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Editors Selection IGR 21-2
Diagnostic Methods: OCT: Screening with time- and spectral-domain OCT
Comment by Chris Leung on:
49920 Performance of time-domain and spectral-domain Optical Coherence Tomography for glaucoma screening, Bengtsson B; Andersson S; Heijl A, Acta Ophthalmologica, 2012; 90: 310-315
Optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) analysis has been widely adopted in the clinic for evaluation of glaucoma. Less is known, however, about its role in population screening. Bengtsson, Andersson and Heijl compared the sensitivity, specificity, positive and negative predictive values between a time-domain (TD) OCT (Stratus OCT, Carl Zeiss Meditec) and a spectral-domain (SD) OCT (Cirrus HD-OCT, Carl Zeiss Meditec) in a random population-based sample of 307 subjects. With a response rate of 55%, 170 subjects were examined. The authors showed that the TD OCT had higher specificity and positive predictive values than SD HD-OCT and recommended the Stratus OCT average RNFL thickness, with a cutoff at p < 1%, could be the best choice for population screening purposes.
High specificity and positive predictive values are important attributes of a screening test. With 100% specificity and 100% positive predictive value, the TD OCT average RNFL thickness is likely to be informative for glaucoma screening. However, it is not entirely clear if TD OCT is significantly better than SD HD-OCT. Without a statistical comparison, the specificity of the SD HD-OCT average RNFL thickness (cutoff at p < 1%) at 98% might well be considered comparable to that of the TD OCT. Another factor contributing to the disparities in specificity and positive predictive values between the instruments could be related to the use of different image quality standards in the study. For the TD OCT scans, images included for analysis had a signal strength ≥ 7 (range: 1-10) whereas for the SD HD-OCT scans, the signal strength was ≥ 5 (range: 1-10). OCT RNFL thickness values is positively associated with signal strength. With a lower signal strength quality requirement, SD HD-OCT RNFL thickness values might be smaller, leading to a lower specificity (and a higher sensitivity) compared with the Stratus OCT.
The role of the new OCT technology in glaucoma screening undoubtedly deserves more of our attention
The views on the cost effectiveness of glaucoma screening are divergent and OCT studies in the literature are largely clinic-based. The role of the new OCT technology in glaucoma screening undoubtedly deserves more of our attention.
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