Longitudinal changes in objective accommodative response, pupil size and spherical aberration: A case study.

PURPOSE: Previous transverse and a handful of longitudinal studies have shown that the slope of the static accommodation response/stimulus curve declines as complete presbyopia is approached. Changes in pupillary miosis and ocular spherical aberration (SA) are also evident. This study further investigated longitudinal changes in the relationships between the monocular static accommodative response, pupil diameter and SA of a single adult. METHODS: A wavefront analysing system, the Complete Ophthalmic Analysis System, was used in conjunction with a Badal optometer to allow continuous recording of the aberration structure of the dominant eye in a low myope for a range of accommodative demands (-0.83 to 7.63 D) over a period of 17 years until the age of 50. Monocular accommodative response was calculated as the equivalent refraction minimising wavefront error. The associated longitudinal changes in pupil size and SA with accommodation were also recorded. RESULTS: A decrease in accommodation response with age was found at almost all target vergences, with the changes being greatest for higher vergences. In addition, although absolute pupil diameter decreased with age, the rate of change in pupil diameter with accommodative stimulus remained approximately constant with age. Pupil constriction occurred for near stimuli even in full presbyopia. SA changed linearly with the accommodation response at all ages. CONCLUSIONS: The objective amplitude of accommodation declined linearly with age as complete presbyopia was approached, while the slope of the response/stimulus curve also fell. It was hypothesised that the retinal image blur associated with the larger lags of accommodation at higher accommodative stimuli was reduced by pupil constriction and the resulting lower levels of SA.

Additional measures of macular function beyond visual acuity.

PURPOSE: Visual function is a complex process in which external visual stimuli are interpreted. Patients with retinal diseases and prolonged follow-up times may experience changes in their visual function that are not detected by the standard visual acuity measure, as they are a result of other alterations in visual function. With the advancement of different methods to evaluate visual function, additional measurements have become available, and further standardization suggests that some methods may be promising for use in clinical trials or routine clinical practice. The objectives of this article are to review these additional measurements and to provide guidance on their application. METHODS: The Vision Academy's membership of international retinal disease experts reviewed the literature and developed consensus recommendations for the application of additional measures of visual function in routine clinical practice or clinical trials. RESULTS: Measures such as low-luminance visual acuity, contrast sensitivity, retinal fixation and microperimetry, and reading performance are measures which can complement visual acuity measurements to provide an assessment of overall visual function, including impact on patients' quality of life. Measures such as dark adaptation, color vision testing, binocular vision testing, visual recognition testing, and shape discrimination require further optimization and validation before they can be implemented in everyday clinical practice. CONCLUSION: Additional measurements of visual function may help identify patients who could benefit from earlier diagnosis, detection of disease progression, and therapeutic intervention. New and additional functional clinical trial endpoints are required to fully understand the early stages of macular disease, its progression, and the response to treatment.

Efficacy οf Wet Age-related Macular Degeneration Treatment οn Reading: A Pilot Study Using Eye-movement Analysis.

SIGNIFICANCE: Functional vision, as evaluated with silent passage reading speed, improves after anti-vascular endothelial growth factor (anti-VEGF) treatment in patients with wet age-related macular antidegeneration (wAMD), reflecting primarily a concomitant reduction in the number of fixations. Implementing eye movement analysis when reading may better characterize the effectiveness of therapeutic approaches in wAMD. PURPOSE: This study aimed to evaluate silent reading performance by means of eye fixation analysis before and after anti-VEGF treatment in wAMD patients. METHODS: Sixteen wAMD patients who underwent anti-VEGF treatment in one eye and visual acuity (VA) better than 0.5 logMAR served as the AMD group. Twenty adults without ocular pathology served as the control group. Central retinal thickness and near VA were assessed at baseline and 3 to 4 months after their first visit. Reading performance was evaluated using short passages of 0.4-logMAR print size. Eye movements were recorded using EyeLink II video eye tracker. Data analysis included computation of reading speed, fixation duration, number of fixations, and percentage of regressions. Frequency distributions of fixation durations were analyzed with ex-Gaussian fittings. RESULTS: In the AMD group, silent reading speed in the treated eye correlated well with central retinal thickness reduction and improved significantly by an average of 15.9 ± 28.5 words per minute (P = .04). This improvement was accompanied by an average reduction of 0.24 ± 0.38 in fixations per word (P = .03). The corresponding improvement in monocular VA was not statistically significant. Other eye fixation parameters did not change significantly after treatment. No statistically significant differences were found in the control group. CONCLUSIONS: Visual acuity tests may underestimate the potential therapeutic effects after anti-VEGF treatment in patients with relatively good acuity who are being treated for wAMD. Evaluating silent reading performance and eye fixation parameters may better characterize the effectiveness of therapeutic approaches in wAMD patients.

Modelling changes in the prevalence of childhood myopia.

PURPOSE: To re-examine the changes with time in the underlying patterns of individual refraction at different ages, which have led to an increased prevalence of myopia in a population of Asian children. METHODS: Using published cross-sectional longitudinal data, the frequency distributions of spherical equivalent refractive error (SE) in yearly cohorts of 6- and 12-year-old Japanese children during the period 1984-1996 were modelled in terms of ex- and bi-Gaussian distributions. RESULTS: Both models suggested that over the period of the study, little change occurred in the SE frequency distributions for 6-year-olds, with most children having SEs near emmetropia. In contrast, in each annual cohort of 12-year-olds, although the SE of some children remained near-emmetropic, a sub-set failed to maintain emmetropia. Most of this group became more myopic between 6 and 12 years of age. The proportion of children showing myopic progression increased over the period of study. CONCLUSIONS: The observed increase in mean levels of myopia in older Japanese children in the late 20th century is due to a greater proportion of children failing to maintain emmetropisation between the ages of 6 and 12, rather than to myopic shifts in all children. Some children, with small SE changes between 6 and 12 years of age, would not have benefitted from any treatment intended to slow myopia progression.

Mutations in CEP78 Cause Cone-Rod Dystrophy and Hearing Loss Associated with Primary-Cilia Defects.

Cone-rod degeneration (CRD) belongs to the disease spectrum of retinal degenerations, a group of hereditary disorders characterized by an extreme clinical and genetic heterogeneity. It mainly differentiates from other retinal dystrophies, and in particular from the more frequent disease retinitis pigmentosa, because cone photoreceptors degenerate at a higher rate than rod photoreceptors, causing severe deficiency of central vision. After exome analysis of a cohort of individuals with CRD, we identified biallelic mutations in the orphan gene CEP78 in three subjects from two families: one from Greece and another from Sweden. The Greek subject, from the island of Crete, was homozygous for the c.499+1G>T (IVS3+1G>T) mutation in intron 3. The Swedish subjects, two siblings, were compound heterozygotes for the nearby mutation c.499+5G>A (IVS3+5G>A) and for the frameshift-causing variant c.633delC (p.Trp212Glyfs(∗)18). In addition to CRD, these three individuals had hearing loss or hearing deficit. Immunostaining highlighted the presence of CEP78 in the inner segments of retinal photoreceptors, predominantly of cones, and at the base of the primary cilium of fibroblasts. Interaction studies also showed that CEP78 binds to FAM161A, another ciliary protein associated with retinal degeneration. Finally, analysis of skin fibroblasts derived from affected individuals revealed abnormal ciliary morphology, as compared to that of control cells. Altogether, our data strongly suggest that mutations in CEP78 cause a previously undescribed clinical entity of a ciliary nature characterized by blindness and deafness but clearly distinct from Usher syndrome, a condition for which visual impairment is due to retinitis pigmentosa.

Assessing Variability in Reading Performance with the New Greek Standardized Reading Speed Texts (IReST).

SIGNIFICANCE: This article evaluates the standardized Greek version of the International Reading Speed Texts (IReST) set, which enriches interlanguage comparisons and international clinical studies of reading performance. Moreover, it investigates how specific textual and subject-related characteristics modulate the variability of reading speed across texts and readers. PURPOSE: The purpose of this study was to develop a standardized Greek version of the IReST set and investigate how specific textual and subject-related factors modulate the variability of reading speed across texts and readers. METHODS: The English IReST texts were translated to Greek and matched for length, content, and linguistic difficulty. The Greek IReSTs were presented at a distance of 40 cm and size of 1 M to assess reading speeds of 25 normally sighted native speakers (age range, 18 to 35 years). The participants read the texts aloud while reading time was measured by stopwatch. Reading performance included measurement of reading speed in three units of analysis. Reading efficiency was assessed using a word-level oral reading task. Statistical analysis included evaluation of subject- and text-related variability, as well as correlations between reading speed and specific textual and subject-related factors. RESULTS: The average reading speed between texts was 208 ± 24 words/min, 450 ± 24 syllables/min, and 1049 ± 105 characters/min. Differences between readers accounted for the 76.6%, whereas differences across texts accounted for the 23.4% of the total variability of reading speed. Word length (in syllables per word) and median word frequency showed a statistically significant contribution to the variability of reading speed (r = 0.95 and 0.70, respectively). Reading speed was also statistically correlated with word reading efficiency (r = 0.68). CONCLUSIONS: The addition of the Greek version in the IReST language pack is expected to be a valuable tool for clinical practice and research, enriching interlanguage comparisons and international studies of reading performance.

Photoacoustic imaging methodology for the optical characterization of contact lenses.

We demonstrate photoacoustic microscopy as a metrology method for the optical characterization and quality control of contact lenses (CLs). Dual-wavelength excitation is applied to CLs tinted on both sides with two thin ink layers, each of them possessing distinctly different optical absorption properties. Thus, the method is capable of measuring the elevation maps of both CL surfaces during two subsequent imaging sessions and extracting the CL thickness, curvatures, and dioptric power. We show that such an easily implementable technique provides robust, high-precision, cost-effective three-dimensional imaging and characterization of both rigid and soft CLs, which renders it highly favorable for a broad range of applications.

Do small-aperture presbyopic corrections influence the visual field?

PURPOSE: To explore the effect of small-aperture optics, designed to aid presbyopes by increasing ocular depth-of-focus, on measurements of the visual field. METHODS: Simple theoretical and ray-tracing models were used to predict the impact of different designs of small-aperture contact lenses or corneal inlays on the proportion of light passing through natural pupils of various diameters as a function of the direction in the visual field. The left eyes of five healthy volunteers were tested using three afocal, hand-painted opaque soft contact lenses (www.davidthomas.com). Two were opaque over a 10 mm diameter but had central clear circular apertures of 1.5 and 3.0 mm in diameter. The third had an annular opaque zone with inner and outer diameters of 1.5 and 4.0 mm, approximately simulating the geometry of the KAMRA inlay (www.acufocus.com). A fourth, clear lens was used for comparison purposes. Visual fields along the horizontal meridian were evaluated up to 50° eccentricity with static automated perimetry (Medmont M700, stimulus Goldmann-size III; www.medmont.com). RESULTS: According to ray-tracing, the two lenses with the circular apertures were expected to reduce the relative transmittance of the pupil to zero at specific field angles (around 60° for the conditions of the experimental measurements). In contrast, the annular stop had no effect on the absolute field but relative transmittance was reduced over the central area of the field, the exact effects depending upon the natural pupil diameter. Experimental results broadly agreed with these theoretical expectations. With the 1.5 and 3.0 mm pupils, only minor losses in sensitivity (around 2 dB) in comparison with the clear-lens case occurred across the central 10° radius of field. Beyond this angle, sensitivity losses increased, to reach about 7 dB at the edge of the measured field (50°). The field results with the annular stop showed at most only a slight loss in sensitivity (≤3 dB) across the measured field. CONCLUSION: The present theoretical and experimental results support earlier clinical findings that KAMRA-type annular stops, unlike circular artificial pupils, have only minor effects on measurements of the visual field.

Problems in comparisons of data for the prevalence of myopia and the frequency distribution of ametropia.

PURPOSE: There is currently great interest in comparing data for the prevalence of myopia in different parts of the world, particularly in view of the suggestion that, in recent decades, marked increases have occurred in prevalence among children and young adults in some areas. This work investigates the factors that affect the comparison and interpretation of sets of myopia prevalence data for different age groups, locations and dates. RECENT FINDINGS: Using data from the literature, the problems caused by the effect of the reliability and validity of the method used to measure refraction, the threshold chosen to define an eye as myopic are discussed. The influence of slow drifts in refraction with age is considered and it is recommended that if mean refractions at different ages are to be compared, the interpretation of the results should take account of the normal age-dependent trends in refraction. The value of specifying the distribution of refractive errors, rather than simply their mean and standard deviation, is emphasised and possible parametric fits to describe these distributions are reviewed. SUMMARY: There remains a need for greater standardisation in sampling strategies, refractive measurement procedures and definition of myopia in prevalence studies. The use of an ex-Gaussian or other approximations to describe the refractive error distribution appears to give useful insights into the nature of the changes that may occur with age and other factors.

Silicone oil insulation effects on flash electroretinogram and visual evoked potential in patients with retinal detachment.

BACKGROUND: Silicone oil is used as endotamponade following vitreoretinal surgery to maintain the retina reattached when indicated. This study investigates the hypothesis that silicone oil causes insulation effects on the retina by affecting its response to light. METHODS: Electrophysiological responses to a flash stimulus were recorded using full-field electroretinography (ERG) and visual evoked potentials (VEP). Recordings were performed in 9 patients who underwent surgery for retinal detachment, before (1-2 days) and after (2-3 weeks) silicone oil removal (SOR) in both the study and the control eye. Flash ERG and VEP recordings were performed according to the ISCEV standard protocol. RESULTS: Statistically significant differences were found in the study eye in the amplitudes of the ERG responses and their corresponding ratios, i.e. the amplitude after SOR over the amplitude before SOR, in all conditions tested. No differences were observed in the control eye. The mean ratio of photopic ERG response was 3.4 ± 2.4 for the study and 1.0 ± 0.3 for the control eye (p<0.001). The mean ratio of ERG flicker response was 3.1 ± 2.4 and 1.0 ± 0.3, respectively (p = 0.003). Scotopic flash ERG ratio was 5.0 ± 4.4 for the study and 1.3 ± 0.6 for the control eye (p = 0.012). No differences were observed for the amplitude and latency of flash VEP response after SOR. CONCLUSIONS: Silicone oil causes a reduction in flash ERG responses; no effect was found on flash VEP responses. ERGs in eyes filled with silicone oil should not be considered representative of retinal functionality, in contrast to VEPs, which are not affected by silicone oil presence.

BCLA CLEAR presbyopia: Mechanism and optics.

With over a billion adults worldwide currently affected, presbyopia remains a ubiquitous, global problem. Despite over a century of study, the precise mechanism of ocular accommodation and presbyopia progression remains a topic of debate. Accordingly, this narrative review outlines the lenticular and extralenticular components of accommodation together with the impact of age on the accommodative apparatus, neural control of accommodation, models of accommodation, the impact of presbyopia on retinal image quality, and both historic and contemporary theories of presbyopia.

Binocularity enhances visual acuity of eyes implanted with multifocal intraocular lenses.

PURPOSE: To investigate the effect of binocularity on long-term visual acuity in patients who have undergone bilateral implantation of a presbyopia-correcting diffractive multifocal intraocular lens (IOL). METHODS: Twenty patients (9 men and 11 women) with an average age of 70 ± 7 years (range: 56 to 78 years) underwent bilateral implantation of a diffractive multifocal IOL (AcrySof IQ ReSTOR IOL, SN60D3; Alcon Laboratories, Inc., Fort Worth, TX). Uncorrected visual acuity was measured monocularly and binocularly on average 26 ± 6 months following implantation in the second eye (range: 17 to 40 months) using the University of Crete European-wide modified Early Treatment Diabetic Retinopathy Study charts at the following distances: (1) 4 m, uncorrected distance visual acuity (UDVA), (2) 66 cm, uncorrected intermediate visual acuity (UIVA), and (3) 33 cm, uncorrected near visual (UNVA). RESULTS: Mean ± standard deviation UDVA was 0.07 ± 0.10 and 0.21 ± 0.12 logMAR (20/23 and 20/32 Snellen) in the better and worse eye, respectively, improving to 0.00 ± 0.09 logMAR (20/20 Snellen) binocularly. Mean ± standard deviation UIVA was 0.18 ± 0.14 and 0.32 ± 0.15 logMAR (20/30 and 20/42 Snellen) in the better and worse eye, respectively, improving to 0.08 ± 0.15 logMAR (20/24 Snellen) binocularly. Mean ± standard deviation UNVA was 0.20 ± 0.09 and 0.32 ± 0.12 logMAR (20/32 and 20/42 Snellen) in the better and worse eye, respectively, improving to 0.11 ± 0.10 logMAR (20/26 Snellen) binocularly. Binocular summation, defined as the difference between the binocular and better eye visual acuity, was found to be statistically significant at all distances: 0.07 ± 0.05 logMAR at 4 m, 0.10 ± 0.11 logMAR at 66 cm, and 0.09 ± 0.08 logMAR at 33 cm. CONCLUSIONS: The results confirm that there is substantial benefit of binocular vision in individuals with bilateral multifocal IOL implantation in terms of increased visual acuity. This effect is evident at all distances.

Visual outcomes and safety of a refractive corneal inlay for presbyopia using femtosecond laser.

PURPOSE: To evaluate the outcomes and safety of a refractive inlay (Flexivue Micro-Lens, Presbia Coöperatief U.A.) for the corneal compensation of presbyopia. METHODS: This prospective, interventional clinical study comprised 47 emmetropic presbyopes with a mean age of 52±4 years (range: 45 to 60 years). The inlay was inserted, centered on the line of sight, inside a corneal pocket created in the patient's nondominant eye, using a femtosecond laser. Follow-up was 12 months. Visual acuity, corneal topography, wavefront aberrometry, contrast sensitivity, structural corneal alterations, and questionnaires were evaluated. RESULTS: Twelve months after surgery, uncorrected near visual acuity was 20/32 or better in 75% of operated eyes, whereas mean uncorrected distance visual acuity (UDVA) of operated eyes was statistically significantly decreased from 0.06±0.09 logMAR (20/20) (range: -0.08 to 0.26) preoperatively to 0.38±0.15 logMAR (20/50) (range: 0.12 to 0.8) (P<.001), and mean binocular UDVA was not significantly altered (P=.516). Seventeen patients lost one line of corrected distance visual acuity in the operated eye. No patient lost 2 lines in CDVA in the operated eye. Overall, higher order aberrations increased and contrast sensitivity decreased in the operated eye. No tissue alterations were found using corneal confocal microscopy. No intra- or postoperative complications occurred. CONCLUSIONS: Twelve months after implantation, the Flexivue Micro-Lens intracorneal refractive inlay seems to be an effective method for the corneal compensation of presbyopia in emmetropic presbyopes aged between 45 and 60 years old.

Xerophthalmia and acquired night blindness in a patient with a history of gastrointestinal neoplasia and normal serum vitamin A levels.

A 69-year-old male patient presented to our department with a 3-month history of nyctalopia. Reviewing of his general health revealed a history of gastrointestinal tumor treated with a modified WHIPPLE operation. Ocular findings at presentation included mild xerophthalmic features and nonspecific pigmentary retinal changes. A standard full-field electroretinogram (ERG) was obtained that showed normal photopic function and extinguished scotopic function. The ocular symptoms, the history and the ERG findings suggested vitamin A deficiency as a possible cause for his complaints. Serum vitamin A levels were subsequently requested, but the results were within normal limits. Despite the normal serum vitamin A levels, the patient was instructed to commence treatment with high doses of oral vitamin A supplements. One month after the onset of the treatment, the patient reported that his visual function has significantly improved, while repeat ERG testing revealed that scotopic function has improved to normal levels. This case highlights that in patients with acquired night blindness due to vitamin A deficiency, the ERG responses possibly represent a more sensitive marker compared to the serum levels of vitamin A.

Power profiles of multifocal contact lenses and their interpretation.

PURPOSE: Many contact lens (CL) manufacturers produce simultaneous-image lenses in which power varies either smoothly or discontinuously with zonal radius. We present in vitro measurements of some recent CLs and discuss how power profiles might be approximated in terms of nominal distance corrections, near additions, and on-eye visual performance. METHODS: Fully hydrated soft, simultaneous-image CLs from four manufacturers (Air Optix AQUA, Alcon; PureVision multifocal, Bausch & Lomb; Acuvue OASYS for Presbyopia, Vistakon; Biofinity multifocal- "D" design, Cooper Vision) were measured with a Phase focus Lens Profiler (Phase Focus Ltd., Sheffield, UK) in a wet cell and powers were corrected to powers in air. All lenses had zero labeled power for distance. RESULTS: Sagittal power profiles revealed that the "low" add PureVision and Air Optix lenses exhibit smooth (parabolic) profiles, corresponding to negative spherical aberration. The "mid" and "high" add PureVision and Air Optix lenses have bi-aspheric designs, leading to different rates of power change for the central and peripheral portions. All OASYS lenses display a series of concentric zones, separated by abrupt discontinuities; individual profiles can be constrained between two parabolically decreasing curves, each giving a valid description of the power changes over alternate annular zones. Biofinity lenses have constant power over the central circular region of radius 1.5 mm, followed by an annular zone where the power increases approximately linearly, the gradient increasing with the add power, and finally an outer zone showing a slow, linear increase in power with a gradient being almost independent of the add power. CONCLUSIONS: The variation in power across the simultaneous-image lenses produces enhanced depth of focus. The through-focus nature of the image, which influences the "best focus" (distance correction) and the reading addition, will vary with several factors, including lens centration, the wearer's pupil diameter, and ocular aberrations, particularly spherical aberration; visual performance with some designs may show greater sensitivity to these factors.

Comparison of visual acuity charts in young adults and patients with diabetic retinopathy.

PURPOSE: To compare visual acuity (VA) assessed in healthy eyes and eyes with diabetic retinopathy (DR) using three different logMAR charts: the Sloan letter European-wide chart, the tumbling E chart, and the Landolt C chart. METHODS: Measurements on one eye of 40 volunteers (aged 29 ± 4 years) without visual impairment and 31 DR patients (aged 70 ± 9 years) with mild/moderate visual impairment were included. Visual acuity was assessed, with habitual refractive correction, using each of the three charts. Bland-Altman charts were constructed, and 95% limits of agreement were calculated to measure agreement. RESULTS: Mean VA in the group of young adults was -0.05 ± 0.10 (Sloan letter), -0.02 ± 0.13 (tumbling E), and 0.00 ± 0.12 (Landolt C) logMAR. Average VA estimates differed to a statistically significant extent between all charts. Mean VA in the DR group was 0.46 ± 0.25 (Sloan letter), 0.48 ± 0.26 (tumbling E), and 0.59 ± 0.28 (Landolt C). A statistically significant difference was observed for average Sloan letter versus Landolt C (p < 0.001) and tumbling E versus Landolt C (p < 0.001) acuities. Moreover, in healthy eyes, a moderate correlation (r = -0.38, p = 0.015) was found between the discrepancy in Sloan letter and Landolt C acuity and the mean VA estimate. The 95% limits of agreement were wide (more than approximately 0.2 logMAR for each comparison) and wider in the DR group chart comparisons than in healthy eyes. CONCLUSIONS: Landolt C charts resulted in worse VA estimates compared with letter and tumbling E charts in both young adults and visually impaired subjects with DR. These differences seem more pronounced in DR patients who exhibit worse VAs. The specific study population must be considered in comparing outcomes from different clinical practices.

Contrast sensitivity in the 'good eye' of adult patients with severe impairment in the other eye.

PURPOSE: It is widely accepted that monocular deprivation results in improved visual performance in the non-pathological eye. The current study investigates the effect of deprivation due to severe impairment in one eye during late childhood or adulthood, on the spatial performance of the fellow 'good' eye. METHODS: Twenty patients (age: 29 ± 9 years) with severe visual impairment in one eye (visual acuity equal or worse than count fingers at 1 m), for a period longer than 2 years, participated in the study. Only patients with an age less than 50 years and monocular deprivation onset greater than 9 years were included. On the basis of the time of deprivation the patients were categorised into two subgroups: (i) long-past deprivation (N = 8, age 28 ± 8 years, 9-20 years of deprivation) and recent deprivation (N = 12, age 30 ± 11 years, 2-4 years of deprivation). Eighteen more participants (age: 28 ± 5 years) with normal binocular vision served as the control group. Best-corrected contrast sensitivity was evaluated using reversing (2 Hz) vertical sinusoidal gratings. Seven spatial frequencies (1, 2, 4, 8, 12, 16 and 24 c/deg) were tested. Performance of the control group was tested both monocularly (dominant eye) and binocularly. RESULTS: In normal subjects, binocular viewing improved contrast sensitivity on average by 4.2 dB (corresponding to a 70% improvement in contrast threshold) compared to monocular recordings. Average contrast sensitivity in subjects with impaired vision in one eye was found to be higher by 5.0 dB (corresponding to an 83% improvement in contrast threshold) compared with the dominant eye of the control group. The increase in sensitivity was independent of spatial frequency. No differences were observed between the two subgroups with recent and long-past deprivation. CONCLUSIONS: Notable improvement in contrast sensitivity was found in the non-pathological eye of patients with severe impairment in the other eye at an age after the "critical" period of visual development. These findings are consistent with growing evidence supporting functional changes as a result of altered experience or injury in the adult vision system.

Effect of blur and subsequent adaptation on visual acuity using letter and Landolt C charts: differences between emmetropes and myopes.

PURPOSE: To compare the effects of defocus induced blur and blur adaptation on visual acuity and to evaluate any differences between emmetropes and myopes using letter and Landolt C logMAR charts. METHODS: The sample consisted of 26 volunteers, with a mean age of 27 ± 3 years, comprising 13 emmetropes (spherical equivalent range: -0.63 to +0.50 D) and 13 myopes (spherical equivalent range: -0.75 to -5.00 D). Monocular visual acuity (VA) was measured in each eye using letter and Landolt C logMAR charts under the following conditions: (1) with the distance refractive correction, (2) immediately after exposure to +2.00 D defocus and (3) following 60 min of binocular adaptation to +2.00 D blur. Objective refraction at the beginning and at the end of the experimental procedure was evaluated. Averaged VA data between the two eyes were used for analysis. RESULTS: Deterioration in VA with +2.00 D defocus was greater in the emmetropes compared to myopes for both charts. The mean difference between the two refractive groups was more pronounced for the Landolt-C (0.17 logMAR) compared to the letter chart (0.10 logMAR). The reduction in VA with blur was related to the amount of the refractive error. Following 60 min of adaptation, a significant improvement in VA was observed in both groups that did not differ between the two charts. The improvement in VA following adaptation using the letter chart was linearly correlated with spherical equivalent refractive correction. CONCLUSIONS: Myopes show higher tolerance to retinal defocus compared to emmetropes, which could be attributed to previous blur experience. The effect of blur on VA is more pronounced using Landolt C optotypes than with letters. Prolonged exposure to blur results in equally improved performance for both refractive groups.

Through-focus performance with multifocal contact lenses: effect of binocularity, pupil diameter and inherent ocular aberrations.

PURPOSE: To evaluate the effects of the wearer's pupil size and spherical aberration on visual performance with centre-near, aspheric multifocal contact lenses (MFCLs). The advantage of binocular over monocular vision was also investigated. METHODS: Twelve young volunteers, with an average age of 27 ± 5 years, participated in the study. LogMAR Visual Acuity (VA) was measured under cycloplegia for a range of defocus levels (from +3.0 to -3.0 D, in 0.5 D steps) with no correction and with three aspheric MFCLs (Air Optix Aqua Multifocal) with a centre-near design, providing correction for 'Low', 'Med' and 'High' near demands. Measurements were performed for all combinations of the following conditions: (1) artificial pupils of 6 and 3 mm diameter, (2) binocular and monocular (dominant eye) vision. Depth-of-focus (DOF) was calculated from the VA vs defocus curves. Ocular aberrations under cycloplegia were measured using iTrace. RESULTS: VA at -3.0 D defocus (simulating near performance) was statistically higher for the 3 mm than for the 6 mm pupil (p = 0.006), and for binocular rather than for monocular vision (p < 0.001). Similarly, DOF was better for the 3 mm pupil (p = 0.002) and for binocular viewing conditions (p < 0.001). Both VA at -3.0 D defocus and DOF increased as the 'addition' of the MFCL correction increased. Finally, with the centre-near MFCLs a linear correlation was found between VA at -3.0 D defocus and the wearer's ocular spherical aberration (R(2) = 0.20 p < 0.001 for 6 mm data), with the eyes exhibiting the higher positive spherical aberration experiencing worse VAs. By contrast, no correlation was found between VA and spherical aberration at 0.00 D defocus (distance vision). CONCLUSIONS: Both near VA and depth-of-focus improve with these MFCLs, with the effects being more pronounced for small pupils and for binocular rather than monocular vision. Coupling of the wearer's ocular spherical aberration with the aberration profiles provided by MFCLs affects their functionality.

Interocular differences in visual latency induced by reduced-aperture monovision.

PURPOSE: To explore the interocular differences in the temporal responses of the eyes induced by the monocular use of small-aperture optics designed to aid presbyopes by increasing their depth-of-focus. METHODS: Monocular and binocular pattern-reversal visual evoked potentials (VEPs) were measured at a mean photopic field luminance of 30 cd/m(2) in seven normal subjects with either natural pupils or when the non-dominant eye wore a small-aperture contact lens (aperture diameter 1.5, 2.5 or 3.5 mm, or an annular opaque stop of inner and outer diameters 1.5 and 4.0 mm respectively). Responses were also measured with varying stimulus luminance (5, 13.9, 27.2 and 45 cd/m(2)) and a fixed 3.0 mm artificial pupil. RESULTS: Mean natural pupil diameters were 4.7 and 4.4 mm under monocular and binocular conditions respectively. The small-aperture contact lenses reduced the amplitude of the P100 component of the VEP and increased its latency. Inter-ocular differences in latency rose to about 20-25 ms when the pupil diameter of the non-dominant eye was reduced to 1.5 mm. The measurements with fixed pupil and varying luminance suggested that the observed effects were explicable in terms of the changes in retinal illuminance produced by the restrictions in pupil area. CONCLUSIONS: The anisocoria induced by small-aperture approaches to aid presbyopes produces marked interocular differences in visual latency. The literature of the Pulfrich effect suggests that such differences can lead to distortions in the perception of relative movement and, in some cases, to possible hazard.