If an ophthalmologist believes that you may have Best disease they will thoroughly examine your retina.
Your vision will be checked and your pupils dilated to allow the ophthalmologist to observe the macula. The drops used to dilate your pupils generally take around 30 minutes to work. These drops will cause your vision to become blurry and heighten your sensitivity to light. The drops are necessary to allow your ophthalmologist to see the insides of your eyes more easily. The effects of the drops normally pass in about six hours however sometimes it can happen overnight. It is not safe or advisable to drive until the effects of the drops have fully disappeared.
A special lamp called a slit lamp is used to inspect the inside of your eye. Your ophthalmologist will ask you to look in various directions while shining a light directly into your eye (although bright, this light will not cause any damage to your eye). This will allow them to identify any changes that Best may have caused.
It is not always possible to identify if you have Best disease using this examination alone. Further tests may be needed to find out for certain if you have Best disease including:
Fluorescein angiogram
This test allows your ophthalmologist to find out more about your Best disease. Although a slit lamp allows your ophthalmologist to see the damage to your retina it does not allow them to view the network of blood vessels beneath it. A fluorescein angiogram allows them to photograph these blood vessels and see if any changes have occurred that may be causing problems.
In order for the pictures to display properly, a yellow dye is injected into your arm which travels through your bloodstream to your eye. The injection is not painful but can make some people feel nauseous. The dye allows the blood cells to become visible when a picture is taken. After the dye has been injected you will be asked to look at a special machine. The machine will photograph the back of your eye as the dye travels through the blood vessels. The test usually takes around 10 minutes and you will experience a series of flashing lights as the pictures are taken.
It is a very common test and does not have any serious side effects to the majority of people. The injection may give your skin a slight yellow complexion from the dye, however, this passes into your urine (which also may appear a darker yellow than normal).
Optical Coherence Tomography
Optical Coherence Tomography allows photos to be taken of the back of your eye which provides your ophthalmologist with cross-sectional images of the retina, similar to a 3D image of the inside of your eye. No dye is required for this test. Often optical coherence tomography and fluorescein angiogram are used simultaneously to obtain a thorough picture of the retina.
Electroretinography
Electroretinography is a test used by ophthalmologists to assess how the retinal rod and cone cells are functioning. During this test, you are asked to look at a screen which displays patterns of lights including flashes and checkerboard patterns. During this time you are normally comfortable sitting upright or lying down. Your pupils are dilated with eye drops and anaesthetic drops will also be put into your eye to numb them. A small electrode is then placed on or near to the front of your eyes. This is similar to placing a contact lens in your eye. The electrode then measures your retinas response to the light patterns. Another electrode is placed on the skin near to your eyes.
The test does not cause any pain. There is, however, a very rare possibility that the electrode placed on the cornea may graze it and cause an abrasion. If your eyes feel uncomfortable or painful over the days following the test it is important to contact your local hospital immediately. Corneal abrasions are easy to treat when caught early.
Electro-oculogram
The electrooculogram test measures how your retina responds to light and eye movement in response to light. This test can be carried out with or without your pupils being dilated. If your pupils are dilated then the test may take longer. If you have a heightened sensitivity to light and are concerned about dilation during the test, please discuss this with your hospital in advance. Electrode pads are placed on the skin near to the nose side of your eye and on the hairline side of your eye. The electrodes will not be placed on or in your eye.
During the test, you will be asked to look at different lights when they appear. This often means that you are looking back and forth between illuminated targets. These lights will alternate back and forth at different speeds whilst your eyes follow them. Parts of the test will be performed with the overhead room lights on, and some of the tests will be performed with them off.
There are no risks involved in this test. Some people find that their eyes become tired during the test and may become itchy afterwards, these feelings will quickly wear off.