A refraction is usually performed as a part of a routine eye examination. The purpose of this test is to determine if a person has a refractive error which would then mean the patient would need glasses or contact lenses.
A value of 20/20 is normal (optimum) vision. This means that individuals who have 20/20 vision are able to read letters that are 3/8-inch (1 centimeter) tall from 20 feet (6 meters) away. The normal uncorrected vision (without glasses or contact lenses) refractive error is zero (plano). Individuals who don’t have 20/20 vision, have a refractive error. This means that the light passing through the eye does not focus on the retina (back of the eye) because it is either bending to little or too much. The refraction tells us what prescription lens is needed in to move the focus onto the retina to provide 20/20 vision.
For people over age 40 who have normal distance vision but difficulty with near vision, a refraction with a small type size is used to determine normal near vision and the correct power for reading glasses.
The test is performed by having the patient look through a special device called a phoropter. The patient looks through the phoropter and focuses on an eye chart 20 feet (6 meters) away. The phoropter contains hundreds of lenses of different strengths that are shown to the patient to provide the clearest vision. The test is performed one eye at a time. If the patient is wearing contact lenses, they should be removed before the test.
In case the final vision is less than 20/20 even with lenses, then this is a indication that there may be some underlying pathology, which would warrant further testing.
Astigmatism (abnormally curved cornea causing blurred vision)
Presbyopia (inability to focus on near objects that develop with age)
All conditions above should be able to obtain 20/20 vision with glasses or contacts
Conditions below that may not be able to obtain 20/20 vision with a refraction
Corneal ulcers and infections
Loss of sharp vision due to macular degeneration
Retinal detachment (separation of the light-sensitive membrane (retina) in the back of the eye from its supporting layers)
Retinal vessel occlusion (blockage in a small artery that carries blood to the retina)
Retinitis pigmentosa (an inherited disorder of the retina)
There is an art to refraction and we will always answer the your questions and as well as discuss their findings. Based on the results of the refraction, we can determine the amount of myopia, hyperopia or astigmatism.
Children should be refracted every 1-2 years, starting at no later than 3 years of age. Healthy adults under age 60 who aren’t experiencing vision problems should have a refraction every 2 years, while adults currently wearing prescription glasses or contact lenses or with a refractive error should be refracted every 1-2 years or if they notice their vision changing. The refraction allows us to determine what lens changes are needed to bring the vision back to 20/20. In the case of encountering vision problems between exams, another refraction may be needed. Patients with Diabetes often require multiple refractions.
It is important that patients with diabetes have an eye examination every year. A number of eye conditions are associated with diabetes, such as diabetic retinopathy and glaucoma. According to the American Diabetes Association, people with diabetes are at a greater risk for blindness than other Americans.
Adults over 60 or who have a family history of glaucoma, should also be refracted every year. Glaucoma occurs when pressure builds up in the eye, damaging the retina and the optic nerve. Regular exams will help the eye doctor screen for glaucoma and other eye conditions associated with aging and when necessary, begin early treatment.