What you call peripheral vision tests, doctors call central fields (CFs). As a science it’s known as perimetry. It tests your visual sensitivity 300 up, down, right and left. Truthfully it’s a 300 circular pivot around fixation (spot where you’re looking).
Perimeters do way more than “check your side vision.” These overpriced digital contrivances can detect and locate brain tumors and strokes. They quantify such diseases as retinitis pigmentosa, glaucoma, macular degeneration, optic neuropathy, and the extent of toxicity of drugs like hydroxychloroquine (Plaquenil), methotrexate, and chlorpromazine. This is not mention perimetry’s usefulness in multiple sclerosis, increased cranial pressure, atherosclerosis and those faking it (factitious disorders).
Commentators and coaches frequently ballyhoo accolades of great peripheral vision which baffles me as much as 110%, chippy, physicality, in space, in the flat and athleticism. Maybe they mean the athlete is aware of action out of the line of sight. Still, bet you dollars to donuts they’ll perform no better than young healthy non-athletes on perimeters.
Be that as it may, perimetry has advanced by leaps and bounds. Using computer algorithms, autoperimetry collects, compares, averages, analyzes, slices and dices data to the nth degree. For some conditions, autoperimetry is as good as MRIs (Magnetic Resonance Imaging) and/or CAT-scans (Computerized Axial Tomography). In some cases, autoperimetry is better.
You see, glaucoma, for example, has certain CF defect patterns, and such an internal eye problem is way different than a problem in the optic nerve (the nerve exiting the back of the eye toward the brain).
The optic nerves do something very unique. They cross. In doing so the visual nerves which receive information for the right side of the right eye unite with the right side nerves of the left eye then travel in parallel to the brain making it much easier for you to interpret and for doctors to make predictions.
I’ll draw you a simple diagram so it makes more sense.
The crossing area is called the chiasm. After the optic nerves cross they are no longer called optic nerves. They are called optic tracts.
For example, if there is a lesion totally disrupting the left optic nerve (#1) then the left eye will lose all its vision, but the right eye will be unaffected.
If a lesion totally disrupts the right optic tract (#3), it will totally wipe out the right side of both eyes causing the left field to be lost in each eye.
A lesion at the optic chiasm (#2) causes a bi-temporal CF defect.
Of course very few neurological problems are this easy. Seldom does an optic nerve, tract or the chiasm get so neatly and totally interrupted. Still you get a picture of the usefulness of perimetry.
We can tell other things about these conditions based upon how complete, congruous, or whether the fixation point is affected. Also autoperimeters give us other useful data such as loss variance and mean deviation.
On occasion we’ve had requests from general practitioners for CFs on someone having severe headaches and vomiting. On some of these requests we’ve been able to say something like, “Our visual fields pattern suggests a mass is in the right temporal lobe of the brain.”
Of course no patient wants to hear such unique news, but under the circumstances, it’s better than not hearing it.