Identification of contrast-defined letters benefits from perceptual learning in adults with amblyopia.
(49/126)
Amblyopes show specific deficits in processing second-order spatial information (e.g. Wong, Levi, & McGraw (2001). Is second-order spatial loss in amblyopia explained by the loss of first-order spatial input? Vision Research, 41, 2951-2960). Recent work suggests there is a significant degree of plasticity in the visual pathway that processes first-order spatial information in adults with amblyopia. In this study, we asked whether or not there is similar plasticity in the ability to process second-order spatial information in adults with amblyopia. Ten adult observers with amblyopia (five strabismic, four anisometropic and one mixed) were trained to identify contrast-defined (second-order) letters using their amblyopic eyes. Before and after training, we determined observers' contrast thresholds for identifying luminance-defined (first-order) and contrast-defined letters, separately for the non-amblyopic and amblyopic eyes. Following training, eight of the 10 observers showed a significant reduction in contrast thresholds for identifying contrast-defined letters with the amblyopic eye. Five of these observers also showed a partial transfer of improvement to their fellow untrained non-amblyopic eye for identifying contrast-defined letters. There was a small but statistically significant transfer to the untrained task of identifying luminance-defined letters in the same trained eye. Similar to first-order spatial tasks, adults with amblyopia benefit from perceptual learning for identifying contrast-defined letters in their amblyopic eyes, suggesting a sizeable degree of plasticity in the visual pathway for processing second-order spatial information. (+info)
The relationship between anisometropia, patient age, and the development of amblyopia.
(50/126)
PURPOSE: Anisometropia is a common cause of amblyopia. The relationship between anisometropia, patient age, and the development of amblyopia is unknown. Photoscreening identifies children with anisometropia in a manner that is not biased by visual acuity and allows a unique opportunity to evaluate how patient age influences the prevalence and depth of anisometropic amblyopia. METHODS: A statewide preschool photoscreening program screened 120,000 children and identified 792 with anisometropia greater than 1.0 diopter. Age was correlated with visual acuity and amblyopia depth. Data were compared with those from 562 strabismic children similarly identified. RESULTS: Only 14% (6/44) of anisometropic children aged 1 year or less had amblyopia. Prevalence was 40% (32/80) for 2-year-olds, 65% (119/182) for 3-year-olds, and peaked at 76% (age 5). Amblyopia depth also increased with age. Moderate amblyopia prevalence was 2% (ages 0 to 1), 17% (age 2), and rose steadily to 45% (ages 6 to 7). Severe amblyopia was rare prior to age 4, 9% at age 4, 14% at age 5, and 9% at ages 6 to 7. In contrast, children with strabismus had a stable prevalence of amblyopia (30% at ages 0 to 2, 42% at ages 3 to 4, 44% at ages 5 to 7). CONCLUSIONS: Younger children with anisometropic refractive error have a lower prevalence and depth of amblyopia than do older children. By age 4, when most children undergo traditional screening, amblyopia has usually already developed. New vision screening technologies that allow early detection of anisometropia provide ophthalmologists an opportunity to intervene early, perhaps retarding, or even preventing, the development of amblyopia. (+info)
Binocular interactions in accommodation control: effects of anisometropic stimuli.
(51/126)
In binocular viewing of real targets, the accommodative demand in the two eyes is not in general identical, yet the accommodation response in the two eyes is equal. In order to investigate how the accommodative signals from the two eyes are combined, this study has examined the effects of several forms of dynamic anisometropic stimulation on the accommodation response in both man and the rhesus monkey (Macaca mulatta). All experiments were performed in a computer-controlled haploscopic apparatus to allow independent control of the accommodative stimuli to the two eyes and of the vergence stimulus. The vergence stimulus was held constant while the accommodation demand was modulated independently in each eye. Accommodation was monitored continuously with a dynamic infrared optometer. Four anisometropic conditions were used. In two of these conditions, accommodation demand was varied sinusoidally with time in both eyes, but with phases differing by 90 degrees or 180 degrees between the two eyes. In the two remaining conditions, accommodation demand in one eye varied sinusoidally, while the accommodation demand was constant in the other. In all cases, the form of the target pattern was identified in the two eyes. The accommodation responses observed with these stimulus conditions were similar in both man and the monkey. When presented with conflicting stimuli in the two eyes, the accommodation response appeared to be best described as a compromise between the inputs to the two eyes; there were no indications of a purely random alternation of eye dominance of the form seen in binocular contour rivalry. When the accommodation demand was modulated in only one eye, there was a modulated accommodation response of similar phase to the control condition (i.e., both eyes modulated in phase) but with a much smaller gain (mean, 39% of control gain). When the accommodation demand was modulated in both eyes with a phase difference of 180 degrees, no significant modulation was observed in the accommodation response at the stimulation frequency. When the interocular phase difference was 90 degrees, a modulated response was observed that showed a mean phase lag 41 degrees more than that observed in the control condition (both eyes modulated in phase) and an appreciably smaller gain (mean, 55% of control gain). The extent to which the results can be described by a linear vector average of the uniocular inputs is considered. (+info)
Factors associated with recurrence of amblyopia on cessation of patching.
(52/126)
PURPOSE: In a prospective observational study, we previously reported that weaning (tapering or gradually reducing) treatment in children treated with 6 to 8 hours of daily patching for amblyopia resulted in a 4-fold reduction in odds of recurrence. We now report the association of additional factors with recurrence or regression of amblyopia in this same cohort. DESIGN: Prospective, nonrandomized, observational study. PARTICIPANTS: Sixty-nine children aged <8 years with successfully treated anisometropic or strabismic amblyopia (improved > or =3 logarithm of the minimum angle of resolution [logMAR] lines). METHODS: Patients were enrolled at the time they stopped patching for amblyopia. Patients were classified according to whether patching was stopped abruptly or weaned before cessation. They were followed off treatment for 52 weeks to assess recurrence of amblyopia. MAIN OUTCOME MEASURE: Recurrence of amblyopia defined as a > or =2-logMAR level reduction of visual acuity from enrollment (cessation of patching) confirmed by a second examination. Recurrence was also considered to have occurred if treatment was restarted with a > or =2-logMAR level reduction of visual acuity, even if it was not confirmed by a second examination. RESULTS: The risk of recurrence was higher with better visual acuity at the time of cessation of treatment (adjusted risk ratio [RR], 0.68 per line of worse visual acuity; 95% confidence interval [CI], 0.51-0.90), a greater number of lines improved during the previous treatment (adjusted RR, 1.5 per line increase; 95% CI, 1.1-2.0), and a history of recurrence (adjusted RR, 2.7; 95% CI, 1.5-4.9). Orthotropia or excellent stereoacuity at the time of patching cessation did not appear to have a protective effect on the risk of recurrence. CONCLUSIONS: The higher risk of recurrence in the most successfully treated children with amblyopia and absence of protection from orthotropia and excellent random dot stereoacuity suggests that careful and prolonged follow-up is needed for all children who have been previously treated for amblyopia. (+info)
The use of the scanning laser ophthalmoscope in the evaluation of amblyopia (an American Ophthalmological Society thesis).
(53/126)
PURPOSE: The purpose of this study was to evaluate amblyopic patients with scanning laser ophthalmoscope microperimetry to determine whether the scanning laser ophthalmoscope data provide useful information in our understanding of amblyopia and assess its utility in the evaluation of amblyopic patients. METHODS: In this retrospective case-series, clinical data of 46 patients with amblyopia were examined after treatment for anisometropic or strabismic amblyopia. Ten normal patients served as controls. All patients were tested with the scanning laser ophthalmoscope, evaluating for the presence of macular scotomata. Scanning laser ophthalmoscope findings were assessed within each group and between groups. RESULTS: A macular scotoma was found in the amblyopic eye of 25 of 26 anisometropic amblyopic patients and all 20 strabismic amblyopia patients. Twenty of 26 patients with anisometropic amblyopia had a relative scotoma in the nonamblyopic eye. All 20 patients with strabismic amblyopia had a nonamblyopic eye scotoma. None of the control patients had a scotoma in either eye. Several clinical features were correlated to scotoma findings within and between groups. CONCLUSIONS: The scanning laser ophthalmoscope proved to be a useful tool for the assessment of some features of amblyopia. A scotoma was identified in not only the amblyopic eye of all but one of the amblyopic patients, but also in almost all of the nonamblyopic, presumably "normal" eyes. Thus, ocular effects of amblyopia may not be strictly limited to the amblyopic eye. (+info)
Spatial and temporal crowding in amblyopia.
(54/126)
Spatial crowding is a well-known deficit in amblyopia. We have previously reported evidence suggesting that the inability to isolate stimuli in space in crowded displays (spatial crowding) is a largely independent component of the amblyopic deficit in visual acuity, which is typically found in strabismic amblyopia [Bonneh, Y., Sagi, D., & Polat, U. (2004a). Local and non-local deficits in amblyopia: Acuity and spatial interactions. Vision Research, 44, 3009-3110]. Here, we extend this result to the temporal domain by measuring visual acuity (VA) for a single pattern in a rapid serial visual presentation (RSVP-VA, N=15) for fast ("crowded") and slow ("uncrowded") presentations. We found that strabismic amblyopes but not anisometropic amblyopes or normal controls exhibited a significant difference between VA under the fast and slow conditions. We further compared the "temporal crowding" measure to two measures of spatial crowding: (1) static Tumbling-E acuity in multi-pattern crowded displays (N=26) and (2) Gabor alignment with lateral flankers (N=20). We found that all three measures of crowding (one temporal and two spatial) were highly correlated across subjects while being largely independent of the visual acuity for a single isolated pattern, with both spatial and temporal crowding being high and correlated in strabismus and low in anisometropia. This suggests that time and space are related in crowding, at least in amblyopia. (+info)
Modeling dose-response in amblyopia: toward a child-specific treatment plan.
(55/126)
PURPOSE: This article describes an empirically derived mathematical model of the treatment dose-response of occlusion therapy for amblyopia based on outcome data obtained from the Monitored Occlusion Treatment for Amblyopia Study (MOTAS). METHODS: The MOTAS protocol comprised three discrete phases: baseline, refractive adaptation, and occlusion. Only data from the occlusion phase were used in this dose-response model. Seventy-two participants, 3 to 8 years of age, mean +/- SD age 5.2 +/- 1.4 years (anisometropia [n = 18]); strabismus [n = 22]); both anisometropia and strabismus [n = 32]) completed the occlusion phase. All participants were prescribed 6-h/d patching, which was objectively monitored by an occlusion dose monitor (ODM). RESULTS: Simple normal linear regression modeling of the data on an interval-by-interval basis (interval between clinic visits) indicates that increasing cumulative dose within interval (hours) yields an increase in visual acuity (R2 = 0.918; 684 data points). Most of the children achieved their best visual acuity with 150 to 250 hours' cumulative dose. Specific patient characteristics (especially age) modify the steepness of this function. For example, a 0.20-logMAR (2-line logarithm of the minimum angle of resolution) gain in visual acuity requires a cumulative dose of 170 hours for children at age 48 months and 236 hours at age 72 months. CONCLUSIONS: Mathematical modeling of amblyopia therapy is a novel approach that elucidates the kinetics of the therapeutic response in humans. This response is age-influenced so that older children require a greater dose to achieve the same outcome--evidence of altered plasticity of the visual system. Fine-tuning the dose-response in amblyopia therapy will facilitate the development of child-specific, evidence-based treatment plans. (+info)
Ocular dominance, laterality, and refraction in Singaporean children.
(56/126)
PURPOSE: To explore the effect of dominance and laterality on refractive error and axial length. METHODS: Ocular dominance was assessed with the hole-in-the-card test in 543 children during their 2006 follow-up visits for the Singapore Cohort study Of the Risk factors for Myopia (SCORM). Data were compared to cycloplegic refractions and axial lengths measured by ultrasound. RESULTS: The spherical equivalent refraction was essentially the same between the right and left eyes, although there was a small but statistically significant longer axial length in the right eyes. Right and left ocular dominance was noted in 58% and 30% of the subjects, respectively, with 12% having no eye preference. There was no significant difference in spherical equivalent refraction (2.56 +/- 2.46 D [mean +/- SD] vs. -2.45 +/- 2.52 D, P = 0.22) or axial length (24.36 +/- 1.19 mm vs. 24.32 +/- 1.18 mm, P = 0.05) between dominant and nondominant eyes. In subjects with anisometropia >or=0.5 D, dominant eyes were more myopic in 52%. Dominant eyes, however, had less astigmatic power (-0.88 +/- 0.80 D versus -1.00 +/- 0.92 D; P < 0.001). CONCLUSIONS: Ocular laterality and dominance have no significant effect on spherical equivalent. All axial length and astigmatic differences were small and clinically insignificant. The study findings suggest that in Singaporean children, bias is not present in those investigations that restrict analyses to right or left eyes. Although there is no apparent association between refraction and ocular dominance in young Singaporean children, more research is needed to resolve the disparate results in existing reports. (+info)