How do doctors diagnose retinitis
Because there are so many variants of RP with different symptoms and signs, the diagnosis may not be straightforward at first. Certain clues in the patient's history (especially retinitis pigmentosa in family members) and complaints (such as difficulty with adapting to the dark) may make one suspect RP. On dilated eye examination, the ophthalmologist may find characteristic clumping of pigment in the retina (a pattern described as bone spicules). This is due to changes in the retinal pigment epithelium, a layer of cells found under the receptors. Other characteristic findings include narrowed retinal arterioles and a waxy appearance of the optic nerve. Other non-RP eye diseases can show similar patterns in the retina (for example, Kearns-Sayre syndrome and congenital syphilis). Therefore, it may be necessary to perform additional testing to confirm the diagnosis of RP.
Visual field (side-vision) testing is important to making the diagnosis of RP and to document the degree of peripheral visual loss.
The electro retinal exam (ERG) is a test that measures the electrical signals produced by the retinal cells when responding to light. The classic ERG pattern seen in RP shows a markedly diminished rod photoreceptor light-sensing response. The ERG helps distinguish between diseases that predominantly affect rod cells (like RP) from diseases that affect other cells of the retina. For example, the ERG can help distinguish RP from cone-rod dystrophy (CORD), a group of disorders that, as opposed to RP, typically affects central and daytime vision more than peripheral and night vision.
Other conditions such as toxicity from drugs, inflammatory conditions, infections, ischemia, and other forms of age-related retinal degeneration and inherited retinal dystrophy can affect the retinal pigment epithelium, resulting in pigmentary changes that resemble RP on exam. Here again, the ERG pattern is useful in distinguishing these other retinopathies from RP.
ERG is a painless test. The electroretinogram (ERG), in conjunction with a visual field exam to detect constriction of the visual fields, will usually make the diagnosis of RP.
Additional specialized tests such as EOG, macular optical coherence tomography (OCT), and fluorescein angiography can help define which portions of the retina are secondarily affected in RP.
Genetic testing may identify the presence of one of the genes associated with RP, and evolving treatment modalities may target these specific gene abnormalities. For example, researchers are developing a promising new gene therapy for congenital amaurosis with the RPE65 gene mutation. Clinical trials are under way to treat some types of Usher syndrome with targeted gene therapy, as well.