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Nancy J Coletta, Lenna Walker, Fuensanta A Vera-Diaz; Refractive Error and Fixation Stability. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1091.
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© ARVO (1962-2015); The Authors (2016-present)
Individuals with myopia show greater variability of eye position while reading acuity letters, compared to emmetropic individuals (Coletta et al., ARVO 2016). Uncorrected myopic refractive error increases the amplitude of fixational microsaccades (Ghasia and Shaikh, 2015). The stability of eye position during fixation has not been reported specifically when myopia is corrected, so in this study we examined whether the stability of steady fixation was different in individuals with corrected myopia and corrected hyperopia during a fixation task.
Ten young, healthy subjects (mean age 24.2 ± 2.6 years) were tested monocularly with the dominant eye. The spherical equivalent range was +3.13 to -8.38 D. Axial lengths were measured with a Lenstar biometer (mean 23.75 ± 2.40 mm). Subjects wore soft contact lenses if correction was needed for the 4 m test distance. Fixation stability was assessed while subjects looked at a 30 min arc black cross on a white background, viewed for a duration of 60 sec. Eye movements were recorded using a video-based eye tracker (EyeLink 1000; SR Research) with 0.6 min arc spatial resolution and 2 msec sampling rate. Stability of fixation was expressed as the standard deviation (SD) of vertical eye and horizontal eye position, as well as the bivariate contour ellipse area (BCEA) which represents the area over which fixation is maintained 68% of the time. For t-test comparisons, subjects were divided into two refractive groups: myopia with refractions ranging from -4.50 D to -8.38 D (mean -6.82 D) and hyperopia with refractions ranging from +0.50 to +3.13 D (mean +1.62 D).
The mean BCEA, vertical SD and horizontal SD for myopic subjects showed a trend toward fixation instability (2.395 deg2, 0.878 deg, and 0.680 deg, respectively) compared with hyperopic subjects (1.153 deg2, 0.640 deg and 0.433 deg, respectively). The difference in BCEA for refractive groups was nearly significant (p = 0.06), as was a trend for the mean BCEA to increase with axial length (r=0.608; p=0.06).
Individuals with myopia show greater instability of eye position during a steady fixation task compared to individuals with hyperopia. This is consistent with our previous findings concerning eye position during a visual acuity reading task. We hypothesize that longer axial lengths and stretched retinas in myopic eyes are associated with increased variability of fixational eye movements.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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