Regional variation in the attenuation coefficient of the sclera measured in vivo using optical coherence tomography

Abstract

Purpose : Optical Coherence Tomography (OCT) has been used to image the ciliary muscle through the sclera. The imaging depth in the ciliary muscle is limited due to optical attenuation in the sclera and ciliary body. A better understanding of the factors that contribute to scleral attenuation can help optimize transscleral image quality. The purpose of this study was to determine if there are regional variations in the scleral attenuation coefficient.

Methods : Using an IRB-approved protocol, images of the sclera were acquired on the left eye of 48 healthy subjects (average age 36.5 ± 16.9, range: 16-79) using a Spectral-Domain OCT system (Telesto 1, Thorlabs Inc.) operating at a central wavelength of 1320 nm. Software was developed to enable manual selection of regions of interest (ROI) within the sclera containing 10 neighboring A-lines covering a depth of 0.4 mm above the boundary of the sclera and cilliary muscle when measuring at the inner apex and 0.3 mm when measuring temporally to the apex. The average intensity profile of the ROI is calculated and fit with an exponential function to produce a value of the attenuation coefficient. The attenuation coefficient was quantified in an ROI centered on the ciliary muscle apex and an ROI located on average 0.34 ± 0.25 mm temporally form the apex. In each ROI, the measurement was repeated 5 times. The average values obtained in the two regions were compared.

Results : The attenuation coefficient was 3.06 ± 1.10 mm^-1 (range: 0.93-5.19 mm^-1) at the apex and 3.22 ± 1.52 mm^-1 (range: 0.054-7.34 mm^-1) at the temporal location. The average standard deviation of measurements was 0.31 mm^-1 (range: 0.028-1.072 mm^-1) at the apex and 0.20 mm^-1 (range: 0.045-1.29 mm^-1) temporal to the apex. Per the t-test, the difference in attenuation coefficients regionally was not found to be statistically significant (p-value: 0.50).

Conclusions : No significant regional variation of the scleral attenuation coefficient was found.

This is a 2020 ARVO Annual Meeting abstract.

 

Figure 1: A. In the transscleral image shown on the right, the A-line taken at the inner apex of the ciliary muscle was used to calculate the corresponding intensity profile. B. The A-line taken temporally to the apex was used to calculate the corresponding intensity profile. The attenuation coefficient for this subject was determined to be 3.68mm^-1 at the inner apex and 4.65mm^-1 at the temporal apex.