Timothy C. Hain, MD Page last modified: January 25, 2011
Retinitis Pigmentosa (RP) is usually the result of one of several rare inherited oculardisorders that generally result in blindness. RP presents first with night-blindness, then progresses to tunnel vision, and ultimately blindness.
There are a variety of known causes of RP, including for example, Kearn-Sayre syndrome -- the combination of progressive external ophthalmoplegia and retinitis pigmentosa. This is a mitochondrial disorder. There are also autosomal recessive forms such as the Bardet-Biedl syndrome (Middela et al, 2009) as well as abetalipoproteinemia (Zamel et al, 2008). Vitamin E deficiency due to malabsorption can create an acquired RP.
|Bone spicule pigmentation of fundus from http://www.eyeatlas.com/box/360RP1.jpg|
Bone-spicule pigmentation of the retina is typical of RP. These are the clumps of pigment seen on the image above, in the periphery of the retina. Diagnosis is generally made through a combination of observation of the pigmentary changes, electroretinography (ERG), and visual field testing.
Our purpose here is to talk about the ocular tracking problems exhibited by persons with RP. To our knowledge, no papers have been written about this subject to date.
As patients with RP usually develop tunnel vision, they cannot see objects unless they are directly in front of them.
This tunnel vision makes it difficult for patients with RP to find targets that have been suddenly displaced (as in the saccade test), as well as makes it difficult for them to pursue targets, as they may "vanish" during tracking.
An interesting example of this is shown in the two saccadic traces below, from patients with Retinitis Pigmentosa.
This patient is searching for the target to the right
|Dysmetric saccades in persons with retinitis pigmentosa (RP), which is an ocular disorder which impairs peripheral vision. Latency is long, saccades both under and overshoot or overshoot, depending on the style of the patient who is tracking.|
Similar problems arise during smooth pursuit -- if the person "keeps up" with the target, pursuit may look somewhat normal. If they have very little peripheral vision, they may have no pursuit at all.
|Patients with retinitis pigmentosa (RP). In this condition peripheral vision is poor, but central vision may be good. They have "tunnel vision". This causes a peculiar situation where saccades may be very disorganized, but pursuit may be normal.|
OKN is more difficult to eliminate. The patient below had longstanding RP, and very little peripheral vision.
|Very poor OKN in this patient with retinitis pigmentosa. This man had "bony spicules" in his periphery, and very little peripheral vision. See other images of his pursuit and saccades.|
Patients with these sorts of tracking problems should probably not drive or operate dangerous machinery, as they cannot see anywhere other than straight ahead.