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Khushmit Kaur, Hassan Muhammad, Diane Wang, Jacoby Shelton, Donald Hood; Inter-individual Variations in Foveal Pit Anatomy Do Not Completely Explain False Positives Seen in the Central Retina on OCT Inner Retinal Thickness Maps. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5273.
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© ARVO (1962-2015); The Authors (2016-present)
In healthy controls, apparent circum-foveal abnormalities can be seen on retinal ganglion cell plus inner plexiform (RGC+) thickness maps derived from cube scans obtained with optical coherence tomography (OCT). To better understand these false positives (FPs), the variation in foveal pit morphology was studied.
OCT macular cube scans, 6x6 mm, were obtained on one eye of 126 healthy individuals. The center of the fovea was marked manually to identify the B-scan corresponding to the horizontal meridian. A fourth-order negative Gaussian was fitted to the border between the inner limiting membrane and vitreous. Based upon the 1st derivative of this Gaussian, the locations of the foveal center and the perifoveal peaks were taken as the locations of the 2 local maxima and one local minimum. The horizontal distance from peak to peak was taken as the foveal width (W), and the average vertical distances from the location of the fovea to each peak as foveal depth (D). The steepest slope of each foveal edge was obtained and averaged for a measure of slope (S). RGC+ thickness was measured from the OCT cube scan for each eye and probability plots generated (Fig.1) relative to the other 125 eyes. The circum-foveal region (± 4°, red circle, Fig. 1) was considered abnormal if there were regions falling below the 1% confidence limit in both hemi-retinas.
12 (9.5%) of the 126 controls met our criteria for circum-foveal abnormalities; 2 are shown in Fig. 1. On average, the fovea of the 12 eyes was wider, less deep and less steep. However, only the S values were significantly different than the other eyes at p≤0.05: W:(222.5±42.1 vs. 212.7±31.9um, p=0.33); D:(38.0±8.2. vs. 41.4±5.4um, p=0.06); and S:(0.35±0.09 vs. 0.40±0.06; p<0.02). Further, only 3 of the 12 eyes fell outside the 95% confidence limits (CI) on one or more of the 3 metrics (all 3 for S and 2 for W and D). The 12 eyes were on average older, but the difference was not significant (44.8±15.2 vs. 37,8±14.3yrs, p=0.11).
Variations in foveal pit anatomy do not provide a reliable indicator of circum-foveal FPs seen on OCT inner retinal thickness maps. These FPs are partially due to normal variations in RGC+ thickness that are not well correlated with foveal pit anatomy.
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