Do you think that eye tests are only for those with poor vision? You couldn t be more wrong. Your eyes act as windows to your health. You must get your eye tested regularly till you are 40, and every two years after that. Visit the eye doctor every 6 to 12 months after you turn 65. A few minutes at the ophthalmologist can help pick up early symptoms of conditions like cataract, glaucoma, macular degeneration, diabetes, high blood pressure and arthritis. Did you know that there s also an eye test that could detect Alzheimer s? You can now get an eye test online too!
Computerised testing is not the only eye test. Eye tests include a series of tests that assess the health of your eyes and provide evidence of other diseases. So make sure to visit an ophthalmologist and not an optician. An optician simply prescribes glasses based on your eyesight problems without telling you about the underlying cause of your problem.
When you visit an eye doctor, he/she will first examine the pupils and check your eye muscle movement. Then the doctor may prescribe one or more of the several eye tests. Get acquainted with these various eye tests.
1. Visual acuity test
This test checks how well each eye can see details of an alphabet or symbol. You will need to identify random letters of the alphabet printed on a standardised chart (Snellen chart) placed at a particular distance away from you. The alphabets are arranged in rows and columns that get smaller and smaller down the chart. The doctor will note down how far down can you accurately distinguish the alphabets. A result of 20/20 is considered the normal vision. It means that you can identify the alphabets till the standardised line near the bottom of the chart but not the smaller ones below it. Typically, the smallest alphabets at the bottom of the chart correspond to 20/10 visual acuity, and if can identify them, you have 20/10 visual acuity. The higher the line above the standardised one on the chart you stop identifying the alphabets, the worse is your visual acuity.
2. Refraction test
Refractive errors of the eye like myopia, hyperopia, and astigmatism occur when the light rays don't focus perfectly on your retina. They result in blurred or distorted vision. Refraction test helps detect whether you need glasses and determines what corrective eyeglass you need. You will have to look through a device called phoropter which has a series of lens pairs.
3. Slit-Lamp Examination
This test evaluates your eye health by detecting any signs of infection or disease. You will need to place your chin on the chin rest of the slit lamp of the instrument. The doctor will then shine a light from the lamp at your eye and microscopically examine your eyelids, cornea, iris, conjunctiva and sclera one by one. An eye drop containing fluorescein dye may often be used. A different lens may be used to examine your retina and optic nerve at the back of your eye.
4. Keratometry
This test measures the shape and curvature of your cornea. The test helps determine the proper fit for contact lenses. Your doctor will focus light on the cornea of your eye and measure its reflection.
5. Stereopsis
Due to front facing eyes, the visual fields of your two eyes overlap. The coordinated use of the two eyes produces a single impression in the brain. As a result, you are able to perceive the shape, depth, and distance of an object. This ability is termed stereopsis. The stereopsis test checks if you have a proper three-dimensional (3D) vision by analysing how you view the randomly positioned red and green dots stereograms.
6. Perimetry (Visual field test)
The visual field test or perimetry checks your peripheral vision, i.e., the full extent to which you can see objects on the sides of your field of vision without moving your eyes. It helps check the blind spot. The test is subjective to your response. You may need to respond to a flashed light by pressing a button on a machine. In a confrontation visual field testing, you one eye is covered, while the other eye is fixated straight ahead on a target object. The extreme edges of your field of vision are noted. The test checks the outer limit of your visual field.
7. Ophthalmoscopy
Ophthalmoscopy checks the inside of your eyes with an instrument called ophthalmoscope. The test helps evaluate your retina, the optic disk and the choroid (blood vessels that nourish the retina). It helps detect retinal detachment or tear, damage to optic nerve, retinal infection, glaucoma and macular degeneration. Eye drops may be used before the examination to dilate your pupils. The test is of two types - direct ophthalmoscopy and indirect ophthalmoscopy.
In a direct ophthalmoscopy, you will be asked to look through an instrument that has several small lenses and light while you are seated on a chair. Your doctor will look through the lenses and examine your eye. In indirect ophthalmoscopy, the light is attached to a headband worn by your doctor. You will be seated in a lying down or reclined position and will have to look into a small handheld lens which provides the doctor with a better view of the inside of your eye.
8. Tonometry
It is a test that measures the intraocular pressure (IOP), i.e. the pressure inside your eye. The test helps determine your risk of developing glaucoma. Eye drops are administered to numb your eye so that the test doesn t hurt. After placing your chin on the chin rest of a slit lamp, the doctor moves the tonometer towards your eye to gently touch the cornea. The tonometer measures the internal eye pressure.
9. Optical coherence tomography
It is a non-invasive test that uses infrared light to provide cross-sectional images of different layers of the retina and helps measure the thickness of your retina. It can be a useful tool to predict your risk of glaucoma many years in advance. OCT can also be used to monitor glaucoma treatment. It is also used to detect diabetic retinopathy.
10. Fluorescein angiography
The test helps determine your retinal circulation. It can pinpoint blood vessels that are broken down, closed or leaking fluid into the retinal tissue. During the test, the doctor gives pupil-dilating eye drops and takes pictures of the inside of your eye. Then a fluorescein dye is injected into a vein in your arm. Pictures are taken as the dye moves through your retinal blood vessels.
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