The refraction test (also called vision test,) is an exam that measures a person's prescription for eyeglasses or contact lenses.
How the test is performed?
Your eyes wll be measured using a special device called a phoroptor or refractor. You will look through the device and focus on an eye chart 20 feet away. The device contains lenses of different strengths that can be moved into your view. The test is performed one eye at a time and you will be asked if the chart appears more or less clear when different lenses are in place.
If your uncorrected vision (without glasses or contact lenses) is normal, then the refractive error is zero (plano) and your vision should be 20/20.
A value of 20/20 is normal vision. This means you can read 3/8-inch letters at 20 feet. A small type size is also used to determine normal near vision.
You have a refractive error if you need a combination of lenses to see 20/20. Glasses or contact lenses should give you good vision. If you have a refractive error, you have a "prescription." Your prescription is a series of numbers that describe the powers of the lenses needed to make you see clearly.
If your final vision is less than 20/20, even with lenses, then there is probably another, non-optical problem with your eye. The vision level you achieve during the refraction test is called the best-corrected visual acuity (BCVA).
Abnormal results may be due to:
- Hyperopia (farsightedness)
- Myopia (nearsightedness)
- Presbyopia (inability to focus on near objects that develops with age)
Other conditions under which the test may be performed:
- Corneal ulcers and infections
- Macular degeneration
- Retinal detachment
- Retinal vessel occlusion
- Retinitis pigmentosa