The impact of intraorbital, intracranial, and sinus lesions on visual function and eye movement can be difficult to quantify. Imaging yields information on lesion location and possible etiology. The role of the neuro-ophthalmologist is to provide quantifiable measurements of the damage caused by disease processes in the orbit, skull base, and sinuses. This quantification allows for more concise decision making regarding lesion progression, surgical timing, and potential lesion recurrence. Functional changes may precede obvious structural progression on imaging studies. The neuro-ophthalmologist also aids in managing temporary or permanent patient issues such as diplopia and vision loss. Diagnostic tools for monitoring vision and ocular motility are reviewed, followed by use of these techniques in case presentations.
Techniques for Assessing Visual Function
The hallmarks of optic nerve dysfunction include afferent pupillary defect, color vision deficits or dyschromatopsia, and visual field loss. Afferent pupillary defect is evaluated using the standard swinging flashlight test. It is usually graded on a subjective 0 to + 4 scale or by a logMAR scale (0.3 to 1.8) as measured with photo gray filters.
Color vision is assessed using Ishihara or AOH-R-R (Hardy, Rand, and Rittler) color plates or the D-15 disks. The most common test is done with the Ishihara booklet; testing is performed on each eye separately. A quick in-office test for dyschromatopsia is subjective red desaturation using any bright red object. The patient is shown the object with one eye at a time. He or she is asked whether the color red is the same or different in each eye and which eye looks the most “true red.” Optic nerve dysfunction may produce a darker red, more orange, or more pink appearance. Color vision testing is not dependent on visual acuity except in cases of severe vision loss or macular degeneration.
Visual Field Testing and Automated Perimetry
Automated perimetry provides the best technology for monitoring visual field changes. Humphrey (Zeiss, Oberkochen, Germany) and Octopus (Haag-Streit USA, Mason, OH) visual field machines both give quantitative measures of peripheral vision valuable for monitoring change over time. A 24-2 visual field, measuring 24 degrees from fixation, is the standard for ophthalmic disease. I prefer to use a 30-2 test. Testing 30 degrees from fixation can allow for earlier detection of compressive optic neuropathy. This test checks for 30 degrees on all sides from fixation, providing an additional 6 degrees of periphery ( Fig. 8.1 ).
When evaluating the visual field the physiologic blind spot is located on the temporal side of the field from the patient perspective. The right eye blind spot is on the right of the field. The left eye blind spot is on the left ( Fig. 8.2 ).