7 Eye tests that look at more than just your vision
Posted on 4 October 2018
When you go to the optometrist because you’re having trouble seeing, a vision test is usually conducted. This test assesses how well you can see and your ability to discern objects. However, many eye conditions and diseases present no symptoms, so there’s a range of tests available to see what your eyes can’t. An ophthalmologist and an eye surgeon explain.
Optical Coherence Tomography (OCT scan)
“An OCT scan uses light to produce a microscopic image of the retina and the optic nerve at the back of the eye,” says Dr Rob Daniel, an ophthalmologist at Mediclinic Morningside. This picture can help the ophthalmologist tell if a patient has glaucoma by looking at the thickness of the nerve. Glaucoma is the second most common cause of blindness and occurs when the nerve at the back of the eye starts to die, causing patients to develop tunnel vision before losing all vision.
Dye disappearance test
Topical fluorescein is a nontoxic, water-soluble dye that’s inserted into the eye before the tear meniscus (that’s the thin strip of tear fluid on the margin of your eyelid) is observed for the disappearance of fluorescein. If the dye takes a while to disappear, it suggests a blockage of the drainage system.
Dilated pupillary exam
This test looks at the back of the eye by dilating your pupils with dilating eye drops. It helps diagnose conditions such as diabetes, macular degeneration, and retinal detachment.
Extraocular muscle eye test
Strabismus (crossed eyes) is a condition in which the eyes are not aligned and point in different directions. “During this test the patient will be asked to look in different directions and at varying distances with both and each eye separately. This identifies uncoordinated muscle movement in the eyes,” says Dr Wicus Malherbe, an eye surgeon at Mediclinic Potchefstroom.
Meibomian gland dysfunction testing
Meibomian glands secrete lipids to prevent evaporation of the tear film in your eye. Tear breakup time (TBUT) is measured by instilling fluorescein dye, asking the patient to hold the eyelids open after one or two blinks, and counting the seconds until a dry spot appears. If a dry spot appears in less than 10 seconds, it’s regarded as abnormal.
This test checks the pressure in your eye through direct contact. Drops are put in your eyes to numb them, then the doctor or assistant gently touches the front surface of your eye with a device that glows with a blue light. This applies a small amount of pressure to the eye, and the pressure inside can then be measured.
Baseline eye exam
This exam should take place at the age of 40, says Dr Malherbe, to identify signs of eye disease at an early stage. If you display risk factors, such as diabetes or high blood pressure, don’t wait until you’re 40 to have this exam.