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Heather Heitkotter, Alexander E Salmon, Rachel E Linderman, Jason Porter, Joseph Carroll; The Effect of Trial Lenses on AOSLO Image Scale. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1429.
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© ARVO (1962-2015); The Authors (2016-present)
Trial lenses are often used to correct high magnitude, lower order aberrations during adaptive optics scanning light ophthalmoscope (AOSLO) imaging. Such lenses affect the scale of the retinal image, which can in turn affect metrics of the cone mosaic. We investigated the impact of trial lens power on AOSLO image scale and compared this to theoretical estimates.
AOSLO images of the cone mosaic were obtained from 12 subjects with no known ocular abnormalities. Images were obtained with trials lenses (-5.0 – +5.0 D; 1.0 D steps) and manually aligned to a reference image collected without a trial lens at the same retinal location. The cone nearest neighbor distance (NND) was measured in each image, and the magnification for a given trial lens was estimated from the relative NND change. We also used an affine transformation to determine the scale difference between the reference image and the trial lens images for each subject. The predicted magnification (Mp) for each trial lens was computed by incorporating measures of ocular biometry for each subject in an algorithm for a 4-surface schematic eye modified from previous studies.1,2
There was a linear relationship between image magnification and trial lens power, though the slope varied across subjects. Image magnification estimates acquired from the two empirical methods were in high agreement, with a mean bias of 0.2% and the scatter of differences being homoscedastic as a function of the mean. We thus averaged these estimates for comparison to the Mp for each image. For positive lenses, the Mp underestimated the measured value, while for negative lenses, the Mp overestimated the measured value – however the effect was variable across subjects, with a mean difference of 1.9%. The maximum difference was 7.8%, which would result in errors in cone density of about 15%.
Caution should be used when analyzing images acquired with trial lenses. While the origin of the inter-subject variability in agreement between Mp and the empirical estimates of magnification remains unclear, collecting multiple reference images using positive and negative trial lenses may enable estimation of the scaling relationship for a given eye.1PMID: 20688730; 2PMID:21546533
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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