Ophthalmology, Medical College of Wisconsin, Wauwatosa, Wisconsin
Commercial Relationships: A.M. Dubis, None; J.T. McAllister, None; J. Rha, None; J. Kuchenbecker, None; J. Carroll, None.
Support: The Gene & Ruth Posner Foundation, RD & Linda Peters Foundation, Fight for Sight, Research to Prevent Blindness
Purpose:The fovea centralis is a characteristic feature of nearly all primate retinae. Here we sought to compare foveal topography (pit depth, slope, & diameter) with other measures such as cone packing density and axial length.
Methods:Fourteen myopes and 11 emmetropes were imaged using a Zeiss Stratus OCT. In addition, we retrospectively examined foveal OCT scans of 3 BCM carriers (for whom images of the cone mosaics had been previously acquired using an adaptive optics ophthalmoscope). An IOL master was used to obtain axial length measurements in all subjects. All image processing was done using custom MatLab software, and foveal reconstructions were fit to a 2D difference-of-gaussian function in order to extract quantitative parameters describing individual fovea.
Results:We found little intra-subject variation in the shape of the fovea. Even with the most variable parameter (pit depth), there was high correlation between any given subjects' 2 eyes, indicating near-perfect symmetry (p < 0.0001, paired T-test). All other metrics (pit diameter, axial length, radius of curvature, and slope) showed similar correlation. We tested one prediction of a current model of foveal development: retinal stretch during development should result in more shallow foveal pits. Interestingly, we found that in myopes, but not emmetropes, individuals with longer axial lengths had more shallow foveal pits (p = 0.045). Previously, using adaptive optics imaging it was shown that BCM carriers have fewer numbers of cones. For the BCM carriers, we found that they had more shallow foveal pits (in addition to dramatically reduced cone density).
Conclusions:We have developed a new analytical technique to increase the utility of time domain OCT in both clinical and research settings. This can be used on existing OCT data sets, and in the future could easily be integrated to provide a real time analysis (currently done off-line). We observed significant variation in foveal topography across subjects. It is known that the peak cone density in individuals with normal vision can vary by a factor of 3, so future work will combine adaptive optics imaging and this new OCT technique to examine the relationship between the cone mosaic and the fovea. Preliminary data from the BCM carriers (with dramatic reduction in cone density) suggests that the relationship in normals may not be profound. Our data supports the hypothesis that foveal pit development is correlated to retinal stretch, however the relationship only held in myopes. The absence of this correlation in emmetropes suggests that other mechanisms must modulate pit depth.
Keywords: retinal development image processing imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)
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