Comparison of SD-OCT with slit lamp grading of anterior chamber cell in a rabbit model of anterior uveitis

Abstract

Purpose : Slit lamp examination is currently the gold standard for grading anterior chamber cells in patients with anterior uveitis. However, this method requires specialized training and suffers from inter-observer variability. We evaluated a method to count anterior chamber cell using spectral domain optical coherence tomography (SD-OCT) compared wtih traditional slit lamp based methods.

Methods : Anterior uveitis was induced by injection of M. tuberculosis (Tb) H37RA antigen into the anterior chamber of adult dutch-belted rabbits. One week following induction, SD-OCT of the anterior chamber was performed followed by slit lamp examination. 1mmx1mm cube scans were performed and cell counts were obtained manually. Grading of anterior chamber cell was performed according to the Standardization of Uveitis Nomenclature (SUN) scale by two trained, non-clinicians. Following each imaging session, an anterior chamber tap was performed and the actual cell concentration in the aqueous was determined using a hemocytometer. SD-OCT and SUN grading were compared with aqueous sampling as the reference standard. The Spearman correlation coefficient (Rho) was determined for each pairwise comparison.

Results : SD-OCT grading of anterior chamber cells correlated well with aqueous sampling (Rho=0.53, p<0.001). The rabbit Tb model produced an exuberant anterior chamber reaction with iris nodules, fibrin, corneal neovascularization, and corneal edema. Correlation between SD-OCT and aqueous sampling improved when the corneal thickness was below 470 microns (Rho=0.65, p<0.001), with an efficiency of 82±10%. SUN grading on the other hand, correlated poorly with aqueous sampling (Rho=0.02, p=0.88) and did not improve with decreasing corneal thickness. Corneal thickness ranged from 300 microns to 600 microns, with 84% of eyes below 470 microns.

Conclusions : SD-OCT grading of anterior chamber cell correlated better with aqueous sampling, compared to SUN grading. SD-OCT grading improved as corneal thickness decreased. Automated counting schemes may improve the speed and/or accuracy of SD-OCT anterior chamber cell counts and is currently being investigated.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.