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Anand C Joshi; Correlation of fixation instability and accommodative microfluctuations in normal and strabismic monkeys. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4577. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Accommodative microfluctuations (MF) are small oscillations in the accommodative level observed during fixation and can potentially degrade retinal image quality. Fixational eye movements are small amplitude involuntary eye movements produced during attempted fixation. Prior studies in our lab and by others have shown that strabismic subjects exhibit larger fixation instability compared to normal. The goal of this study was to compare the relationship between MF and fixation instability and whether increased MF during near target viewing is correlated with increases in vergence fixation instability in strabismus.
1 exotropic strabismic monkey and 1 normal monkey performed a fixation task at different depths (1D – 5D) under monocular viewing conditions with the target aligned on the viewing eye. A custom-built binocular eccentric photorefraction system was used to acquire accommodation data from the viewing and non-viewing eye. Eye position data were acquired using a scleral search coil system.
Accommodative gain as well as AC/A ratio for the strabismic monkey (S1 - AC/A: 3.34Δ/D) was low compared to the normal (N1- AC/A:4.67Δ/D). Correlation between accommodative microfluctuation (MF), quantified as standard deviation (SD) of the accommodative response, and the mean accommodative response was poor for the normal monkey (Pearson correlation; r value = 0.13); however there was a significant positive correlation for the strabismic monkey (r value = 0.87, p<0.05). Vergence fixation instability, quantified as mean SD of the vergence eye position (left eye position – right eye position), exhibited no correlation with MF for the normal monkey (r value = 0.01); however, for the strabismic monkey a significant positive correlation was observed (r value = 0.62, p =0.02).
A significant positive correlation is observed between fixation instability and accommodative microfluctuation in strabismic monkey compared to the normal monkey. We hypothesize that excess microfluctuations observed in strabismic monkey can produce increased vergence instability through the AC/A cross-link. Therefore fixation stability and MF may have either a causal/reciprocal dependency relationship or alternatively are influenced by a common source in the developmental disorder of strabismus.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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