as those observed in the patients with RP. (4) Alterations in spatial sampling density did not completely account for the patients' deficits. None of the retinally based explanations alone was sufficient to account for our findings. Additionally, we suggest that alterations of sensory input may affect the perceptual encoding of the relationship among pattern elements.

We measured contrast processing as a function of spatial and temporal frequency using three measurement techniques: psychophysical thresholds, visual evoked potential (VEP) thresholds and VEP amplitudes. Measurements were made using the same stimulus parameters and on the same group of subjects. The agreement among these functions depended upon the particular spatio-temporal stimulus employed and in general, there were more differences than similarities among these measures. For example, VEP derived functions (both amplitude and threshold) peaked at 4 c/deg, whereas, the psychophysical functions peaked at 1 c/deg. VEP amplitude functions were maximum at > or = 3.5 Hz, whereas both psychophysical and VEP sensitivity were maximum at < or = 2.5 Hz. VEP thresholds were broad and low pass in shape and in contrast, the psychophysical and VEP amplitude functions were band pass. In summary, comparisons among these measures of contrast processing must be made with caution.

The timing of visual evoked potential (VEP) amplitude and phase changes following abrupt increases or decreases in contrast was examined. Gratings (1 c/deg) were presented at a low contrast for 8 sec, increased to a higher contrast for 8 sec, and then decreased to the initial lower contrast for another 8 sec. Second harmonic VEP amplitude and phase were recorded continuously and averaged in 1 sec epochs. Both amplitude and phase exhibited delays in reaching a stable level following the contrast change. For amplitude, the length of the delay was dependent on the magnitude and direction of the contrast step and on the spatial frequency of the stimulus. Time constants for the change in amplitude following step increases in contrast ranged from 0.2 sec for a 12% contrast step to 1.34 sec for a 37% contrast step. The timing of phase changes, however, was independent of the size of the contrast increases (tau = 0.7 sec). For step decreases in contrast, both amplitude and phase were relatively independent of the size of the change (tau = approx. 0.9 sec for amplitude and tau = 0.15 sec for phase). Amplitude time constants also increased with increasing spatial frequency (tau = 1.2 sec for 1 c/deg, tau = 1.6 sec for 4 c/deg and tau = 2.3 sec for 8 c/deg); phase time constants, however, did not change as a function of spatial frequency (tau = 0.7 for all spatial frequencies). These findings demonstrate that a unitary process may not always be tapped by signal averaging techniques. Additionally, swept stimulus VEP techniques may produce considerable errors in threshold estimation depending on the stimulus spatial frequency and on the slope and direction of the contrast change.

It has been assumed that the 'ON' and 'OFF' responses of the human electroretinogram (ERG) interact to produce a single waveform when brief flashes are used. To test this assumption, we examined the separate effects of stimulus intensity, the level of retinal illuminance and stimulus duration on the ERG. Both 'ON' and 'OFF' response amplitude decreased as stimulus intensity was decreased and as the level of retinal illumination was reduced. When stimulus duration was reduced, the amplitude of the 'OFF' response decreased; however, the amplitude of the 'ON' response increased. Summing of the 'ON' and 'OFF' response waveforms could not account for the increased amplitude in response to brief stimuli or for the changes in ERG wave shape. These results indicate that there is not a significant corneally recordable 'OFF' response elicited by brief stimuli, such as those commonly used to record the flash ERG.

Single-cell electrophysiologic studies have shown that dopamine modulates retinal activity, but its role in human retinal processing is unclear. We investigated the effects of short-term oral administration of dopaminergic receptor blocking agents on the flash electroretinogram in humans. Both chlorpromazine (25 and 50 mg) and fluphenazine (1 and 2 mg) significantly reduced electroretinogram b-wave amplitudes and also selectively reduced the amplitude of the first oscillatory potential. Implicit times were not altered. Metoclopramide (10 and 20 mg) had no effect on any electroretinographic variable. Our study indicates that dopamine receptor blocking agents with both D-1 and D-2 receptor affinities reduce the amplitude of the electroretinogram in humans.

Purpose: To examine the sites of cone sensitivity loss in patients with retinitis pigmentosa by comparing focal electroretinographic and psychophysical modulation thresholds., Methods: Both psychophysical and electrophysiologic increment threshold curves were obtained in retinitis pigmentosa patients and a group of age-matched, normally-sighted adults., Results: The majority of the retinitis pigmentosa data could be accounted for by a vertical displacement of the normal curve. The retinitis pigmentosa patients showed similar patterns of cone sensitivity losses using both techniques., Conclusions: The combined electrophysiologic and psychophysical results provide support for an outer retina locus for these cone sensitivity losses. The data suggest that these deficits may be caused by a spatially independent loss of cone photoreceptors with normal adaptation properties in the remaining photoreceptors.

The P300 cortical evoked potential was compared to the P100 wave of the visual evoked potential by means of appearance/disappearance gratings. The spatial frequency of the novel stimulus was varied to compare the effect of task sensory difficulty on both P100 and P300 potentials. The P100 showed a steady increase in latency with the spatial frequency of the uncommon stimulus, and a degree of amplitude tuning consistent with the contrast sensitivity function. The P300 showed marked changes in both amplitude and latency dependent almost wholly on the proximity of the uncommon stimulus spatial frequency to that of the common stimulus. Motor reaction time showed elements of both the P100 and P300 response patterns. The results are consistent with a model in which, after visual information arrives at the visual cortex, processing is parallel and interdependent. In this model, the amplitude and latency of the P100 cortical evoked potential are governed solely by properties intrinsic to the stimulus, whereas the amplitude and latency of the P300 are functions of the degree of stimulus mismatch.