Silicone oil insulation effects on flash electroretinogram and visual evoked potential in patients with retinal detachment / Efectos del aislamiento del aceite de silicona sobre el electrorretinograma flash y el potencial evocado visual en pacientes con desprendimiento de retina

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.(AU)

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.

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.

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.

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.

Dichoptic Game Training in Strabismic Amblyopia Improves the Visual Evoked Response.

Dichoptic video gaming offers an alternative approach in amblyopia treatment by allowing different information to be presented in the two eyes, resulting to reduced suppression and/or enhanced fusion. The aim of this case report series is to evaluate the outcome of supervised dichoptic training, with the use of video games in a virtual reality (VR) system, on far and near visual acuity (VA), stereoacuity, and the visual evoked response of an adult and two children with strabismic amblyopia. Results suggest that despite the absence of improvement in VA following supervised dichoptic training, a remarkable increase in stereoacuity was evident with a concurrent decrease in phorias. Moreover, an improvement in the P100 latency of the pattern visual evoked potentials (VEPs) in the amblyopic eye was observed in all participants. Finally, at least two sessions per week were completed for each patient under continuous supervision, implying sufficient compliance and treatment efficiency with dichoptic video gaming. Supervised dichoptic training, consisting of at least 20 hours of video gaming using a VR system, improves stereoacuity and the latency of the visual evoked response in the amblyopic eye. This probably occurs by overcoming its suppression, indicating that the speed of visual processing, as evaluated by pattern VEPs, may precede improvements in VA.

Comparing silent reading performance for single sentences and paragraphs: an eye movement-based analysis.

CLINICAL RELEVANCE: Reading performance in clinical practice is commonly evaluated by reading 'aloud' and 'as fast as possible' single sentences. Assessing comprehensive silent reading performance using passages, composed of multiple sentences, is the preferred reading mode in real-life reading conditions. BACKGROUND: The purpose of this study was to compare eye movement-based silent reading performance for standardised short sentences and paragraphs. METHODS: A group of 15 young volunteers (age range: 22-36 years) read silently and comprehensively in two sessions: (a) a paragraph with continuous text and (b) standardised short sentences. Text print size was 0.4 logMAR (1.0 M at 40 cm distance). Eye movements during reading were recorded using video oculography (EyeLink II, SR Research Ltd). Data analysis included computation of reading speed, fixation duration, the number of fixations, saccadic amplitude and percentage of regressions. Moreover, frequency distributions of fixation durations were analysed with ex-Gaussian fittings. RESULTS: Repeatability coefficient in silent reading speed was found better for the paragraph (66 wpm) than for short sentences (88 wpm). The superiority in repeatability coefficient for the corresponding eye movement parameters, i.e. fixation duration (35 vs 73 ms), regressions (10.1 vs. 22.3%) and fixations per word (0.21 vs. 0.37 fpw), was even more pronounced. In addition, a statistically significant improvement with the paragraph was found in average fixation duration (19 ± 26 ms, p = 0.02), regressions (4.2 ± 7.0%, p = 0.04) and ex-Gaussian fixation parameter, τ (82 vs. 111 ms). No statistically significant difference was found between average reading speed with the paragraph (220 ± 59 wpm) and the short sentences (206 ± 57 wpm) (p = 0.11). DISCUSSION: Due to their superior repeatability, paragraphs are preferable to short sentences when evaluating silent comprehensive reading. The concurrent recording of eye movement parameters in silent reading further improves variability and could offer an efficient measure of reading performance and a reliable biomarker of visuo-motor function.

Presbyopia correction with multifocal contact lenses: Evaluation of silent reading performance using eye movements analysis.

PURPOSE: Many activities of daily living rely on reading, thus is not surprising that complaints from presbyopes originate in reading difficulties rather in visual acuity. Here, the effectiveness of presbyopia correction with multifocal contact lenses (CLs) is evaluated using an eye-fixation based method of silent reading performance. ΜETHODS: Visual performance of thirty presbyopic volunteers (age: 50 ± 5 yrs) was assessed monocularly and binocularly following 15 days of wear of monthly disposable CLs (AIR OPTIX™ plus HydraGlyde™, Alcon Laboratories) with: (a) single vision (SV) lenses - uncorrected for near (b) aspheric multifocal (MF) CLs. LogMAR acuity was measured with ETDRS charts. Reading performance was evaluated using standard IReST paragraphs displayed on a screen (0.4 logMAR print size at 40 cm distance). Eye movements were monitored with an infrared eyetracker (Eye-Link II, SR Research Ltd). Data analysis included computation of reading speed, fixation duration, fixations per word and percentage of regressions. RESULTS: Average reading speed was 250 ± 68 and 235 ± 70 wpm, binocularly and monocularly, with SV CLs, improving statistically significantly to 280 ± 67 (p = 0.002) and 260 ± 59 wpm (p = 0.01), respectively, with MF CLs. Moreover, fixation duration, fixations per word and ex-Gaussian parameter of fixation duration, µ, showed a statistically significant improvement when reading with MF CLs, with fixation duration exhibiting the stronger correlation (r = 0.79, p < 0.001) with improvement in reading speed. The correlation between improvement in VA and reading speed was moderate (r = 0.46, p = 0.016), as was the correlation between VA and any eye fixation parameter. CONCLUSION: Average silent reading speed in a presbyopic population was found improved with MF compared to SV CL correction and was faster with binocular compared to monocular viewing: this was mainly due to the faster average fixation duration and the lower number of fixations. Evaluating reading performance using eye fixation analysis could offer a reliable outcome of functional vision in presbyopia correction.

TFOS Lifestyle: Impact of the digital environment on the ocular surface.

Eye strain when performing tasks reliant on a digital environment can cause discomfort, affecting productivity and quality of life. Digital eye strain (the preferred terminology) was defined as "the development or exacerbation of recurrent ocular symptoms and/or signs related specifically to digital device screen viewing". Digital eye strain prevalence of up to 97% has been reported, due to no previously agreed definition/diagnostic criteria and limitations of current questionnaires which fail to differentiate such symptoms from those arising from non-digital tasks. Objective signs such as blink rate or critical flicker frequency changes are not 'diagnostic' of digital eye strain nor validated as sensitive. The mechanisms attributed to ocular surface disease exacerbation are mainly reduced blink rate and completeness, partial/uncorrected refractive error and/or underlying binocular vision anomalies, together with the cognitive demand of the task and differences in position, size, brightness and glare compared to an equivalent non-digital task. In general, interventions are not well established; patients experiencing digital eye strain should be provided with a full refractive correction for the appropriate working distances. Improving blinking, optimizing the work environment and encouraging regular breaks may help. Based on current, best evidence, blue-light blocking interventions do not appear to be an effective management strategy. More and larger clinical trials are needed to assess artificial tear effectiveness for relieving digital eye strain, particularly comparing different constituents; a systematic review within the report identified use of secretagogues and warm compress/humidity goggles/ambient humidifiers as promising strategies, along with nutritional supplementation (such as omega-3 fatty acid supplementation and berry extracts).

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.

Self-reported visual symptoms and high visual demand activities in professional football players: a cross-sectional survey.

Background: Vision is crucial for football players, impacting decision-making and athletic performance. Despite its global popularity, football lacks comprehensive evaluations of the impact of digital device use on ocular symptoms during high-demand activities. Purpose: To gain knowledge about the time spent by football players in high visual demand activities, the symptoms associated with binocular vision dysfunction, and their relationship with sports performance. Methods: A cross-sectional observational study was conducted in 2020 using an online survey targeting football players from Portugal, England, Spain, and Saudi Arabia. The survey, distributed over 5 weeks, aimed to collect data from approximately 5,000 football players. Information on player profiles, competitive levels, vision habits, and symptoms related to binocular vision dysfunctions was collected. The Convergence Insufficiency Symptom Survey (CISS) employed a 5-point Likert scale to indicate the average frequency of each symptom. Due to non-normality, non-parametric tests were used (p < 0.05). Specifically, Mann-Whitney U, Kruskal-Wallis, Chi-square, and Spearman's rank correlation tests were used as appropriate. Results: Analyzing male professional football players (mean age: 27.4 ± 5.0 years, 95% CI, 26.7-28.1), it was found that 38.1% of the players had been called up to the national team and 6.9% had played over 50 games. Self-rated last season's performance had a mean score of 6.5 ± 2.1 (95% CI, 6.2-6.8)(on a scale of 1 to 10). Smartphone use exceeded 1 h daily for all players, with 36.0% surpassing 4 h. Visual symptoms, notably associated with smartphone use (35.5%), were observed. Regarding the CISS score, the mean was 7.1 ± 7.7 (IC95%: 6.6 to 8.8). A weak negative correlation (rho = -0.215, p = 0.003) emerged between CISS scores and self-perceived sports performance. Football players using prescription lenses had significantly higher CISS scores (11.9 ± 10.4, 95% CI, 12.3-7.7) compared to non-users (6.2 ± 6.8, 95% CI, 7.8-5.7) (p < 0.001). Conclusion: This study reveals that professional football players engage in high visual demand tasks, notably on smartphones. One-third of the players link smartphone use to ocular symptoms. The Convergence Insufficiency Symptoms Survey indicates that 6.3% exhibit binocular vision dysfunction symptoms. Those with fewer ocular symptoms perceive that they have better sports performance than their counterparts.

CLEAR - Contact lens optics.

The most fundamental aspect of a contact lens is its optics; the manner in which the refraction of light is managed to optimise vision to the clinical benefit of the lens wearer. This report presents contemporary information on the optical structure of the eye and the optical models employed to understand the correction of refractive error. The design, measurement and clinical assessment of spherical, aspheric, toric, multifocal and myopia control contact lenses are described. The complexity and variety of multifocal lenses is recognised and detailed information is provided for alternating, simultaneous, diffractive, annular, aspheric and extended depth of field lens designs. In terms of clinical assessment, a contemporary review is provided for the measurement of: visual acuity, contrast sensitivity, through focus curves, reading performance, peripheral refraction, toric displacement realignment and patient reported outcomes. Overall, the paper aims to serve as a resource for the prescribing clinician, who can optimise contact lens corrections for patients by building on the optical rationale of these devices; and also highlights future opportunities for research innovation.

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.

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.

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.

Orientation and Spatial Frequency Selectivity following Adaptation: A Reaction Time Study.

The aim of the study was to determine orientation and spatial frequency sensitivity using reaction times (RTs) in an adaptation paradigm. Simple RTs were measured to the onset of a Gabor patch (SD = 1.2 deg, spatial frequency = 4 cycles deg(-1)). Observers adapted for 10 s to a 4 cycles deg(-1) grating presented at a series of orientations (0, 2, 5, 10, 22.5, 45, 90°) or spatial frequencies (±0.5, 1, and 2 octaves). The contrast of the test grating was 4x each participant's unadapted threshold. The effect of adaptation was evaluated by transforming RTs to effective contrast reduction using RT-based contrast response functions. RTs increased by between ∼ 100 ms to 150 ms when the test and adapting gratings were of the same orientation or spatial frequency. The effect became less pronounced as the difference in orientation or spatial frequency increased. The average bandwidths for orientation and spatial frequency were 17.4° and 1.24 octaves, respectively. The method has some advantages over traditional approaches. It reveals a rapid time course of adaptation recovery with a half-life of about 13 s to 23 s. RTs form a rapid and easily implemented technique for assessing the underlying physiological mechanisms that control adaptation at suprathreshold levels of contrast.

Ocular higher-order aberrations in a school children population / Aberraciones oculares de alto orden en una población de escolares

Purpose: The primary objective of the study was to explore the statistics of ocular higher-order aberrations in a population of primary and secondary school children. Methods: A sample of 557 children aged 10---15 years were selected from two primary and two secondary schools in Heraklion, Greece. Children were classified by age in three subgroups: group I (10.7 ± 0.5 years), group II (12.4 ± 0.5 years) and group III (14.5 ± 0.5 years). Ocular aberrations were measured using a wavefront aberrometer (COAS, AMO Wavefront Sciences, USA) at mesopic light levels (illuminance at cornea was 4 lux). Wavefront analysis was achieved for a 5 mm pupil. Statistical analysis was carried out for the right eye only. Results: The average coefficient of most high-order aberrations did not differ from zero with the exception of vertical (0.076 m) and horizontal (0.018 m) coma, oblique trefoil (−0.055 m) and spherical aberration (0.018 m). The most prominent change between the three groups was observed for the spherical aberration, which increased from 0.007 m (SE 0.005) in group I to 0.011 m (SE 0.004) in group II and 0.030 m (SE 0.004) in group III. Significant differences were also found for the oblique astigmatism and the third-order coma aberrations. Conclusions: Differences in the low levels of ocular spherical aberration in young children possibly reflect differences in lenticular spherical aberration and relate to the gradient refractive index of the lens. The evaluation of spherical aberration at certain stages of eye growth may help to better understand the underlying mechanisms of myopia development (AU)

Objetivo: El objetivo primario del estudio fue la investigación de la distribución de las aberraciones oculares de alto orden en una población de niños de enseñanza primaria y secundaria. Métodos: Se seleccionó una muestra de 557 niños, de edades comprendidas entre 10 y 15 años, de dos escuelas de enseñanza primaria y secundaria en Heraklion, Grecia. Se clasificó a los niños por edades en tres subgrupos: el grupo I (10,7 ± 0,5 años), el grupo II (12,4 ± 0,5 años) y el grupo III (14,5 ± 0,5 años). Se midieron las aberraciones oculares utilizando un aberrómetro de frente de onda (COAS, AMO Wavefront Sciences, USA) en condiciones de de visión mesópica (la iluminancia en la córnea fue de 4 lux). El análisis con frente de onda se logró para una pupila de 5 mm. El análisis estadístico se llevó a cabo únicamente con los datos del ojo derecho. Resultados: El coeficiente medio para la mayoría de aberraciones de alto orden no difirió de cero, a excepción del coma vertical (0,076 m) y horizontal (0,018 m), el astigmatismo oblicuo (-0,055m) y la aberración esférica (0,018 m). El cambio más sobresaliente entre los tres grupos se observó en la aberración esférica, que pasó de ser de 0,007 m (SE 0,005) en el grupo I a 0,011 m (SE 0,004) en el grupo II y 0,030 m (SE 0,004) en el grupo III. También se hallaron diferencias significativas para el astigmatismo oblicuo y la aberración comática de tercer orden. Conclusiones: Las diferencias en los bajos niveles de aberración esférica ocular en niños reflejan posiblemente las diferencias en cuanto a aberración esférica lenticular y se refieren al gradiente de índice de refracción del cristalino. La evaluación de la aberración esférica en ciertas edades del crecimiento ocular puede ayudar a comprender mejor los mecanismos subyacentes al desarrollo de la miopía (AU)

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.