The impact of traumatic brain injury on inhibitory control processes assessed using a delayed antisaccade task.

It has been well established that traumatic brain injury (TBI) can affect cognitive function such as attention, working memory and executive functions. In the present study, we further investigated TBI-related changes in cognitive functions by investigating the ability to reorient visuospatial attention using a modified antisaccade task. Performing an antisaccade requires disengaging attention, inhibiting a reflexive saccade, and then engaging attention to execute a voluntary saccade in a direction opposite to a peripheral target. Particularly we quantified the time (latency), and accuracy (directional and disinhibition errors) of 26 TBI and 33 normal participants in making an antisaccade after a variable period of delay (0, 0.0625, 0.125, 0.250, 0.500 or 1.0 s). Changing the delay period allowed to systematically quantify the temporal and spatial characteristics of preparing and initiating an antisaccade and whether this process is affected by TBI. TBI participants took longer (approximately 33-66 ms for variable delays) to generate correct delayed antisaccades and showed increased directional errors (2-11 % for variable delays) and increased disinhibition prosaccade errors (2-6 % for variable delays) compared to controls. However, both groups made similar disinhibition antisaccade errors. These findings indicate that TBI participants required a longer time to process information, and a possible poorer response inhibition and poor spatial information processing due to head injury.

Vision screening outcomes of 4-5 year-olds reflect the social gradient.

CLINICAL RELEVANCE: Children in socioeconomically disadvantaged communities often do not access follow-up eye care services when referred from vision screenings; whether this is due to lack of availability is not known. This paper highlights the need for vision and eye care for vulnerable children with practicing clinical optometrists well placed to provide vision care. BACKGROUND: Vision impairments develop from a young age and may inhibit learning experiences and impact life outcomes. Vision screening to detect and refer vision abnormalities supports children in their education and prevents minor vision impairments from worsening. This research describes outcomes from a vision screening programme for 4- to 5-year-olds delivered in Queensland, Australia. METHODS: The programme involved all prep children from participating schools in Queensland. Vision screening was conducted with the Parr 4 m Visual Acuity Test and Welch Allyn Spot Vision Screener. A cross-sectional study design was adopted. Descriptive data analyses explored the frequency of vision screening and referral outcomes. Inferential analyses examined associations between vision screening and referral outcomes with socio-economic indexes for areas (SEIFA) scores . RESULTS: Of 71,003 prep students screened, 4,855 (6.8%) received a referral recommendation. A higher proportion of children who received a referral recommendation was from more disadvantaged locations (?2 = 109.16, p < 0.001). Of the students referred, 3,017 were seen by an eye health professional. Further vision assessment of students by an eye health professional revealed that 43.3% of the referred children were diagnosed with a vision abnormality, 18.9% had no vision abnormality and 37.7% had an 'undetermined' diagnosis. A higher proportion of children confirmed with a vision abnormality were from more disadvantaged locations (?2 = 52.27, p < 0.001). CONCLUSION: It is important that vision screening programmes target disadvantaged populations and support families of children who require further health assessment to access health services.

Associations between Binocular Vision Disorders and Contact Lens Dissatisfaction.

SIGNIFICANCE: These data demonstrate that binocular vision disorders (BVDs) contribute to contact lens (CL) dissatisfaction independently of CL discomfort (CLD) in myopic, pre-presbyopic, adult, single-vision CL wearers. PURPOSE: This study aimed to determine whether BVDs contribute to CL dissatisfaction and whether this contribution is independent of CLD. METHODS: Participants attended one clinical visit while wearing their habitual CLs. Symptoms from CLD and BVDs were measured with the Contact Lens Dry Eye Questionnaire-8 (CLDEQ-8) and Convergence Insufficiency Syndrome Survey (CISS), respectively. A comprehensive binocular vision (BV) assessment was performed. The Ocular Surface Disease Index (OSDI) was used to measure CL dissatisfaction from CLD and BVDs based on reported correlations between the CLDEQ-8 and the CISS with the OSDI. Participants were categorized according to their CL comfort status (CLD [≥12 on CLDEQ-8] or non-CLD [<12 on CLDEQ-8]) and BV status (BVD or non-BVD). RESULTS: Seventy-six participants completed the trial, and 19 (25%) were diagnosed with BVD. Those diagnosed with BVD scored higher than did those diagnosed with non-BVD for the OSDI (25.1 ± 12.7 vs. 10.7 ± 7.3, P < .001) and CISS (18.7 ± 7.7 vs. 11.9 ± 5.9, P = .001), but not the CLDEQ-8 (P = .25). Those categorized as having CLD scored higher than did those categorized as having non-CLD for the OSDI (19.0 ± 12.3 vs. 9.3 ± 5.9, P = .003) and CISS (16.1 ± 6.8 vs. 11.0 ± 6.2, P = .001). There were no significant interactions between BV status and CL comfort status for any questionnaire (P > .08). CONCLUSIONS: Higher scores for OSDI in those with CLD or BVD indicate that both conditions contribute to CL dissatisfaction. Higher scores for the CISS in those with CLD suggest a degree of overlap for some BVD symptoms. Nonsignificant differences between BVD and non-BVD for the CLDEQ-8 suggest that BVDs contribute to CL dissatisfaction independently of CLD.

Treatment and compliance with virtual reality and anaglyph-based training programs for convergence insufficiency.

BACKGROUND: Convergence insufficiency may be treated by visual exercises designed to increase convergence while maintaining single, clear, binocular vision. However, compliance with treatment is problematic, as patients often cease treatment when symptoms start to improve and before treatment is complete. The purpose of the present study was to assess the feasibility of using gamification of vision training to: (a) treat convergence insufficiency; and (b) improve compliance to treatment in comparison to a conventional treatment over a six-week treatment period. METHODS: Two interventions, anaglyphs and a virtual reality game of Snakes, were evaluated for their effectiveness in treating adults with convergence insufficiency. The prescribed training regimen was 20 minutes, three times per week for six weeks. Vision was assessed before and after the treatment period. Participants also filled in the Core Elements of the Gaming Experience Questionnaire to gauge impact of game design on compliance. RESULTS: Eighteen participants (mean age 20.8 ± 1.8 years) met the inclusion criteria for convergence insufficiency and nine participants were randomly assigned to each intervention. Repeated measures analysis of variance showed a significant effect of visit for near point of convergence (F1,16 = 38.32, p < 0.0001), near positive fusional reserves break (F1,16 = 21.94, p < 0.0001) and recovery (F1,16 = 26.87, p < 0.0001), but not of intervention type. Total time played was significantly longer for the virtual reality Snake Game than the anaglyph intervention (p < 0.0001), which translated to mean compliance of 82 per cent and 51 per cent respectively. CONCLUSION: Gamification of vision training in a virtual reality environment is feasible and associated with increased compliance, hence may be a useful strategy to treat convergence insufficiency.

Smartphone Use and Effects on Tear Film, Blinking and Binocular Vision.

Purpose: Smartphone use is now ubiquitous and is associated with a range of ocular and visual symptoms. However, little is known about the etiology of the symptoms which accompany smartphone use and the relative contribution of accommodation/vergence versus that of the ocular surface and of blinking. This study examined the effects of 60 min reading on a smartphone on ocular symptoms, binocular vision, tear function, blinking and working distance.Methods: Twelve young adults (18-23 years; 9F:3M) with normal vision and without dry eye, or major accommodative/binocular vision disorders, completed this pilot study. Participants read a novel on a smartphone for 60 min and the following were measured before and after the reading task: eye strain and ocular surface symptoms, non-invasive tear break-up time (NIBUT), lipid layer appearance, tear meniscus height, horizontal fixation disparity, binocular accommodative facility. Spontaneous blink rate and amplitude were counted every 10 min, and viewing distance was measured at the same timepoints. Pre- and post-task comparisons were made using Wilcoxon signed-rank test and changes during the task were assessed using Friedman test. Associations were examined using Spearman's correlation.Results: Eyestrain symptoms and ocular surface symptoms increased after smartphone use, specifically comfort, tiredness and sleepiness items (p ≤ .02). Binocular accommodative facility decreased from a median of 11.3 (IQR 6.6) cycles/min pre-task to 7.8 (2.5) cycles/min post-task (p = .01), but there was no significant change in fixation disparity or working distance. There were no changes in NIBUT, lipid layer or tear meniscus height. Number of incomplete blinks per minute increased from a median of 6 blinks at 1 min to 15 at 60 min (p = .0049). Total blink rate (complete plus incomplete blinks) gradually increased over time, but this trend was not significant (p = .08). A greater increase in incomplete blinks over 60 min of reading was associated with worsening of the overall ocular surface symptoms score (ρ = -0.65, p = .02) and of the tiredness item (ρ = 0.70, p = .01).Conclusions: Extended use of smartphones appears to have important implications for ocular surface health and binocular function.

Ocular and visual discomfort associated with smartphones, tablets and computers: what we do and do not know.

Smartphone and tablet use in Australia and worldwide is reaching saturation levels and associated visual and ocular discomfort such as headaches, eyestrain, dry eyes and sore eyes are widespread. This review synthesises the available literature and considers these symptoms in the context of a binocular vision and/or ocular surface aetiology. Eye discomfort with smartphones and tablets is discussed alongside similar symptoms reported with desktop computer use. Handheld devices differ from computers in viewing position and distance, screen size and luminance, and patterns of use. Accommodation is altered with handheld device use, with increased lag and decreased amplitude. Smartphone and tablet use results in reduced fusional convergence and possibly a receded near point of convergence. This is similar to what happens with computer use. Findings related to blink rate with smartphone and tablet use are contradictory, perhaps due to the influence of task difficulty, and there is limited evidence related to blink amplitude. Reduced blink rate and amplitude are consistently reported with computer use. Use of handheld digital devices, like computers, may adversely impact tear stability. There is insufficient evidence to support the impact of handheld devices on tear volume, although this is reduced with computer use. The available literature does not conclusively link eye and visual discomfort symptoms reported with handheld digital devices, with changes in binocular vision, blinking or ocular surface. However, there is a gap in our understanding of symptoms which occur with smartphone and tablet use in the context of how these devices are used. In addition, studies are required in high users such as teenagers, and in patients with dry eye or accommodative/binocular vision anomalies, all of whom may have a higher risk of symptoms. A better understanding of symptom aetiology can guide clinical advice to minimise adverse impacts on visual and ocular surface health and discomfort.

Deficits in saccades and smooth-pursuit eye movements in adults with traumatic brain injury: a systematic review and meta-analysis.

PURPOSE: To conduct a review of literature and quantify the effect that traumatic brain injury (TBI) has on oculomotor functions (OM). METHODS: A systematic review and meta-analysis was conducted from papers that objectively measured saccades and smooth-pursuit eye movements in mild and severe TBI. RESULTS: The overall impact of TBI on OM functions was moderate and significant with an effect size of 0.42 from 181 OM case-control comparisons. The heterogeneity, determined using the random effect model, was found to be significant (Q (180) = 367, p < 0.0001, I2 = 51) owing to the variety of OM functions (reflexive saccades, antisaccades, memory-guided saccades, self-paced saccades and pursuits) measured and varying post-injury periods.The overall effect on OM functions were similar in mild and severe TBI despite differences in combined effect size of various OM functions. OM functions involving complex cognitive skills such as antisaccades (in mild and severe TBI) and memory-guided saccades (in mild TBI) were the most adversely affected, suggesting that OM deficits may be associated with cognitive deficits in TBI. CONCLUSION: TBI often results in long-standing OM deficits. Experimental measures of OM assessment reflect neural integrity and may provide a sensitive and objective biomarker to detect OM deficits following TBI.

Optical treatment of amblyopia: a systematic review and meta-analysis.

BACKGROUND: Despite evidence that amblyopia can often be treated by optical treatment alone, many practitioners still do not use an optical-correction-only phase in amblyopia treatment and some investigators omit this important step in their research. This paper aims to systematically review the evidence for the optical treatment of strabismic, refractive and combined-mechanism amblyopia and to quantify the evidence via a meta-analysis. METHODS: A search of online databases MEDLINE, EMBASE, PsycInfo, the Cochrane Library, and bibliographies of review papers, along with subsequent personal communication, resulted in 29 papers that met our inclusion criteria, with 20 providing sufficient data for the calculation of effect sizes. A meta-analysis was performed to determine effect sizes and the heterogeneity thereof. Meta-regression was used to evaluate the contribution of the possible moderating factors of age, duration of optical correction, and initial visual acuity to the heterogeneity of the studies. In addition, effect sizes were analysed in subgroups based on amblyopia aetiology, that is refractive or strabismic or combined, and also in the fellow eyes. RESULTS: No evidence of publication bias in the included studies was found using a Galbraith plot. Optical treatment of amblyopia resulted in a large positive effect size of 1.07 (±0.49, 95 per cent confidence limits) on visual acuity, although the heterogeneity was significant (Q = 597.05, I2 = 96.65 per cent, p < 0.0001). Meta-regression indicated that effect sizes significantly decreased with age, increased with treatment duration, and that better initial acuity was associated with higher effect sizes. CONCLUSION: Effect sizes were always moderate to large, whether participants were younger or older children, or whether the aetiology was refractive or strabismic. Thus, optical treatment of amblyopia should be considered prior to other treatment in those with refractive error. Improved acuity before initiating other treatment would presumably make occlusion or penalisation less onerous and may improve compliance with further treatment.

Viewing distance and eyestrain symptoms with prolonged viewing of smartphones.

BACKGROUND: This paper investigates viewing distances and eyestrain symptoms in young adults reading from a smartphone for 60 minutes. METHODS: A survey related to common asthenopic (eyestrain) symptoms was administered to subjects before and after they read an extract from a novel on a smartphone for 60 minutes. Subjects rated their symptoms on a scale from zero (not at all) to four (extremely). The viewing distance to the smartphone was measured on a photograph taken of the subject every minute. Each subject used the same smartphone and read the same text. RESULTS: Subjects were 18 young adults (mean age: 21.5 ± 3.3 years) with self-reported good health, normal visual acuity and no accommodative or binocular vision disorders. The mean viewing distance while using a smartphone over 60 minutes was 29.2 ± 7.3 cm. The viewing distance was significantly greater during the first, second and fifth 10-minute time periods (30.6 ± 7.2 cm, 29.7 ± 7.3 cm and 28.9 ± 8.5 cm, respectively) than during the final 10-minute time period (27.8 ± 7.7 cm) (Wilcoxon, p = 0.023, 0.02 and 0.04, respectively). The total symptom score was significantly greater post-experiment (score = 8.06) than pre-experiment (score = 3.56) (Wilcoxon, p < 0.001). Symptoms of tired eyes, uncomfortable eyes and blur increased significantly after 60 minutes of smartphone use (Wilcoxon, p < 0.05). There was a significant correlation between change in total symptom score and change in viewing distance (ρ = -0.51; p = 0.03). The only single symptom that correlated with a change in viewing distance was 'uncomfortable eyes' (ρ = -0.52, p = 0.03). CONCLUSION: Viewing distances are closer and eyestrain symptoms are greater after reading from a smartphone for 60 minutes. The viewing distances measured were closer than those previously reported in the literature.

The Effects of Vertical Yoked Prism on Horizontal Heterophoria.

PURPOSE: Vertical yoked prisms (VYPs) have been recommended for the remediation of vergence dysfunction, but the evidence base for their use is mostly low level. This study investigates the effect of VYP on horizontal subjective dissociated heterophoria. METHODS: Phoria measurement was performed in primary gaze with the Modified Thorington technique at 3 m and at 40 cm on 40 nonpresbyopic young adults. Subjects were seated and head position was held constant. Baseline measures (without yoked prism) of distance and near phoria were measured. Phorias were measured again through the following range of VYP, randomly presented: 2 prism diopters (Δ) base up (BU), 2Δ base down (BD), 5Δ BU, and 5Δ BD. Twenty-six subjects also had their phorias measured with control lenses of +0.125 DS OU (because of unavailability of Plano trial lenses) randomly presented along the other conditions. RESULTS: There was no significant difference overall between phoria measured in any of the yoked prism conditions, including the baseline measure, at distance or near. Neither was there evidence of a predictable esophoric or exophoric shift with either BU or BD prism. CONCLUSIONS: Vertical yoked prisms did not exert any immediate effect on horizontal phoria in young adults when posture was controlled. This suggests that, if VYPs do indeed improve horizontal vergence problems, they do not do so by a direct or immediate impact on horizontal phoria.

Negligible impact on posture from 5-diopter vertical yoked prisms.

PURPOSE: Yoked prisms are used by some optometrists to adjust posture, but evidence to support this practice is sparse and low level. The aim of this research was to investigate whether vertical yoked prisms have an impact on posture in healthy adults. METHODS: Posture was assessed objectively in 20 healthy adults, by recording a range of joint angles or body segment locations at the ankle, hip, torso, neck, and head during participant observation of a straight-ahead target, and subsequently with eyes closed. Recording occurred before, during, and after wearing goggles with control plano lenses, and 5-diopter (D) base-up and 5-D base-down yoked prisms. In each viewing condition, the goggles were worn for 30 minutes. Interaction effects of lens/prism condition by time on joint angles and body orientation were determined. RESULTS: In the eyes-open and eyes-closed conditions, no significant lens/prism × time interaction effects were found at the torso, neck, hip, or ankle (P > 0.1). However, in both eyes-open and eyes-closed conditions a significant lens/prism × time interaction was found at the head (P = 0.031 and 0.006, respectively), with head extended (tilted backward) by up to 2.5 degrees more while viewing with base-down prisms than with plano lenses. CONCLUSIONS: In healthy adults, 5-D base-down yoked prisms were not associated with a change in body posture. A small effect on head orientation and not at other locations suggests a minimal effect on posture. Research in a larger sample and in individuals with abnormal posture is needed to verify this.

Context and crowding in perceptual learning on a peripheral contrast discrimination task: context-specificity in contrast learning.

Perceptual learning is an improvement in sensitivity due to practice on a sensory task and is generally specific to the trained stimuli and/or tasks. The present study investigated the effect of stimulus configuration and crowding on perceptual learning in contrast discrimination in peripheral vision, and the effect of perceptual training on crowding in this task. 29 normally-sighted observers were trained to discriminate Gabor stimuli presented at 9° eccentricity with either identical or orthogonally oriented flankers with respect to the target (ISO and CROSS, respectively), or on an isolated target (CONTROL). Contrast discrimination thresholds were measured at various eccentricities and target-flanker separations before and after training in order to determine any learning transfer to untrained stimulus parameters. Perceptual learning was observed in all three training stimuli; however, greater improvement was obtained with training on ISO-oriented stimuli compared to CROSS-oriented and unflanked stimuli. This learning did not transfer to untrained stimulus configurations, eccentricities or target-flanker separations. A characteristic crowding effect was observed increasing with viewing eccentricity and decreasing with target-flanker separation before and after training in both configurations. The magnitude of crowding was reduced only at the trained eccentricity and target-flanker separation; therefore, learning for contrast discrimination and for crowding in the present study was configuration and location specific. Our findings suggest that stimulus configuration plays an important role in the magnitude of perceptual learning in contrast discrimination and suggest context-specificity in learning.

The effects of vertical yoked prisms on gait.

PURPOSE: To investigate the influence of base down (BD) and base up (BU) yoked prism wear on gait. METHODS: Gait was assessed in 31 young healthy adults (mean age, 24.0 ± 5.1 years) during and after wearing 5 prism diopter ((Δ)) BU yoked prisms, 5(Δ) BD yoked prisms, and plano (PL) (zero power; control condition) lenses, worn in a pseudorandom order. Velocity; cadence; step length; double support phase; step width; and variability in step time, step width, step length, and swing time were measured as participants walked at a freely chosen walking speed along a 5.3-m electronic mat placed in the center of a 7.5-m walkway. Gait parameters were analyzed for each viewing condition before, during, and after prism wear. RESULTS: BD yoked prisms, when compared with PL, led to slower velocity, lower cadence, decreased step length, and increased step time variability (P ≤ 0.001) These gait parameters did not significantly differ between BU yoked prisms and PL lenses (P > 0.05). Measurements taken immediately on removal did not differ from those taken after a time delay of 5 minutes. CONCLUSIONS: BD yoked prisms affected gait in young healthy adults walking across an unobstructed path at their freely chosen walking speed, in that participants adopted a slower, apparently more cautious gait pattern; BU yoked prisms did not significantly affect gait. The effect of BD prism on gait may be due in part to a perception of increased height.

The development of crowding and interocular interactions in a resolution acuity task.

PURPOSE: To investigate the impact of interocular similarities of a surround stimulus on foveal resolution acuity in the normally developing visual system. METHODS: Liquid crystal shutter goggles synchronized with the monitor frame rate were used to present a Landolt C and surround bars to one or both eyes, in monocular, dichoptic, half-binocular, and binocular viewing conditions. Resolution acuity was measured under each condition in 56 normally sighted children (7 to 14 years of age) and 22 adults (21 to 38 years of age). The effect of the surround bars (crowding) was tested in a subgroup of nine children, and 10 adults. RESULTS: Across all age groups resolution acuity was significantly better in the binocular condition than in the other three viewing conditions (binocular summation), and was significantly better in the half-binocular (with target presented to the test eye and bars presented to both eyes) than in the dichoptic condition (target presented to test eye and bars presented to the nontested eye only). In children, but not in adults, resolution acuity was significantly better without than with bars. CONCLUSIONS: The interocular similarities may explain the better visual resolution in the half-binocular condition than in the dichoptic condition for all age groups tested. The results suggest that interocular interactions underpinning resolution acuity under these viewing conditions are developed in early childhood. The foveal crowding effect was found to be apparent at the beginning of school age, and diminished with maturation.

Configuration specificity of crowding in peripheral vision.

Peripheral vision is characterized in part by poor spatial resolution and impaired visual performance, particularly when the object is surrounded by flanking elements, a phenomenon popularly known as "crowding". Crowding scales with eccentricity irrespective of the target size, both in terms of magnitude and spatial extent, which is determined by varying the target-flanker separation. However, the extent to which crowding depends upon the flanking stimuli parameters alone without separating target and flankers is poorly understood. In the present study, we investigated the effect of flanking stimulus parameters on crowding in orientation and contrast discrimination tasks using closely located "chain" lateral Gabor stimuli in order to enhance our understanding of the underlying mechanisms of crowding in peripheral vision. We found a strong configural effect on crowding in both orientation and contrast discrimination tasks, with reduced crowding when the flanker parameters enhanced the target salience and increased crowding when the flankers were perceptually grouped with the target. While in orientation discrimination crowding was dependent on eccentricity, and in contrast discrimination it was dependent on flanker contrast and eccentricity, crowding showed little dependence on the number of flankers in either task. We conclude that crowding in peripheral orientation and contrast discrimination is configuration specific, which can be reduced without alterations to the target-flanker separation and that crowding is a combination of low-level as well as high-level cortical processing.

Enhancement of resolution acuity in a half-binocular viewing condition.

PURPOSE: To investigate the effect of interocular stimulus similarity on foveal resolution acuity. METHODS: Liquid crystal shutter goggles synchronized with the monitor refresh rate were used to present a Landolt C and surround bars to one or both eyes, in four viewing conditions (monocular, dichoptic, half-binocular, and binocular). Resolution acuity was measured in each condition in 22 normally sighted adults. RESULTS: Resolution acuity was significantly better in the binocular condition than in the other three viewing conditions (binocular summation) and was significantly better in the half-binocular condition (with target presented to the test eye and bars presented to both eyes) than in the dichoptic condition (target presented to the test eye and bars presented to the nontested eye only). CONCLUSIONS: Monocular resolution acuity depends in part on interocular similarities of the stimulus surrounding the central target. This finding may have implications in the design of stimuli for vision-training therapies.

A psychophysical study of human binocular interactions in normal and amblyopic visual systems.

During infancy and childhood, spatial contrast sensitivity and alignment sensitivity undergo maturation, and during this period the visual system has considerable plasticity. The purpose of this study was to compare the nature of interocular interactions of these spatial functions in normally sighted children and adults, and to study the extent to which interocular interactions are impaired in anisometropic amblyopia. Spatial functions were measured under three viewing conditions: monocular (fellow eye occluded), dichoptic (uniform stimulus presented to the fellow eye but with a peripheral fusion lock), and binocular. Measurements were made in each eye during monocular and dichoptic viewing. In the contrast sensitivity task, Gabor stimuli were presented in one of two temporal intervals. For the alignment task, a three-element Gabor stimulus was used. The task of the subject was to indicate the direction of displacement of the middle patch with respect to the outer patches. The findings indicate that in children, binocular contrast sensitivity was better than monocular (binocular summation) but so too was dichoptic sensitivity (dichoptic summation). The magnitude of binocular/dichoptic summation was significantly greater in children than in normally sighted adults for contrast sensitivity, but not for alignment sensitivity. In anisometropic amblyopes, however, we find that for the group as a whole the amblyopic eye does not benefit when the fellow eye views a dichoptic stimulus, compared to dark occlusion of that eye. In addition, we found considerable inter-individual variation within the amblyopic group. Implications of these findings for techniques used in vision therapy are discussed.

Interocular interactions during acuity measurement in children and adults, and in adults with amblyopia.

The binocular interactions that occur during dichoptic and binocular viewing were investigated using a letter acuity task in normally sighted children (age range 6-14 years) and adults, and in adults with anisometropic amblyopia. Our aims were to investigate the nature of binocular interactions that occur in each group, and the extent to which the characteristics of binocular interactions differ across the groups. The non-tested eye was occluded during monocular (baseline) viewing, and was allowed to view a uniform stimulus with fusion lock in dichoptic viewing. In adults and children with normal vision, acuity under dichoptic viewing was unchanged relative to monocular baseline in the dominant eyes, while acuity of the non-dominant eye improved under dichoptic viewing relative to baseline. The magnitude of dichoptic change in the non-dominant eyes was similar in the two normally sighted groups, but the dichoptic advantage was found to decrease with increasing age within the children tested. Binocular acuity was better than monocular acuity in normal subjects, and a decrease in binocular summation with age was noted within the age range of the children tested. In contrast, the amblyopic observers showed no change in acuity with viewing conditions. The results demonstrate development of interocular interactions during childhood, and wide inter-individual variation in pattern of interocular interactions among anisometropic amblyopic adults.

Strabismic amblyopia. Part 2. Neural processing.

This is the second of a two-part survey of current literature concerning strabismic amblyopia. The aim of this review is to bring the optometric community up to date on the status of scientific research into strabismic amblyopia. Part 1 in this series discussed research into strabismic amblyopia from the viewpoint of psychophysical experiments, which investigate both spatial and temporal behavioural deficits accompanying strabismic amblyopia. These include deficits in contrast sensitivity, spatial localisation, fixation, ocular motility, accommodation, crowding, attention, motion perception and temporal processing. Part 2 concerns neural processing in regards to strabismic amblyopia. It discusses current understanding of more fundamental aspects of central processing of visual information and in particular current theories regarding neural sites and mechanisms involved in amblyopia.

Strabismic amblyopia. Part 1. Psychophysics.

This is a two-part survey of current literature concerning strabismic amblyopia. The aim of this review is to bring the optometric practitioner up to date on the status of scientific research into strabismic amblyopia. Part 1 in this series discusses research into strabismic amblyopia from the viewpoint of psychophysical experiments that investigate both spatial and temporal behavioural deficits accompanying strabismic amblyopia. These include deficits in contrast sensitivity, spatial localisation, fixation, ocular motility, accommodation, crowding, attention, motion perception and temporal processing. Part 2 will evaluate neural processing in regard to strabismic amblyopia. It will discuss current understanding of aspects of central processing of visual information and theories regarding neural sites and mechanisms involved in amblyopia.