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Gina Mitzel, Joost Felius, Mitch Cruz, Yi-Zhong Wang; The Longitudinal Relationship Between Visual Acuity and Fixation Instability in Patients with Age -Related Macular Degeneration. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4137. doi: https://doi.org/.
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Previous findings have shown that patients with advanced age-related macular degeneration (AMD) present fixation abnormalities. Deterioration of visual acuity and changes in fixation location presumably both result in fixation instability. This study compared the relationship between visual acuity (VA) and fixation instability in patients with various stages of AMD. We investigated whether the relationship between fixation instability and VA is driven by the preferred eye.
A longitudinal study was conducted among 51 eyes of 28 AMD patients, categorized as early (10), intermediate (13), and advanced (5), who had at least two visits at ~6-month intervals (range 2-7, median 3). VA was measured by using the EVA E-ETDRS. Fixation was recorded with the Nidek MP-1 for 30 sec while the subject fixated on a 2 degree circle monocularly and fixation instability was quantified by calculating the 68%-bivariate contour ellipse area (BCEA, 1 SD).
At baseline, patients showed mean±SD BCEA=1.6±2.4 deg2 and VA=0.23±0.30 logMAR. Mixed-effects modeling of the longitudinal data showed fixation instability was associated with visual acuity (P=0.006) and with disease stage (P=0.05). Overall, the BCEA increased at a mean rate of 0.36 deg2/y; this change was associated with the rate of VA change for the preferred eye (P=0.03) of each patient, but not for the poorer eye (P=0.48).
The findings support the hypothesis that VA loss in AMD is associated with the loss of fixation stability in the preferred eye. Assessment of fixation on the MP-1 is useful for demonstrating the shift of stability of fixation related to the disease progression. While fixation stability may not be affected significantly in early stages of macular degeneration, the deterioration of macular function over time leads to fixation instability in patients with AMD.
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