Common Neuro-Ophthalmic Ancillary Tests to Assist in the Diagnosis and Localization of Afferent Disorders

Chart of the common neuro-ophthalmic ancillary tests to assist in the diagnosis and localization of afferent disorders.

Common neuro-ophthalmic ancillary tests to assist in the diagnosis and localization of afferent disorders Daniel R. Gold, D.O., Departments of Neurology, Ophthalmology, Neurosurgery, Otolaryngology - Head & Neck Surgery, Emergency Medicine, The Johns Hopkins School of Medicine Test Fundus photos OCT RNFL/GCL1 FA FAF Perimetry (static or dynamic)3 Orbital ultrasound Visual-evoked potentials4 Electroretinogram4 Optic nerve disorder (no swelling) + ++ ++ Optic nerve swelling (not AION) ++ ++ + ++ Optic nerve swelling (AION) Optic nerve head drusen BRAO or CRAO Unexplained central vision loss Unexplained peripheral vision loss Chiasmal disorder Retrochiasmal disorder + + + ++ Chronic retinal /macular disorder suspected + ++ ++ ++ ++ ++ ++ + ++ ++ + ++ + + + + ++ ++ + + + + ++ + + ++ +2 ++ + ++ + - ++ - - ++ - - - + - - - - - ++ (mf/p) ++ (ff) ++ (p) - - OCT = optical coherence tomography; RNFL = retinal nerve fiber layer; GCL = ganglion cell layer; FA = fluorescein angiography; FAF = fundus autofluorescence imaging; mf = multifocal electroretinogram; p = pattern electroretinogram; ff = full field electroretinogram; AION = anterior ischemic optic neuropathy (vasculitic or non-vasculitic) - Not usually helpful + May be helpful ++ Very helpful OCT of the retinal nerve fiber layer (RNFL) is most beneficial when interpreted in conjunction with OCT of the macula and ganglion cell layer (GCL). When clear optic nerve swelling is present, OCT of the RNFL is less helpful and OCT of the GCL is most helpful since these measurements reflect the integrity/structure of the neurons without the confounding presence of optic nerve edema. OCT angiography is relatively new technology that is expensive, not widely available, and its benefits and pitfalls/artifacts are not as well understood as more established testing such as FA. 1 OCT may be helpful in some cases of chronic retrochiasmal lesions following retrograde trans-synaptic degeneration. In these cases, a homonymous pattern of hemi-macular thinning may be demonstrated on the GCL analysis. 2 Perimetric testing mainly consists of static (e.g., Humphrey, Octopus) or dynamic (e.g., Goldmann) testing. Static perimetry is more widely available, and tends to be less technician dependent and more reproducible. Typically, 10-2 field testing is for disorders affecting central vision (maculopathies) while 24-2 and 30-2 are excellent for optic nerve disorders (including glaucoma). Patients who are uncooperative, inattentive, cognitively impaired, or who perform poorly with static perimetry are usually better served by dynamic (Goldmann) testing. Dynamic testing can also evaluate the entire field 3 © Copyright 2020 Dan Gold of vision (e.g., 30-2 will only evaluate the central 30 degrees of vision because the vast majority of the neurons making up the optic nerve subserve this area), which can be helpful when complaints are mainly of peripheral vision loss (e.g., retinitis pigmentosa). When the clinician is unsure as to whether vision loss is due to retinopathy/maculopathy or optic neuropathy, ordering an electroretinogram (ERG) along with visual-evoked potentials (VEP) is often beneficial. If the VEP is abnormal while ERG is normal, the localization is usually optic nerve. If the ERG is abnormal while the VEP is normal, the localization is usually retina/macula. More specifically, when central vision loss is present (but unclear if nerve or retina), multifocal and pattern ERG are the preferred tests while when peripheral vision loss is present (but unclear if nerve or retina), full field ERG is the preferred test. 4 © Copyright 2020 Dan Gold