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Relationship of slow-phase velocity to visual acuity in infantile nystagmus associated with albinism
Avery H Weiss1, John P Kelly, James O Phillips
1Roger Johnson Clinical Vision Laboratory, Division of Ophthalmology, Seattle Children's Hospital, and Department of Ophthalmology, University of Washington, Seattle, WA 98105, USA. avery.weiss@seattlechildrens.org
Insights
Visual acuity in children with albinism is not limited by nystagmus speed. Macular hypoplasia, a structural issue, appears to be the primary factor affecting vision in these patients.
Area of Science:
- Ophthalmology
- Neuroscience
- Genetics
Background:
- Albinism is a genetic disorder characterized by reduced pigmentation.
- Infantile nystagmus is common in albinism, causing involuntary eye movements.
- The relationship between nystagmus characteristics and visual acuity in albinism requires further investigation.
Purpose of the Study:
- To determine if slow-phase velocity of nystagmus impacts visual acuity in children with albinism.
- To compare measured eye movement velocities with predictions from the dynamic visual acuity (DVA) model.
Main Methods:
- Eye movements of 12 children with albinism and infantile nystagmus were recorded using video-oculography or scleral search coil.
- Visual acuity was assessed using Teller acuity cards and corrected for age in children under 3.
- Horizontal eye velocities were analyzed using gamma distribution, and peak velocities were compared to DVA model predictions.
Main Results:
- Histograms of slow-phase eye velocity showed a peak distribution between 5-20 degrees/second.
- The peak velocity in all subjects was at or below the DVA model's limiting velocity.
- The DVA model predicted a visual acuity of 20/50 at the average peak velocity, which is better than typical albinism visual acuity.
Conclusions:
- Visual acuity in albinism is primarily limited by macular hypoplasia, not slow-phase eye velocity.
- Nystagmus speed does not appear to be the main determinant of visual acuity in this population.
- Macular development is a critical factor for visual function in albinism.
Purpose:
To investigate the relationship between slow-phase velocity of nystagmus and visual acuity in children with albinism.
Methods:
Twelve children with infantile nystagmus associated with albinism had eye movements recorded by binocular video-oculography (10 patients) or by scleral search coil (2 patients). In children younger than 3 years of age visual acuities was assessed by means of Teller acuity cards and corrected for age. Histograms of horizontal eye velocities were fit by a gamma distribution in all patients (r2>0.85). The velocity at the peak of the gamma distribution was compared with the limiting velocity predicted by the dynamic visual acuity (DVA) model.
Results:
All histograms of slow-phase eye velocity were skewed toward lower velocities, with the peak distribution ranging from 5 to 20 degrees/second. The velocity at the peak of the gamma distribution for each subject was uniformly equal to or below the limiting velocity predicted by the DVA model. The average of the gamma distribution across all subjects corresponded to an upper limit to eye velocity of 17 degrees/second. At this velocity the DVA model predicted visual acuity of 20/50, which is lower than the average visual acuity reported in albinism. The distributions of eye velocity were lower than the limiting eye velocity predicted on the basis of DVA almost 50% of the time.
Conclusions:
Visual acuity in albinism is limited by macular hypoplasia rather than by slow-phase eye velocity of nystagmus.
