Manuela Bossi

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

Current treatments for amblyopia in children, occlusion and pharmacological blurring, have had limited success, with less than two-thirds of children achieving good visual acuity of at least 0.20 logMAR in the amblyopic eye, limited improvement of stereopsis, and poor compliance. A new treatment approach, based on the dichoptic presentation of movies or computer games (images presented separately to each eye), may yield better results, as it aims to balance the input of visual information from each eye to the brain. Compliance may also improve with these more child-friendly treatment procedures. To determine whether binocular treatments in children aged three to eight years with unilateral amblyopia result in better visual outcomes than conventional occlusion or pharmacological blurring treatment. We searched the Cochrane Eyes and Vision Group Trials Register (last date of searches: 14 April 2015), the Cochrane Central Register of Controlled Trials (CENTRAL; 2015, Issue 3), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to April 2015), EMBASE (January 1980 to April 2015), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov), and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. Two review authors independently screened the results of the search in order to identify studies that met the inclusion criteria of the review: randomised controlled trials (RCTs) that enrolled participants between the ages of three and eight years old with unilateral amblyopia, defined as best-corrected visual acuity (BCVA) worse than 0.200 logMAR in the amblyopic eye, and BCVA 0.200 logMAR or better in the fellow eye, in the presence of an amblyogenic risk factor such as anisometropia, strabismus, or both. Prior to enrolment, participants were to have undergone a cycloplegic refraction and comprehensive ophthalmic examination including fundal examination. In addition, participants had to have completed a period of optical treatment, if indicated, and BCVA in the amblyopic eye had to remain unchanged on two consecutive assessments despite reportedly good compliance with glasses wearing. Participants were not to have received any treatment other than optical treatment prior to enrolment. We planned to include any type of binocular viewing intervention; these could be delivered on different devices including computer monitors viewed with LCD shutter glasses or hand-held screens including mobile phone screens with lenticular prism overlay. Control groups were to have received standard amblyopia treatment; this could include occlusion or pharmacological blurring of the better-seeing eye. We planned to include full-time (all waking hours) and part-time (between 1 and 12 hours a day) occlusion regimens. We planned to use standard methodological procedures expected by The Cochrane Collaboration. We had planned to meta-analyse the primary outcome, that is mean distance BCVA in the amblyopic eye at 12 months after the cessation of treatment. We could identify no RCTs in this subject area. Further research is required to allow decisions about implementation of binocular treatments for amblyopia in clinical practice. Currently there are no clinical trials offering standardised evidence of the safety and effectiveness of binocular treatments, but results from non-controlled cohort studies are encouraging. Future research should be conducted in the form of RCTs, using acknowledged methods of visual acuity and stereoacuity assessment with known reproducibility. Other important outcome measures include outcomes reported by users, compliance with treatment, and recurrence of amblyopia after cessation of treatment.