I am sometimes referred patients with abnormal ganglion cell maps or retinal nerve fibre layer thickness maps with a query of glaucoma. I often say to patients and optometrists that these analyses are based on normative data in the machine, and should always be combined with a good clinical opinion because they can be misleading.
This study looked at 104 healthy eyes of 104 normal participants and found that some 40% had an abnormal Ganglion Cell Analysis (GCA) map, and 30% had an abnormal retinal nerve fibre layer (RNFL) map! These false positive abnormalities were more likely in longer eyes and with smaller optic disc areas. Interestingly an abnormal GCA map was also more likely in eyes with a more inferiorly located fovea: