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Esther G Gonzalez, Graham E Trope, Saba Samet, Luminita Tarita-Nistor; Asymmetry of optokinetic nystagmus in early glaucoma. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1826.
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© ARVO (1962-2015); The Authors (2016-present)
In humans with normal stereopsis, nasal and temporalward motion elicit symmetrical horizontal optokinetic nystagmus (OKN), but a preponderance of nasalward OKN is found in very young children and in people with amblyopia. Because glaucoma patients exhibit deficits in stereoscopic vision, we conducted a prospective, observational studyto examine the symmetry of their OKN.
Twelve patients with a diagnosis of early stage open angle glaucoma (mean age = 65.33 , SD = 12.74) and 12 age-matched controls (mean age = 68.75, SD = 8.40) participated. Patients did not differ from controls in age or functional measures (acuity, stereoscopic thresholds, visual fields), but they had abnormal structural values (retinal nerve fibre layer, cup-to-disc ratio). For the patients, both structure and field functions were the same in the two eyes.Horizontal “stare” OKN (i.e., with passive, relaxed fixation) was tested with sinusoidal luminance gratings (spatial frequency 0.5 cy/deg) moving to the right and to the left at 3, 12 and 24 deg/s. Participants were tested monocularly (left and right eye) and binocularly in 10 s trials with all three viewing conditions randomized. OKN gain was obtained by dividing the velocity of the mean smooth pursuit component of the OKN by the stimulus velocity, and its naso-temporal asymmetry index (NT) by dividing the difference of the nasal (Ng) and temporal (Tg) gains by their sum: NT = (Ng-Tg)/(Ng+Tg).
The binocular OKN gains of both groups were not different from each other (p = 0.77) and their magnitude decreased as a function of stimulus velocity (p < 0.001). Controls showed no difference between the eyes (p = 0.15) but glaucoma patients did (p = 0.01), showing a positive NT asymmetry for the left eye (mean NT = 0.08; SD = 0.13) and a negative NT asymmetry for the right eye (mean NT = -0.06; SD = 0.11), which is equivalent to a right-to-left (RL) preponderance that has not been reported before. The mean RL preponderance of the patients correlated significantly with their stereo thresholds [r(10) = 0.52, p = 0.04].
This study shows that, in early glaucoma, there is a right-to-left asymmetry in the gain of OKN. This asymmetry may be related to a delay of the input from one eye relative to the other which may alter the binocular interactions in visual cortex.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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