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Editors Selection IGR 12-4

Structure Measurement: OCT and RNFL changes

Comment by Marco Vizzeri on:

46514 Pressure-cornea-vascular index (PCVI) for predicting disease progression in normal tension glaucoma, Leung DYL; Iliev ME; Chan P et al., British Journal of Ophthalmology, 2011; 95: 1106-1110

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Many clinicians are confident that the advent of Spectral Domain Optical Coherence Tomography (SD-OCT) truly represents a turning point in glaucoma diagnosis and management. With enhanced scan registration features and reduced measurement variability, this technology has the potential to capture subtle glaucomatous structural changes, such as RNFL thinning over time. Leung et al. (1382) evaluated the performance of Cirrus HD-OCT and Stratus OCT in detecting significant RNFL changes (i.e., a change in RNFL thickness significantly different from 0) in patients with OCT scans taken every 4 months for at least 24 months, with a maximum follow-up time of 33 months. They reported that Cirrus detected more eyes with significant RNFL thinning than Stratus OCT, while Stratus OCT detected more eyes with significant RNFL improvement than Cirrus. As a result, the agreement between the two instruments for detecting glaucomatous progression was poor. Did Cirrus truly outperform Stratus OCT in detecting progression? Unfortunately, this study leaves this question and many others largely unanswered. Firstly, it is unclear whether significant RNFL thinning, as detected by Cirrus, truly means clinically relevant glaucomatous change. Could these RNFL changes represent the effect of aging alone? The authors make no attempt to determine whether progression could have been confirmed by optic disc photography. Secondly, the authors only hypothesize but do not verify whether misalignment of the Stratus OCT scans over time or other factors, such as differences in signal strength, could be responsible for the detection of RNFL improvement. A more in-depth analysis would have helped unveil additional important clues. Thirdly, there is no information with regard to IOP levels and disease intervention in the study population. Surgical or medical treatment to lower IOP could have significantly influenced RNFL patterns over time. Clinicians remain optimistic that future studies will provide stronger arguments in support of SD-OCT use for glaucoma management and follow-up.

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