Search

Nonlinearity in the luminance profile of eccentric, infrared photorefraction may be used to differentiate corneal diseases such as keratoconus that distort the cornea, relative to regular refractive errors.This study aimed to determine the profile of eccentric, infrared photorefraction in keratoconus as a prototypical disease model for distorted corneas and identify a parameter in this profile for differentiating such disease conditions from healthy controls.Photorefraction reflex of 75 eyes with forme fruste to advanced keratoconic cases and that of 75 eyes of controls with regular refractive errors (spherical equivalent, +0.50 to -11.75 D; astigmatism, -0.50 to -4.50 D across 0 to 180° axes) were obtained over their natural pupils under unaided viewing using a custom-designed photorefractor placed at 1 m from the subject. The test was repeated in 10 controls with 4 and 6 D of trial-lens-induced myopia and myopic astigmatism at 0, 90, 45, and 135°. Linear regression was performed on the luminance profile across the pupil, and the departure of the data from linearity was estimated using the average residual error of the fit (Res avg ).Photorefraction profiles varied linearly across the pupil in controls, with slopes increasing with refractive error ( r = 0.87; P.001) and Res avg remaining invariant of refractive error ( r = -0.29; P.4). Corresponding profiles in keratoconus significantly departed from linearity, with Res avg progressively increasing with disease severity ( r = 0.66; P.001). Res avg of 0.03 gray-scale units/pixel distinguished keratoconus from controls with sensitivity increasing from 66.7 to 100% for mild to advanced keratoconus and specificity remaining ≥97.1% across disease severity. Induced myopia and myopic astigmatism produced predictable changes in luminance profile slopes but with no change in Res avg values.Unlike regular myopia and astigmatism, the photorefraction reflex is significantly nonlinear in keratoconus because of the distorted cornea. Measures of nonlinearity in luminance profile may be incorporated in commercial photorefractors for differentiating such disease conditions from regular refractive errors.

In the Pulfrich illusion, the depth of a moving object is misperceived due to induced retinal disparity and/or interocular velocity differences arising from differences in luminance, contrast, or spatial frequency between the two eyes. These effects have been shown to occur both for visual deficits and for optical corrections that introduce significant binocular differences between the retinal images. However, it remains unknown to what extent the illusion might arise given normal variation between the eyes, such as natural interocular variation in pupil diameter (anisocoria). To assess this, we examined the threshold interocular retinal illuminance difference required to experience illusory depth in two random-dot fields moving in opposite directions in 24 normally-sighted observers with dilated pupils. Interocular difference in retinal illuminance was induced by placing neutral density filters of different intensities before the left eye. A minority of subjects (n = 8) did not provide meaningful data on changes in the experience of illusory depth with interocular difference in retinal illuminance and four subjects showed biases >±10% from the 50% point of subjective equality in the psychometric function. For the remaining 12 participants, the retinal illuminance had to differ by approximately 40% for the depth between the planes to become visible at threshold levels. This difference was approximately constant over a range of absolute luminance levels from 10 to 80 cd/m2. Our results suggest that while motion-in-depth illusions due to interocular differences in retinal illuminance may be pronounced in certain ophthalmic diseases or following certain optical interventions, it is unlikely to be manifest as a result of normal interocular variations in retinal illuminance. Further, our results also point towards the existence of substantial individual differences in the experience of what is otherwise thought of as a readily appreciable motion-in-depth illusion.

High-contrast visual acuity is disproportionately poor in patients with accommodative spasm subtype of near reflex (SNR-A), relative to uncorrected refractive errors of equivalent magnitude. This exaggerated loss of performance in SNR-A may be explained by the combination of pseudomyopia and its fluctuations, vis-à-vis, each factor considered separately.To determine how combinations of pseudomyopic refraction and its temporal variations in SNR-A impact high-contrast visual acuity by inducing these patterns in healthy cyclopleged adults, relative to their baseline acuity.Refractive profiles of 15 patients with SNR-A were obtained from a previous study, averaged, and induced before the right eye of 14 cyclopleged adults (mean ±1 SD age: 22.7 ± 2.6 yrs) by feeding the profile into a coaxially placed, motorised, Badal optometer. LogMAR acuity was measured using the method of constant stimuli: (1) before cycloplegia, (2) after cycloplegia and post-cycloplegia with (3) combination of pseudomyopia and its temporal fluctuations, (4) only pseudomyopia, (5) only temporal fluctuations in refraction about emmetropia, (6) condition 5 with double the amplitude of induced fluctuations and (7) condition 5 with half the amplitude of induced fluctuations.The induced refractive fluctuations ranged from -0.80 to -1.75D, around a mean pseudomyopia of -1.20D. Visual acuity deterioration was maximum for the combination of pseudomyopia and temporal fluctuations condition (0.51 ± 0.07logMAR), followed by only pseudomyopia (0.27 ± 0.05logMAR) and only refractive fluctuations conditions (0.17 ± 0.04logMAR), all relative to baseline post-cycloplegia (0.13 ± 0.04logMAR) (p 0.001). Visual acuity loss increased with doubling of refractive fluctuations (0.20 ± 0.04logMAR), relative to native fluctuations or halving the amplitude (0.15 ± 0.03logMAR) (p 0.01). Task precision, as adjudged from the slope of psychometric function, followed a similar pattern of loss as visual acuity.Combination of induced pseudomyopia and temporal fluctuations in refraction produces an additive loss of visual acuity and task precision, relative to baseline and each factor considered separately.

PURPOSE: Clinical assessment of rod and cone photoreceptor sensitivity often involves the use of extended dark adaptation times to minimise cone involvement or the use of bright adapting backgrounds to saturate rods. In this study we examine a new rod/cone sensitivity test, which requires minimal dark adaptation. The aim was to establish whether rod/cone sensitivity losses could be measured reliably in patients with retinal diseases that selectively affect rods or cones when compared to age-matched subjects with normal vision.\ud \ud METHODS: Flicker modulation thresholds (FMTs) were measured psychophysically, using cone- and rod-enhanced stimuli located centrally, and in four quadrants, at 5° retinal eccentricity in 20 patients (age range: 10-41 years) with cone-dominated (Stargardt's disease or macular dystrophy; n = 13) and rod-dominated (retinitis pigmentosa; n = 7) disease. These data were compared against age-matched normals tested with identical stimuli.\ud \ud RESULTS: Across all retinal locations, cone FMTs in cone-dominated diseases (Median ± IQR: 32.32 ± 28.15% for central location) were greater than a majority (83%; 49/59) of corresponding rod FMTs (18.7 ± 3.29%; p = 0.05) and cone FMTs of controls (4.24 ± 2.00%). Similarly, rod FMTs in rod-dominant disease (14.99 ± 22.58%) were greater than a majority (88%; 29/39) of the corresponding cone FMTs (9.09 ± 10.33%) (p = 0.13) and rod FMT of controls (6.80 ± 2.60 %).\ud \ud CONCLUSIONS: Cone-specific deficits were larger than rod-specific deficits in cone-dominated diseases, and vice versa in rod-dominated disease. These results suggest that the new method of assessing photoreceptor sensitivity has potential application in detecting specific rod/cone losses without the need for dark adaptation.

Optical imperfections of the eye, characterized by higher-order wavefront aberrations, are exaggerated in corneal disease (e.g., keratoconus) and iatrogeny (e.g., keratorefractive surgery for myopia correction, keratoplasty for optical clarity restoration). This article reviews the recent advances on this topic for a comprehensive understanding of how optical degradations in disease models impact retinal image quality and monocular and binocular visual performance.Published literature over the last decade on retinal image quality and/or monocular and binocular visual functions with corneal irregularity was reviewed based on their relevance to the current topic, study population and strength of study design. The literature was summarized into four themes: 1) wavefront errors and retinal image quality of highly aberrated eyes, 2) monocular and binocular vision loss consequent to degraded optics and visual strategies to optimize performance, 3) impact of optical correction modalities on visual performance and 4) implications for clinical management of patients.Across the 46 articles reviewed, the results clearly indicated that an increase in higher-order aberrations across these conditions had a significant negative impact on the patient's retinal image quality, and monocular and binocular visual functions. Interocular differences in retinal image quality deteriorated visual performance more than an overall worsening of image quality bilaterally. Minimizing optical degradation using rigid contact lenses and adaptive optics technology significantly improves retinal image quality and monocular and binocular vision, but performance remains sub-optimal relative to age-similar healthy controls.Corneal disease and iatrogeny are useful models to understand the impact of optical degradation on retinal image quality and visual performance. Clinical management will greatly benefit from equalizing retinal image quality of both eyes of these patients. Future studies that deepen our understanding of the structure-function relation in these conditions are desirable for advancing vision science in this area and for developing novel clinical management strategies.

While several advanced contact lens (CL) designs are commercially available for vision correction in keratoconus, their visual performance and optical quality, relative to each other and controls remains unclear. This prospective, crossover study tested the hypothesis that these CL designs would have a differential impact on visual performance and optical quality in subjects with advanced keratoconus, but not in early to moderate disease states.Spatial vision (logMAR acuity and contrast sensitivity), depth vision (stereoacuity) and optical quality (higher-order wavefront aberrations) were measured on 28 bilaterally mild to advanced keratoconics (age: 20-28yrs; 15 males), novice to CL wear, and in 10 age-matched controls using well-established psychophysical and aberrometry techniques. All data were collected on keratoconic subjects with their spectacles and with conventional RGP, Kerasoft®, Rose K2® and Scleral RGP® CL's in randomized order, atleast a week apart from each other.All outcome variables deteriorated with keratoconus severity and improved with CL wear, relative to spectacles (p 0.05). This improvement was smaller for Kerasoft CL (p 0.05) and higher but comparable for the other three CL designs (p = 0.3), across all disease severity. Visual functions and optical quality outcomes never reached control levels for any correction modality (p 0.05).Visual performance and optical quality in keratoconus does not appear to improve commensurately with the sophistication of CL design across disease severity. Non-visual factors like quality of CL fit, wearing comfort and cost may therefore drive the choice of CL dispensed in keratoconus more than the performance efficacy of these lenses.

Purpose: To objectively evaluate surgically induced astigmatism (SIA) after phacotrabeculectomy using keratometry and topography and to compare the magnitude of SIA and the refractive outcomes of single-site and twin-site phacotrabeculectomies. Methods: Forty prospective subjects were enrolled in the study and were randomized into single-site and twin-site cohorts. SIA was objectively assessed using keratometry and Orbscan before and at three months after surgery. For both cohorts, the changes in SIA were assessed using power vector analysis compared at the third month after surgery. Results: Each cohort consisted of 20 eyes. The preoperative parameters and postoperative IOP were comparable and similar, respectively, in both the cohorts (P = 0.1). Majority of the patients in both the cohorts had preoperative against-the-rule (ATR) astigmatism. The median change in SIA at the three-month postoperative visit was similar in both the cohorts, with a small increase in ATR astigmatism. Although the SIA change measured by keratometry in the J0 component was similar in both the groups (P = 0.54), that of J45 was significantly different (P = 0.01). However, the median change in SIA was similar in both the groups for both the J0 (P = 0.52) and J45 components (P = 0.94) when measured by Orbscan. The SIA in both the groups measured with keratometry (P = 0.62) and topography (P = 0.52) were clinically and statistically similar. In both the groups, the refraction was similar at 1 month and 3 months. Conclusion: The SIA as measured with keratometry and topography was similar in the single-site and twin-site phacotrabeculectomy cohorts at the end of 3-months. The postoperative refraction was stabilized in 1-month in both the groups.

To determine 1) the relative differences in optical quality of keratoconic eyes fitted with four routinely used CL designs and 2) the Zernike coefficients in the residual wavefront aberration map that may be responsible for differences in the optical quality of keratoconic eyes fitted with these CLs.Wavefront aberrations over a 3-mm pupil diameter were measured without and with Kerasoft IC®, Rose K2®, conventional spherical Rigid Gas Permeable (RGP), and Scleral CLs in 15 mild to moderate keratoconic eyes (20 - 28 years) and under unaided viewing in 10 age-similar non-contact lens wearing controls. The resultant through-focus curves constructed for the logarithm of Neural Sharpness (logNS) Image Quality (IQ) metric were quantified in terms of peak value, best focus, and depth of focus. Sensitivity analyses determined the impact of the residual Zernike coefficients of keratoconic eyes fitted with CLs on the IQ of controls at emmetropic refraction.The peak IQ and depth of focus were similar with Rose K2®, conventional RGP, and Scleral CLs (p 0.05, for all) but significantly better than Kerasoft IC® CLs (p 0.01 for all). Best focus was similar across all four CLs (p 0.2 for all). However, the IQ parameters of all the lenses remained significantly poorer than the controls (p 0.01, for all). The IQ of the controls dropped to keratoconic levels with induced residual lower-order Zernike terms and 3rd-order coma across all lenses in the sensitivity analysis (p 0.001).IQ of keratoconic eyes remain suboptimal with routinely dispensed CL designs, largely due to residual lower-order aberrations and coma, all relative to the controls. The performance drop appears greater for the Kerasoft IC® CL relative to the other CL designs. These results may provide the optical basis for psychophysical spatial visual performance reported earlier across these four CL designs for keratoconus.

Psychophysical estimates of spatial and depth vision have been shown to be better after bilateral ReLEx small-incision lenticule extraction (SMILE) refractive surgery for myopia, relative to photorefractive keratectomy (PRK) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). The present study provides the optical basis for these findings using computational image quality analysis.This study aimed to compare longitudinal changes in higher-order wavefront aberrations and image quality before and after bilateral PRK, FS-LASIK, and SMILE refractive procedures for correcting myopia.Wavefront aberrations and image quality of both the eyes of 106 subjects (n = 40 for FS-LASIK and SMILE and n = 26 for PRK) were determined pre-operatively and at 1-week, 1-month, 3-month, and 6-month post-operative intervals using computational through-focus analysis for a 6-mm pupil diameter. Image quality was quantified in terms of its peak value and its interocular difference, residual defocus that was needed to achieve peak image quality (best focus), and the depth of focus.The increase in root mean squared deviations of higher-order aberrations post-operatively was lesser after SMILE (1-month visit median [25th to 75th interquartile range], 0.34 μm (0.28 to 0.39 μm]) than after PRK (0.80 μm [0.74 to 0.87 μm]) and FS-LASIK (0.74 μm [0.59 to 0.83 μm]; P ≤ .001), all relative to pre-operative values (0.20 μm [0.15 to 0.30 μm]). The peak image quality dropped and its interocular difference increased, best focus shifted myopically by 0.5 to 0.75 D, and depth of focus widened significantly after PRK and FS-LASIK surgeries, all relative to pre-operative values (P.001). All these changes were negligible but statistically significant in a minority of instances after SMILE surgery (P ≥ .01).Although all three refractive surgeries correct myopia, the image quality and its similarity between eyes are better and closer to pre-operative values after SMILE, compared with FS-LASIK and PRK. These results can be explained from the underlying increase in higher-order wavefront aberrations experienced by the eye post-operatively.

Purpose To determine the utility of root mean squared (RMS) deviations of steady-state accommodation as a noncycloplegic marker for spasm of near reflex (SNR) vis-a-vis regular refractive errors. Methods Binocular steady-state responses of accommodation, pupil, and vergence of 20 patients with accommodative spasm subtype of SNR (SNR-A; 9-23 years) and 91 with regular refractive errors (29 emmetropes, 41 myopes, 21 hyperopes; 19-38 years) was recorded in the uncorrected refractive error state for 120 seconds using a dynamic (50 frames per second), infrared photorefractor. Mean and RMS deviation of raw data was calculated for three 20-second-long epochs and their diagnostic utility was determined using standard ROC curves. Results RMS deviations of accommodation increased with mean refractive error in SNR-A (y = -0.23x + 0.38; r2 = 0.69; P < 0.001) and regular refractive error (y = -0.02x + 0.10; r2 = 0.14; P = 0.002) cohorts, albeit with steeper slope and higher y-intercept in the former rather than the latter cohort. RMS deviation of 0.19D reliably distinguished SNR-A from regular refractive errors with a sensitivity and specificity of 95.2% and 92.2%, respectively [mean (±1 SEM) area under ROC curve: 0.98 ± 0.01]. The sensitivity, specificity, and area under ROC curve for RMS deviations of pupil (66.7%, 80%, and 0.70 ± 0.09) and vergence (52.4%, 84.6%, and 0.68 ± 0.08) were smaller than accommodation. Conclusions RMS deviations of steady-state accommodation is a robust noncycloplegic marker for differentiating SNR-A from regular refractive errors. Pupil and vergence fluctuations have limited utility in this regard. Translational Relevance RMS deviations of accommodation may be easily obtained using commercial photorefractors, and the cut-off values reported herein may be implemented to identify SNR-A during refractive error screening.

Significance This study highlights potential differences that can arise in gaze-position estimates from first Purkinje image-based eye trackers based on how individual Hirschberg ratios (HRs) are calculated. Purpose The purpose of this study was to evaluate the accuracy and repeatability of eccentric-viewing, prism-based, and theoretical techniques that are routinely used to calibrate HR in first Purkinje image-based eye trackers. Methods Hirschberg ratios of 28 participants (18 to 40 years old) were obtained using the PlusOptix PowerRef 3 photorefractor and eye tracker. In the gold standard eccentric-viewing technique, participants viewed eccentric targets (±12°, 4° steps) at 2 m. In the prism-based technique, 4 to 16Δ-D base-out and base-in prisms were placed in 4Δ-D steps before an eye occluded with an infrared filter; the fellow eye fixated a target at 1 m. Each participant's HR was calculated as the slope of the linear regression of the shift in Purkinje image relative to the pupil center for each target eccentricity or induced prism power. Theoretical HR was calculated from the participant's corneal curvature and anterior chamber depth measures. Data collection was repeated on another visit using all three techniques to assess repeatability. Data were also obtained from an Indian cohort (n = 30, 18 to 40 years old) using similar protocols. Results Hirschberg ratio ranged from 10.61 to 14.63°/mm (median, 11.90°/mm) in the eccentric-viewing technique. The prism-based and theoretical techniques demonstrated inaccuracies of 12 and 4% relative to the eccentric-viewing technique. The 95% limits of agreement of intrasubject variability were ±2.00, ±0.40, and ±0.30°/mm for the prism-based, eccentric-viewing, and theoretical techniques, respectively (P > .05). Intraclass correlation coefficients (95% confidence interval) were 0.99 (0.98 to 1.00) for eccentric, 0.99 (0.99 to 1.00) for theoretical, and 0.88 (0.74 to 0.94) for prism-based techniques. Similar results were found for the Indian cohort. Conclusions The prism-based and theoretical techniques both demonstrated relative inaccuracies in measures of HR compared with the eccentric-viewing technique. The prism-based technique exhibited the poorest repeatability.

Accommodative responses of humans operate seamlessly to ensure clear vision of targets at different viewing distances, up until the onset of presbyopia. To achieve this, the visual system must correctly decipher the polarity and magnitude of retinal defocus in real-time, and often under very challenging viewing conditions. The past seven decades of research in this area has identified several retinotopic cues that may potentially provide the desired odd- and even-error information to the visual system for solving these challenges. These studies have used a variety of technology, experimental paradigms and outcome measures to determine the putative contribution of a given cue, or set of cues, in solving this problem. A variety of results, some offering consensus and others conflicting, have been observed in these studies. The present review distils this large volume of literature into specific, take-away points for the early reader of this topic, acknowledging that the problem is non-trivial and far from being solved. The review also reveals that many of these studies may not have used appropriate/sensitive methodology or outcome measures to tease apart the relative contribution of a cue in solving the direction and magnitude challenge. The review concludes with the proposal that, since a multitude of cues may be used by the visual system for solving these problems, future studies could employ a Bayesian statistical cue-combination approach to address this problem. Such approaches have yielded very meaningful insights in other areas of human decision-making involving multiple inter- and intra-modal combination of cues.

Purpose: Keratoconus results in image quality loss in one or both eyes due to increased corneal distortion. This study quantified the depth of monocular suppression in keratoconus due to this image quality loss using a binocular contrast rivalry paradigm.\ud \ud Methods: Contrast rivalry was induced in 50 keratoconic cases (11–31 years) and 12 age-matched controls by dichoptically viewing orthogonal Gabor patches of 5 cycles per degree (cpd) and 1.5 cpd spatial frequency for 120 seconds with their best-corrected spectacles and rigid gas permeable (RGP) contact lenses. The dwell time on each eye's percept was determined at baseline (100% contrast bilaterally) and at varying contrast levels (80–2.5%) in the stronger eye of keratoconus or dominant eye of controls. The contrast reduction needed in the stronger eye to balance dwell times on both eyes was considered a measure of suppression depth.\ud \ud Results: At baseline with 5 cpd stimuli and spectacle correction, the rivalry switches were less frequent and biased toward the stronger eye of cases, all relative to controls (P < 0.001). The contrast balance point of cases (20.51% [10.7–61%]) was lower than the controls (99.80% [98.6–100%]; P < 0.001) and strongly associated with the overall and interocular difference in disease severity (r = 0.83, P < 0.001). The suppression depth reduced for 1.5 cpd (70.8% [21.7–94%]), relative to 5 cpd stimulus (P < 0.001) and with contact lenses (80.1% [49.5–91.7%]), relative to spectacles (P < 0.001).\ud \ud Conclusions: The eye with lesser disease severity dominates binocular viewing in keratoconus. The suppression depth of the poorer eye depends on the extent of bilateral disease severity, optical correction modality, and the target spatial frequency.

Spot-the-difference, the popular childhood game and a prototypical change blindness task, involves identification of differences in local features of two otherwise identical scenes using an eye scanning and matching strategy. Through binocular fusion of the companion scenes, the game becomes a visual search task, wherein players can simply scan the cyclopean percept for local features that may distinctly stand-out due to binocular rivalry/lustre. Here, we had a total of 100 visually normal adult (18–28 years of age) volunteers play this game in the traditional non-fusion mode and after cross-fusion of the companion images using a hand-held mirror stereoscope. The results demonstrate that the fusion mode significantly speeds up gameplay and reduces errors, relative to the non-fusion mode, for a range of target sizes, contrasts, and chromaticity tested (all, p

CITATION: Marmamula, S. et al. 2020. An approach to reduce the blindness burden in sub-Saharan Africa : special focus on childhood blindness, in Macnab, A., Daar, A. & Pauw, C. 2020. Health in transition : translating developmental origins of health and disease science to improve future health in Africa. Stellenbosch: SUN PReSS, doi:10.18820/9781928357759/13.

Purpose The purpose of this study was to determine the accuracy and repeatability of refractive errors obtained using three autorefractors based on different measurement principles, vis-à-vis, gold-standard retinoscopy. Methodology Accuracy of noncycloplegic, sphero-cylindrical refractive error of 234 eyes was obtained using the rotary prism-based RM-8900 closed-field autorefractor, photorefraction based Spot vision screener, wavefront aberrometry based E-see, and streak retinoscopy by four different examiners, masked to the results of each other. Intersession repeatability of autorefractors was determined by repeat measurements in a subset of 40 subjects. Results Retinoscopy values of M, J0, and J45 power vectors for the cohort ranged from −10.2 to 8 D, −1.4 to 1.8 D, and −0.9 to 1.2 D, respectively. Across autorefractors, the interequipment bias of M and J0 power vectors were statistically insignificant (< ±0.5 D; P > 0.05) but the corresponding limits of agreement were ±2.5 and ±1 D, respectively, without any trend across instruments or the patient's age (P > 0.5). Repeatability of M and J0 power vectors were ±0.75 D and ±0.40 D, respectively, across autorefractors. The range of J45 power vector was too narrow for any meaningful analysis. Conclusions Refractive errors measured using autorefractors operating on different principles show minimal bias and good short-term repeatability but relatively large agreement limits, vis-à-vis, retinoscopy. Among them, the wavefront aberrometry based E-see autorefractor performs relatively better in all measurement parameters evaluated here. Translational Relevance Although autorefractor estimates of noncycloplegic refractive error appears independent of their measurement principle, their relatively poor agreement with gold-standard retinoscopy warrants caution while used for screening and quantification of refractive errors.

Purpose To report a consolidated management protocol for patients with spasm of near reflex (SNR), including classification of cases as mild, moderate, and severe based on treatment outcomes. Methods Patients with SNR treated at a single institution between August 2016 and November 2018 were included. Management of SNR included modified optical fogging, vision therapy, and pharmacological intervention (cyclopentolate eye drops and, if required, atropine eye drops). Outcome measures were visual acuity (20/25 or better) and refractive error (reduction of excessive myopia). Results Of 1,306 patients examined during the study period, 66 were diagnosed with SNR, yielding a prevalence of 5% among first-time patients visiting our binocular vision and orthoptics clinic. Of the 45 patients recruited for this study (mean age, 14 ± 5 years; 24 males), all three near-triad components were involved in 11 patients (24%), only the accommodation component in 32 (71%), and only the convergence component in 2 (4%). SNR was relieved in the first post-cyclopentolate refraction visit or with the modified optical fogging technique in 29 patients (66%; mild SNR) and with one-time usage of atropine eyedrops in 10 patients (22%; moderate SNR). In 6 patients (13%), atropine was continued long-term (severe SNR). Of 15 patients with long-term follow-up (1 year), 11 (73%) had persistent relief of SNR. Conclusions In our study cohort, SNR with accommodation component was the most common and could be largely relaxed through a one-time use of cycloplegic eye drops and optical intervention. Only severe forms of SNR may require extended use of strong cycloplegics.

Purpose\ud \ud Rod and cone photoreceptor-specific tests can be time-consuming. A new non-invasive test is described. The test is based on the measurement of flicker modulation thresholds with rod- and cone-enhanced visual stimuli, which requires only minimum adaptation time. Here, we investigated how the rod-and cone-mediated flicker thresholds vary with age.\ud \ud Methods\ud \ud Monocular thresholds with rod and cone–enhanced stimuli were measured in 140 healthy adults, (age range: 18–75 years), foveally (0°) and at four parafoveal locations, at an eccentricity of 5° in each of the four quadrants using five, adaptive, interleaved staircases. Temporal frequencies, stimulus sizes, background luminance and spectral composition, were adjusted appropriately to achieve approximately 1 log unit separation in sensitivity between the rod- and cone-enhanced stimuli. Spectrally calibrated, ‘neutral density’ filters were used to enable adequate control of display luminance for rod enhanced stimuli.\ud \ud Results\ud \ud The magnitude of central and parafoveal rod thresholds was significantly higher than the central and parafoveal cone thresholds, respectively (p < 0.001) in both the age groups. However, the rate of increase in central rod thresholds (y = 0.45x—12.79; linear regression equation) was not significantly steeper than the rate of increase in central (y = 0.29x—8.53) cone thresholds (p = 0.15). Centrally, cone thresholds showed a better correlation with rod central thresholds for the age > 45 years (Spearman correlation, ρ = 0.74, p < 0.001) compared to age ≤ 45 years (ρ = 0.41, p < 0.001).\ud \ud Conclusions\ud \ud Thresholds with rod- and cone-enhanced stimuli are largely invariant below 45 years of age and increase rapidly above this age. This age-wise normative database can be used as an effective functional-marker to assess photoreceptor sensitivities in retinal diseases.

SIGNIFICANCE Laser refractive surgery procedures are efficacious at correcting myopia, but they result in long-term deterioration of optical quality that affects monocular and binocular visual performance. The study shows that the optical quality of the two eyes needs to be similar to optimize binocular visual performance after surgery. PURPOSE This study aimed to systematically analyze longitudinal changes in optical quality, high- and low-contrast logMAR acuity and random-dot stereoacuity before and after three refractive surgery procedures for correcting myopia. METHODS A total of 106 subjects (laser-assisted in situ keratomileusis, 40; photorefractive keratectomy, 26; small-incision lenticule extraction, 40) with myopia and astigmatism ≤1.5 D participated in this prospective cohort-based study. All aforementioned outcome variables were measured in both eyes pre-operatively and 1 week and 1, 3, and 6 months post-operatively. RESULTS Pre-operative myopic spherical equivalent of refraction (median [25th to 75th interquartile range], -6.4 D [-8.0 to -4.2 D] for laser-assisted in situ keratomileusis, -4.3 D [-5.0 to -3.5 D] for photorefractive keratectomy, -5.5 D [-6.5 to -4.3 D] for small-incision lenticule extraction) was corrected to within ±0.75 D of emmetropia in all cohorts up to 6 months post-operatively (P < .001). Higher-order wavefront aberrations, uncorrected high- and low-contrast logMAR acuity, and stereoacuity all worsened and remained so up to 6 months post-operatively, relative to pre-operative values (P < .001). Stereoacuity worsened with both interocular average and difference in the magnitude of higher-order aberrations, whereas logMAR acuities worsened only with interocular average of these aberrations (r ≥ 0.40; P < .01 for all). CONCLUSIONS Although the refractive surgery procedures tested here correct myopia, they result in a sustained (up to 6 months) loss of optical quality and spatial and depth-related visual functions post-operatively. Both interocular average and difference in the eye's optical quality seem to impair binocular visual functions after refractive surgery for myopia.

SIGNIFICANCEThis study showed an improvement in three-dimensional depth perception of subjects with bilateral and unilateral keratoconus with rigid gas-permeable (RGP) contact lens wear, relative to spectacles. This novel information will aid clinicians to consider RGP contact lenses as a management

Purpose: The present study's objectives are 1) to describe a novel model of Diabetic Retinopathy Capacity Building (DRCB) for optometrists in the detection of diabetes-related retinal pathology in India and 2) to assess the outcomes of this model by comparing the ability of optometrists to detect these diseases using retinal photographs, vis-à-vis, a specialist ophthalmologist. Methods: The DRCB model for optometrists conducted between August 2016 and August 2018 included training, certification in the screening, and referral guidelines for Diabetic Retinopathy (DR) and hospital-and community-based service delivery. Training included a 7-month long fellowship in DR and mentored participation as cofacilitators in 1-day orientation workshops on DR screening guidelines across India. The sensitivity and specificity of study optometrists in screening for DR by fundus photography were compared to a retina specialist before certification. Results: A total of eight optometrists successfully completed their DR fellowship in the project duration of 24 months. The sensitivity and specificity of detection of any DR were 95 and 79%, any Diabetic macular edema (DME) was 80 and 86%. The sensitivity and specificity of detection of sight threatening DR were 88 and 90% and DME was 72% and 92% respectively. Seven workshops were cofacilitated by study optometrists training 870 optometrists in DR screening guidelines across India. Conclusion: The present DRCB model results advocate for an optometry coordinated DR screening in India. Lessons learnt from this model can be useful in designing community-based task sharing initiatives for optometrists in DR screening.

Purpose To characterize binocular steady-state accommodation, pupil and convergence responses (near triad) in spasm of near reflex (SNR) before and after optical and pharmacological intervention. To identify the putative source of SNR in the neural control schema of accommodation-vergence interaction using controls-engineering modeling. Methods Near-triad of 15 patients with SNR (9 to 23 years) was recorded using an infrared photorefractor at 2m viewing distance for 120s during clinical presentation, after optical fogging intended to relieve spasm, with cycloplegia, post-cycloplegia and long-term follow-up visits. Data were also collected without cycloplegia in 15 age-matched controls. Schor (1999) model was used to computationally simulate accommodation and vergence responses of controls and SNR. Results Both eyes of SNR exhibited significant myopia and refraction fluctuations ( 0.1). Conclusions Exaggerated fluctuations of steady-state accommodation may be a signature feature of SNR, even while their pupil and convergence responses may remain unaffected. These fluctuations may arise from the tonic accommodation controller, the properties of which could be potentially altered after optical fogging to relieve the disorder.

Higher-order aberrations (HOA’s) are exaggerated in eyes with keratoconus but little is known about their impact on the retinal image quality (IQ) of these eyes. This computational study determined changes in IQ [peak IQ, best focus and depth of focus (DOF)] of 12 subjects with manifest keratoconus in both eyes (KCE cohort), 9 subjects with very asymmetric ectasia (VAE cohort) with and without their Rigid Gas Permeable contact lenses (RGP CL’s) and 20 age-matched controls, using a HOA-based through-focus analysis performed on the logNS IQ metric over 5 mm pupil diameter following cycloplegia. All IQ parameters were significantly worse in the KCE cohort with their native HOA’s, relative to controls and in the ectatic eye of the VAE cohort, relative to the fellow non-ectatic eye (p ≤ 0.008 for all). Reduction in HOA’s of these eyes with RGP CL’s resulted in a significant improvement in all IQ parameters but they all remained significantly poorer than controls (p ≤ 0.02 for all). The inter-subject variability of best focus and the DOF range were inversely related to peak IQ in these eyes (r = 0.85; p

PURPOSE To determine the combined impact of uncorrected astigmatism, pupil diameter, and wavefront aberrations on the distance and near visual performance of pseudophakic eyes with monofocal intraocular lens (IOL) implants using objective image quality (IQ) metrics. METHODS Monocular distance (4 m) and near (40 cm) logMAR acuities of 15 emmetropic pseudophakic eyes were obtained without astigmatism and with 2.5 diopters myopic to 2.5 diopters hyperopic astigmatism induced along a 90-degree axis. The IQ metrics were calculated from the participant's wavefront aberrations and habitual pupil diameter for all values of astigmatism and correlated with logMAR acuity. The analysis was repeated without higher-order aberrations (HOAs) and with the entire wavefront data for 6-, 3-, and 1.5-mm pupil diameters. RESULTS Distance acuity deteriorated with uncorrected astigmatism (p < 0.01), whereas near acuity improved with uncorrected myopic astigmatism and deteriorated with uncorrected hyperopic astigmatism (both p < 0.01). The logEW IQ metric showed the best correlation with logMAR acuity (r = 0.86). Distance logEW values deteriorated whereas near logEW values improved in the presence of HOAs for all values of uncorrected astigmatism (p < 0.01). Distance logEW values for 6- and 3-mm pupil diameters were worse than that of the 1.5-mm pupil diameter for all values of uncorrected astigmatism and for both viewing distances (p < 0.01). CONCLUSIONS Image quality metrics analysis can be used successfully to determine the impact of uncorrected astigmatism, pupil diameter, and HOAs on the distance and near logMAR acuities of pseudophakic eyes with monofocal IOL implants. The improvement in near IQ with uncorrected myopic astigmatism and HOAs suggests that these two factors supplement each other to improve near visual performance of pseudophakic eyes. Such an improvement in near vision is however associated with a loss of distance vision in these eyes.

Stereoacuity losses are induced by increased magnitudes and interocular differences in high-order aberrations (HOAs). This study used keratoconus as a model to investigate the impact of HOAs on disparity processing and stereoacuity. HOAs and stereoacuity were quantified in subjects with keratoconus (n = 21) with HOAs uncorrected (wearing spectacles) or minimized (wearing rigid gas-permeable contact lenses) and in control subjects without keratoconus (n = 5) for 6-mm pupil diameters. Disparity signal quality was estimated using metrics derived from binocular cross-correlation functions of stereo pairs convolved with point-spread functions from these HOAs. Metrics computed for all subjects were compared with stereoacuities. The effects of contrast losses and phase shifts on disparity signal quality were studied independently by manipulating the amplitude and phase components of optical transfer functions. The magnitudes, orientations, interocular relationships in magnitude, and shape of the point-spread function affected the cross-correlation metrics that determine disparity signal quality. Stereoacuity covaries strongly with cross-correlation metrics and moderately with image-quality metrics. Both phase distortions and contrast losses due to HOAs significantly influence computations of binocular disparity. HOA-induced stereoacuity reductions are attributable to disparity blur and noise from image properties that reduce the height and kurtosis of the peak stimulus disparity match of the cross-correlation. Phase distortions and contrast losses due to HOAs are both partly responsible for the greater stereoacuity losses seen with spectacles compared to rigid gas-permeable contact lenses in keratoconus.

PURPOSE To compare the accommodative gain and pupil miosis of children with only one functional eye with the binocular and monocular accommodative and pupil responses of typically developing age-matched controls. METHODS Forty-one uniocular cases and 43 controls (3-14 years for both cohorts) watched a cartoon movie on an LCD screen that ramped between 90 and 30 cm, with a stable period of 4 seconds at both viewing distances. Cases performed the task with their only functional eye whereas controls performed the task binocularly and monocularly. A subset of subjects also repeated the task while reading 20/40-sized letters on the LCD screen. Accommodative and pupil responses were recorded using the Plusoptix PowerRef3 photorefractor. RESULTS Accommodative gain of cases [median (25th-75th IQR): 0.73 (0.60-0.85)] was larger than the monocular gain of controls [0.56 (0.47-0.79)] (P = .03). Both responses were lower than the binocular gain of controls [0.95 (0.81-1.11)] (P < .001). Uniocular pupil miosis of cases [0.14 mm (0.06-0.24 mm)] were similar to monocular [0.12 mm (0.05-0.29 mm)] (P = .69) and smaller than binocular [0.23 mm (0.14-0.34 mm)] (P < .001) responses of controls. The increase in accommodative gain from movie watching to reading was significant only for controls (P = .02) but not for cases (P = .15). Age and time of visual deficit were poorly correlated with accommodative gain and pupil miosis of cases (r ≤ 0.25; P ≥ .1 for all). Age was also poorly correlated with the binocular and monocular accommodative and pupil performance of controls (r ≤ -0.3; P = .33). CONCLUSIONS The accommodative gain of children with permanent loss of binocularity is in between the binocular and monocular gains of typically developing children. Their accommodative gains do not show any significant increase with a cognitively demanding task even while such a behavior is observed in controls. Pupil responses of uniocular children are similar to the monocular responses of age-matched controls.

Positive- and negative-powered ophthalmic lenses are used in eccentric infrared photorefraction to calibrate the device, correct the subject's baseline refractive error before an experimental manipulation, or stimulate blur-driven accommodation. Through theoretical modeling of luminance gradients formed across the pupil and empirical measurements of the eye's refractive error using a commercial photorefractor, this study shows that image magnification by positive lenses and image minification by negative lenses under- and overestimates the refractive error, respectively, all independent of image defocus. The impact of image magnification/minification therefore appears non-trivial in experimental paradigms involving ophthalmic lenses to manipulate the eye's optics during photorefraction.

Pseudo emulsion based hollow fiber strip dispersion technique (PEHFSD) is the first of its kind ever explored in radioactive environment for the extraction of uranium from acidic process streams. Permeation of U(VI) was investigated as a function of various experimental variables such as hydrodynamic conditions (flow rates of pseudo-emulsion and feed phase), concentration of U(VI) in the feed phase, concentration of tri-n-butylphosphate (TBP), HNO3 concentration in feed phase, O/A ratio and 0.01 M HNO3 as stripping agent in pseudo-emulsion phase. The mass transfer coefficient was calculated from the experimental results and a model has been presented for determining mass transfer characteristics. PEHFSD has been demonstrated for separation/recovery of uranium from oxalate supernatant waste generated during plutonium precipitation by oxalic acid. PEHFSD and HFSLM (hollow fiber supported liquid membrane) performance has been compared in order to analyze the efficiency of the technique.

Purpose To test the hypothesis that binocular depth of field can be expanded while retaining high-quality vision at intermediate distances by combining anisometropia (monovision) and simultaneous vision bifocals. setting School of Optometry, Indiana University, Bloomington, Indiana, USA. Design Prospective research study. Methods A computational polychromatic model was used to simulate retinal images as seen through a pseudophakic eye with a diffractive bifocal for a range of target distances. Computationally blurred stimuli were presented dichoptically, simulating a binocular pseudophakic person with 1 emmetropic eye and 1 eye with myopia of 0.40 diopter (D), 0.80 D, or 1.20 D. Binocular visual acuity was measured for computationally blurred high-contrast Sloan letters. Results Ten subjects participated in this study. The emmetropic eye achieved best vision at infinity and near distance specified by the addition (add) power, while the myopic eye peak acuities were achieved at shorter viewing distances. Having 1 myopic bifocal eye had no effect on distance acuities. With a bifocal add of 2.20 D and 1.20 D of anisometropia, the binocular depth of focus was more than 3.00 D and provided binocular acuities of better than 20/20 throughout this range. For each target distance, the binocular acuities closely approached those of the better-focused eye. Conclusions By careful selection of unilateral myopia and bilateral use of high-quality bifocal lenses, high intermediate distance acuities can exist with a large depth of field. This approach can improve intermediate vision and expand depth of field without compromising best achievable distance and near acuities. Financial Disclosure None of the authors has a financial or proprietary interest in any material or method mentioned.

Laser refractive surgery for myopia increases the eye's higher-order wavefront aberrations (HOA's). However, little is known about the impact of such optical degradation on post-operative image quality (IQ) of these eyes. This study determined the relation between HOA's and IQ parameters (peak IQ, dioptric focus that maximized IQ and depth of focus) derived from psychophysical (logMAR acuity) and computational (logVSOTF) through-focus curves in 45 subjects (18 to 31 yrs) before and 1-month after refractive surgery and in 40 age-matched emmetropic controls. Computationally derived peak IQ and its best focus were negatively correlated with the RMS deviation of all HOA's (HORMS) (r≥-0.5; p0.16 for all). Increase in HOA's after refractive surgery is therefore associated with a decline in peak IQ and a persistence of this sub-standard IQ over a larger dioptric range, vis-à-vis, before surgery and in age-matched controls. This optical deterioration however does not appear to significantly alter psychophysical IQ, suggesting minimal impact of refractive surgery on the subject's ability to resolve spatial details and their tolerance to blur.

This study was conducted to evaluate the range of services provided by optometrists in various modes of optometric practice in India.An online questionnaire was administered to 1674 optometrists to collect information on the range of optometric services offered. Data were analyzed based on variables including sex, educational qualification, and modes of practice. Two-sample Wilcoxon rank sum tests, χ tests, and Fisher exact text were used to conduct inferential statistics.A total of 563 valid and completed survey questionnaires were received from graduates of 41 optometry institutes working across 23 states of India. Of these, 225 (40.0%) were female, 288 (51.2%) had completed postgraduate education, and 340 (60.5%) were involved in more than one mode of practice. The top three modes of practice were hospital-based practice (44.8%), academia (42.8%), and optical retail (33.0%). Of the 441, out of 563 (78.3%) respondents involved in patient care, the majority (98.4%) performed refraction and routine eye examination, 70.3% dispensed contact lenses, and 66.9% practiced optical dispensing. Lower involvement was seen in providing binocular-vision (45.1%) and low-vision services (30.2%). Higher education was associated with advanced level of practice (p0.05) except clinical investigative procedures. There was a significant association between postgraduate studies and involvement in academics and research (p0.01).Most optometrists are engaged in multiple modes of practice, with optical practice, hospital-based practice, and academia being the leading modes. Optometrists need to be more involved in providing the core optometric services of binocular vision and low vision. Higher education has an impact on the level of optometric practice.

Peak velocity and peak acceleration of disaccommodation step responses remain invariant of response magnitude for a constant starting position and they increase linearly with proximity of starting position. This suggests that disaccommodation response is initiated towards an initial (default) destination and is switched mid-flight to attain the desired final destination. The dioptric location of initial destination was estimated from the x-intercept of regression of peak velocity on response starting position. The x-intercept correlated well with subject’s cycloplegic refractive state and poorly with their dark focus of accommodation. Altering the dark focus by inducing fatigue in the accommodative system did not alter the x-intercept. These observations suggest that cycloplegic refractive state is a good behavioral correlate of initial destination of disaccommodation step responses.

Velocity and acceleration characteristics provide valuable information about dynamic control of accommodation. We investigated velocity and acceleration of disaccommodation (near-far focusing) from three starting positions. Peak velocity and peak acceleration of disaccommodation increased with the proximity of starting position however for a given starting position they were invariant of response magnitude. These results suggest that all disaccommodation responses are initiated towards a constant primary destination and are switched mid-flight to attain the desired final position. Large discrepancies between the primary destination and desired final position appear to produce overshoots and oscillations of small responses from proximal starting positions.

Dynamic properties and control strategies of step responses by accommodation and disaccommodation differ from one another. Peak velocity of accommodation increases with response magnitude, while peak velocity and peak acceleration of disaccommodation increase with starting position. These dynamic properties can be modeled as control strategies that use independent acceleration-pulse and velocity-step components that are integrated respectively into phasic-velocity signals that control movement and tonic-position signals that control magnitude. Accommodation is initiated toward its final destination by an acceleration-pulse whose width increases with response magnitude to increase peak velocity. Disaccommodation is initiated toward a default destination (the far point) by an acceleration-pulse whose height increases with dioptric distance of the starting position to increase peak velocity and peak acceleration. Both responses are completed and maintained by tonic-position signals whose amplitudes are proportional to the final destination. Mismatched amplitudes of phasic-velocity and tonic-position signals in disaccommodation produce unstable step responses.

Eccentric infrared photorefraction is an attractive tool for measuring refractive errors of young children and uncooperative subjects, for it allows quick and non-invasive acquisition of data from both eyes simultaneously over a reasonably large dioptric range. Accuracy of refraction in this technique depends on calibration of luminance slope formed across the pupil into diopters (defocus calibration factor). Commercial photorefractors, like the PowerRef 3™ used in this study, employ an universal defocus calibration factor from one population (Caucasian) to convert raw data of all populations. This study reports significantly larger defocus calibration factors of PowerRef 3™ in 132 East Asian, African and Indian eyes, relative to the machine's default calibration (p < 0.001). The calibration slope of 50 Indian eyes was over-estimated by 64 ± 11% (mean ± 95%CI), vis-à-vis, retinoscopy (p < 0.001). The error reduced to ~6–7% upon rescaling the data using a calibration factor specific for Indian eyes or to that individual (p > 0.9, relative to no over-estimation). Our results therefore strongly suggest the use of an ethnicity- or individual-specific defocus calibration factor for accurate estimation of refraction using photorefraction. Inaccurate refraction estimates due to calibration errors will otherwise severely undermine the advantages of this technique.

Induced myopic astigmatism improves the monocular near logMAR (logarithm of the minimal angle of resolution) acuity of pseudophakes with monofocal intraocular lens implants but with a small loss in distance acuity. The impact of induced astigmatism on binocular vision of pseudophakes remains unknown. This study determined the impact of bilaterally induced astigmatism on binocular distance and near logMAR and stereoacuity of bilateral pseudophakes with monofocal intraocular lens implants.Distance (3 m) and near (40 cm) logMAR acuity and near (40 cm) stereoacuity were measured in 15 bilateral pseudophakes with 10 different combinations of induced astigmatism. Combinations were chosen such that one eye had no astigmatism or 1 diopter (D) myopic astigmatism at 90 degrees axis or 1 D hyperopic astigmatism at 90 degrees axis. The fellow eye had the same error or that with orthogonal axis (180 degrees) or different magnitude (2.5 D) or opposite polarity.Distance logMAR acuity deteriorated by up to 0.2 logMAR units from median best-corrected values (-0.06 logMAR) only for bilaterally induced (p0.01) but not for unilaterally induced (p0.9) astigmatism. Near logMAR acuity and stereoacuity improved by up to 0.25 logMAR units and 130 arc sec from their respective median uncorrected values (0.65 logMAR and 225.8 arc sec) for induced myopic astigmatism (p0.001). Near acuity was similar or worse than uncorrected values for induced hyperopic astigmatism (p ≥ 0.003). Stereoacuity was better with parallel than with orthogonal axes of induced myopic astigmatism in the two eyes (p = 0.001). LogMAR acuity did not change with axis of astigmatism in the two eyes (p0.6).Distance and near logMAR acuity and stereoacuity of bilateral pseudophakes vary with the combination of astigmatism induced before two eyes. Combinations with myopic astigmatism partly benefit binocular near vision, albeit with a loss of distance vision. Near stereoacuity is better with parallel than with orthogonal axes of myopic astigmatism in the two eyes. Visual performance is equal to or worse than uncorrected condition for hyperopic astigmatism.

PURPOSE Gaze position is calibrated in first Purkinje image-based eye trackers using the population-average Hirschberg ratio (HR) that is prone to inaccuracies or using the individual's HR that is cumbersome to obtain empirically. This study investigated (1) the agreement between HR calculated theoretically from the individual's corneal curvature and anterior chamber (AC) depth and those obtained empirically and (2) the contribution of corneal curvature and AC depth in the intersubject variance of the two HRs. METHODS Twenty-four subjects (mean ± SD age, 23.6 ± 3.5 years) fixated monocularly on a light-emitting diode array spanning ±24 degrees of horizontal or vertical gaze angle, in 4-degree steps, at 95 cm viewing distance. Empirical HR was determined using a custom-designed infrared eye tracker as the magnitude of separation between Purkinje image position and entrance pupil center per unit change in angular eccentricity. Theoretical HR was calculated from the subject's corneal curvature and AC depth using the model of Brodie (1987). RESULTS Empirical and theoretical HRs for horizontal and vertical gaze directions were well correlated (r ≥ 0.83) and not significantly different from each other (p ≥ 0.23; mean difference [±95% limits of agreement], -0.35 [0.85 to -1.55] degrees/mm for horizontal HR and -0.16 [1.01 to -1.33] degrees/mm for vertical HR). Corneal curvature and AC depth together accounted for greater than or equal to 80% and greater than or equal to 91% of intersubject variance in empirical and theoretical HR, respectively (p < 0.001). Hirschberg ratios changed at -2.3 to -2.8 degrees/mm per millimeter change in corneal curvature and at 2.0 to 2.4 degrees/mm per millimeter change in AC depth. CONCLUSIONS Theoretical HR calculated from the individual's corneal curvature and AC depth can be used in lieu of the empirical HR for gaze position calibration to within approximately 2 degrees/mm of accuracy. Gaze position accuracy significantly improves by using the theoretical HR, relative to the population-average HR. Corneal curvature and AC depth combined explain the majority of intersubject variability in HR.

PURPOSE.: The end point of astigmatic correction after cataract surgery will depend on how uncorrected astigmatism impacts distance and near vision of pseudophakic eyes. This study determined the impact of induced astigmatism and pupil size on the distance and near acuity of otherwise emmetropic pseudophakic eyes implanted with monofocal intraocular lenses. METHODS.: Monocular high-contrast distance (4 m) and near (40 cm) logMAR acuity was determined in 15 subjects (mean ± 1 SD, 57.9 ± 9.0 years) without astigmatism and with 2.5 diopters (D) myopic to 2.0 D hyperopic astigmatic lenses induced in 0.5-D steps at 0-, 45-, 90-, and 135-degree axes. This experiment was repeated for the same range of induced astigmatism with 1.5-, 3-, and 6-mm artificial pupil diameters placed before one eye of 10 subjects dilated with 10% phenylephrine HCl. RESULTS.: Distance acuity deteriorated with astigmatism for all axes tested (p < 0.01). Near acuity deteriorated with hyperopic astigmatism (p < 0.1), whereas it improved with up to 1 D of myopic astigmatism before saturating for all axes tested (p < 0.01). Distance and near acuity improved with a reduction in pupil diameter (p < 0.01). The change in distance and near acuity with induced astigmatism was smaller for 1.5-mm than for 3-mm and 6-mm pupil diameters (p < 0.01). CONCLUSIONS.: Partial restoration of near acuity with uncorrected myopic astigmatism comes with a proportional loss of distance acuity in pseudophakic eyes. Uncorrected myopic astigmatism more than 1 D results in a large loss of distance acuity at no additional benefit to near acuity. Both distance and near acuities with and without astigmatism are benefited with a reduction in pupil diameter. Uncorrected hyperopic astigmatism results in deterioration of both distance and near acuities of pseudophakic eyes.

Accommodative and vergence responses of the typically developing visual system are generated using a combination of cues, including retinal blur and disparity. The developmental importance of blur and disparity cues in generating these motor responses was assessed by placing the two cues in conflict with each other. Cue-conflicts were induced by placing either -2 D lenses or 2 MA base-out prisms before both eyes of 140 subjects (2.0 months to 40.8 years) while they watched a cartoon movie binocularly at 80 cm. The frequency and amplitude of accommodation to lenses and vergence to prisms increased with age (both p < 0.001), with the vergence response (mean +/- 1 SEM = 1.38 +/- 0.05 MA) being slightly larger than the accommodative response (1.18 +/- 0.04 D) at all ages (p = 0.007). The amplitude of these responses decreased with an increase in conflict stimuli (1 to 3 D or MA) (both p < 0.01). The coupled vergence response to -2 D lenses (0.31 +/- 0.06 MA) and coupled accommodative response to 2 MA base-out prisms (0.21 +/- 0.02 D) were significantly smaller than (both p < 0.001) and poorly correlated with the open-loop vergence (r = 0.12; p = 0.44) and open-loop accommodation (r = -0.08; p = 0.69), respectively. The typically developing visual system compensates for transiently induced conflicts between blur and disparity stimuli, without exhibiting a strong preference for either cue. The accuracy of this compensation decreases with an increase in amplitude of cue-conflict.