Visual improvement in amblyopic eye following treatment-induced vision loss in dominant eye with uveal melanoma

Leveraging neural plasticity for the treatment of amblyopia

Amblyopia is a form of visual cortical impairment that arises from abnormal visual experience early in life. Most often, amblyopia is a unilateral visual impairment that can develop as a result of strabismus, anisometropia, or a combination of these conditions that result in discordant binocular experience. Characterized by reduced visual acuity and impaired binocular function, amblyopia places a substantial burden on the developing child. Although frontline treatment with glasses and patching can improve visual acuity, residual amblyopia remains for most children. Newer binocular-based therapies can elicit rapid recovery of visual acuity and may also improve stereoacuity in some children. Nevertheless, for both treatment modalities full recovery is elusive, recurrence of amblyopia is common, and improvements are negligible when treatment is administered at older ages. Insights derived from animal models about the factors that govern neural plasticity have been leveraged to develop innovative treatments for amblyopia. These novel therapies exhibit efficacy to promote recovery, and some are effective even at ages when conventional treatments fail to yield benefit. Approaches for enhancing visual system plasticity and promoting recovery from amblyopia include altering the balance between excitatory and inhibitory mechanisms, reversing the accumulation of proteins that inhibit plasticity, and harnessing the principles of metaplasticity. Although these therapies have exhibited promising results in animal models, their safety and ability to remediate amblyopia need to be evaluated in humans.

Visual acuity improvement in the amblyopic eye of a 50-year-old man following strabismus surgery

It is generally believed that the visual acuity of an amblyopic eye cannot improve significantly in adulthood. However, there have been reports of this occurring following visual loss in the fellow eye. Best-corrected visual acuity improvement in amblyopic eyes of children with strabismic amblyopia following strabismus surgery has also been reported. We present the case of an adult whose visual acuity in his amblyopic eye improved 4 Snellen lines over 28 months following strabismus surgery.

Human deprivation amblyopia: treatment insights from animal models

Amblyopia is a common visual impairment that develops during the early years of postnatal life. It emerges as a sequela to eye misalignment, an imbalanced refractive state, or obstruction to form vision. All of these conditions prevent normal vision and derail the typical development of neural connections within the visual system. Among the subtypes of amblyopia, the most debilitating and recalcitrant to treatment is deprivation amblyopia. Nevertheless, human studies focused on advancing the standard of care for amblyopia have largely avoided recruitment of patients with this rare but severe impairment subtype. In this review, we delineate characteristics of deprivation amblyopia and underscore the critical need for new and more effective therapy. Animal models offer a unique opportunity to address this unmet need by enabling the development of unconventional and potent amblyopia therapies that cannot be pioneered in humans. Insights derived from studies using animal models are discussed as potential therapeutic innovations for the remediation of deprivation amblyopia. Retinal inactivation is highlighted as an emerging therapy that exhibits efficacy against the effects of monocular deprivation at ages when conventional therapy is ineffective, and recovery occurs without apparent detriment to the treated eye.

Recovery from Amblyopia in Adulthood: A Meta-Analysis

Purpose

The effectiveness of traditional amblyopia therapies is largely restricted to childhood. However, recovery in adulthood is possible following removal or vision-limiting disease of the fellow eye. Study of this phenomenon is currently limited to isolated case reports and a few case series, with reported incidence ranging from 19-77% 1-5 . We set out to accomplish two distinct goals: (1) define the incidence of clinically meaningful recovery and (2) elucidate the clinical features associated with greater amblyopic eye gains.

Methods

A systematic review of 3 literature databases yielded 23 reports containing 109 cases of patients ≥18 years old with unilateral amblyopia and vision-limiting fellow eye pathology.

Results

Study 1 revealed 25/42 (59.5%) of adult patients gained ≥2 logMAR lines in the amblyopia eye after FE vision loss. The overall degree of improvement is clinically meaningful (median 2.6 logMAR lines). Study 2 showed that for cases with amblyopic eye visual acuity improvement, recovery occurs within 12 months of initial loss of fellow eye vision. Regression analysis revealed that younger age, worse baseline acuity in the amblyopic eye, and worse vision in the fellow eye independently conferred greater gains in amblyopic eye visual acuity. Recovery occurs across amblyopia types and fellow eye pathologies, although disease entities affecting fellow eye retinal ganglion cells demonstrate shorter latencies to recovery.

Conclusions

Amblyopia recovery after fellow eye injury demonstrates that the adult brain harbors the neuroplastic capacity for clinically meaningful recovery, which could potentially be harnessed by novel approaches to treat adults with amblyopia.

Partial Recovery of Amblyopia After Fellow Eye Ischemic Optic Neuropathy

BACKGROUND

Recovery from amblyopia in adulthood after fellow eye (FE) vision loss is a well-known phenomenon. Incidence of recovery varies widely following different FE pathologies, and the rate of recovery after FE ischemic optic neuropathy (ION) has not been examined. We aimed to determine the frequency and degree of improvement in amblyopic eye (AE) visual function after ION in the FE.

METHODS

We performed a retrospective chart review of patients between 2007 and 2021 confirmed to have amblyopia and ischemic optic neuropathy in different eyes. Patients with unstable ocular pathology potentially limiting vision were excluded. We compared the best-corrected visual acuity (VA) in each eye before and after FE ION over time. For patients with available data, we examined change in perimetric performance over time.

RESULTS

Among the 12 patients who met the inclusion criteria (mean age 67 ± 8 years), 9 (75%) improved ≥1 line and 2 (17%) improved ≥3 lines. The median time from ION symptom onset to maximal improvement was 6 months (range: 2-101 months). Reliable perimetric data were available for 6 patients. Mean sensitivity improved in the AE for all patients, with mean improvement of 1.9 ± 1.1 dB. There was no correspondence between foci of ION-related field loss and gains in field sensitivity in the AE.

CONCLUSIONS

A high proportion of patients with amblyopia and contralateral ION experience improvement in AEVA. Modest gains in perimetric sensitivity in the AE may accompany FE ION. These findings support the view that residual plasticity in the adult visual cortex can be tapped to support functional improvement in amblyopia.

Eccentric Fixation and Good Visual Acuity in a Child with Large Traumatic Macular Hole: A Case Report

A girl of 8 years old was referred to our clinic with a history of penetrating injury to her left eye 6 years ago with light perception vision and a large traumatic macular hole in her right eye. Her right eye's vision was 4/10 when she first visited our clinic. Considering the patient's one-eye status, her parents' reluctance to undergo surgery, and the possibility of spontaneous closure of traumatic macular holes, it was determined to observe the patient and evaluate her visual acuity and macular hole condition. In 2 years, the final best corrected visual acuity was 8/10 in the right eye, with infratemporal eccentric fixation in visuoscopy. In addition to evaluating and reporting this case as a traumatic macular hole, we will discuss the role of nonsurgical treatment and the possibility of good visual acuity with eccentric fixation in a child with large traumatic macular hole.

Metaplasticity: a key to visual recovery from amblyopia in adulthood?

PURPOSE OF REVIEW

We examine the development of amblyopia and the effectiveness of conventional and emerging therapies through the lens of the Bienenstock, Cooper, and Munro (BCM) theory of synaptic modification.

RECENT FINDINGS

The BCM theory posits metaplastic adjustment in the threshold for synaptic potentiation, governed by prior neuronal activity. Viewing established clinical principles of amblyopia treatment from the perspective of the BCM theory, occlusion, blur, or release of interocular suppression reduce visual cortical activity in the amblyopic state to lower the modification threshold and enable amblyopic eye strengthening. Although efficacy of these treatment approaches declines with age, significant loss of vision in the fellow eye by damage or disease can trigger visual acuity improvements in the amblyopic eye of adults. Likewise, reversible retinal inactivation stimulates recovery of amblyopic eye visual function in adult mice and cats.

SUMMARY

Conventional and emerging amblyopia treatment responses abide by the framework of BCM theory. Preclinical studies support that the dramatic reduction in cortical activity accompanying temporary retinal silencing can promote recovery from amblyopia even in adulthood, highlighting a promising therapeutic avenue.