Most people are diagnosed with a juvenille dystophy after visiting an optician who identifies a potential problem. The optician will refer the person to an ophthalmologist (specialist eye doctor) who is a genetic specialist at a hospital. Further tests to determine the specific dystrophy the person has might include:
Visual field testing
Visual field testing assesses the full horizontal and vertical range and sensitivity of a person’s vision, and detects blind spots (scotomas) which could be a sign of eye disease. There are several types of test but they are not painful or invasive. The most common type of visual field test is often seen in local opticians. The patient sits at the machine with their chin on a rest and a patch over one eye. They have a button which they are asked to press when they see one or more flashing lights. This process results in a map of the person’s visual field, and can point to areas of the retina where there is vision loss.
A dye called fluorescein is injected into the bloodstream via the patient’s arm. This travels to the eye and highlights blood vessels in the retina. A photograph is taken of the back of the eye.
ERG measures electrical signals produced by the retina following flashes of light. The test uses electrodes placed on the cheek under each eye. The patient looks at black and white checks moving across a TV screen and a lamp flashes light into the eye three times per second. The electrical responses are viewed and recorded on a monitor. Abnormal patterns of light response suggest the presence of macular disease.
Optical coherence tomography (OCT)
CT is a scanning device that works a little like ultrasound. Ultrasound captures images by bouncing sound waves off living tissues; OCT does it with light waves. The patient places his or her head on a chin rest and invisible, near-infrared light is focused on the retina. Cross-sectional pictures of the retina are analysed for any abnormalities which could indicate retinal degeneration. OCT is sometimes combined with infrared scanning laser ophthalmoscopy (ISLO) to provide additional surface images of the retina.
A genetic test usually involves having a blood sample taken. DNA is extracted from blood cells and analysed in the laboratory. The analysis involves looking very carefully at the genetic code to try and identify the genetic alteration that is causing the condition. Many people have the genetic cause identified, although it’s not always possible. More information can be found in our Genetics factsheet.