Abstract
Purpose :
To assess the normative corneal optical density values of normal eyes for Anterior Segment Optical Coherence Tomography (AS-OCT) images to serve as a control group for future study.
Methods :
We analyzed 52 corneal AS-OCTs (Spectralis, Heidelberg) from 16 eyes of 8 patients with ImageJ (NIH). Inclusion criteria comprised (1) the central 3 images above or below the central corneal vertex image (2) quality index >=25 and <= 34. Exclusion criteria comprised (1) presence of significant image artifact or (2) large peak air density. The central 5.5 mm were analyzed. The maximum epithelial reflectance (MER) and average stromal density (ASD) were recorded for 11 sectors, each sector was 500 um in width.
In each scan, the maximum epithelial reflectance (MER) and average stromal density (ASD) were calculated in each sector. In the aggregate data set, the average maximum epithelial reflectance (AMER) and the overall average stromal density (OASD) were calculated irrespective of horizontal position and with respect to horizontal position (AMER(x), OASD(x)).
Results :
Qualitatively, the MER and ASD for individual scans decreased with respect to lateral position in a linear or quadratic manner.
Quantitative results of the aggregate data set irrespective of position showed there was a high linear correlation coefficient (LCC) between AMER and OASD (r =0.86 ). The relative standard deviation of AMER (RSDAMER) and the relative standard deviation of OASD (RSDOASD) also showed a high LCC ( r = 0.82 ).
Quantitative results of the aggregate data respective of position showed a parabolic relationship between AMER(x) versus position and OASD(x) versus position. A quadratic function was fit to the data set using the standard error of the mean (SEM). For the AMER(x) fit, the reduced chi-squared (RCS) was 8, for the OASD(x), it was 6.42.
Quality versus AMER and OASD irrespective of position were analyzed and a linear relationship between AMER and OASD versus quality was found (RCS of 0.54 and 0.40 respectively). An attempt to analyze the relative SDOASD and relative SDAMER showed a complex relationship with a quality index of 29 being the nadir.
Conclusions :
A relationship between MER and ASD was demonstrated both respective and irrespective to position. The overall backscatter of the stroma is related to the reflectance of the epithelium. In addition, the MER and ASD may vary in a parabolic fashion with respect to position from the center of the cornea.
This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.