Purpose:
To compensate for differences in foveal size among individuals and reduce the variance of ganglion cell plus inner plexiform layer (GCL+IPL) thickness maps using the fact that normal maculas have similar shapes.
Methods:
GCL+IPL thickness maps from SD-OCT macular images of the right eyes of 23 normal subjects (11 female, 12 male) aged 18-75 years were rendered in polar coordinates centered on the fovea. Foveal size for each eye was defined as the mean radius of the 50 μm contour line on the foveal edge. Compensation for foveal size was achieved by shifting radial profiles of an individual map so its foveal size matched the mean foveal size of the population.
Results:
Population average maps of GCL+IPL thickness were formed before and after compensation for foveal size. The figure shows a radial profile of the GCL+IPL thickness that extends into the superior-temporal retina. Foveal size varied widely among subjects (mean radius ± 1 s.d. = 0.44 ± 0.08 mm; range = 0.29 - 0.63 mm), which resulted in large variation in the mean foveal edge (blue curves). Radial shifting of all profiles in each individual retina to give the same foveal size as the mean produced little change in the mean thickness map (compare red and blue solid lines) or in the variance in the periphery, but greatly reduced the variance of the rising edge of the fovea (compare red and blue dashed lines).
Conclusions:
Radial shifting of GCL+IPL thickness maps in polar coordinates can compensate for variations of foveal size among subjects without changing the overall shape of the macula. This compensation technique may provide a means to correct for demographic variation in foveal size. The reduced variance at the foveal edge should improve sensitivity to glaucomatous damage.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • ganglion cells • macula/fovea