Visual acuity Research Papers - Academia.edu (original) (raw)

PURPOSE. Amblyopia is a common developmental visual impairment characterized by a substantial difference in acuity between the two eyes. Current monocular treatments, which promote use of the affected eye by occluding or blurring the fellow eye, improve acuity, but are hindered by poor compliance. Recently developed binocular treatments can produce rapid gains in visual function, thought to be as a result of reduced interocular suppression. We set out to develop an effective home-based binocular treatment system for amblyopia that would engage high levels of compliance but that would also allow us to assess the role of suppression in children's response to binocular treatment. METHODS. Balanced binocular viewing therapy (BBV) involves daily viewing of dichoptic movies (with ''visibility'' matched across the two eyes) and gameplay (to monitor compliance and suppression). Twenty-two children (3–11 years) with anisometropic (n ¼ 7; group 1) and strabismic or combined mechanism amblyopia (group 2; n ¼ 6 and 9, respectively) completed the study. Groups 1 and 2 were treated for a maximum of 8 or 24 weeks, respectively. RESULTS. The treatment elicited high levels of compliance (on average, 89.4% 6 24.2% of daily dose in 68.23% 6 12.2% of days on treatment) and led to a mean improvement in acuity of 0.27 logMAR (SD 0.22) for the amblyopic eye. Importantly, acuity gains were not correlated with a reduction in suppression. CONCLUSIONS. BBV is a binocular treatment for amblyopia that can be self-administered at home (with remote monitoring), producing rapid and substantial benefits that cannot be solely mediated by a reduction in interocular suppression. A mblyopia is a developmental disorder of vision with a prevalence of 2% to 5%, 1 defined as a monocular (rarely binocular) reduction of the best-corrected visual acuity (henceforth, acuity) in an otherwise healthy eye. Amblyopia is caused by a prolonged period of abnormal retinal stimulation (mainly) due to strabismus (ocular misalignment), anisometro-pia (refractive imbalance), or both (combined) and leads to functional deficits, including reduced contrast sensitivity, 2 poor spatial localization, 3 poor stereovision, 4 and foveal crowding. 5 Typically, amblyopia is treated only if the interocular acuity difference between the amblyopic eye (AE) and the fellow eye (FE) is at least 0.2 logMAR. 6 Current treatment commences with 12 to 24 weeks of wearing prescribed optical correction, which improves AE acuity to normal levels in 27% to 32% of cases. 7,8 Otherwise, treatment to promote the use of the AE is administered, which consists of patching the FE (2–12 h/d) 9 or blurring the FE with atropine eye drops 10 for up to 24 months. 11,12 Such occlusion therapies improve acuity in approximately 70% of patients by 0.2 logMAR or more. 9 However, their impact on binocular vision is less certain 13 and amblyopia recurs within a year in approximately 25% of patients younger than 8 years. 14,15 Moreover, compliance is poor: on average, only 44% of the prescribed daily dose is received in 58% of days ascribed for treatment. 16 Central to current treatment is the idea of a critical period for visual development. In humans, acuity and contrast sensitivity are adversely affected by periods of monocular deprivation before the age of 10 years, even though adult-like performance is reached at 6 years. 17 However, the notion that amblyopia is not treatable outside of this period has been challenged by studies finding that adults forced to use their AE show substantial improvements in contrast sensitivity, 18 crowded acuity, 19 and stereopsis. 20 Interocular suppression (henceforth, suppression) is widely considered to be central to the mechanisms underlying amblyopia, although functional definitions vary. When measured with a dichoptic motion-coherence task, 21 suppression has been quantified as the contrast offset between the eyes at which binocular integration fails. 22,23 Others have measured suppression as the ''effective contrast ratio'' necessary to