Case report: Amblyopia reversal in an adult
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The term amblyopia literally means “dullness of vision.”
It is defined as “a decrease of visual acuity in one eye when caused by abnormal binocular interaction or occurring in one or both eyes as a result of pattern vision deprivation ... for which no cause can be detected during the physical examination of the eye(s) and which in appropriate cases is reversible by therapeutic measures.” The three main causes of amblyopia are strabismus, anisometropia and stimulus deprivation. Amblyopia onset is usually in childhood. Occlusion therapy works on the principle that increasing the stimulus to the amblyopic eye can increase visual acuity. Rarely, the amblyopic eye can gain vision or show improvement due to increased stimulus to the eye due to a drop in vision of the fellow eye.
Source: Dhivya Ashok Kumar, MD, FRCS, FICO, FAICO, Shajitha Parveen, MBBS, DO, DNB, and Amar Agarwal, MS, FRCS, FRCOphth
In this column, we present a case report of a 49-year-old woman with anisometropic amblyopia who demonstrated improvement in distance and near visual acuity in the amblyopic eye after spontaneous diminution of vision in the contralateral eye due to uveitis and retinal detachment.
Case summary
A 49-year-old woman visited the ophthalmology outpatient department in March 2018 with complaints of itching and foreign body sensation in the right eye for 4 days. On examination, best corrected visual acuity in the right eye was 6/18 in parts for distance and N24 for near and in the left eye was 6/6 for distance and N6 for near. She gave a history of reduced vision in the right eye since childhood that was optically corrected only for a short period of about 6 months at 12 years of age, without any occlusion therapy to the sound eye. On refraction, the right eye did not improve (Figure 1). On examination, her eyes were quiet in the anterior and posterior segments with a few papillae noted in the upper palpebral conjunctiva of both eyes. She was treated with topical allergy medications and lubricants. After symptomatic improvement, she was prescribed glasses and asked to follow up annually.
Sequence of events
The patient came back in August 2018 with complaints of diminution of vision, redness and pain in the left eye for 2 weeks. She had not used the spectacles prescribed during the previous visit. BCVA in the right eye was the same as before while the left eye had reduced to 6/60 and N24. She had mild anterior chamber reaction with fine keratic precipitates and grade 3 vitritis in the left eye. She was started on topical steroids and cycloplegics. A thorough systemic uveitis workup was performed, and glycemic status was confirmed. Oral steroids were started after checking her glycemic control, and systemic antiviral was started after her workup. After control of inflammation in follow-up, she was noted to have a posterior subcapsular cataract in the left eye with BCVA of 6/24 and N36 in October 2018.
Management
When the patient visited in December 2018, she had gross diminution of vision in the left eye to perception of hand movements, while BCVA in the right eye had improved for distance by two lines, reaching 6/12, and near vision improved by three lines, reaching N8. On examination, she had mild anterior chamber reaction and posterior synechiae, and the posterior subcapsular cataract was denser than before. On fundus examination, there was grade 3 vitritis in the left eye with rhegmatogenous inferior detachment. Ultrasound B-scan suggested an inferior retinal detachment in the left eye (Figure 2). She was put on an antiviral and systemic steroids preoperatively and then underwent phacoemulsification with IOL implantation and vitreoretinal surgery (band buckle and pars plana vitrectomy with membrane peeling, endolaser and silicone oil implantation) under steroid and antibiotic cover. Oral immunosuppressants were continued on tapering doses postoperatively. During follow-up visits, the eye was quiet (Figure 3) in the postoperative period. Fundus exam showed an attached retina with intravitreal steroid injected (Figure 4). BCVA in the right was sustained at 6/9 and N6 and in the left eye was 6/36 and N12 at 6 months postoperative. On a contact lens trial, BCVA was 6/6 and N6 in right eye. During follow-up, the left eye developed cystoid macular edema, so silicone oil removal was combined with Ozurdex (dexamethasone intravitreal implant 0.7 mg, Allergan) in the left eye. Postoperatively, left eye vision improved to 6/24 and N8 (Figure 1).
Anisometropia and amblyopia
The direct effect of image blur caused by defocusing, due to higher refractive error in one eye and the interocular competition between the two eyes, is proposed to be responsible for anisometropic amblyopia. It is estimated that anisometropia in association with unilateral amblyopia is seen in 46% to 79% of cases. Anisohyperopia of more than 1.5 D, anisomyopia of more than 3 D and anisoastigmatism of more than 2 D can lead to amblyopia. The main treatment strategy for anisometropic amblyopia is to enhance neural stimulus from the amblyopic eye to the visual cortex. This is achieved by occlusion, pharmacological penalization or optical defocusing of the dominant eye.
Ocular plasticity and age
The time period during which amblyopia can be therapeutically reversed is under debate. The ocular plasticity to visual cortical modification is considered to be less likely beyond a critical period that is believed to grossly fall between eye opening and puberty. Nevertheless, detailed studies of different visual functions suggest that the critical period cannot be fixed. It depends on the anatomical level of the system affected, the period during which the stimulus deprivation is effective, and the severity of deprivation. It is also proved by the Amblyopia Treatment Studies that, although the treatment response is considered to be lesser after 7 years of age, dramatic response can still be demonstrated in patients older than 7 years.
In recent years, there is increased interest in proving the existence of a significant amount of ocular plasticity in adults. Perceptual learning has been proved to improve visual performance in adults in terms of visual acuity, contrast sensitivity, vernier acuity and contour detections. Based on these observations, recovery of visual performance in adult amblyopic eyes following loss of vision in the dominant eye has also been documented in the literature.
Vereecken and Brabant did a retrospective study on 203 patients (59 from the literature, 144 from a questionnaire sent to ophthalmologists) with one eye amblyopic and the sound eye lost to trauma or disease. They reported that the amblyopia reversal attained after loss of vision in the dominant eye was independent of the age at which the dominant eye lost vision and the cause and degree of visual loss in the dominant eye. However, the presence of foveal fixation was considered to be a favorable prognostic factor. Thus, anisometropic amblyopia, which is generally associated with foveal fixation, would be expected to show a better prognosis. Rabin reported a case of anisometropic amblyopia wherein the patient regained useful vision in the amblyopic eye following loss of central vision in the dominant eye due to subfoveal choroidal neovascular membrane and hemorrhage. He suggested that latent neuronal inputs from the amblyopic eye exist and are activated once the influences from the sound eye are removed.
Our patient had unilateral anisometropic amblyopia that had not been adequately corrected nor was she given any amblyopia therapy in childhood. She showed spontaneous improvement of visual acuity in the amblyopic eye following loss of vision in the contralateral sound eye. Patients in previous case reports (except some patients in Vereecken and Brabant’s study) and our patient demonstrated spontaneous improvement in visual acuity in the amblyopic eye. Moreover, in these cases, amblyopia therapy was not instituted at all in childhood, or the patients defaulted and lost follow-up to the therapy.
Conclusion
The potential for improvement in the amblyopic eyes of these patients was apparently unexplored until the patients lost their sound eye to disease or accident. Thus, these observations support the earlier remarks that ocular plasticity is not limited to childhood and that adult patients with childhood amblyopia have the potential to regain and maintain vision in the amblyopic eye. However, the duration of therapy and the type of stimulation needed to achieve the improvement need to be further explored. Prompt medical and surgical management resulted in improvement of visual acuity in the eye with uveitis. Surprisingly, the visual improvement attained in the amblyopic eye was also found to have been sustained. To the best of our knowledge, this is the first case report in an Indian scenario to demonstrate reversal of amblyopia in an adult following loss of vision in the contralateral eye due to uveitis-related complications.
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- For more information:
- Amar Agarwal, MS, FRCS, FRCOphth, director of Dr. Agarwal’s Eye Hospital and Eye Research Centre, is the author of several books published by SLACK Books, sister company of Healio publisher Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at aehl19c@gmail.com; website: www.dragarwal.com.
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