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J. B. Jacobs, E. Bala, N. S. Peachey; Mutlifocal Electroretinographic Study of Patients With Oculocutaneous Albinism and Infantile Nystagmus Syndrome. Invest. Ophthalmol. Vis. Sci. 2008;49(13):142.
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© ARVO (1962-2015); The Authors (2016-present)
Patients with infantile nystagmus syndrome (INS) often have reduced visual acuity because of their reduced ability to sufficiently foveate the target. However, some patients also have an afferent visual deficit that may be the limiting factor for acuity, so even if their eyes were perfectly stable they would still have reduced vision. This possibility must be taken into account when determining a treatment plan. We used multifocal electroretinogram recordings (mfERG) to quantify the limitations of retinal function in INS patients with oculocutaneous albinism and estimate the effect on vision.
We recorded mfERGs from 5 patients - 3 with albinism and 2 without - using a standard stimulus consisting of a scaled array of 103 hexagons covering the central 45°. Recordings were made under continuous fundus monitoring, allowing us to re-record trial segments with insufficient fixation. Results were compared to age-matched hypoplastic retinas recorded in our laboratory. We used the eXpanded Nystagmus Acuity Function (NAFX) to analyze the foveation characteristics of nystagmus waveforms to determine the best potential visual acuity that could be expected in the absence of an afferent deficit.
Useable data were obtained from 8 of 10 eyes. Two eyes, from separate patients, could not be recorded due to large-amplitude nystagmus with insufficient foveation durations. In the usable albinotic eyes, concentric ring averages showed reduced response amplitude only in the central areas, and normal amplitudes peripherally. Implicit times were normal at all locations. The non-albinotic patients exhibited a near-normal central amplitude peak.
Our results indicate that, with care, it is feasible to obtain meaningful mfERG recordings from patients with nystagmus. The reduced central function in albinotic retinas is consistent with anatomical studies indicating decreased cone density, suggesting an afferent upper limit for visual acuity, independent of ocular motor stability. We determined that for one patient this underdevelopment, rather than the nystagmus, was the limiting factor, and she was less likely to receive enough increase in visual acuity to warrant surgery. It is important, however, to remember that the effects of nystagmus surgery can lead to improvement in acuity over a broad range of gaze angles; therefore performance at central position is only one consideration.
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