Diagnosis of glaucoma requires a thorough history and comprehensive eye exam. Along with elevated IOP, many symptoms play a role in the proper diagnosis. When IOP falls within the normal range, the diagnosis can sometimes be less clear. Here are five cases when neurologic imaging can help you distinguish a nonglaucomatous optic neuropathy from glaucoma.
1. Pallor Greater Than Cupping
Presence of pallor over cupping — especially with correlating pupillary abnormalities or color deficits — warrants further evaluation with neuroimaging. Greenfield et al., for example, found that pallor greater than cupping was 90 percent specific for a nonglaucomatous optic neuropathy caused by a compressive lesion.1
In glaucomatous optic neuropathy, pallor does not typically present until advanced disease — although the neuroretinal rim can be lost. Loss of color vision and pupillary defects can also occur with glaucoma; however, they are usually present in more advanced or asymmetric glaucoma cases.
2. Visual Field Defects that Respect the Vertical Midline
Glaucomatous optic neuropathies are typically associated with visual field defects that respect the horizontal midline. Conversely, defects respecting the vertical midline often accompany nonglaucomatous optic neuropathies. The Greenfield study found these defects to be 81 percent specific for such optic neuropathies. Therefore, visual field defects respecting the vertical midline — or any visual field defects that do not correlate with the optic nerve appearance or level of cupping — should prompt imaging for a nonglaucomatous optic neuropathy.
3. Younger Age (<50 Years)
Nonglaucomatous optic neuropathies are more common in younger patients. In fact, the Greenfield study found that age less than 50 was 83 percent specific for a nonglaucomatous optic neuropathy. Therefore, a suspicious optic nerve, particularly with pallor, in a patient younger than 50 years old should raise concern for nonglaucomatous optic neuropathy. Follow up such cases with prompt neuroimaging.
4. Poor Visual Acuity
Visual acuity less than 20/40 can suggest a nonglaucomatous optic neuropathy. The Greenfield study found it to be 77 percent specific for a nonglaucomatous optic neuropathy.
5. Patients Progressing at Normal Pressures
When previously well-controlled glaucoma patients begin progressing at normal or acceptable IOPs, it is important to consider neuroimaging to rule out a concurrent process. Although glaucoma patients can progress at normal pressures, be sure to rule out a compressive lesion or other cause of optic neuropathy.
1 Greenfield DS et al. Ophthalmology. 1998;105(10):1866-1874.
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About the author: Nisha Chadha, MD, is an assistant professor of ophthalmology at the Icahn School of Medicine at Mount Sinai and the New York Eye and Ear Infirmary. She also serves as the associate director of medical student education at Mount Sinai and is a member of the Academy’s EyeCare America committee. Dr. Chadha completed her residency at The George Washington University and her glaucoma fellowship at Yale University.