The macula is responsible for detailed, central vision, and is important for activities such as reading, driving, and distinguishing faces. As a result, Stargardt disease is often detected when the patient experiences difficulty with these activities, or with similar activities that involve seeing fine detail and colour.
As the disease advances, a person’s vision will become less distinct, and a blind spot in the central visual field may develop and grow. By mid-life, many affected by the disease are legally blind as a result of central vision loss, but peripheral vision is in most cases minimally affected and remains throughout life; the perception of colour often diminishes during the later stages of the disease.
Early stages of Stargardt disease may also be accompanied by a slight blurring in the field of central vision. Such blurring can be detected via an eye test, but also at home using an Amsler Grid, a simple visual tool that can help you see distortions in your visual field.
Eye care professionals will sometimes use an Amsler Grid as well, since it is a straightforward and reliable way to detect anomalies in central vision. Other tests that may be used during an exam include the following:
- Fluorescein Angiogram: this test uses a dye called fluorescein to exam the back of the eye. The dye is injected into the arm and recorded by a camera as it passes through the blood vessels at the back of the eye. Patients with Stargardt disease usually show a “dark choroid effect” due to the buildup of lipofuscin under the retina, which makes the background of the retinal image appear darker.
- 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 the 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.
- 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 testing and counselling: Genetic testing and genetic counselling are an essential 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.