Efficacy of coloured lenses for patients diagnosed with visual stress.

CLINICAL RELEVANCE: Colour overlays and lenses are used to relieve symptoms in some patients diagnosed with visual stress, but evidence to support this practice is lacking. In this small randomised crossover trial, a range of colours are beneficial and precise colour specification does not enhance this effect. BACKGROUND: This randomised, double-masked crossover trial aimed to test effectiveness of precisely selected lens tints for visual stress. METHODS: Twenty-nine participants aged 11 to 72 (mean 30) years diagnosed with visual stress were issued with their selected coloured overlay then with tinted lenses at two colour settings. An eye examination and coloured overlay test were followed by intuitive colorimetry to select a colour to minimise symptoms (optimal tint) and the closest setting at which the symptoms returned (sub-optimal, or placebo tint). The tints were worn for one month each in randomised order. Reading speed was measured using the Wilkins Rate of Reading Test, a subjective scale was used to gauge symptoms, and the patient was asked to indicate whether one of the tints alleviated their symptoms more than the other. RESULTS: Reading speed was significantly higher with colour than without (p < 0.001), but was similar with the overlay and both tints (p = 1.0). Discomfort/distortion rating (1-7) was lower with colour than without (p < 0.001), but no difference was found between the overlay and both tints (p > 0.1). About half (47%) of the patients preferred/strongly preferred their optimal tint, and 39% preferred/strongly preferred their sub-optimal tint, while 14% had no preference. CONCLUSIONS: While our patients read more quickly and were more comfortable when using a tint, there was no difference in outcome between the optimal and sub-optimal tints. These results suggest that for patients diagnosed with visual stress, precision tints are no more helpful than sub-optimal, placebo tints.

The development of meridional anisotropies in neurotypical children with and without astigmatism: Electrophysiological and psychophysical findings.

It is important to understand the development of meridional anisotropies in neurotypical children since those with poor visual development, such as amblyopia, can have different patterns of meridional anisotropies. While the oblique effect is usually observed in adults, neurotypical children who have normal 20/20 visual acuity tend to demonstrate a horizontal effect electrophysiologically. In this longitudinal study, orientation-specific visual evoked potentials (osVEPs) and psychophysical grating acuity were used to investigate the changes in the meridional anisotropies in children aged 3.8 to 9.2 years over two visits averaging four months apart. While it was hypothesized that the electrophysiological horizontal effect may shift towards an oblique effect, it was found that the electrophysiological horizontal effect persisted to be present in response to the suprathreshold moderate contrast 4 cycles-per-degree grating stimuli. Psychophysical grating acuity, however, demonstrated an oblique effect when assessed binocularly. In addition, a significant effect of visit, representing an increase in the average age over this period, was observed in the average osVEP C3 amplitudes (4.5 µV) and psychophysical grating acuity (0.28 octaves or approximately 1-line on the logMAR chart). These findings are relevant when evaluating amblyopia treatments and interventions, as it confirms the necessity to take into account of the effect of normal maturation and learning effects when evaluating young children. Special attention should also be given to children with early-onset myopia and high astigmatism even when their visual acuity is 20/20 as the electrophysiological findings are suggestive of poor visual development, which warrants further investigation.

Interocular Contrast Balancing Partially Improves Stereoacuity in Keratoconus.

SIGNIFICANCE: Partial improvement in stereoacuity may be achieved by balancing the contrast input to the two eyes of patients with bilaterally asymmetric keratoconus. PURPOSE: Interocular differences in image quality, characterized by dissimilar contrast loss and phase shifts, are implicated in stereoacuity loss in keratoconus. This study determined whether contrast balancing improves stereoacuity in this disease condition and, if so, whether it is dependent on the baseline interocular contrast imbalance. METHODS: Interocular contrast imbalance and stereoacuity of 43 subjects (16 to 33 years) with bilaterally asymmetric keratoconus were tested with spectacle correction as baseline using a binocular rivalry paradigm and random-dot stereograms, respectively. Stereoacuity measurements were repeated in a subset of 33 subjects at their contrast balance point (i.e., contrast level in stronger eye allowing balanced rivalry with 100% contrast in weaker eye) and with contrast levels biased in favor of stronger or weaker eye, all conditions in randomized order. RESULTS: Contrast imbalance level was significantly correlated with the subject's stereoacuity at baseline ( r = -0.47, P = .002). The median (25th to 75th interquartile range) stereoacuity improved by 34.6% (19.0 to 65.1%) from baseline (748.8 arc sec [261.3 to 1257.3 arc sec]) to the contrast balanced condition (419.0 arc sec [86.6 to 868.9 arc sec]) ( P < .001), independent of their baseline stereoacuity or contrast imbalance levels ( r < 0.2, P > .26 for both). Contrast bias in favor of the weaker eye (881.3 arc sec [239.6 to 1707.6 arc sec]) worsened stereoacuity more than a bias toward the stronger eye (502.6 arc sec [181.9 to 1161.4 arc sec]), both relative to the contrast balanced condition ( P < .002). CONCLUSIONS: Interocular contrast balancing partially improves stereoacuity in bilaterally asymmetric keratoconus, independent of their baseline contrast imbalance level. Cyclopean viewing may be inherently biased toward the input from the stronger eye in keratoconus.

Refractive prescribing for preschool children by optometrists in England.

PURPOSE: Correction of refractive error in children is important for visual and educational development. The aim of this questionnaire-based study was to explore paediatric refractive correction by optometrists in England. METHODS: An online questionnaire was piloted and distributed to optometrists in England. The questionnaire asked about respondents' characteristics (such as type of practice), management of refractive error in 1- and 3-year-old children and sources of information used as a basis for decisions on prescribing refractive error in children. RESULTS: Two hundred and ninety-three questionnaires were returned, although only 139 (47%) were fully completed. In an average month, about half of respondents examined no children between 0 and 2 years of age, and about half examined no more than five children aged 3-4 years. A significant proportion indicated they would refer children aged 1 or 3 years with refractive error and no other signs or symptoms into the hospital eye service. Almost a quarter would prescribe in full or in part an isometropic refractive correction of +2.00 D for a 3-year-old (within the normal range) with no other signs or symptoms, suggesting a degree of unnecessary prescribing. Almost all would act in cases of clinically significant refractive error. Respondents made similar use of their colleagues, optometric or postgraduate/continuing education, professional guidance and peer-reviewed research as sources of evidence on which to base decisions about prescribing for paediatric refractive errors. Most reported 'never' or 'rarely' using Cochrane reviews. CONCLUSIONS: These results suggest optometrists often defer management of paediatric refractive error to the hospital eye service, with implications in terms of underutilisation of community optometric expertise and burden on the National Health Service. In some cases, the results indicate a mismatch between respondents' reported management and existing guidance/guidelines on paediatric prescribing.

Prevalence of refractive errors among school-going children in a multistate study in India.

AIM: Much existing data on childhood refractive error prevalence in India were gathered in local studies, many now dated. The aim of this study was to estimate the prevalence, severity and determinants of refractive errors among school-going children participating in a multistate vision screening programme across India. METHODS: In this cross-sectional study, vision screening was conducted in children aged 5-18 years at schools in five states using a pocket vision screener. Refractive error was measured using retinoscopy, and subjective refraction and was defined both by spherical equivalent (SE) and spherical ametropia, as myopia ≤-0.5 diopters (D), hyperopia ≥+1.0 D and/or astigmatism as >0.5 D. Data from the eye with less refractive error were used to determine prevalence. RESULTS: Among 2 240 804 children (50.9% boys, mean age 11.5 years, SD ±3.3), the prevalence of SE myopia was 1.57% (95% CI 1.54% to 1.60%) at 5-9 years, 3.13% (95% CI 3.09% to 3.16%) at 10-14 years and 4.8% (95% CI 4.73% to 4.86%) at 15-18 years. Hyperopia prevalence was 0.59% (95% CI 0.57% to 0.61%), 0.54% (95% CI 0.53% to 0.56%) and 0.39% (95% CI 0.37% to 0.41%), respectively. When defined by spherical ametropia, these values for myopia were 0.84%, 2.50% and 4.24%, and those for hyperopia were 2.11%, 2.41% and 2.07%, respectively.Myopia was associated with older age, female gender, private school attendance, urban location and state. The latter appeared to be driven by higher literacy rates. CONCLUSIONS: Refractive error, especially myopia, is common in India. Differences in prevalence between states appear to be driven by literacy rates, suggesting that the burden of myopia may rise as literacy increases.

Characterising the orientation-specific pattern-onset visual evoked potentials in children with bilateral refractive amblyopia and non-amblyopic controls.

PURPOSE: An orientation-specific visual evoked potential (osVEP) protocol was developed to probe meridional anisotropies in children with refractive amblyopia. The aim was to characterise the osVEP response in children with bilateral refractive amblyopia, evaluate the intra-session repeatability of the main osVEP components (C1, C2 and C3), coefficient of repeatability (CoR) of the response to gratings in different meridians and determine if refractive amblyopes have poorer repeatability as compared with non-amblyopic controls. METHODS: Children aged 4-7 years with newly diagnosed and untreated bilateral refractive amblyopia and non-amblyopic controls were recruited. Orientation-specific pattern-onset VEPs were recorded in response to an achromatic sinewave grating stimulus of 4 cycles per degree under monocular and binocular stimulation. The grating lines used for monocular stimulation were parallel with the subjects' most positive and negative astigmatic meridians when considered in sphero-minus cylinder form (Meridians 1 and 2, respectively). In subjects without astigmatism, meridians 1 and 2 were designated horizontal and vertical gratings, respectively. Binocular stimuli were presented with grating lines parallel to meridians 45, 90, 135 and 180°. The repeatability of latencies of the main osVEP components (C1, C2 and C3) were investigated using two successive osVEPs recordings for each stimulus meridian and the CoR for each component's latencies were assessed. RESULTS: Seven amblyopic children (Visual acuity (VA) ranging from 0.08 to 0.40 LogMAR in the less amblyopic eye and 0.26-0.52 LogMAR in the more amblyopic eye) and 7 non-amblyopic controls (VA ranging from 0.00 to 0.02 LogMAR in either eye), with a median age of 4.6 and 7.0 years, respectively, completed the study. C1 had the highest CoR for most conditions assessed. Ratio of CoRs C1:C2 was > 2 for all binocular meridians in controls and the 90 and 180 meridians in the amblyopes; C1:C3 was > 2 for the binocularly assessed 45, 90 and 135 meridians in the controls and the 90 and 180 meridians in the amblyopes; C2:C3 were all < 2 for all meridians assessed in both groups. CONCLUSIONS: The osVEP waveforms are reliable and useful for future investigations into the meridional anisotropies in children with refractive amblyopia, particularly the C3 component. Component C1 had the poorest repeatability, which consequentially affected C2 amplitude estimation. Only C3 amplitude and latency could be consistently estimated as C2 and C3 latencies were similarly repeatable. Coefficients of repeatability of osVEP latencies did not appear to systematically differ between non-amblyopic and amblyopic children.

Electrophysiological and Psychophysical Studies of Meridional Anisotropies in Children With and Without Astigmatism.

Purpose: We investigated the pattern of meridional anisotropies, if any, for pattern onset-offset visual evoked potential (POVEPs) responses and psychophysical grating acuity (GA) in children with normal letter visual acuity (20/20 or better). Methods: A total of 29 children (aged 3-9 years), nine of whom were astigmatic (AS), were recruited. Orientation-specific monocular POVEPs were recorded in response to sinewave grating stimuli oriented along the subjects' principal AS meridians. Horizontal and vertical gratings were designated Meridians 1 and 2, respectively, for nonastigmatic patients (Non-AS). Binocular POVEPs in response to the same stimuli, but oriented at 45°, 90°, 135°, and 180°, were recorded. Psychophysical GAs were assessed monocularly and binocularly along the same meridians using the same stimuli by a 2-alternative-forced-choice staircase technique. The C3 amplitudes and peak latencies of the POVEP and GAs were compared across meridians using linear mixed models (monocular) and ANOVA (binocular). Results: There were significant meridional anisotropies in monocular C3 amplitudes regardless of astigmatism status (P = 0.001): Meridian 2 (mean ± SE Non-AS, 30.13 ± 2.07 µV; AS, 26.53 ± 2.98 µV) was significantly higher than Meridian 1 (Non-AS, 26.14 ± 1.87 µV; AS, 21.68 ± 2.73 µV; P = 0.019), but no meridional anisotropies were found for GA or C3 latency. Binocular C3 amplitude in response to horizontally oriented stimuli (180°, 29.71 ± 3.06 µV) was significantly lower than the oblique (45°, 36.62 ± 3 .05 µV; P = 0.03 and 135°, 35.95 ± 2.92 µV; P = 0.04) and vertical (90°, 37.82 ± 3.65 µV; P = 0.02) meridians, and binocular C3 latency was significantly shorter in response to vertical than oblique gratings (P ≤ 0.001). Conclusions: Meridional anisotropy was observed in children with normal vision. The findings suggest that horizontal gratings result in a small, but significantly lower POVEP amplitude than for vertical and oblique gratings.

Efficacy of coloured overlays and lenses for treating reading difficulty: an overview of systematic reviews.

Coloured overlays or lenses are widely available for use by children and adults with difficulties or discomfort while reading. In recent years, systematic reviews have been conducted in an attempt to establish the strength of the evidence base for this intervention. The aim of this overview is to systematically review these reviews. The methodology was published prospectively as a protocol (Prospero CRD42017059172). Online databases Medline, Cinahl, Embase and the Cochrane Library were searched for systematic reviews on the efficacy of coloured overlays or lenses for the alleviation of reading difficulty or discomfort. Included studies were appraised using the AMSTAR 2 checklist. Characteristics of included studies such as aspects of methods, results and conclusions were recorded. Both processes were conducted independently by two reviewers and any discrepancies were resolved by discussion. Thirty-one studies were found via databases and other sources. After excluding duplicates and those not fitting the inclusion criteria, four reviews were included in the analysis. While all reviews were systematic, their methodology, results and conclusions differed. Three of the four concluded that there is insufficient good quality evidence to support the use of coloured overlays or lenses for reading difficulty, while one concluded that, despite research limitations, the evidence does support their use. On balance, systematic reviews to date indicate that there is not yet a reliable evidence base on which to recommend coloured overlays or lenses for the alleviation of reading difficulty or discomfort. High quality, low bias research is needed to investigate their effectiveness in different forms of reading difficulty and discomfort for adults and children.

Coloured overlays and precision-tinted lenses: poor repeatability in a sample of adults and children diagnosed with visual stress

PURPOSE: Visual stress consists of perceived distortions or discomfort while reading. It is claimed that these symptoms are alleviated by viewing through coloured lenses or overlays, with a specific colour required for each individual. This has been explained on the basis of altered visual cortex excitation as affected by the spectral content of the viewing light. If symptoms are indeed alleviated by a particular colour that has an impact on the individual's visual system, we would expect that selection of the most beneficial colour would be repeatable. The aim of this study was to determine whether this is the case. METHODS: Twenty-one participants (mean age 26 years (range 8-55 years); 12 female, nine male) with visual stress and no other uncorrected ocular or visual anomaly were recruited. Each participant selected the colour most beneficial in alleviating their symptoms from a standard set of 10 coloured overlays, and underwent intuitive colorimetry in which the most beneficial of a wide range of chromatic illuminance settings was selected. Without prescribing an overlay at the first appointment, this process was repeated on a second occasion at a mean of 25 days later. RESULTS: About half of the participants (n = 10) chose the same (n = 7) or similar (with one common colour in both choices; n = 3) coloured overlay on the two occasions, while 11 participants chose a completely different overlay colour. Across all participants, the colorimetry setting shifted by, on average, 9.6 just noticeable differences, indicating that the colours were perceptually very different. CONCLUSION: These findings suggest that people with visual stress are unlikely to find exactly the same colour to be optimal on different occasions, and raise questions about the need for precise colour specification in tinted lenses for visual stress.

Does Gender Influence Colour Choice in the Treatment of Visual Stress?

PURPOSE: Visual Stress (VS) is a condition in which words appear blurred, in motion, or otherwise distorted when reading. Some people diagnosed with VS find that viewing black text on white paper through coloured overlays or precision tinted lenses (PTLs) reduces symptoms attributed to VS. The aim of the present study is to determine whether the choice of colour of overlays or PTLs is influenced by a patient's gender. METHODS: Records of all patients attending a VS assessment in two optometry practices between 2009 and 2014 were reviewed retrospectively. Patients who reported a significant and consistent reduction in symptoms with either overlay and or PTL were included in the analysis. Overlays and PTLs were categorized as stereotypical male, female or neutral colours based on gender preferences as described in the literature. Chi-square analysis was carried out to determine whether gender (across all ages or within age groups) was associated with overlay or PTL colour choice. RESULTS: 279 patients (133 males and 146 females, mean age 17 years) consistently showed a reduction in symptoms with an overlay and were included. Chi-square analysis revealed no significant association between the colour of overlay chosen and male or female gender (Chi-square 0.788, p = 0.674). 244 patients (120 males and 124 females, mean age 24.5 years) consistently showed a reduction in symptoms with PTLs and were included. Chi-square analysis revealed a significant association between stereotypical male/female/neutral colours of PTLs chosen and male/female gender (Chi-square 6.46, p = 0.040). More males preferred stereotypical male colour PTLs including blue and green while more females preferred stereotypical female colour PTLs including pink and purple. CONCLUSIONS: For some VS patients, the choice of PTL colour is influenced not only by the alleviation of symptoms but also by other non-visual factors such as gender.

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.

Attitudes and barriers to evidence-based practice in optometry educators.

PURPOSE: Evidence-based practice (EBP) is an essential component of good quality, patient-centered health care. This requires practitioners to acquire EBP skills and knowledge during undergraduate and continuing education. Evidence-based practice education exists in a range of health care disciplines, including optometry. Evidence-based practice education, however, depends on relevant skills and knowledge in educators. Courses and workshops exist for the development of EBP teaching skills in some areas of health care but not in optometry. Here, we describe a pilot workshop designed to enhance the teaching of EBP and to investigate the perspectives of optometric educators on EBP including their attitudes and perceived barriers to EBP and its teaching. METHODS: Twenty-seven optometric educators including 8 facilitators participated. Of these, 14 were academics (including the 8 facilitators) and 13 were practitioners. Evidence-based practice attitudes were assessed using the Evidence-Based Practice Attitude Scale-50 with appropriate modifications for optometry. Workshop design incorporated strategies to trigger discussion among participants. A nominal group technique was used to identify, prioritize, and reach consensus on barriers to EBP. RESULTS: Although some participants expressed reservations about EBP, a common understanding of the contemporary definition of EBP emerged in educators. Thirty-five barriers to EBP were identified; "time" was selected in the top five barriers by most participants and attracted the highest total score, well above any other barrier (negative attitude to EBP, volume of evidence, integration with clinical practice, and lack of lifelong learning mind-set). Attitudes toward EBP were generally positive and negatively correlated with age and time since graduation, respectively. CONCLUSIONS: A group of optometrists and academics new to implementing education in EBP displayed positive attitudes to EBP but considered that its application and teaching could be significantly hindered by a lack of time to access and appraise the large volume of available research evidence in the field of eye care.

Optometrists show rudimentary understanding of evidence-based practice but are ready to embrace it: can barriers be overcome?

BACKGROUND: Evidence-based practice (EBP) involves integration of the best available evidence from research, the patient's preferences or circumstances, the clinical environment and the health practitioner's expertise. There have been several qualitative studies of EBP in health-care but none has focused on the profession of optometry. Therefore, the aim of the present study was to assess optometrists' perceptions of EBP in optometry. METHODS: This exploratory qualitative study employed focus group meetings and individual telephone interviews to gauge understanding of and opinions about EBP in a convenience sample of Australian and Saudi Arabian optometrists. Results were summarised in accordance with the Consolidated Criteria for Reporting Qualitative Research (COREQ) checklist. NVivo software was used for qualitative analysis of the results. RESULTS: Most participants were supportive of EBP; however, their perceptions did not generally reflect a deep understanding of the definition or process of EBP. Participants reported using a combination of low and high level evidence to inform their clinical decisions. In line with findings from other health professions, barriers included lack of time and lack of access to information, while enablers such as education, organisational support and self-motivation were cited. DISCUSSION: Our findings suggest a need for better training of optometrists in EBP as well as resources and approaches that support EBP in optometry, such as an EBP database of pre-appraised evidence and more secondary sources of evidence, such as systematic reviews and critically appraised topics.

Development of a novel approach to the assessment of eye-hand coordination.

BACKGROUND: Current methods to measure eye-hand coordination (EHC) have been widely applied in research and practical fields. However, some aspects of the methods, such as subjectivity, high price, portability, and high appraisal contribute to difficulties in EHC testing. NEW METHODS: The test was developed on an Apple iPad(®) and involves tracing up to 13 shapes with a stylus pen. The time taken to complete each trace and the spatial accuracy of the tracing is automatically recorded. The difficulty level for each shape was evaluated theoretically based on the complexity and length of outline. Ten adults aged 31.5±7.8 years and five children aged 9.4±1.1 years with normal vision participated. RESULTS: In adults, the time taken to trace and number of errors significantly decreased from the first to the second attempt (p<0.05) but not thereafter, suggesting a learning effect with repeatability after a practice attempt. Time taken and number of errors in children were both higher in monocular than binocular viewing conditions (p=0.02 and p<0.01, respectively) while adults' performance was similar in both viewing conditions. COMPARISON WITH EXISTING METHODS: Existing EHC tests are subjective in clinics and require higher skills and cost in research, and measure gross EHC. This novel test has been developed to address some of the limitations. CONCLUSIONS: The test is engaging for children and adults and is an objective method with potential for the assessment of fine EHC, suited to clinic-based and research use in ophthalmic or brain trauma settings, and in developmental disorders.

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.