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Editors Selection IGR 7-1
Visual function: Longitudinal OCT
Comment by John Flanagan on:
12031 Optical coherence tomography longitudinal evaluation of retinal nerve fiber layer thickness in glaucoma, Wollstein G; Schuman JS; Price LL et al., Archives of Ophthalmology, 2005; 123: 464-470
The purpose of this study by Wollstein et al. (176) was to evaluate the use of OCT RNFL thickness measurements in a longitudinal study compared to both clinical assessment and standard automated perimetry. Interestingly, it was a retrospective study of data collected prospectively every six months over a seven year period for another study. All patients included in the review had at least five 'reliable' visual fields and five 'good-quality' OCT scans. Visual fields were a mixture of full threshold and SITA standard, program 24-2. OCT images were acquired using a prototype instrument that collated 100 data points around the optic nerve. Three circular scans were acquired at each visit, with a diameter of 3.4 mm. The sample consisted of 37 patients (64 eyes), five of whom were defined as glaucoma suspects and the majority of whom were of Caucasian origin (28/32). In spite of the small sample size and its retrospective design the study is important as it marks the first attempt to evaluate the clinical performance of the OCT with respect to disease progression. OCT progression was defined as RNFL thinning of > 20 m compared to baseline, in two of three consecutive scans. Several definitions of VF progression were evaluated with a decline in MD > 2dB compared to baseline showing the most similar performance to expert evaluation. The study found a higher progression rate by OCT than by perimetry. Over the median follow-up period of 4.7 years, 22% progressed by OCT alone, 9% by VFs alone, and 3% by both techniques. The study has obvious shortcomings and a few unanswered questions, such as why there were so few valid OCT scans (median of five) and VFs (median of six) over the follow-up period and how did the serial analysis allow for image alignment, but still provides interesting preliminary data and the justification for confidence that future prospective studies will demonstrate equally positive results.
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