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A. H. Weiss, J. P. Kelly, J. O. Phillips; Oculomotor Model of Acuity Limitations in Albinism. Invest. Ophthalmol. Vis. Sci. 2008;49(13):139.
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To investigate whether visual acuity in children with albinism is limited by visual sensory deficits, nystagmus, or both.
Ages ranged from 0.3 to 10 years. Visual acuity was measured by either Teller acuity cards or optotypes (Snellen, Allen, HOTV) depending upon age and ability. Acuities were corrected for the average of age-normative data. Conjugate eye movements were recorded with videooculography (n = 10) or magnetic search coil technique (n = 3). The range of eye velocities (binned into 5 deg/sec increments) was well-described by a gamma distribution. The criterion of slow-phase velocity was estimated to be 0.84 s.d. below the mean of the gamma distribution (the slowest 20% of the distribution). To model the relationship between acuity and eye velocity we used the adult dynamic acuity data of Demer & Amjadi, 1993 (logMAR = k + 0.64 log(retinal slip velocity)). We then compared the observed eye velocities with respect to the limiting velocity predicted by each subject’s acuity.
LogMAR acuities relative age-norms ranged from 0.04 to 1.14. All subject had 100 ms periods of average eye velocity 5 deg/sec or less. Upper range of binned eye velocities varied from 15 to 80 deg/sec. Data of observed eye velocity was compared to predicted eye velocity that would limit performance to their measured age-corrected LogMAR acuity. All, but 2 subjects, had eye velocities that were matched or lower than the predicted eye velocity that would limit acuity. The correlation between observed and predicted eye velocity was not significant (r2 = 0.12; p = 0.24). Conversely, observed acuity was worse than predicted by dynamic visual acuity reduction in all but 2 subjects. The correlation between observed and predicted eye velocity was not significant the (r2 = 0.20; p = 0.13).
Visual acuity in children with albinism is limited by the visual sensory defect rather than the retinal image slip velocity due to nystagmus.
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