When it comes to interpreting visual fields, one of the more subtle aspects of visual fields is distinguishing between absolute scotomas and relative scotomas. On the surface, this may seem fairly simple; on a grayscale readout, absolute scotomas tend to be completely black, while relative scotomas are varying shades of lighter gray. However, some relative scotomas can still look fairly dense.
I’ve had a few patients referred to me for subjective complaints of visual field constriction, worse temporally, which progressively worsens over time. The complaint is often expressed as a comparison between the excellent vision they had in their youth compared to where it is now. It is painless and is often described as progressive.
The concern with bitemporal visual field constriction, of course, often results in neuroimaging to look for a pituitary tumor or some other lesion that affects the optic chiasm, even if the automated perimetry appears to be normal. But what happens if the MRI or CT is normal?
What Is Perimetry?
Perimetry, the measuring and documentation of the visual fields, has a long and exhaustive history (Thompson HS, Wall M. History of Perimetry. Imaging and Perimetry Society website). There are many methods of testing perimetry, which have evolved with technology and greater understanding of neuroanatomy and functional vision.