Neurophthalmological conditions mimicking glaucomatous optic neuropathy: analysis of the most common causes of misdiagnosis

Background: To analyze the most common neurophthalmological conditions that may mimic glaucomatous optic neuropathy and to determine which most often lead to misdiagnosis when evaluated by a glaucoma specialist. Methods: We reviewed the charts of consecutive patients with optic neuropathies caused by neurophthalmological conditions screened in a single Eye Clinic within a period of 24 months. Within these enrolled patients, we selected the eyes whose fundoscopic appearance could resemble glaucoma based in pre-defined criteria (vertical cup-to-disc ratio >= 0.6, asymmetry of the cup-to-disc ratio >= 0.2 between eyes, presence of localized retinal nerve fiber layer and/or neuroretinal rim defects, and disc haemorrhages). Then, color fundus photographs and Humphrey Visual Field tests (HVF) of these eyes were mixed with tests from 21 consecutive glaucomatous patients (42 eyes with normal tension glaucoma). These images were mixed randomly and a masked glaucoma specialist was asked to distinguish if each set of exams was from a patient with glaucoma or with a neurophthalmologic condition. Results: Among the 101 eyes (68 patients) enrolled with neurophthalmological diseases, 16 (15.8%) were classified as conditions that could mimic glaucoma. The most common diagnoses were ischemic optic neuropathy (25%), compressive optic neuropathy (18.7%) and hereditary optic neuropathy (18.7%). Based on the analysis of fundus photographs and HVF tests, 25% of these were misdiagnosed as glaucoma (two ischemic optic neuropathies and two congenital optic disc anomalies). Conversely, 11.9% of the glaucomatous neuropathies were misdiagnosed as neurophthalmological disorders. Overall, the glaucoma specialist correctly diagnosed 84.5% of the eyes. Conclusions: Some neurophthalmological disorders can mimic glaucoma. In our study, isquemic and compressive optic neuropathies were the ones that most often did so. Almost one quarter of the eyes were misdiagnosed when evaluated by a glaucoma specialist, which can lead to inadequate management and influence the prognosis of these patients.