Decreased vision at night or in low light
Loss of side (peripheral) vision
Loss of central vision (in advanced cases)

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.