At Reenders Square Eye Centre , the examination usually starts with pre-testing by one of the assistants. Our pre-testing instruments perform several screening tests including a computerized measurement of how far-sighted or near-sighted the eyes are, a central visual field test, and a measurement of the pressure in your eyes to screen for glaucoma. Digital pictures are also taken of the inside of the eyes of all adults.
The Optometrist then starts by asking questions about your vision, general health, medications and family history of any health problems or eye diseases that may have a hereditary component.
We then ask you to read the letter chart with or without your glasses, or both. Your vision is recorded as 20/something. The first 20 stands for the “standard” test distance of 20 feet (or 6 metres in metric notation). The second number indicates the distance someone with so-called “normal” vision could be away from that chart and still be able to see the smallest letters you were able to see. In other words, if the smallest letters you can read are 20/40, it means that you have to be no further than 20 feet from that chart to be able to read letters that a person with 20/20 vision could still read from 40 feet away. Your reading vision may also be measured and recorded in a similar manner.
An assessment of your eye movements is another part of the examination. The ability to move your eyes smoothly through their complete range of motion indicates the health of the eye muscles and the nerves that control those muscles. Subtle misalignment of the eyes may also be detected with these tests. Even a small misalignment can contribute to discomfort while reading or doing other detailed visual tasks. The nerves that control the change in size of the pupils of the eyes are assessed by shining a light in each eye and watching for the expected response.
The “refraction” is the part of the exam that measures your need for prescription lenses. Part of this test may be performed by the Optometrist shining a light across your eyes while looking through various lenses. A reflection from inside your eyes tells the Optometrist if that lens is close to the optimum lens power for your eyes. This measurement is particularly useful for young children and others who are unable to accurately tell the Optometrist what they are seeing through the test lenses. The next phase is the familiar “Which is better, one or two?” The lens prescription is refined with your input. The final prescription is determined from these results, as well as from the results of all other tests and measurements done during the examination.
The health assessment is usually left until the end. We want to finish the visual part of the examination before we start looking into the eyes with bright lights. The external parts of the eye – cornea, lids, etc. – are usually examined with a biomicroscope, which gives a clear magnified view of the structures of the eye. The inside of the eye is examined with one or more types of ophthalmoscopes, which allow us to see the retina, optic nerve and other internal structures. You may or may not require drops to dilate your pupils for this test. Our retinal camera also takes a picture of the inside of the eye for future comparison. Recommendations are then discussed based on the results of the tests.
More or less testing may be required, depending on the individual. Children’s examinations will vary also, depending on the age of the child and their ability to read the eye chart and answer questions. They will often be shown a 3D test to determine how well their eyes work together. Young boys, in particular, are also tested for colour vision deficiencies. About 8% of males have a genetic colour vision defect, or are “colour blind”, while less than 1% of females are affected. It is useful to know about a colour vision defect at a young age as some career choices require good colour vision.