Various non-glaucomatous optic nerve (NGON) disorders may produce optic disc cupping and visual field disturbances that resemble the clinical profile of glaucomatous optic neuropathy (GON), and it is important that clinicians recognize them. These disorders include hereditary optic neuropathy, antecedent optic nerve infarction, trauma, syphilis, demyelinating optic neuritis, fusiform enlargement of the intracranial carotid artery and intraorbital and intracranial mass lesions. Pallor of the neuroretinal rim has been reported to be highly specific in predicting non-glaucomatous cupping, and focal or diffuse obliteration of the neuroretinal rim is highly specific for predicting glaucomatous cupping. Yet, clinically differentiating non-glaucomatous optic nerve disorders from glaucoma remains a subjective and often difficult challenge. Thus, ancillary tests, in particular neuroimaging, have been proposed in the diagnostic evaluation of glaucoma with normal intraocular pressure.In this retrospective review, Donaldson and colleagues retrospectively examined 82 patients with atypical features of GON referred by a diverse group of clinicians (ophthalmologists, optometrists and primary care physicians) for neuro-ophthalmic consultation to exclude NGON. All patients underwent perimetry and OCT imaging; bloodwork, genetic testing and neuroimaging were selectively performed. GON was defined as increased optic disc cupping, lack of pallor of the remaining neuroretinal rim, and relative preservation of central visual acuity. Most patients (71) underwent neuroimaging of whom approximately 70% were diagnosed with GON. Among the 14 patients with NGON a diagnosis could not be identified in approximately 50%. The others were found to have ischemic optic neuropathy, optic neuritis, or optic neuropathy associated with inherited, toximetabolic, or compressive mechanisms. The three patients with compression included two patients with anomalous vasculature and 1 case with optic nerve sheath meningioma. Neural rim pallor was identified in 86% patients with NGON, however nerve fiber bundle visual field defects were common in both GON and NGON eyes and not found to be a helpful differentiating feature.
Nerve fiber bundle visual field defects were common in both GON and NGON eyes and not found to be a helpful differentiating feature
Unfortunately, due to the relatively small number of patients found to have an identifiable cause for NGON the ability to draw significant conclusions from this study is limited. However, there are a few important lessons to be learned from this interesting study. First, careful inspection of the optic nerve is critical with attention to neural rim integrity, color, and presence of optic disc hemorrhage. Among the five optic disc photographs illustrated in Figure 1, the two left images with GON had focal loss of the inferior rim (one with a flame hemorrhage), and the three right images with NGON had obvious rim pallor in excess of cupping. Thus, the classification could have been easily established in these eyes based solely on the disc appearance. Second, most patients referred for neuro-ophalmic consultation are eventually found to have GON. Third, eyes with NGON often do not yield a definitive diagnosis despite blood work, genetic testing and cranial neuroimaging. Fourth, routine neuroimaging in patients with GON is costly, and rarely identifies a compressive lesion responsible for the associated visual field abnormality. Selective neuroimaging in eyes with atypical features is warranted.
Routine neuroimaging in patients with GON is costly, and rarely identifies a compressive lesion responsible for the associated visual field abnormality