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Purpose: Orthokeratology is defined as the temporary reduction in myopia by the programmed application of rigid gas-permeable contact lenses. New reverse geometry contact lens designs and materials have led to a renewed interest in this field. The purpose of this study is to assess visual, refractive, topographic, and corneal thickness changes in subjects undergoing overnight orthokeratology., Methods: Ten myopic subjects (mean age, 25.9+/-3.9 years) were recruited for a 60-day trial of overnight orthokeratology using reverse geometry rigid contact lenses. After commencing lens wear, subjects were examined on days 1, 7, 14, 30, and 60 at several times throughout the day. High- and low-contrast logarithm of the minimum angle of resolution (logMAR) visual acuity, monocular subjective refraction, autorefraction, autokeratometry, corneal topography, corneal thickness, and slit lamp examinations were performed at each session., Results: Eight subjects completed the study. Both high- and low-contrast uncorrected visual acuity improved significantly by day 7. The mean change in uncorrected high contrast visual acuity at day 60 was -0.55+/-0.20 logMAR (mean at day 60, -0.03+/-0.16; Snellen equivalent, 20/19). The mean change in uncorrected low-contrast visual acuity at day 60 was -0.48+/-0.26 logMAR (mean at day 60, +0.22+/-0.23; Snellen equivalent, 20/33). The mean subjective refraction and autorefraction were significantly reduced from baseline at day 60 (mean change in subjective refraction, +1.83+/-1.23 D; mean change in autorefraction, +0.64+/-0.52 D). Corneal topography showed significant central flattening (mean change in apical radius, +0.20+/-0.9 mm; mean change in shape factor, -0.11+/-0.18 at day 60). The central cornea also showed significant thinning (mean change, -12+/-11 microm at day 60). All visual, refractive, and topographic outcomes were sustained over the course of an 8-h day., Conclusions: Overnight orthokeratology is an effective means of temporarily reducing myopia. The possible mechanism of corneal remodeling through central corneal thinning is discussed.

Purpose: To determine the influence of normal aging on contrast sensitivity for frequency doubling technology (FDT) perimetry., Methods: Contrast sensitivity measures were obtained for frequency-doubled stimuli (0.25 cycles per degree sinusoidal gratings undergoing 25 Hz counterphase flicker) at 17 target locations (4 per quadrant plus the central 5 degrees ) using a prototype of the Welch Allyn (Skaneateles, NY)/Humphrey Systems FDT perimeter (Humphrey Systems, Dublin, CA). A total of 407 normal subjects (761 eyes) between the ages of 15 and 85 years were tested., Results: Between the ages of 15 and 60 years there was an approximately linear decrease in contrast sensitivity of 0.6 dB per decade. After the age of 70, there was a slightly greater sensitivity loss with age. There were no meaningful differences in sensitivity loss as a function of age for different visual field locations. A small but consistent reduction in contrast sensitivity (approximately 0.7 dB) was found at all visual field locations for the second eye tested that may be due to a central adaptation process., Conclusions: Normal aging effects for FDT perimetry are similar to those obtained for conventional automated perimetry, except that the FDT perimetry aging effects do not appear to be eccentricity dependent. These normative data provide a basis for establishing a statistical analysis procedure and probability plots for FDT perimetry.

Purpose: To prospectively examine the effect of photorefractive keratectomy with a 6-mm ablation zone on best-spectacle-corrected visual performance., Methods: A prospective study was conducted of 164 eyes of 164 patients with an average (+/-SD) of -4.02 +/- 1.74 diopters (range, -0.63 to -8.38 diopters spherical equivalent). Best-spectacle-corrected high-contrast and low-contrast visual acuity (18% Weber contrast) was measured with both natural and dilated pupils. Patients were tested preoperatively and at 3, 6, and 12 months after photorefractive keratectomy. Photorefractive keratectomy was performed with an argon fluoride excimer laser. Fifty-five eyes of 55 patients also underwent astigmatic keratotomy., Results: Twelve months after photorefractive keratectomy, best-spectacle-corrected high-contrast visual acuity with natural pupils showed no significant change from preoperative values; mean (+/-SD) change was 0.004 +/- 0.10 logMAR (t = 0.45, P = .65). Best-spectacle-corrected low-contrast visual acuity with natural pupils was significantly reduced compared to baseline; mean (+/-SD) change was 0.04 +/- 0.13 logMAR (t = 3.3, P = .001). The low-contrast loss was larger (1.5 lines) with dilated pupils; mean (+/-SD) change was 0.13 +/- 0.15 logMAR (t = 9.31, P < .001). Greater losses in dilated low-contrast visual acuity were associated with concurrent astigmatic ketatotomy (t = 2.28, P = .025) and corneal haze of grade 1 or greater (t = 2.71, P = .005)., Conclusions: Reductions in visual performance occur after photorefractive keratectomy with a 6-mm zone. These changes are greatest for low-contrast visual acuity with dilated pupils. Corneal haze and concurrent astigmatic keratotomy are associated with greater losses in low-contrast visual acuity. Best-spectacle-corrected low-contrast visual acuity is a sensitive measure for evaluating visual performance after refractive surgery.

Purpose: To re-evaluate definitions of low vision, visual impairment, and disability., Methods: We review current definitions of legal blindness and low vision and how these definitions are variably based on disability or impairment. We argue for a definite distinction being made between criteria for visual impairment and visual disability, low vision being defined as the presence of a visual impairment that results in a disability. Visual impairment is defined according to population norms and a statistical cut-off is used. Visual disability is defined by consideration of the level of visual measures which result in measurable or reportable disability. We consider the evidence that contrast sensitivity should be a criterion for visual disability in addition to visual acuity and visual field., Conclusions: According to the current information, we define visual impairment as best monocular or binocular visual acuity <(worse than) 6/7.5, total horizontal visual field <146 degrees (Goldmann III-4e) or <109 degrees (III-3e), and contrast sensitivity <1.5 (PelliRobson); we define visual disability as best monocular or binocular visual acuity <6/12 or contrast sensitivity <1.05.

Purpose: Auto-refractors are used as a starting point for clinicians' refractions and in studies of refractive error. We investigated the repeatability of the Hoya AR-570 and clinician refraction., Methods: Eighty-six subjects, aged 11 to 60 years, were recruited by mailing inquiries to 500 randomly selected patients who had received recent examinations at the University of California Optometric Eye Center. Contact lens wearers, patients with best corrected visual acuity worse than 20/30 in either eye, and patients with a history of diabetes were excluded. Each subject was examined by two clinicians during one visit. The first clinician obtained five auto-refractor readings for each eye (which were later averaged), performed a balanced subjective refraction (with spherical masking lenses in the phoropter), and repeated the automated refractor measurements. This protocol was then repeated by the second clinician. Clinicians were randomized with regard to testing order and masked to automated refractor results, each other's refractions, and previous spectacle prescriptions., Results: To quantify repeatability, we used mixed model analyses of variance to estimate the appropriate variance components while accounting for the correlation among, for example, repeated measurements of the same eye. Astigmatic data were analyzed by converting into Fourier form: two cross-cylinders at axis 0 degrees (J0) and axis 45 degrees (J45). For mean spherical equivalent, the average difference between five averaged automated refractor readings, taken by two different optometrists, was +0.02 D (95% limits of agreement = -0.36 to +0.40 D). The average difference between the two optometrists' subjective refractions was -0.12 D (95% limits of agreement = -0.90 to +0.65 D). The 95% limits of agreement for the automated refractor were about half those of the clinician for both astigmatic terms (J0 and J45) and for all comparisons., Conclusions: Automated refraction is more repeatable than subjective refraction and therefore more appropriate for studies of myopia progression.

Purpose: This study investigates features of visual acuity chart design and acuity testing scoring methods which affect the validity and repeatability of visual acuity measurements., Methods: Visual acuity was measured using the Sloan and British Standard letter series, and Landolt rings. Identifiability of the different letters as a function of size was estimated, and expressed in the form of frequency-of-seeing curves. These functions were then used to simulate acuity measurements with a variety of chart designs and scoring criteria., Results: Systematic relationships exist between chart design parameters and acuity score, and acuity score repeatability. In particular, an important feature of a chart, that largely determines the repeatability of visual acuity measurement, is the amount of size change attributed to each letter. The methods used to score visual acuity performance also affect repeatability., Conclusions: It is possible to evaluate acuity score validity and repeatability using the statistical principles discussed here.

Aims: To determine the improvements in clinical and functional vision and perceived visual disability after first and second eye cataract surgery., Methods: Clinical vision (monocular and binocular high and low contrast visual acuity, contrast sensitivity, and disability glare), functional vision (face identity and expression recognition, reading speed, word acuity, and mobility orientation), and perceived visual disability (Activities of Daily Vision Scale) were measured in 25 subjects before and after uncomplicated cataract surgery (10 first eye surgery and 15 second eye surgery) and in 10 age matched controls., Results: Significant improvements were found after surgery in clinical and functional vision and perceived visual disability. Greater improvements were found after first eye surgery than after second eye surgery. However, first eye surgery did not return all scores to age matched normal levels. There were significant improvements in several of the tests measured after second eye surgery, and all postoperative values were similar to those from age matched normals., Conclusions: Significant improvements in clinical, functional, and perceived vision are obtained by cataract surgery. The improvements in objective measures of functional vision found in this study support previous findings of improvements in patients' perceived functional vision. In addition, these data provide support to the necessity of second eye surgery in some patients to improve certain aspects of visual function to age matched normal levels.

Background: Low-vision care is a widely accepted and valued service provided by many optometrists. As in other areas of health care, evaluation of the outcome of low-vision care is increasingly necessary so it can be properly positioned in the health care delivery system., Methods: This article reviews the literature relating to the prevalence of low vision, its impact on affected individuals, and how low-vision intervention affects those with visual impairments. This review considers the ways in which the impact of low-vision care has been evaluated., Results: The existing literature demonstrates that low-vision intervention can be highly valued by low-vision patients and can have a significant impact on an individual's daily life and activities. Evaluating this impact is a significant challenge-particularly if the goal is to gauge the outcome of low vision care as broadly as possible., Conclusions: Evaluation of health-related quality of life is a desirable option for evaluation of outcomes, and the application of quality of life instruments to the visually impaired population is necessary. There remain unresolved issues of optometric research that need to be addressed.

A commonly used clinical technique for determining whether visual function is abnormal, particularly when a patient is suspected of having unilateral or asymmetric disease, is to compare the visual function of the 'suspect' eye to that of the normal eye. This assumes that in normal patients visual function in each eye is equal and that this symmetry is maintained with age. To determine the extent of normal symmetry for clinical measures of visual function, we assessed high and low contrast visual acuity, letter contrast sensitivity and motion sensitivity (Dmin) in both eyes of a group of 91 subjects spanning an age range of 21 to 82 years. For the whole group the interocular differences in sensitivity for each of the tests approximated a Gaussian distribution. The results demonstrate that interocular differences should exceed more than 0.16 and 0.17 logMAR (approximately 2 lines) for high and low contrast visual acuity respectively, before patients can be considered to be outside the range of normality. For the Pelli-Robson Chart, interocular differences must exceed 0.23 log CS (1.5 triplets, 4.5 letters) and for Dmin, more than 0.35 log minarc for the differences to be considered abnormal. For low contrast letter visual acuity, there was a trend for the absolute interocular differences to increase significantly with age, but asymmetry remained relatively constant for the other visual measures.

Aims/background: Many reports have indicated that some patients with cataract can retain good visual acuity but complain of significant visual problems. This is the first in a series of papers trying to determine what causes these symptoms and whether other clinical tests can predict the real world vision loss., Methods: The effect of a cataract simulation with a similar angular distribution of light scatter as real cataract on clinical (visual acuity, contrast sensitivity, and disability glare) and real world vision (face recognition, reading speed, and mobility orientation) was investigated., Results: The simulation had a relatively small effect on visual acuity (6/6 with the simulation), but much larger effects on contrast sensitivity and low contrast acuity with and without glare. The simulation had no effect on high luminance and high contrast real world tasks, such as mobility orientation in room light and optimal reading speed. A small, but significant deterioration was found for the slightly lower contrast task of face and expression recognition. However, under low luminance conditions, substantial defects in mobility orientation were obtained (despite 6/6 acuity)., Conclusions: Although the relative effect of the cataract simulation on acuity and contrast tasks is not typical of the average cataract, it can be found in those cataract patients with visual problems despite good visual acuity. This corroborates the suggestion that it is large amounts of wide angle light scatter (forward and/or backward) which are at least partly responsible for visual disability in cataract patients with good visual acuity. A patient's reported visual disability may depend on the percentage of time he or she spends under low contrast and/or low luminance conditions, such as walking or reading in dim illumination, and walking or driving at night, in fog, or heavy rain.

Reading characteristics were studied in age-related maculopathy (ARM) by monitoring eye movement patterns as subjects read word charts and text charts that contain a wide range of print sizes. Eye movements were monitored with an infrared scleral reflection device and subjects were tested over a wide range of chart luminances. In normal subjects, as print size approaches threshold, reading speed slows mainly because of a decrease in fixation rate, whereas regressive saccades remain infrequent. There is little change in the ratio of number of letters read per forward saccade. With decreased luminance, there is a decreased reading acuity but the relation between reading speed and the size of print relative to the threshold size remains relatively constant. Subjects with ARM show similar fixation rates to normals, but they average fewer letters per forward saccade and make more frequent regressions. ARM subjects are more likely to have reading performance strongly affected by luminance. The number of letters per forward saccade can show a strong dependence on luminance, whereas fixation rates remain relatively unchanged. It is proposed that reduced reading performance in ARM is predominantly the result of a reduced perceptual span, with poor oculomotor control playing a secondary role. Optimal print size may be best predicted from letter chart acuity (r = 0.70) or word reading acuity (r = 0.69). Word reading acuity is the best predictor of peak reading speed (r = -0.74), whereas peak reading speed is poorly correlated with contrast sensitivity (r = 0.26) and scotoma area (r = -0.42).

Previous studies have alleged that the ability to perceive motion remains constant with age. We investigated the effect of age on minimum displacement thresholds using computer-generated random dot stimuli in 91 healthy, visually normal subjects (age range 21-82 years). High and low contrast visual acuity and letter contrast sensitivity were also tested. We found that minimum displacement thresholds increased significantly at a rate of 0.07 log min arc per decade (approximately 17%). The relationship between age and performance was very similar for all visual tests.

Information provided by manufacturers of low vision magnifiers is usually insufficient to allow the clinician to predict accurately the resolution improvement that patients may be expected to achieve. We have measured and tabulated the key optical parameters of 92 stand magnifiers and 53 hand-held magnifiers. For the fixed focus stand magnifiers, the image location and the equivalent power of the lens system have been determined and the enlargement ratio has been derived. For each magnifier, 3 different eye-to-lens distances (2.5, 10, and 25 cm) have been considered and, for each of these, the Equivalent Viewing Distance (EVD), the eye-to-image distance, and the theoretically predicted field width have been computed. The EVD is useful in predicting resolution performance because, for a given patient, the visual resolution limit will be directly proportional to the EVD. The eye-to-image distances allow the clinician to consider whether the patient will be in satisfactory focus or whether adjustments need to be made to the power of any reading addition. The stand magnifiers are listed in order of the EVD they give when the eye is a moderate (10 cm) distance from the magnifier. For the hand-held magnifiers, the equivalent powers have been measured. The EVD for a hand-held magnifier will be the same as the equivalent focal length of the magnifier if the lens is used so that the image is at or close to infinity. The tables include supplementary information on the size of the magnifier lenses and whether the magnifiers incorporate battery, electric, incandescent, or halogen lighting systems. Examples are presented to illustrate how the tables might be used in the selection of magnifiers to meet the resolution and other needs of individual patients.

Background: Many Human Immuno-Deficiency Virus (HIV) patients develop ocular involvement during the course of the disease, including HIV retinopathy and cytomegalovirus (CMV) retinitis. It is well established that contrast sensitivity and color vision may be affected in other retinal diseases, such as diabetes, before obvious signs and symptoms. We therefore examined patients with early HIV disease for visual involvement., Methods: Subjects consisted of 19 HIV-positive patients and 15 controls. None of the HIV-positive patients showed any signs of HIV retinopathy. High and low contrast visual acuity, luminance contrast sensitivity (CS), short wavelength cone (S-cone) CS, and color vision were assessed in the right eye of each subject., Results: S-cone CS was significantly reduced in the HIV-positive group (HIV mean = 0.91 +/- 0.15 log CS; normal mean = 1.10 +/- 0.09 log CS, t = 4.19, p < 0.001). Consistent with this finding, four of the HIV-positive patients demonstrated tritanopic D-15 results. High and low contrast visual acuity and CS were not significantly different in the HIV-positive and control groups., Conclusion: These findings indicate that HIV-positive patients can have S-cone/tritanopic abnormalities despite normal appearing fundi and that there may be damage to the visual system early in HIV infection.

Background: Diurnal variations in vision have been reported in radial keratotomy (RK) patients. Applicants to certain professions may meet an uncorrected vision standard at the time of testing but fail to meet that standard at another time., Methods: Ten firefighter applicants who had undergone RK and nine normal subjects attended for two morning visits, and two afternoon visits. At each visit subjective refraction, uncorrected visual acuity, best-corrected visual acuity, automated refraction, and keratometry were measured for each eye. Monocular contrast sensitivity was measured using the Pelli-Robson chart with and without a glare source (brightness acuity tester, BAT) and for both natural and dilated pupils., Results: The RK group showed a significant myopic shift from morning to afternoon (mean = -0.41 +/- 0.33 D; t = 3.92, p = 0.004), which was well correlated (r = -0.86) with significant steepening of the corneal curvature (mean = +0.41 +/- 0.36 D; t = -3.65, p = 0.005). The controls showed no change in either refractive error (mean change = +0.06 +/- 0.42 D) or corneal curvature (mean change = +0.05 +/- 0.08 D). No significant difference in corrected visual acuity or contrast sensitivity was found between the RK and control groups for natural pupils. For dilated pupils, the RK patients showed significantly poorer log contrast sensitivity both with and without glare (RK mean = 1.49 +/- 0.11; control mean = 1.67 +/- 0.11; t = 3.21, p = 0.005). All RK subjects met the firefighter visual acuity standard on the initial visit, three subjects did not meet the standard at an afternoon examination., Discussion: We propose that, if RK applicants are to be considered for employment, existing visual standards be amended to include visual acuity testing in both the early morning and late afternoon. Clinicians and agencies should also be aware that contrast sensitivity may be reduced at low light levels.

Purpose: This study was performed to investigate motion perception in patients with glaucoma., Methods: A random dot motion test was used to measure three aspects of central motion perception: minimum displacement threshold (Dmin), maximum displacement threshold (Dmax), and coherence threshold (signal to noise). Motion perception was assessed in 15 patients with primary open-angle glaucoma, 23 low-risk patients in whom glaucoma was suspected, and 24 age-matched normal subjects., Results: Central motion perception was significantly impaired in patients with glaucoma; in particular, the Dmin was nearly twice that for the normal subjects (glaucoma mean, -0.27 +/- 0.24 log minutes of arc; normal mean, -0.56 +/- 0.13 log minutes of arc; F = 21.79, P < 0.001). Furthermore, Dmin values fell outside the normal range in 10 of the 15 patients with glaucoma, despite normal visual acuity and normal foveal perimetric thresholds. Coherence thresholds and Dmax did not discriminate between patients with glaucoma and normal subjects. Dmin was not correlated with any indices of perimetric sensitivity, and none of the tests of motion perception showed any abnormalities in patients in whom glaucoma was suspected., Conclusions: Central motion perception can be affected in glaucoma and may reflect preferential damage to larger retinal ganglion cells. Future work will measure Dmin in a larger population of patients with suspected glaucoma and those with glaucoma, and investigate peripheral motion perception in glaucoma.

The subjective classification of lens opacities is a fundamental component in both the clinical evaluation of the individual patient and in large-scale clinical trials. This procedure has been improved substantially by the implementation of standardized photographic systems depicting various levels of nuclear opacity and color, cortical, and posterior-subcapsular cataract. Comparison can also be made with recently developed objective measurements of opacity and color. Further improvements in reliability and sensitivity to change can be achieved by modifying traditional integer scaling systems by interpolating between photographic standards.

Subjective and objective techniques were used to assess the on-eye performance of soft bifocal contact lenses. In the subjective technique a young observer whose accommodation had been paralyzed with a cycloplegic agent was fitted with the contact lens type under investigation and aligned with a Maxwellian view Badal optometer using a bite-bar. Visual acuity was measured as a function of both target vergence (0.00 to -4.00 D) and pupil size (1 to 5 mm). Aspheric, concentric, and diffractive soft bifocal contact lens designs were investigated. Diffractive and concentric bifocal designs with +2.00 D near additions showed "twin peaks" of visual acuity with one peak at 0.00 D target vergence (equivalent to distance viewing) and the second at -2.00 D target vergence (equivalent to a target at 50 cm). Some aspheric designs produced a relatively constant visual acuity across this vergence range, whereas others gave poor acuity at near. Visual acuity with the Echelon diffractive lens was relatively unaffected by pupil size, confirming theoretical predictions. Visual acuity with concentric designs was also relatively free of pupil size effects. In the objective technique, the variation in surface power across the lens was assessed using video-keratography. This technique provided an elegant means of visualizing the power profile of the lens. The location of the zones of increased power and the magnitude of power variations allowed an accurate prediction of the visual performance measured subjectively. Temporal displacement of lenses may explain the occasions where visual performance did not vary with pupil size.

Objective: To develop the Lens Opacities Classification System III (LOCS III) to overcome the limitations inherent in lens classification using LOCS II. These limitations include unequal intervals between standards, only one standard for color grading, use of integer grading, and wide 95% tolerance limits., Design and Results: The LOCS III contains an expanded set of standards that were selected from the Longitudinal Study of Cataract slide library at the Center for Clinical Cataract Research, Boston, Mass. It consists of six slit-lamp images for grading nuclear color (NC) and nuclear opalescence (NO), five retroillumination images for grading cortical cataract (C), and five retroillumination images for grading posterior subcapsular (P) cataract. Cataract severity is graded on a decimal scale, and the standards have regularly spaced intervals on a decimal scale. The 95% tolerance limits are reduced from 2.0 for each class with LOCS II to 0.7 for nuclear opalescence, 0.7 for nuclear color, 0.5 for cortical cataract, and 1.0 for posterior subcapsular cataract with the LOCS III, with excellent interobserver agreement., Conclusion: The LOCS III is an improved LOCS system for grading slit-lamp and retroillumination images of age-related cataract.

Purpose: To gather information regarding the reliability, discriminative ability, and validity of disability glare tests., Methods: The following glare tests were evaluated: the Miller-Nadler, Vistech MCT8000, Berkeley, van den Berg Straylightmeter, and the Brightness Acuity Tester used with the Pelli-Robson and Regan charts. Three test evaluation criteria were used: (1) repeatability--comparing test scores on two visits; (2) discriminative ability--the tests' ability to differentiate between young and old subjects and between old normal and cataract subjects; (3) validity--comparing cataract test scores with the reference standard of the van den Berg Straylightmeter. Three subject groups were evaluated: young normals (n = 24, mean age 24.3 +/- 3.3 yr), older normals (n = 22, mean age 66.0 +/- 6.2 yr), and early cataract (n = 33, mean age 70.6 +/- 8.1 yr)., Results and Conclusions: Data indicate that contrast sensitivity or low contrast acuity measured in the presence of glare are superior to disability glare scores in assessing cataract patients with normal neural function. Under glare conditions, contrast sensitivity and low contrast acuity scores from the Pelli-Robson, Regan, and Berkeley tests provide similarly reliable, discriminative, and valid measures of visual assessment in cataract. The Miller-Nadler glare tester poorly detects and measures subtle changes in the ocular media, such as early cataract, because of its large step sizes at low contrast thresholds. The poor reliability of the Vistech MCT8000 limits its usefulness. The study suggests that unless good chart design and psychophysics are used, the geometry and intensity of the glare source are of little importance.

When control of the pupil size is required, the simplest method is to use a physical artificial pupil or aperture that is placed in the spectacle plane. In some clinical applications (e.g., the potential acuity meter) an optical artificial pupil is imaged in the plane of the natural pupil by a Maxwellian view optical system. We compared visual performance with physical and Maxwellian artificial pupils by measuring the effects of the pupil diameter (0.5-5 mm in range) and defocus (5-D myopia to 4-D hyperopia) on minimum angles of resolution (MAR's) and on angular blur disk diameters. For pupil diameters down to ~ 2.0 mm there were no meaningful differences between the visual resolution that is obtained with the physical and the Maxwellian pupils. At the smallest diameter (0.5 mm) the physical artificial pupils caused the MAR to increase because of the diffraction limitation on resolution, and defocus no longer affected MAR. With the small Maxwellian pupils vision did not become diffraction-limited so that maximum resolution could still be obtained. MAR was still affected by defocus. The angular blur disk diameters measured with the smaller Maxwellian pupils were slightly but significantly larger than those found with physical artificial pupils. For physical artificial pupils, field-of-view restrictions may result from vignetting with the eye pupil. Thus small physical artificial pupils can act as pinholes causing resolution to become impaired but insensitive to defocus. Also vignetting by the eye pupil can restrict the field of view. Small optical artificial pupils from Maxwellian viewing do not impair resolution, and the resolution may remain sensitive to defocus. The eye pupil does not cause any field restriction, although, if small, it may filter higher spatial frequencies out of the retinal image.

We review the research which has attempted to determine whether the characteristics of autonomic innervation of ciliary smooth muscle are relevant to the process of accommodative adaptation. The effect of various topical autonomic drugs on the three phases of adaptation were analyzed: pre-task tonic accommodation (open-loop); within-task accommodative response (closed-loop); and post-task regression of accommodation to pre-task tonic levels. Although it is clear that parasympathetic innervation predominates, there is evidence that some individuals utilize supplementary inhibitory sympathetic innervation. When sympathetic innervation is augmented by substantial levels of concurrent parasympathetic accommodative activity, it may serve to attenuate the magnitude and duration of post-task shifts in tonic accommodation. It is proposed that individuals with a deficit in sympathetic inhibition may therefore be predisposed to anomalies of accommodative adaptation. However, the mechanism by which the oculomotor system responds to such predisposition is at present obscure.

The steady-state accommodative responses of emmetropes and late-onset myopes was measured for an array of numbers located at -1, -3 and -5 dioptres using an objective infra-red optometer. Responses were compared for passive (reading numbers) and active (adding numbers) conditions. For the passive condition, the late-onset myopes showed a significantly lower accommodative response than the emmetropic group. No significant differences were found between the two groups for the active condition. Ocular biometric characteristics were also measured in emmetropes, late-onset myopes and early-onset myopes using keratometry and ultrasonography. No significant differences in corneal curvature, anterior chamber depth and crystalline lens thickness were found between the groups. Late-onset myopes exhibited significantly deeper vitreous chambers than emmetropes, which more than accounted for the difference in refractive error between the two refractive groups. We conclude that, while significant differences exist in the accommodative responses of late-onset myopes and emmetropes, late-onset myopia is due predominantly to elongation of the vitreous chamber.

We describe a new glare test that uses low contrast letters and a variable surround glare source. The test is easy to administer clinically and all test targets, luminance levels, glare geometry, and viewing conditions are well controlled. We found the most useful index of disability glare to be the difference in visual acuity scores for the low contrast chart in the no-glare and high-glare conditions and refer to this as the disability glare index (DGI). We tested a group of normal subjects who were divided into younger (age 15 to 41 years) and older (age 50 to 82 years) groups. The mean DGI value for the older group (10.2 +/- 4.8) was significantly higher than that for the younger group (2.3 +/- 1.9). The DGI is a better discriminator between the two groups than either high or low contrast visual acuity. We attribute the significantly higher DGI values in the older group to increased intraocular light scatter. We find DGI is poorly correlated with high contrast visual acuity (r = 0.33). Our findings suggest that this test of disability glare is sensitive to relatively modest changes in the ocular media. It is a potentially useful tool in detection and assessment of subtle media disturbances and in monitoring changes in the ocular media over a period of time.

Patients with age-related maculopathy (ARM) complain frequently of difficulty with face recognition. The authors attempted to quantify the level of impairment by comparing face recognition with clinical tests of visual function, namely contrast sensitivity, grating acuity, letter-chart acuity, and word-reading acuity. For face recognition, we used 32 black-and-white photographs that had been cropped to remove the outline of hair so that identification was predominantly dependent on the facial features. The observer's distance from the screen on which the photographs were projected was varied. The angular size of the faces was indicated by the equivalent viewing distance (EVD). Four male and four female models were used, and for each model, there were four photographs with different facial expressions--happy, sad, angry, and afraid. For each photograph, the subject's task was to name the model and identify the facial expression. Threshold EVD (50%) was determined for correct identity recognition and expression recognition. For eight subjects all experimental procedures were repeated at a lower luminance level. For ARM subjects, increasing task complexity (grating/letters/words) substantially decreased resolution. Face-recognition abilities were most closely related to word-reading acuity when comparisons were made either across subjects or across luminances within subjects. Contrast sensitivity was associated poorly with face-recognition thresholds. In some subjects with more advanced ARM, identity recognition was substantially poorer than expression recognition.

In clinical practice, there has been a need to grade the magnitude or the severity of the functions and qualities that are assessed in the examination. It is popular to use a four-step grading scale to categorize the severity of clinical findings. The authors discuss clinical grading scales and their influence on the clinician's ability to detect change. These principles have been applied to grades or measures derived from either objective measuring instruments, subjective tests, or techniques in which the clinician makes subjective judgments. A hypothetical data set was used to show the problems associated with using grading scales that are too coarse. The authors presented a mathematic model that helps to estimate the benefits of using use of a finer scale. Data were presented from two separate studies, one on visual acuity measurement and the other on grading nuclear opacity, to show the advantages of using finer scales to enhance the sensitivity of clinical measurement. High levels of concordance between independent observations indicated that the grading scale was too coarse and that these scales needlessly reduced the clinician's ability to detect change in the parameter being assessed. For moderate sensitivity, the size of the scale increments should not exceed one standard deviation of the discrepancy so that the concordance of paired comparisons would not exceed 37%. For fine clinical sensitivity, the size of the scale increments should not exceed one third of the standard deviation of the discrepancy, in which case the concordance of paired comparisons would not exceed 13%. The theory and evidence presented here could prompt re-evaluations of common methods of clinical grading.

The study complements and extends our previous investigation and reports that late-onset myopes (LOM's, N = 15) exhibit differences in adaptation of tonic accommodation (TA) to sustained visual tasks when compared to emmetropes (EMM's, N = 15). Pre- and post-task TA was measured with a modified Canon R-1 objective infra-red optometer under darkroom conditions. Post-task TA was measured immediately after a 10-min counting task and at 1-s intervals over a period of 90 s; the task was located at distances equivalent to 1, 3, and 5 D. The pattern of regression back to the pre-task TA level was used to assess the degree of adaptation generated by the task. The data indicate substantial differences between regression patterns for EMM's and for LOM's which were enhanced as accommodation stimulus levels increased. Using a two-factor split-plot analysis of variance, statistically significant differences between EMM's and LOM's could be attributed to the rates of change of post-task accommodative levels to pre-task TA levels for both the 3 and 5 D tasks.

Pre- and post-task tonic accommodation (TA) was measured using an objective infra-red optometer under two open-loop conditions: a darkroom and a bright empty-field (60 cd m-2). The task was of 10 minutes' duration and was located at -1, -3 and -5 D. Post-task TA was measured immediately after the task and over a period of 90 s. Mean data for the group of 10 young men subjects showed that the open-loop condition adopted had no significant influence on the post-task regression patterns of TA towards pre-task values. Three subjects did, however, show significantly more sustained increases in post-task TA for the bright-field condition; one markedly so. Conversely, two subjects showed more pronounced post-task shifts for the darkroom condition.

An infrared optometer was used to investigate the relation between cognitive induced shifts in tonic accommodation (TA) and ciliary muscle innervation. Twenty emmetropic men volunteers took part in a double-masked protocol which involved high (a reverse counting task) and low levels of mental load and blocking of sympathetic innervation of the ciliary muscle with the nonselective beta receptor antagonist timolol maleate (0.5%). The high level of cognitive demand induced shifts in TA of up to +1 D. There was no clear reason why large differences in intersubject susceptibility to these shifts occurred. The effect of beta-antagonism on these shifts was insignificant for subjects having initial TA values less than 1.2 D. However, sympathetic antagonism induced significant increases in cognitive shifts for the remaining subjects. The inference is that cognitive induced shifts in TA are predominantly parasympathetic mediated although a sympathetic attenuation may occur at higher levels of TA.

The relationship between refractive error and family history, age of onset and personality was investigated in 189 optometry students. Subjects completed a questionnaire requesting details of their refractive history, type of correction and their family history. Subjects also completed an Eysenck Personality Inventory (EPI). Subjects were categorized as hyperopes, emmetropes or myopes on the basis of their questionnaire responses. No significant relationship was found between refractive group and the prevalence of myopia in parents. Myopic subjects, however, showed a significantly higher prevalence of myopic siblings. Furthermore, late-onset myopes showed a higher prevalence of myopic siblings than early-onset myopes. No significant personality differences were found between the refractive groups.

Measurements of tonic accommodation (TA) were made on 25 subjects using He-Ne laser optometry (HNL), infra-red optometry (IR) and near retinoscopy (NR) under darkroom conditions. All three techniques were shown to produce comparable mean estimates of TA (HNL: 1.10 D; IR: 1.15 D; NR: 1.07 D). Significant correlations were found between HNL and IR (r = 0.88, p less than 0.001) and between HNL and NR (r = 0.81. p less than 0.001). Control studies under cycloplegia indicate that the estimates are not seriously affected by fluctuations in accommodative state. These findings indicate that ophthalmic practitioners can gain access to refractive data that aids the clinical management of the "anomalous myopias" and asthenopia associated with VDU work.

The relationship between pupil size and perimetric sensitivity was investigated in a group of clinically normal emmetropic subjects using the Dicon AP3000 computer-assisted perimeter at bowl luminances of 10 asb and 45 asb. Pupil size was modified with the miotic thymoxamine 0.5% and the mydriatic phenylephrine 10%; saline was used as the control. Perimetric sensitivity increased with an increase in pupil size. The effect was greatest for peripheral locations for both bowl luminances. The fluctuations in perimetric sensitivity increased with peripheral angle and with decrease in pupil size for both bowl luminances.

The relationship between accommodative fluctuations and perimetric sensitivity was investigated in a group of 10 clinically normal emmetropic subjects using the Dicon AP3000 computer-assisted perimeter at a bowl luminance of 10 asb. Accommodative microfluctuations were attenuated with the antimuscarinic drug cyclopentolate HCl 1% and the concomitant mydriasis was matched on a separate trial using the sympathomimetic phenylephrine HCl 10%. Saline 0.9% was used as the control. Accommodative microfluctuations were found to play a minor role in determining the magnitude of sensitivity out to an eccentricity of 5 degrees; between 5 degrees and 27.5 degrees, the effect of microfluctuations was masked by the mydriasis produced by the drugs used in the study. The range of sensitivity values at a given location were reduced when accommodative fluctuations were minimized.

This paper discusses stand magnifiers and the optical parameters that clinicians should know in order to understand the viewing requirements and the expected resolution for low vision patients. We report on measurements made of key optical parameters of a new series of stand magnifiers from Combined Optical Industries Limited (COIL) and comparison is made to the previous series of stand magnifiers from the same manufacturer. These results illustrate that manufacturers' specifications of optical parameters are generally inaccurate and misleading. We urge manufacturers to provide clinically relevant information about their optical products.