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A. Roorda, S. Sundquist, Y. Zhang, A. Solovyev, C. Nakanishi, J. Gandhi, J. L. Duncan; Cone Identification and Tracking Measured Using High-Resolution in vivo Imaging. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1850.
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Adaptive optics facilitates the unprecedented ability to identify and track single cells, such as photoreceptors, over time in a living human eye. Our purpose is to establish methods to track cones of healthy retinas in adaptive optics scanning laser ophthalmoscope (AOSLO) images with the intent to apply these methods to eyes with retinal degenerations.
AOSLO was used to image the macular region in one eye of 6 healthy subjects. All subjects were imaged on more than 1 occasion, separated by no more than one year, an interval during which little to no change was likely to occur. High signal-to-noise images of the macula were generated. In regions where unambiguous cones were seen on more than one occasion, individual cones were identified and compared between sessions. We counted cones that were observed in both sessions (common - C), and those that were seen in one session but not in the other (noncommon - NC). Repeatability was quantified as (C-NC)/(C+NC) spanning a possible range from -1 to 1. To quantify changes in cone reflectance we measured the correlation in individual cone intensities between sessions.
Repeatability of 18 locations in 6 healthy eyes was >0.99. Cone reflectivity, however, changed significantly between sessions, with essentially no correlation in reflectivity between sessions. (avg R-squared value = 0.052)
Virtually all cones in healthy eyes can be tracked between imaging sessions. The only errors were due to extreme changes in the reflectivity of some cones rendering them invisible in one of the sessions. Cone reflectivity changes have been observed by others using a flood-illuminated AO system1. In patients with cone abnormalities, for whom repeatability will be more useful and important, greater variability in cone appearance suggests that repeatability in eyes with retinal degenerations will be lower.Pallikaris A, Williams DR, Hofer H. IOVS. 2003;44:4580-4592.
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