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K. Holopigian, W. H. Seiple, W. H. Swanson, R. E. Carr; What Correlates With Visual Acuity Loss in Retinitis Pigmentosa?. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1352.
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Retinitis pigmentosa (RP) is a degenerative disease that produces progressive losses in peripheral and central vision. The losses in central vision include reductions in visual acuity and constriction of the visual field, which acerbate the quality of life changes in these patients. In the current study, we sought to identify correlates of visual acuity loss by comparing measures of local central visual function with visual acuity over time in patients with RP.
We have follow-up data on central vision changes in 32 patients with RP who were followed for periods of 4 to 13 years (average = 7.6 yrs). On the initial visit, the patients had visual acuity of 20/40 or better and no evidence of any other ocular or systemic abnormalities. On each follow-up visit, we obtained best corrected visual acuity (ETDRS charts), threshold visual fields and standard multifocal electroretinograms (mfERGs). In the current study, we compared the measures of visual function for the central 2 degrees.
Over time, the change in acuity for these patients was quite gradual. The average change over follow-up was a 0.11 increase in logMAR acuity (loss of approximately 1 line of acuity). This acuity change over time was not dependent on age or inheritance mode. At the initial visit, there were differences in the magnitude of the loss in visual fields and mfERG measures for the patients. For visual fields and mfERG implicit times, 74% and 75% of the patients had values within normal limits at that visit; whereas for mfERG amplitude, only 11% had values within normal limits. To study progression, we examined the relationship between acuity, visual fields and mfERGs at each patient’s final visit. An ANOVA on these measures (in percent of normal) indicated that there were significant differences (F (3, 84) = 17.8, p < 0.0001) among the measures. Tukey post hoc tests indicated that the mfERG amplitude was significantly more affected than was acuity, visual field or mfERG implicit time (p < 0.01). There were not significant differences among acuity, field or implicit time measures.
Progressive changes in visual acuity in patients with RP may occur at a very slow rate. For patients with RP and good acuity, loss of mfERG amplitudes within the central 5o occurs prior to acuity loss and mfERG amplitudes are significantly more impaired than our other measures. This loss in amplitude may reflect damage to and/or loss of the cone photoreceptors; whereas visual acuity and our other measures may be more dependent on changes in cone spacing integrity.
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