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Background
Degenerative retinal diseases, such as age-related macular degeneration (AMD) and adult vitelliform, among others, in advanced stages can result in dense central scotoma creating eccentric viewing (EV) with unstable fixation. Unfortunately, to date, apart from recent therapies for neovascular AMD, there are no known treatments for such pathologies.
One EV rehabilitation technique consists of asking patients to move their gaze to different directions and determine the position where they can better perceive a visual target. 1 Using microperimetry biofeedback training (MBFT), vision specialists are able to define a more functional retinal locus to perform oculomotor training sessions, correlating the patient's good retinal sensitivity and fixation characteristics. In such EV training, patients are guided by audio and visual feedback signals to move their gaze to a locus retinal target set inside the microperimetry machine. 2 MBFT has been demonstrated by several authors to be effective in patients with loss of central vision secondary to macular pathologies, particularly in cases with large and absolute central scotoma such as geographic atrophy secondary to AMD. The patient's best or dominant eye has usually been selected for such rehabilitation. 3-5
This case illustrates that MBFT rehabilitation can be performed with important visual acuity improvement, by selecting a correspondent and symmetrical preferred retinal locus (PRL) target (PRT) to rehabilitate patients with similar anatomic-functional characteristics in both eyes; even in cases where fixation demonstrates to be stable in the baseline examination, according to the classification of fixation stability reported in the literature. 6
Case presentation
A 74-year-old woman diagnosed with adult pseudovitelliform dystrophy was recruited from the Low Vision clinic of the Nottingham University Queen's Medical Centre to perform eccentric vision and fixation rehabilitation with MBFT. Best corrected visual acuity was 1.0 LogMAR on both eyes, and reading speed was 117 words per minute.
Investigations
The microperimetry scanning laser ophthalmoscope (SLO) image showed a hyper-reflective area on the central macula of approximately one-fourth optic disc diameter in both eyes, confirming bilateral central dystrophy. A customised sensitivity grid map was designed around the dystrophy area demonstrating 20.7 and 20.1 dB in OD and OS, respectively. The fixation stability was P1=80% and P2=96% in OD and P1=92% and P2=98% in OS. The classification of fixation was stable in both eyes (P1 and P2>75%);...