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The Varying Optical Coherence Tomography Appearance of the Inner Choroid with Age: Possible Explanation and Histologic Correlate.

PURPOSE
To investigate the reflectivity of the structural optical coherence tomography images of the inner choroid as it relates to potential structural composition.


METHODS
The reflectivity of slab images 29 - 49 µm and 45 - 65 µm below the RPE, obtained with the Zeiss Plex Elite 9000, were evaluated. The mean and standard deviation of a group of subjects with no ocular disorders were determined. Binarization of the images was done a threshold level established at the mean plus one standard deviation for each slab depth. The proportion of area binarized was evaluated with generalized estimating equations. Representative histologic images obtained from autopsy donors were stained with Masson's trichrome, a staining method helpful in evaluating collagen and ground substance of tissue.


RESULTS
There were 67 eyes of 38 subjects with a mean age of 44.5 (range 22 - 82) years. Using generalized estimating equations, age was found to be a significant predictor for the proportion of binarized pixels in both the 29 - 49 µm (P=.034) and the 45 - 65 µm (P<.001) slabs. The histologic specimens illustrated the loss of ground substance with increasing compaction of collagen fibers in the choroidal stroma with advancing age.


CONCLUSIONS
The reflectivity from the inner choroid is not uniform and changes with age. As suggested by the histologic specimens, we propose the OCT reflectance from the inner choroid is related, in part, to the packing density of collagen fibers present there.