Comparison of the influence of cataract and pupil size on retinal nerve fibre layer thickness measurements with time-domain and spectral-domain optical coherence tomography

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Abstract
To investigate and compare the effect of cataract and pupil size on retinal nerve fibre layer (RNFL) thickness measurements using spectral-domain optical coherence tomography (Cirrus OCT) and time-domain OCT (Stratus OCT). Prospective, hospital-based study. Twenty-five eyes from 25 normal subjects undergoing cataract surgery. Three retinal nerve fibre layer (RNFL) thickness measurements were taken before and after dilation, preoperatively and postoperatively, using Cirrus 200×200 Optic Disc Scan and Stratus Fast RNFL Scan. Linear regression, intraclass correlation coefficient (ICC) and coefficient of variation analysis. Cataract removal caused significant increase in RNFL measurements in both modalities (Cirrus P0.05). ICC showed excellent reproducibility with Cirrus OCT after mydriasis, preoperatively (ICC=0.78-0.90) and postoperatively (ICC=0.90-0.97), but poor reproducibility before mydriasis (P<0.75). Stratus OCT achieved excellent reproducibility after cataract removal both before (ICC=0.86-0.96) and after mydriasis (ICC=0.92-0.95), but poor reproducibility before cataract surgery (P<0.75). Cataracts, not pupil size, cause significant underestimation of RNFL measurements in both Cirrus and Stratus OCT. The extent of influence exerted does not appear different between the two instruments. Reproducibility of each machine appears to be affected differently. Mydriasis is required to achieve excellent reproducibility with Cirrus OCT, and media clarity is required with Stratus OCT.

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