By Wanda M. Martinez MD, PhD
The authors describe a new OCT-derived biomarker, “VIT/RPE-Relative Intensity,” that has the potential for use as an objective marker of disease activity in patients with uveitis.
For patients with intermediate and posterior uveitis, degree of vitreous haze is one indicator of ocular disease severity. Clinical description of vitreous haze follows the “Nussenblatt scale,” a series of photographs with a number scale depicting varying degrees of clarity of posterior pole structures (optic nerve head, retinal vessels and nerve fiber layer), with a hazier view of the retinal structures correlating with worse vitreous haze. Improvement in vitreous haze is used as an endpoint in uveitis clinical trials. However, evaluation using the above scale is subjective, with fair inter-observer agreement, and the scale is small, which limits description of mild to moderate cases (the most common stages).
In this retrospective study, the authors evaluated OCT as a reproducible quantitative measurement of vitreous inflammation in patients with uveitis. Subjects included 42 patients with uveitis with or without vitreous haze, plus 18 healthy controls. The authors used the National Eye Institute system to classify the presence and severity of vitreous haze.
Analysis of SD-OCT imaging using custom software provided an “absolute” measurement of vitreous signal intensity (VIT), which was then compared with that of the retinal pigment epithelium (RPE), generating an optical density ratio with arbitrary units (“VIT/RPE-Relative Intensity”).
The results showed that the VIT/RPE relative intensity value correlated with clinical vitreous haze scores, was independent of many other variables (including visual acuity and uveitis etiology) and was reproducible among graders. The VIT/RPE-Relative Intensity was significantly higher in uveitic eyes with known vitreous haze than in uveitic eyes without haze or in healthy controls.
Limitations of this technique, however, include the need for standardized protocols in OCT image acquisition, the lack of reliability in OCT segmentation (especially in patients with posterior retinal pathology) and the difficulty of obtaining quality OCT images in patients with other pathology (vitreous hemorrhage, corneal pathology and cataracts). Also the study did not examine patients with severe vitreous haze.
That said, the use of objective and reproducible examination techniques in the evaluation of patients with intermediate and posterior uveitis would be invaluable when recording uveitis severity, addressing effectiveness of therapy, following disease over time and comparing treatment outcomes among patients.