common eye tests
Below are a few common eye tests that you may be asked to perform when you see your eye doctor. The reasons for performing these tests are numerous. The descriptions below serve as a complementary source of information on the tests but not necessarily why these tests were done for your own condition.
visual acuity testing
This is a common, standard test to check how well you can see at a specific distance. Your vision will be checked one eye at a time with your most current glasses for distance vision.
Please remember to bring your glasses with you when you go to see your eye doctor. If you don't have them, then the most recent glasses prescription will do. If you do not have either then do not worry - we will be able to check your refraction for you.
For infants and children, there are special charts and techniques to assess their vision as they cant communicate well and has short attention span.
SLIT LAMP & BINOCULAR INDIRECT OPHTHALMOSCOPY
The eye is a small structure being, on average, a sphere of only 22 mm in diameter. As such, examining all the structures inside it requires the use of a microscope with a light source. This is the slit-lamp - a table-mounted microscope which can be moved very precisely to get a magnified view of all the different parts of your eye.
Sometimes your doctor will also use a binocular indirect ophthalmoscope which comes in the form of a 'hat' with a light source and which requires the use of a lens held in front of your eye so that the structures inside your eye can be brought into focus for the examiner.
OPTICAL COHERENCE TOMOGRAPHY (OCt)
This particular machine produces a cross-sectional image of your retina by shining a special beam of light into your eye and analysing the properties of the reflected beam. It does this many thousands of times a second and with this information can build up a 2D or even 3D model of the micro-structural layers of your retina.
This machine has only been in clinical practice for the past 15 years or so and has given us a much faster way of assessing the retina quickly & accurately with micrometer-scale reproducibility. It is painless and all you need to do is to place your chin on the rest, look straight ahead at the fixation target and stay nice and steady. The machine does the rest, typically in a couple of minutes.
VISUAL FIELD TESTING
A visual field test is particularly useful in assessing the function of the retina and optic nerve. It is an automatic way of plotting how much you can see in your peripheral (side) vision. In people with glaucoma, it is also a useful tool to check for progression, which will help your doctor decide how to treat you.
This test is usually done one eye at a time and all you have to do is look straight ahead at the fixation light and press a button when you see a light in your peripheral vision. The first time you do the test can be daunting especially if you're tired and have been waiting around to see the doctor all day. Therefore, it is sometimes useful to repeat the test at another visit when you're fresh and already familiar with the routine.
Images courtesy of Glaucoma Research Foundation
fundus fluorescein angiogram
This is a diagnostic test which involves a yellow dye into your veins (via a needle) which then circulates throughout your body. As it fills up the vessels in your retina, we quickly take photographs with a special camera and filters. The dye then appears as a bright white. The image shows how well the vessels are highlighted - this helps in diagnosing cases which are caused by leaking blood vessels and is also helpful in planning our treatment strategy.
The whole test takes around 20 - 30 minutes and involves sitting at a camera (like at the slitlamp) for that time. You can certainly take breaks during the test. Sometimes when the dye is injected you may experience transient nausea or vomiting which usually passes with a few deep breaths. Please inform the photographer should you have any symptoms such as nausea, rash or itching as very rarely, some people will have a true allergic reaction to the dye. Please mention any allergies you may have before proceeding with this test. The dye will take a day or two to exit your system and until then, your skin and urine will appear bright yellow so do not be alarmed.