What is Retinitis Pigmentosa?
Retinitis pigmentosa is the most common of a group of hereditary progressive retinal degenerations or dystrophies. There is considerable variation and overlap among the various forms of retinitis pigmentosa. Common to all of them is progressive degeneration of the retina, specifically of the light receptors, known as the rods and cones. The rods of the retina are involved earlier in the course of the disease, and cone deterioration occurs later. In this progressive degeneration of the retina, the peripheral vision slowly constricts and central vision is usually retained until late in the disease.
What causes retinitis pigmentosa?
Retinitis pigmentosa is an inherited condition which involves both eyes. If it starts in one eye, the other eye usually develops the same condition in a number of years. Most cases are familial, inherited in a variety of ways, including dominant, recessive, and sex-linked recessive. Some cases are sporadic and lack a family history of the disease. A thorough genetic pedigree, often with the aid of a genetic counselor, is essential in determining risk of future generations acquiring the disease.
Retinitis pigmentosa is usually diagnosed during the teenage years but may be present at birth. The latter congenital type is usually fairly stable and nonprogressive. Cases that are diagnosed later in life are often milder and may progress more slowly.
There are approximately 75,000 people in the United States with retinitis pigmentosa (RP). RP is sometimes associated with other systemic illnesses. Usher syndrome, characterized by retinitis pigmentosa and neural hearing loss, is the most common cause of deaf-blindness in the United States. The hearing loss usually is diagnosed earlier than the eye changes.
What are retinitis pigmentosa symptoms and signs?
Since retinitis pigmentosa begins as rod degeneration, the patient first notices increasing difficulty in night vision, followed by difficulty seeing in the periphery. Slowly progressive constriction of the visual field leads to tunnel vision. A small area of central vision in both eyes usually persists for years. Generally night blindness precedes tunnel vision by years or even decades. Total blindness eventually ensues in most cases. The age of appearance of legal blindness ranges from as early as childhood to as late as the 40s.
How is retinitis pigmentosa diagnosed?
Although the history (especially the possibility of retinitis pigmentosa appearing in other family members) and complaints of the patient may make one suspect RP, it is primarily diagnosed by examination. The patient may complain of difficulty seeing at night or in low light condition. At some point, the ophthalmologist observes relatively characteristic clumping of pigment in the retina in a pattern described as resembling bone spicules. Fundus examination (looking at the back layers of the eye with the ophthalmoscope, an instrument allowing the visualization of the back of the eye by looking through the pupil) affords the view of the retina. A similar pattern may appear in congenital syphilis which is unrelated and must be distinguished.
Two tests are essential in the diagnosis and the follow-up exams.
Visual field testing will find defects in the peripheral (side vision) with the degree of loss related to defects in relation to the damage occurring in this disease. Over time, the visual field may reduce to a small central island of vision causing "tunnel vision." The final progression may be the complete loss of the remaining central vision.
Electrophysiological testing by the ophthalmologist (often by referral to a university ophthalmology department, since very few private offices would have this equipment) is often diagnostic. Responses to flashes of light are measured via electrodes placed on the surface of the eye. It is a painless test. The electroretinogram (ERG), in conjunction with the visual field exam, will usually make the diagnosis. This will also determine if there is any cone involvement.
Recently, gene testing for defects is being done to clarify the basic cause for RP and assist in ultimately finding a treatment.
When to start treatment
It is important that you decide sooner than later. In many cases, once you lose some vision, it’s gone. It’s harder to work with dead tissue or run the risk of damaging your fibrosis nerve tissue, so the sooner the better. Prevention is very important in this case.
We have found patients come to us with certain concerns about the surgery for Retinitis Pigmentosa. Typically, it starts with their physician telling them that there is nothing they can do about their situation and they will go blind. That’s it. What happens then is they start believing what they hear and don’t bother doing anymore research or very little about other RP treatment options. Sometimes we have found their family isn’t very supportive as well which doesn’t help the situation. They may not fully understand the process or believe it works either. Lastly, some people have religious beliefs that impact their decision to seek treatment. Some people just decide that this is their fate and accept that they are going blind regardless of the proof we show them. We try to encourage and educate people about the treatment but we have found that the best option for us is to let people work it out on their own.