Purpose.: This study had three main goals: to assess the degree of suppression in patients with strabismic, anisometropic, and mixed amblyopia; to establish the relationship between suppression and the degree of amblyopia; and to compare the degree of suppression across the clinical subgroups within the sample. Methods.: Using both standard measures of suppression (Bagolini lenses and neutral density [ND] filters, Worth 4-Dot test) and a new approach involving the measurement of dichoptic motion thresholds under conditions of variable interocular contrast, the degree of suppression in 43 amblyopic patients with strabismus, anisometropia, or a combination of both was quantified. Results.: There was good agreement between the quantitative measures of suppression made with the new dichoptic motion threshold technique and measurements made with standard clinical techniques (Bagolini lenses and ND filters, Worth 4-Dot test). The degree of suppression was found to correlate directly with the degree of amblyopia within our clinical sample, whereby stronger suppression was associated with a greater difference in interocular acuity and poorer stereoacuity. Suppression was not related to the type or angle of strabismus when this was present or the previous treatment history. Conclusions.: These results suggest that suppression may have a primary role in the amblyopia syndrome and therefore have implications for the treatment of amblyopia.

Citation information: Lam CS‐Y, Lam C‐H, Cheng SC‐K & Chan LY‐L. Prevalence of myopia among Hong Kong Chinese schoolchildren: changes over two decades. Ophthalmic Physiol Opt 2012, 32, 17‐24. doi: 10.1111/j.1475‐1313.2011.00886.x Purpose:  Studies have documented an increasing prevalence of myopia among urbanized Asian countries over recent decades. In the early 1990s, the reported prevalence rate was 25% and 64% for 6 and 12 year old children respectively. This cross‐sectional study aims to determine the current prevalence of myopia amongst Hong Kong Chinese schoolchildren and whether there has been any increase over the last two decades. Methods:  Data from 2651 children aged 6–12 (mean age: 8.92 ± 1.77, 53% boys) who participated in vision screening during 2005–2010 were analyzed. Visual parameters including visual acuity (in logMAR) and binocular status under the participants’ habitual correction were assessed. Refractive errors were examined using non‐cycloplegic auto‐refraction and axial lengths were measured by partial coherence interferometry. Results:  The mean spherical equivalent refraction for this population was −1.02 ± 1.70D, ranging from +4.75 to −10.00D. Prevalence of myopia (more than −0.50D) was 18.3% for the 6‐year‐old group and 61.5% for the 12‐year‐old group. Average myopia magnitude was −0.06 ± 1.03D at age 6 and −1.67 ± 1.99D at age 12. Prevalence of high myopia of more than −6.00D was 1.8%, with an increase from 0.7% at the age of 6 to 3.8% at the age of 12. Conclusions:  The prevalence of myopia among the Chinese schoolchildren population in Hong Kong as observed in this cross‐sectional study are similar to our previously reported findings from almost two decades ago. There is no evidence that prevalence of myopia is increasing with time over the last two decades. However, the prevalence and degree of myopia in Chinese children is high as compared with other ethnic groups such as those reported among Caucasians.

Purpose.: Although eye dominance assessment is used to assist clinical decision-making, current understanding is limited by inconsistencies across the range of available tests. A new psychophysical test of sensory eye dominance has been developed that objectively measures the relative contribution of each eye to a fused suprathreshold binocular percept. Methods.: Six standard tests and the newly developed test were used to measure motor and sensory dominance in a group of 44 binocularly normal individuals (mean age, 29.5 ± 9.10 years). The new test required observers to perform a motion coherence task under dichoptic viewing conditions, wherein a population of moving, luminance-defined signal (coherently moving) and noise (randomly moving) dots were presented separately to each eye. The observers judged the motion direction of the signal dots. Motion coherence thresholds were measured by varying the ratio of signal-to-noise dots, in a staircase procedure. Results.: The new dichoptic motion coherence threshold test revealed a clear bimodal distribution of sensory eye dominance strength, wherein the majority of the participants (61%) showed weak dominance, but a significant minority (39%) showed strong dominance. Subsequent analysis revealed that the strong-dominance group showed greater consistency across the range of traditional eye dominance tests used. Conclusions.: This new quantitative dichoptic motion coherence threshold technique suggests that there are two separate sensory eye dominance strength distributions among observers with normal binocular vision: weak and strong eye dominance. This finding may provide a basis for clinical decision-making by indicating whether eye dominance is likely to be an important consideration in a particular patient.

Amblyopia is a neurodevelopmental disorder of vision that occurs when the visual cortex receives decorrelated inputs from the two eyes during an early critical period of development. Amblyopic eyes are subject to suppression from the fellow eye, generate weaker visual evoked potentials (VEPs) than fellow eyes and have multiple visual deficits including impairments in visual acuity and contrast sensitivity. Primate models and human psychophysics indicate that stronger suppression is associated with greater deficits in amblyopic eye contrast sensitivity and visual acuity. We tested whether transcranial direct current stimulation (tDCS) of the visual cortex would modulate VEP amplitude and contrast sensitivity in adults with amblyopia. tDCS can transiently alter cortical excitability and may influence suppressive neural interactions. Twenty-one patients with amblyopia and twenty-seven controls completed separate sessions of anodal (a-), cathodal (c-) and sham (s-) visual cortex tDCS. A-tDCS transiently and significantly increased VEP amplitudes for amblyopic, fellow and control eyes and contrast sensitivity for amblyopic and control eyes. C-tDCS decreased VEP amplitude and contrast sensitivity and s-tDCS had no effect. These results suggest that tDCS can modulate visual cortex responses to information from adult amblyopic eyes and provide a foundation for future clinical studies of tDCS in adults with amblyopia.