Quality factor based correction for SD-OCT measurements in cataract patients

PURPOSE: To correct peripapillary retinal nerve fibre layer (pRNFL) measurements performed with spectral domain optical coherence tomography (SD-OCT) for low image quality factor (QF) in patients with cataract, using measurements before and after cataract surgery.

METHODS: SD-OCT (Topcon 3DOCT-2000) volume scans of the optic disc of 13 cataract patients were used. A set of three reflective filters with optical density ranging from 0.11 to 0.54 were used. The correlation was calculated between the change in thickness measurements and the change in image quality factor. Changes before and after cataract surgery were analysed. A correction for scans with a lower QF was calculated using an equation which was formulated based on the relationship between the change in thickness measurements and the change in image quality factor.

RESULTS: Thirteen right eyes of thirteen cataract patients were included in this study. pRNFL thickness measurements before and after cataract differed significantly (96 versus 99 micron, p < 0.01). Preoperative linear regression lines showed a different slope than postoperative regression lines. Corrected pRNFL thickness measurements of before cataract surgery differed significantly with pRNFL thickness measurements after cataract surgery.

CONCLUSIONS: The presence of cataract influences the QF-pRNFL relationship. The lower the image QF, the higher the pRNFL thickness underestimation. We found a rather curvilinear relationship between QF and pRNFL. Our corrected measurements of the pRNFL thickness in case of lower image QF due to cataract still differed significantly from the pRNFL thickness measurements after cataract surgery.