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Editors Selection IGR 24-3

Clinical Examination Methods: Early diagnosis by OCT

Comment by Chris Leung on:

53479 Comparison of different spectral domain OCT scanning protocols for diagnosing preperimetric glaucoma, Lisboa R; Paranhos A; Weinreb RN et al., Investigative Ophthalmology and Visual Science, 2013; 54: 3417-3425

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While optical coherence tomography affords reproducible measurements of the retinal nerve fiber layer (RNFL), optic disc and macula, studies directly comparing their performance in detecting glaucomatous damage in eyes with a diagnosis of glaucoma suspect are sparse. Lisboa and colleagues eloquently addressed this issue in a study examining 142 eyes of 91 glaucoma suspects (defined as neuroretinal retinal rim narrowing, cupping or suspicious RNFL defects but without visual field defects in standard white-on-white automated perimetry) who had been followed for an average of 13 years. Using serial optic disc stereophotographs as the reference standard, 48 eyes developed progressive glaucomatous changes (focal or diffuse narrowing of neuroretinal rim, increased excavation, or enlargement of RNFL defects during the follow-up period) (disease group) and 94 eyes had no change (control group). No eyes had visual field defects at the time of OCT imaging. RNFL, optic disc and macular measurements were obtained and the areas under the receiver operating characteristic (ROC) curve for detection of pre-perimetric glaucoma were compared. The authors found that the average circumpapillary RNFL thickness had the greatest area under the ROC curves, suggesting that OCT RNFL measurement was more useful than the optic disc and macular parameters to identify glaucomatous damage in eyes with suspicious optic disc features. The availability of long-term serial optic disc stereophotographs in the study provided a powerful reference to define glaucoma. However, it is not certain how many of the 48 eyes showing progressive glaucomatous change had progressive rim narrowing and increased excavation, and how many had 'enlargement' of RNFL defects. The definition of 'suspicious' RNFL defects may also require further elaboration. If most of the 48 eyes already have RNFL defects at the baseline and then develop 'enlargement' of RNFL defects without concomitant increased rim narrowing and cupping, the comparison of areas under the ROC curves may thereby favor RNFL over optic disc measurements. Given the fact that optic disc size would impact the diagnostic performance of OCT, the lack of adjustment of optic disc area in the analysis of area under the ROC curve may weaken the discriminating power of the optic disc parameters. Nevertheless, this study is a valuable addition to the literature as most studies evaluating the diagnostic performance of OCT have been based on established glaucoma patients using perimetry as the reference standard. The authors clearly show us that OCT measurements are informative to glaucoma diagnosis in glaucoma suspects.

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