How Is Retinitis Pigmentosa Diagnosed?
By Frank J. Weinstock, MD
Edited by Maureen A. Duffy, M.S., CVRT
Symptoms of Retinitis Pigmentosa
Some of the most common symptoms of retinitis pigmentosa include:
- Decreased vision at night or in low light
- Loss of side (peripheral) vision, which may cause the person to bump into tables, furniture, or doorways. It may not be noticed by the person with retinitis pigmentosa, but may be apparent to others.
- Loss of central vision (in advanced cases)
- Other indicators of retinitis pigmentosa are your family history (especially the possibility of retinitis pigmentosa appearing in other family members) and expressed visual concerns or complaints, such as not being able to see well at night or in low light conditions.
Tests Essential to the Diagnosis
Although your medical and family history and your visual concerns may cause your doctor suspect a retinitis pigmentosa diagnosis, a definitive diagnosis requires specific examinations and testing.
The Comprehensive Eye Exam
- Primarily, retinitis pigmentosa is diagnosed by a comprehensive medical eye examination.
- During the examination, your ophthalmologist will observe characteristic bone spicule pigment deposits while looking at the back layers of your eye with an ophthalmoscope—an instrument that allows your doctor to examine your retina by shining a beam of light through your pupil.
- A similar pattern appears in congenital syphilis, which is unrelated and must be ruled out.
Visual Field Testing
- Visual field testing can determine how much peripheral (side) vision you have, how much surrounding area you can see, and will locate defects in the peripheral visual field that are related to the damage occurring from retinitis pigmentosa.
- Your eye examination will include visual field testing via a “kinetic” or non-computerized visual field test, such as the Goldmann Perimeter Exam (the recommended field test for retinitis pigmentosa), or a computerized visual field test, such as the Humphrey Field Analyzer.
- The Goldmann Perimeter Exam (pictured below) resembles a large white bowl. One eye is covered and the other eye remains stationary and focused straight ahead. The doctor will move a stimulus (a light) from beyond the edge of your visual field into your visual field. The location at which you first see the stimulus will indicate the outer perimeter of your visual field. The doctor will analyze your exam responses to make a precise map of your visual fields.
The Goldmann Perimeter Exam
The Humphrey Field Analyzer
- The Humphrey Field Analyzer (pictured above) also resembles a large bowl. One eye is covered with a patch and the other eye remains stationary and focused straight ahead. Small white lights of varying sizes and intensities will flash at different locations around the bowl. You are instructed to press a button whenever you see a flashing light. By recording which lights you see and which ones you do not, it creates a map of your visual field.
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 vision. This is usually late in life and is rare.
- This diagnostic testing is done by the ophthalmologist, often by referral to a university Ophthalmology Department, since very few private offices have this equipment.
- The electroretinogram (ERG) measures your responses to flashes of light, via electrodes that are placed on the surface of your eye. It is a painless test.
- The ERG, in conjunction with the visual field exam, will usually make the diagnosis. The ERG will also determine if there is any involvement of the central retina and visual field.
- Periodic follow-up ERG examinations are necessary to follow and track the progression of your retinitis pigmentosa.
Recently, testing for genetic defects is being done to clarify the loss in more detail and to find a treatment.
It is important to make a diagnosis so that the patient and family can be counseled as to the status of the disease, when driving might have to be discontinued, and what low vision interventions and low vision devices (in the case of more advanced disease) might be available to allow maximum use of the patient’s visual potential.
Portions of this article were published originally at http://www.medicinenet.com/retinitis_pigmentosa/article.htm