Background/aims To examine the frequency of abnormal retinal nerve fibre layer thickness (RNFLT) and ganglion cell complex (GCC) measurements among healthy and glaucoma suspect and preperimetric glaucoma (GSPPG) eyes in a prospective longitudinal study.

Methods Normal and GSPPG eyes with ≥18 months follow-up were included. Spectral-domain optical coherence tomography (SDOCT) was performed annually in normal and biannually in GSPPG eyes. One eye was randomly selected for inclusion. RNFLT and GCC parameters with p>5% were classified as ‘within normal limits (WNL)’ and p<1% were classified as ‘outside normal limits (ONL)’.

Results 23 normal and 74 GSPPG eyes were followed for a mean 43.4±9.6 months. During serial follow-up, 100% and 91% of normal eyes had all RNFLT and GCC parameters classified as WNL, respectively. 27 (37%) and 17 (23%) of GSPPG eyes had an ONL classification in at least one RNFLT and GCC parameter, respectively. A high percentage (41%–56%) of RNFLT and GCC measurements classified as ONL were not replicated on subsequent scans. The rates of loss for all parameters were similar (p>0.05) between the groups.

Conclusions Specificity in this sample of healthy eyes was very high for RNFLT and GCC parameters. Confirmation of suspected SDOCT abnormalities is recommended to differentiate reproducible loss from long-term variability.