A refraction test is an eye assessment to check whether a patient has a refractive error. It can be conducted as part of a routine eye exam to determine if a person needs prescription glasses or contact lenses. It is crucial for people over 40 years old with normal distance vision but who experience difficulties with near vision. A refraction test helps to establish the real power of reading glasses.
Patients having a refractive error should take an eye test when they notice a change in vision or every one to two years. Children over three years of age should receive a refraction test every one to two years. Healthy adults under 60 years of age who have no vision problems should take a refraction test every two years.
People who wear eyeglasses or contact lenses should take the vision test every one to two years. It allows the doctor to determine whether the patient’s eyes have changed and a proper prescription. People who experience difficulties with their vision between eye exams should also see an eye doctor for a further refraction test.
Diabetics should go for an eye exam at least once every year because of the many eye disorders associated with the disease such as glaucoma and diabetic retinopathy. The American Diabetes Association reports that people with diabetes have increased chances of blindness.
Also Known As
Eye exam - refraction
Vision test - refraction
A refraction test can be conducted at the eye doctor's office or the eye clinic by:
- a technician
- an optometrist
- an ophthalmologist
It helps the eye professional to better understand the patient’s vision and the most appropriate option in maximizing the patient’s visual potential. It can be achieved by determining the patient’s visual requirements and ensuring that the prescription is tailored to providing better eyesight through contact lenses, eyeglasses, or other visual aids.
The test is used in the diagnosis:
- Nearsightedness: also called Myopia
- Farsightedness: which is also known as Hyperopia
- Presbyopia: an age-related condition that leads to the eye lens having trouble focusing
- Astigmatism: an abnormally curved cornea that causes blurry vision. It is related to the shape of the lens
The test can also help in the diagnosis and treatment of a range of eye disease, including:
- Retinal detachment: a condition in which the retina detaches from the eye
- Retinitis pigmentosa: a rare genetic condition that damages the back of the eye
- Macular degeneration: an age-related condition that affects a patient’s central vision
- Retinal vessel occlusion: an eye disease that causes blockage of the small blood vessels close to the retina
People over 60 years of age, as well as those with a family history of glaucoma should have a refraction test annually. Glaucoma is an eye disease that occurs when the internal eye pressure builds up, causing damage to the optic nerve and the retina. Regular vision tests can help the doctor to screen for glaucoma as well as other eye disorders linked with aging and treat them early, where possible.
Preparation & Expectation
Regular vision tests are crucial in maintaining a person’s vision and are a standard part of an eye doctor visit. The refraction test is a simple, quick, and pain-free eye exam that requires no preparation. There is no discomfort.
Patients who wear contact lenses will have to remove them before the test. Eye drops may be used to assess more complex prescriptions, or in cases where a patient cannot respond verbally. The eye drops dilate the eye and temporarily prevent them from changing focus during the refraction test.
The patient sits in a chair with a measuring instrument called a phoropter or refractor. The patient will look through the phoropter and focus on an eye chart at a distance of 20 feet. For young children and illiterate patients who cannot read, the table will have small pictures of everyday items. The instrument is equipped with lenses of a different power that can be introduced into the patient’s view.
The doctor will ask the patient to read the smallest row of letters that they can see. He/she will switch the lenses on the device until the glass is clear. If the patient is unsure, they should ask the doctor to repeat the choices. The test is conducted on both eyes, one eye at a time.
The doctor can also conduct the vision test without using the phoropter. In this case, he/she shines a light into each of the patient’s eyes and assesses the amount of light bouncing off the back of the eye to measure the refractive score. The doctor may also use a computerized refractor to get an initial estimate of the patient’s prescription. The autorefraction helps to save time and is useful in diagnosing young children or patients who have difficulties with eye examinations. However, the result may not be accurate for a final prescription.
The best-corrected visual acuity (BCVA) is the patient’s vision level achieved during the refraction test. The doctor will discuss the findings with the patient.
The normal vision has a value of 20/20 (1.0). If the patient’s uncorrected vision is normal, the refractive error is Plano (zero). The person can read 3/8-inch symbols or letters at a range of 20 feet.
- Abnormal Results- A patient has a refractive error if they don’t have a 20/20 (1.0) vision. It means light passing through the eye lenses is not bending correctly, and the patient needs a combination of glasses for clear sight. The result of the refraction test enables the doctor to determine the prescription lens the patient should use to have a 20/20 vision. The prescription is a series of values that represent the powers of the lenses the patient needs for a clear vision.
If the patient’s final vision is below 20/20 (1.0), even with corrective lenses, then it is likely that there is another non-optical eye problem. It may be due to:
The result may also reveal other severe eye conditions including:
- Retinal detachment
- Retinitis pigmentosa
- Retinal vessel occlusion
- Corneal ulcers and infections
- Loss of clear vision due to macular degeneration
It is important to note that a patient’s future prescription is not predictable. The doctor can only advise on the probable progression of the patient’s prescription and how often one should undergo refraction.
Risks & Complications
Refraction is a safe eye exam without risks.