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John P Kelly, James O Phillips, Avery H Weiss; Visual Acuity Development with Infantile Nystagmus: Prediction of Visual Acuity Limits. Invest. Ophthalmol. Vis. Sci. 2017;58(8):860.
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© ARVO (1962-2015); The Authors (2016-present)
Visual acuity (VA) is typically reduced in observers with infantile nystagmus (IN) without an afferent disorder. However, eye movements (e.g., eXpanded Nystagmus Acuity Function or NAFX) are poor at predicting VA in IN subjects (r2 < 0.20 across studies). Also, IN subjects don’t show an improvement in VA when motion blur is eliminated by flashing visual targets. A concern is that image motion during early visual development reduces VA in IN (e.g., motion amblyopia). In contrast, the immaturity of the infant visual system should be more tolerant to retinal image motion due to IN. This study provides predictions of eye velocity that should limit visual acuity across infant development and compares the prediction with eye movement recordings.
Nine children (1-4 years age) with idiopathic IN had visual acuity measurements (Teller Acuity Cards or letter optotypes) and eye movement recordings (confocal OCT/SLO imaging in one child). Prediction models of image motion that limits visual acuity development was derived from development of fovea anatomy and from adult data (adjusted for age). Eye movements were collected by VOG.
All subjects showed brief periods (at least 17 - 200 ms) of eye velocity below the predicted value that would limit visual acuity for age. The percentage of time eye velocity was below the predicted limit varied from 14% to 51% across subjects. In subjects with pendular nystagmus, the turn-around points of the waveform were the only locations that did not limit visual acuity. Confocal SLO in a subject with pendular nystagmus showed the fovea was not matched to the target at these turn-around points. Age was not correlated with the percentage of time eye velocity was below the lower limit for age, nor the standard deviation or maximum duration of these low eye velocity periods. Longitudinal visual acuity development was not differentially affected by nystagmus waveform.
The model predicted all subjects had periods during which the visual system could sample high spatial frequency information. Therefore, retinal image motion due to nystagmus was not predicted to limit visual acuity development but indicates the visual system must compensate for improper foveation. Our model can help determine criteria of eye velocity to detect periods of assumed foveation across age.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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