How Is Retinitis Pigmentosa Diagnosed?

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 may cause the person to bump intotables, furniture, or doorways. The person with retinitis pigmentosamay not notice it, but it 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 being unable to see well at night or in low-light conditions.

Tests Essential to the Diagnosis

Although your medical and family history and visual concerns may cause
your doctor to 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 may observe characteristic bone spicule pigment deposits while looking at the back layers of your eye with an ophthalmoscope. This instrument allows your doctor to examine your retina by shining a beam of light through your pupil.
• A similar pattern appears in certain unrelated infectious and inflammatory conditions, which must be ruled out if suspected.

Visual Field Testing

• Visual field testing can determine how much peripheral (side) vision you have and how much surrounding area you can see, and will locate defects in the peripheral visual field related to the damage 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 or the Octopus.
• The Goldmann Perimeter Exam (pictured below) resembles a large white bowl. One eye is covered while the other 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 map your visual fields precisely.

The Humphrey Field Analyzer (pictured below) also resembles a large bowl. One eye is covered with a patch while the other remains stationary and focused straight ahead. White lights of varying sizes and intensities will flash at different locations around the bowl. You will press a button whenever you see a flashing light, recording which lights you see and which you do not creates a visual field map.

• The Octopus is a newer visual field machine that can test your visual field either by kinetic perimetry (by moving the light until you see it, similar to the Goldmann) or by static perimetry (by flashing the light in a particular location and changing the size and intensity until you see it, similar to the Humphrey). 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. Complete blindness is rare.

Electrophysiological Testing

• The ophthalmologist does diagnostic testing, often by referral to a university ophthalmology department, since many private offices don’t have this equipment. However, electrophysiology equipment is becoming more prevalent.

• The electroretinogram (ERG) measures your responses to light flashes via electrodes placed either on the surface of your eye, inside your eyelid, or on your skin. It is a painless test.
• The ERG shows how well your rods and cones are functioning. It will usually make the diagnosis in conjunction with the visual field and eye exam.

Genetic Testing

There are over 100 genes known to cause RP. Genetic testing is recommended, and it can usually identify the cause of disease in up to two-thirds of patients. Identifying the causative gene is valuable for several reasons:

• There are several clinical trials for RP for gene therapy and other treatments. Many of these clinical trials only enroll patients with specific genetic causes of RP. Therefore, genetic testing may help you determine if you are eligible for clinical trials now or in the future.
• Identifying the causative gene will also reveal the mode of inheritance (i.e., how the disease gets inherited from one generation to the next).
• Modes of inheritance include autosomal dominant, autosomal recessive, X-linked, and mitochondrial. Your family history will give your doctor a good clue to the mode of inheritance, but often, it’s not conclusive without genetic testing. The mode of inheritance determines how likely it is for different relatives (like children or siblings) to be affected by the same condition. Therefore, genetic testing may help you determine the risk to your family members.
• Most genetic causes of RP cause only RP, which is called non- syndromic RP. However, some genes cause RP plus other diseases, like hearing loss or kidney disease, and these cases are called syndromic RP. Genetic testing may reveal that you have a gene that typically causes syndromic RP and may be at risk for developing other diseases. In this case, your primary care doctor may be alerted to screen you for these other conditions.

Important to Make a Diagnosis

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. Furthermore, a subset of patients will
be eligible for clinical trials and can be counseled regarding the different
options available and where the trials are being conducted.

By Frank J. Weinstock, MD
Edited and Updated in 2024 by Abigal Fahim, MD

Note: Portions of this article were published originally
at http://www.medicinenet.com/retinitis_pigmentosa/article.htm