Effects of Anatomical Variation on Ganglion Cell and Nerve Fibre Layer Evaluation by Optical Coherence Tomography

<b>Background/Objectives</b>: The automated analyses of optical coherence tomography (OCT) scans of the retina occasionally suggest the presence of tissue deficits when no visual field defects can be detected. This study was made to find the sources of such alerts. <b>Methods:</b> Data from a population-based cohort of 360 participants aged 30-80 years was analysed for the anatomical sources of alerts after the extensive exclusion of participants where any suspicion of abnormality could be raised. An analysis was made of 12 × 9 mm volume scans centred between the disc and the fovea. The exclusions comprised 107 eyes with definite or borderline abnormal visual fields or other potentially confounding characteristics. A statistical analysis of the thickness patterns was made using the manufacturer's proprietary algorithm. The analysis comprised alerts corresponding to local layer thickness values in the lower 5th percentile of an independent reference population. <b>Results:</b> Of the 613 eligible healthy eyes, thickness deficit alerts were seen in 391. They were related to the angle between the temporal nerve fibre ridges being wider, narrower, or rotated compared to the reference template in 174 eyes and to the variations in the size of the macula in 207 eyes. The source was unidentifiable in 28 eyes. The common sources were a thin papillomacular nerve fibre layer accompanied by arcuate nerve fibre ridges spaced far apart and a thinly, but wider than the normal macular ganglion cell layer. <b>Conclusions:</b> Anatomical variation in the retinal nerve fibre and ganglion cell layers was the source of more than 90% of the thickness deficit alerts in the eyes with normal visual fields.