Optical Coherence Tomography and Neuro-Ophthalmology
The initial OCT machines used time-domain technology and had lower resolution, but still allowed for measurement of the peripapillary retinal nerve fiber layer (RNFL) (1). This led to improved detection of optic neuropathies, including glaucoma and nonglaucomatous optic neuropathies. The technology of OCT has been continuously improving, resulting in faster scans, better resolution, and improved analysis of the data, which were discussed in several reviews (2–4). These advances have led to the ability to segment and measure the thickness of the macular ganglion cell-inner plexiform layers, which has many applications in neuro-ophthalmology that were detailed by both Kardon and Lam (5,6). A recent study reported the use of multicolor imaging to view various layers of the retina and optic nerve (7).
OCT is very useful in the setting of papilledema, which was reviewed in an article by Kardon (8), “Optical coherence tomography in papilledema: what am I missing?” OCT can be used to measure the RNFL thickness and quantify the amount of optic disc edema. In addition, analysis of the macula and the ganglion cell layer allows for the ability to detect and monitor optic neuropathy in the presence of disc edema. A recent article reported thinning of the macula in the setting of resolving papilledema, especially in patients with atrophic papilledema (9). Two separate studies showed that retinal ganglion cell layer loss precedes RNFL thinning in optic neuritis (10) and nonarteritic anterior ischemic optic neuropathy (11).
The orientation of Bruch membrane and the retinal pigment epithelium (RPE) has been shown to be helpful in differentiating papilledema for other optic neuropathies. With raised intracranial pressure, there is an upward deflection of peripapillary RPE and Bruch membrane on OCT, which normalizes when papilledema resolves (12,13). Sibony et al (14) found that the peripapillary RPE also has an upward deflection toward the vitreous in patients with optic nerve sheath meningioma. By contrast, a backward deflection of the lamina cribrosa from low intracranial pressure may be detected in normal tension glaucoma (15).
OCT is critical in providing insight into the structural causes for glaucoma and differentiating glaucoma from nonglaucomatous optic neuropathy (16,17). In addition to changes in the lamina cribrosa orientation, enhanced depth-OCT has demonstrated that the lamina cribrosa tends to be thinner with more focal defects in normal tension glaucoma compared with high-pressure glaucoma (18,19).
OCT is helpful in diagnosing and monitoring optic disc drusen. A study using spectral-domain OCT showed that OCT was helpful in differentiating optic disc drusen from papilledema (20). Enhanced depth imaging and swept source OCT allow for deeper imaging and were shown to improve detection and imaging of optic nerve head drusen (21). A recent study showed that peripapillary RNFL thinning correlated with the anatomic location of optic disc drusen and visual field defects, especially in patients with superficial optic disc drusen (22).
OCT can be used to localize lesions along the visual pathway.