Dr. Namita Dave, D16475, Dr. Rohit Shetty, Dr. Padmamalini ahendradas
Purpose: The Current standard for grading activity in intermediate and posterior uveitis (Nussenblatt system) is dependent on subjective assessment of vitreous haze which is prone to inter observer variations, overlooks subtle changes in activity and susceptible to confounding variables like cataract, posterior capsular opacity (PCO) etc. This study assessed objective grading of vitreous inflammation using Swept source optical coherence tomography (SS-OCT), as an alternative to the conventional subjective grading.
Methods: 40 eyes of 25 patients with intermediate uveitis, posterior uveitis and panuveitis were imaged on SS-OCT. For each eye, the average pixel intensity was measured for the vitreous as well as the retinal pigment epithelium (RPE). Their ratio (VIT/RPE) was taken as a surrogate imaging biomarker for vitreous inflammation. 14 eyes of 14 age matched healthy volunteers with normal ocular examination were taken as controls. One way ANOVA test was performed to analyse statistical difference between the two groups. Pearson correlation coefficient was calculated to look for concordance between clinical grading of vitreous haze, vitreous cells and our OCT derived biomarker.
Results: The mean VIT/RPE ratio for eyes with uveitis was 0.245 (SEM 0.038) and for the normal eyes it was 0.182 (SEM 0.011) (p=0.0008). The three groups in the uveitic eyes i.e intermediate, posterior and panuveits showed no significant differences amongst each other. Pearson correlation coefficient of the VIT/RPE ratio with clinical grading of vitreous haze was 0.61 (p=0.0004) showing moderate correlation. Follow up of some eyes after initiation of therapy showed decrease in the VIT/RPE ratio with corresponding clinical improvement.
Conclusions: SS-OCT gives high resolution images of large area of vitreous which can be used for objective assessment of vitreous inflammation. The VIT/RPE ratio obtained from image analysis is a continuously distributed variable for documentation of activity. VIT/RPE is independent of the effect media opacity due to cataract or PCO which is a drawback of the current grading system. More studies, with a larger cohort are required to validate our results. VIT/RPE ratio may form the basis of a new, objective grading of vitreous inflammation.
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