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The gold-standard treatment for childhood amblyopia remains patching or penalizing the fellow eye, resulting in an average of about a one line (0.1 logMAR) improvement in visual acuity following ≈ 120 hours of patching (Stewart et al., 2004, 2007) in children 3 to 8 years old. However, compliance with patching and other treatment options is often poor. In contrast, fast-paced action video games can be highly engaging, and have been shown to yield broad-based improvements in vision and attention in adult amblyopia. Here, we pilot tested a custom-made action video game to treat children with amblyopia. Twenty-one (n=21) children (mean age 9.95 ± 3.14 [se]) with unilateral amblyopia (n=12 anisometropic and n=9 strabismic) completed 20 hours of game play either monocularly, with the fellow eye patched (n=11), or dichoptically, with reduced contrast to the fellow eye (n=10). Participants were assessed for visual acuity (VA), stereo acuity and reading speed at baseline, and following 10 and 20 hours of play. Additional exploratory analyses examined improvements after 6–10 weeks of completion of training (follow-up). Following 20 hours of training, VA improved on average by 0.14 logMAR (≈ 38%) for the dichoptic group and by 0.06 logMAR (≈ 15%) for the monocular group. Similarly, stereoacuity improved by 0.07 log arcsec (≈ 17%) following dichoptic training, and by 0.06 log arcsec (≈ 15%) following monocular training. Across both treatment groups, 7 of the 12 individuals with anisometropic amblyopia showed improvement in stereoacuity, while only 1 of the 9 strabismic individuals improved. Most improvements were largely retained at follow-up. Our feasibility study suggests that the action videogame approach may be used as an effective adjunct treatment for amblyopia in children, achieving results similar to those of the gold-standard treatment in shorter duration.

Accommodation and convergence systems are cross-coupled so that stimulation of one system produces responses by both systems. Ideally, the cross-coupled responses of accommodation and convergence match their respective stimuli. When expressed in diopters and meter angles, respectively, stimuli for accommodation and convergence are equal in the mid-sagittal plane when viewed with symmetrical convergence, where historically, the gains of the cross coupling (AC/A and CA/C ratios) have been quantified. However, targets at non-zero azimuth angles, when viewed with asymmetric convergence, present unequal stimuli for accommodation and convergence. Are the cross-links between the two systems calibrated to compensate for stimulus mismatches that increase with gaze-azimuth? We measured the response AC/A and stimulus CA/C ratios at zero azimuth, 17.5 and 30deg of rightward gaze eccentricities with a Badal Optometer and Wheatstone-mirror haploscope. AC/A ratios were measured under open-loop convergence conditions along the iso-accommodation circle (locus of points that stimulate approximately equal amounts of accommodation to the two eyes at all azimuth angles). CA/C ratios were measured under open-loop accommodation conditions along the iso-vergence circle (locus of points that stimulate constant convergence at all azimuth angles). Our results show that the gain of accommodative-convergence (AC/A ratio) decreased and the bias of convergence–accommodation increased at the 30deg gaze eccentricity. These changes are in directions that compensate for stimulus mismatches caused by spatial-viewing geometry during asymmetric convergence.

Stereopsis is the rich impression of three-dimensionality, based on binocular disparity—the differences between the two retinal images of the same world. However, a substantial proportion of the population is stereo-deficient, and relies mostly on monocular cues to judge the relative depth or distance of objects in the environment. Here we trained adults who were stereo blind or stereo-deficient owing to strabismus and/or amblyopia in a natural visuomotor task—a ‘bug squashing’ game—in a virtual reality environment. The subjects' task was to squash a virtual dichoptic bug on a slanted surface, by hitting it with a physical cylinder they held in their hand. The perceived surface slant was determined by monocular texture and stereoscopic cues, with these cues being either consistent or in conflict, allowing us to track the relative weighting of monocular versus stereoscopic cues as training in the task progressed. Following training most participants showed greater reliance on stereoscopic cues, reduced suppression and improved stereoacuity. Importantly, the training-induced changes in relative stereo weights were significant predictors of the improvements in stereoacuity. We conclude that some adults deprived of normal binocular vision and insensitive to the disparity information can, with appropriate experience, recover access to more reliable stereoscopic information. This article is part of the themed issue ‘Vision in our three-dimensional world’.

© 2015 Elsevier Ltd. Previous studies have employed different experimental approaches to enhance visual function in adults with amblyopia including perceptual learning, videogame play, and dichoptic training. Here, we evaluated the efficacy of a novel dichoptic action videogame combining all three approaches. This experimental intervention was compared to a conventional, yet unstudied method of supervised occlusion while watching movies.Adults with unilateral amblyopia were assigned to either play the dichoptic action game (n=23; 'game' group), or to watch movies monocularly while the fellow eye was patched (n=15; 'movies' group) for a total of 40. hours.Following training, visual acuity (VA) improved on average by ≈0.14. logMAR (≈28%) in the game group, with improvements noted in both anisometropic and strabismic patients. This improvement is similar to that obtained following perceptual learning, video game play or dichoptic training. Surprisingly, patients with anisometropic amblyopia in the movies group showed similar improvement, revealing a greater impact of supervised occlusion in adults than typically thought. Stereoacuity, reading speed, and contrast sensitivity improved more for game group participants compared with movies group participants. Most improvements were largely retained following a 2-month no-contact period.This novel video game, which combines action gaming, perceptual learning and dichoptic presentation, results in VA improvements equivalent to those previously documented with each of these techniques alone. Our game intervention led to greater improvement than control training in a variety of visual functions, thus suggesting that this approach has promise for the treatment of adult amblyopia.

Amblyopia is a deficit in vision that arises from abnormal visual experience early in life. It was long thought to develop into a permanent deficit, unless properly treated before the end of the sensitive period for visual recovery. However, a number of studies now suggest that adults with long-standing amblyopia may at least partially recover visual acuity and stereopsis following perceptual training. Eliminating or reducing interocular suppression has been hypothesized to be at the root of these changes. Here we show that playing a novel dichoptic video game indeed results in reduced suppression, improved visual acuity and, in some cases, improved stereopsis. Our relatively large cohort of adults with amblyopia, allowed us, for the first time, to assess the link between visual function recovery and reduction in suppression. Surprisingly, no significant correlation was found between decreased suppression and improved visual function. This finding challenges the prevailing view and suggests that while dichoptic training improves visual acuity and stereopsis in adult amblyopia, reduced suppression is unlikely to be at the root of visual recovery. These results are discussed in the context of their implication on recovery of amblyopia in adults.

Purpose. Ethnic variations in accommodative amplitude (AA) are not uncommon. Accommodation can become reduced in response to short-term wear of first near spectacles. Whether ethnicity has an influence on the magnitude of this adaptation is not well understood. We investigated the impact of first near spectacles on changes in AA and on convergence cross-link interactions in incipient presbyopes of Chinese and Caucasian ethnicities. Methods. Forty-one subjects (22 Caucasians and 19 Chinese) aged 36 to 44 years completed the study. Accommodative stimulus response function, AA, and AC/A and CA/C ratios were measured before and after single vision reading spectacles were used for near tasks over a 2-month period and then again 2 months after discontinuing near spectacle wear. Results. After wearing reading spectacles for 2 months, the accommodative stimulus response slopes and AC/A and CA/C ratios remained invariant irrespective of ethnicity. The accommodative, but not vergence, bias decreased (p 0.05). The nearpoint of accommodation shifted distally producing an average decrease in AA of 0.52 D from baseline (p 0.05). Recovery to near baseline values occurred after discontinuing the reading glasses for 2 months. Differences based on ethnicity were not significant. The baseline AA vs. age plots showed steeper slopes for Chinese than the Caucasian subjects in the sample. Conclusions. The pattern of adaptation by accommodation and cross-link interactions to short-term first reading spectacles is not influenced by ethnicity. (Optom Vis Sci 2012;89:435–445)

Training studies using action video games have shown enhanced post-training vision in both normally-sighted as well as amblyopic individuals. The purpose of this work has been the development of a game modification or “mod” using Unreal Tournament 2004 in order to combine conventional anti- suppression therapy principles for amblyopia with the benefits rendered by action video games for visual recovery and binocularity in amblyopia. The game system involves a stereo display with a degraded image shown to the "good" eye and game event items shown only to the amblyopic eye. Reward and punishment in the game is partially based on attendance with the amblyopic eye. Current results from a trial with 4 subjects show that all subjects recovered visual acuity and reported a dramatic reduction in switching between eyes with training, and were able to use their eyes simultaneously. A large sample clinical study is currently underway to further assess game efficacy.

Purpose: To investigate objective measures of the effects of accommodative training of a pseudophakic eye implanted with a Crystalens AT-52SE (eyeonics Inc) intraocular lens (IOL) on reading performance, accommodation, and depth of focus. Methods: Objective dynamic measures of accommodation, pupil size, and depth of focus were quantified from wavefront measures before and after 1 week of accommodative training that began 29 months after implantation of an accommodating IOL in one patient. Depth of focus was estimated from 50% cut-off of peak performance levels for defocus curves that were computed from the image quality metric VSOTF based on ocular wavefront aberrations. Results: The patient reported improved near vision reading performance after completing the training procedure. After training, there was a shift in conjugate focus in the hyperopic direction, yet the depth of focus increased significantly for near objects. Simulated retinal images and the calculated modulation transfer function of the eye both demonstrated improved quality for near vision after training. Conclusions: The subjective report of improved near vision after training was correlated with improvement of objective measures. Depth of focus increased for near objects with attempts to accommodate after training. This change was linked to increases in aberrations and pupil size and occurred despite the conjugate focus shifting in the hyperopic direction. These results demonstrate that accommodative training may be useful in improving near vision in patients with accommodating IOLs.

PURPOSE—Accommodation and convergence can adapt to blur and disparity stimuli and to agerelated changes in accommodative amplitude. Does this ability decline with age? The authors investigated short-term adaptation to first near-spectacle reading correction on the accommodativestimulus response (ASR) function, accommodative amplitude (AA), AC/A, and CA/C ratios in a prepresbyopic and an incipient presbyopic population and determined whether changes in these functions recovered after discontinuation of the use of near spectacles. METHODS—Thirty subjects with normal vision participated; their ages ranged from 21 to 30 years (n = 15) and 38 to 44 years (n = 15). Oculomotor functions were measured before and after singlevision reading spectacles were worn for near tasks over a 2-month period and then 2 months after the use of near spectacles was discontinued. RESULTS—The slope of the ASR function and the AC/A and CA/C ratios did not change significantly after near spectacles were worn. There was a hyperopic shift of the ASR function that significantly reduced the near point of accommodation (NPA) and lowered the far-point refraction. These changes were age invariant and did not recover after 2 months of discontinuation of near spectacle wear. CONCLUSIONS—These results imply that the NPA may be enhanced normally by tonic bias of accommodation that elevates the entire ASR function and produces myopic refraction bias. When this bias relaxes after reading spectacles are worn, there is a hyperopic shift of the refractive state and a reduction of the NPA, specified from optical infinity. Difficulty in focusing near material within arm’s reach usually first occurs in the fourth decade of life. This condition, known as presbyopia, results from a longstanding but gradual loss of accommodative amplitude with increasing age.1 The most prominent age-related lenticular changes that limit accommodative amplitude include progressive hardening of the lens,2 , 3 increase in lens friction (viscosity)4 , 5 and stiffness (1/compliance),5 – 7 and geometric changes such as increases in thickness and convexity.8 , 9 Increased lens stiffness also influences crosslink interactions between accommodation and convergence. Accommodation responds directly to perceived distance10 and retinal image defocus and indirectly to binocular disparity through the convergence-accommodation crosslink whose gain is described by the CA/C ratio (accommodation [diopters (D)] associated per unit change in convergence [meter angle (MA)]). The vergence system responds directly to perceived distance11 and to binocular

Recalibration of neural signals allows a biological control system to restore and maintain optimal motor performance in the event of any age-, pathology-, or environment-related changes in the biomechanical plant. Ocular accommodation of humans and nonhuman primates is a good example of a biological control system whose biomechanical plant (comprising the crystalline lens, ciliary muscle, choroid, and zonules) becomes increasingly noncompliant with age, ultimately leading to a complete loss of focusing ability (absolute presbyopia).1 The loss of focusing ability can be primarily attributed to a decrease in lenticular compliance (compliance = 1/elasticity),2–4 increase in lenticular viscoelasticity,4 mechanical restriction in ciliary muscle movement,5,6 and morphologic changes in the accommodative plant.7–9 During the incipient stages of presbyopia, the increasingly noncompliant accommodative plant increases the neuromuscular demands required to generate the desired amount of accommodation.10 Several indirect observations suggest that the neural control of accommodation may undergo adaptive recalibration to suit the biomechanical changes in the accommodative plant. For instance, neural recalibration to age-related loss of plant compliance is suggested by an increase in the myodiopter (the neuromuscular effort required to generate a diopter of accommodation11) during incipient presbyopia.10,12 An increase in the myodiopter is indicated by an age-related increase in the response AC/A ratio (the amount of vergence generated by a diopter of accommodation) and an age-related decline in the response CA/C ratio (the amount of accommodation generated by a meter angle of vergence), within the linear range of the accommodative stimulus–response function.10,13,14 Neural recalibration to an age-related increase in lenticular viscoelasticity is suggested by the lack of a dramatic reduction in the peak velocity of small accommodative step responses (1–3 D).15–17 On a more general level, neural recalibration of disaccommodation (near-to-far accommodation) is suggested by the serendipitous observation of Bharadwaj and Schor18 that repeated pilot experiments over 1 year reduced the speed and acceleration of small disaccommodative step responses of the first author, minimizing the instabilities that are usually associated with such responses. Neural recalibration may have occurred to optimize stability by slowing down the responses.18 Finally, adaptable dynamics are also suggested by the success of orthoptic training exercises (e.g., accommodative flippers and pencil push-ups) that decrease the time constant, speed up abnormally sluggish accommodative responses, and increase the rate at which accommodation responds to repetitive positive and negative focusing errors (accommodative flipper rates).19,20 Apart from these indirect observations, to our knowledge, there has been no direct demonstration of the adaptation capability of accommodative step response dynamics. The main purpose of this study was to provide direct evidence for such an adaptive capacity by employing a double-step adaptation paradigm that optically stimulates increases (increasing-step paradigm) or decreases (decreasing-step paradigm) in neuromuscular efforts. Our results illustrate that the dynamics of accommodative step responses can be modified on a short-term basis, at least in some subjects ranging in age from 18 to 34 years, with increases in neuromuscular effort adapting more readily than decreases in neuromuscular effort.

The binocular interactions that occur during dichoptic and binocular viewing were investigated using a letter acuity task in normally sighted children (age range 6–14 years) and adults, and in adults with anisometropic amblyopia. Our aims were to investigate the nature of binocular interactions that occur in each group, and the extent to which the characteristics of binocular interactions differ across the groups. The non-tested eye was occluded during monocular (baseline) viewing, and was allowed to view a uniform stimulus with fusion lock in dichoptic viewing. In adults and children with normal vision, acuity under dichoptic viewing was unchanged relative to monocular baseline in the dominant eyes, while acuity of the non-dominant eye improved under dichoptic viewing relative to baseline. The magnitude of dichoptic change in the non-dominant eyes was similar in the two normally sighted groups, but the dichoptic advantage was found to decrease with increasing age within the children tested. Binocular acuity was better than monocular acuity in normal subjects, and a decrease in binocular summation with age was noted within the age range of the children tested. In contrast, the amblyopic observers showed no change in acuity with viewing conditions. The results demonstrate development of interocular interactions during childhood, and wide inter-individual variation in pattern of interocular interactions among anisometropic amblyopic adults.