What Is A Refraction?
A refraction is an important part of an ophthalmologic exam. It requires many steps and expertise. It is usually performed as one of the first steps during an eye examination.
First, a patient’s current glasses are read on a machine called a lensometer. Vision is then checked with both current glasses and contact lenses. If a patient is wearing contact lenses, they are next asked to sit in front of a machine called a phoropter.
The examiner determines whether the prescription in the contact lenses is correct. Next, the fit of the contact lenses is checked at the slit lamp. The patient is then asked to remove their contact lenses or glasses.
The refraction is then performed to determine the patient’s refractive error and prescription using a phoropter.
A phoropter contains many lenses of different strengths. The patient sits in a chair with a phoropter attached to it. It is placed in front of the patient. The patient looks through it as they look at a chart 20 feet away. The exam is performed one eye at a time.
The eye not being tested is occluded. Different lenses are moved into view. The examiner will ask if the chart appears clear, blurry or the same. Often time different lenses are placed in front of the patient and the examiner will ask, “Which is better? Option one or option two”. There can be a clear difference but there can also be no difference. It is a subjective refraction and there is no right or wrong answer.
Next, near vision will be tested for patients over 40 years old.
This is often done with a near card, book, or ruler held at a comfortable working distance usually 12 to 18 inches from the patient.
The ophthalmologist will then take the numbers determined from the refraction and decide what prescription to give to the patient.
The ophthalmologist will determine if there is myopia, hyperopia, presbyopia, and or astigmatism. If a patient does not achieve 20/20 vision corrected in each eye the ophthalmologist must then find a non optical reason for this. An ophthalmologist is trained in looking for underlying medical problems that could affect a patient’s vision or change in refraction.
A change in refraction can alert the ophthalmologist to many medical diseases. It is therefore important to have a careful, detailed refraction with an ophthalmologist.
Refractions are not usually covered by most commercial insurance companies and Medicare.
Melanie J. Buttross, M.D.
Board Certified Ophthalmologist
Washington DC and Tyson’s Corner VA
