The symptoms of X-linked retinoschisis are usually noticed around the time a boy enters public school. In families where the disease is inherited, early genetic testing is often done to secure a diagnosis. If there is a mutation in the RS1 gene, genetic testing is able to pinpoint it with a high degree of accuracy—approximately 95% of the time. The most common symptoms are a general loss of vision and difficulty seeing fine detail, especially in cases where the macula is damaged. Peripheral vision may be obscured in cases where the retina’s outer edges are damaged. Some boys may also have nystagmus (rapid involuntary movements of the eye from side to side) and strabismus (eyes turned in or cross-eyed). As a result, the disease is sometimes incorrectly diagnosed as amblyopia (lazy eye).
For affected boys, vision loss tends to stabilize around adulthood and remains at the same level until mid-life (50s or 60s). The disease rarely leads to the complete loss of vision, but it does entail an increased likelihood for developing serious eye complications, including retinal detachment and bleeding into the vitreous body of the eye. Although women are considerably less likely to experience symptoms when they carry a mutated copy of the RS1 gene, some are at a higher risk of experiencing some vision loss, particularly a loss of peripheral vision, later in life.
An ophthalmologist may suspect retinoschisis after a simple eye exam, especially if a wheel-like pattern of splits is visible in the macular. Several tests can clarify and confirm a diagnosis:
- ERG (electroretinography): this is a test that measures the electrical responses of the retina to light, evaluating responses of both rod and cone photoreceptors. Although both rods and cones may be affected in people with RP, the most marked changes early in disease are in the rod cells; this characteristic pattern helps diagnose the condition. The ERG test involves staying in a darkened room for 30 minutes, with drops put into the eye or eyes being tested. A special contact lens or gold-foil electrode is then placed on the eye or lower eyelid, and the eye is exposed to flashes of light.
- OCT (optical coherence tomography): this is an imaging technique that involves taking digital images of the various layers of the retina. The process is uses light rather than sound or radio waves, which is why the images are in high resolution.
- Visual field test: this exam is designed to detect, measure, and monitor blind spots in vision. It involves looking into a device that emits flashes of light, with the patient asked to indicate which flashes can be seen. The flashes that are not seen are recorded. This gives a measure of how much vision is affected.
- Genetic counselling: while not a test in the traditional diagnostic sense, genetic counselling is an important part of the diagnostic process. It can help determine the gene or genes that have been mutated, as well as the hereditary factors that are involved.