What is a Cycloplegic Refraction?
During a comprehensive eye exam, your optometrist uses refraction to determine how much power is needed to bring your eyes to normal, perfectly focused vision. Refraction is a process the optometrist uses to measure your refractive error or vision problem. A refractive error is an optical defect that does not allow light to be brought into sharp focus on your retina, resulting in blurred or distorted vision. Examples of refractive error are myopia, hyperopia, and astigmatism.
Cycloplegic refraction is a procedure used to determine a person's complete refractive error by temporarily relaxing the muscles that aid in focusing the eye. Cycloplegic eye drops are used to temporarily relax the ciliary body, or focusing muscle, of the eyes. When a cycloplegic refraction is performed, the optometrist is trying to find out what the full refractive error is without any influence of the person being tested. For example, when an optometrist performs a regular refraction without cycloplegic eye drops, there could potentially be an influence on the readings from the patient. Sometimes the patient may be subconsciously over-focusing. This may actually make someone appear more nearsighted or less farsighted than they are.
Why Dilate the Eyes?
This ability to over-focus during an eye exam can lead to inaccurate results. When this occurs, the optometrist has to find a way to control a person's ability to accommodate or focus. A careful refraction can help accomplish this. However, the best way to do this is to install a cycloplegic eye drop. The drop temporarily relaxes the focusing muscle inside the eye so that the person can no longer accommodate or focus at all. While it makes the patient very blurry for a bit, it allows the optometrist to measure the entire amount of farsightedness. The optometrist can then measure the 'true' refractive error.
A cycloplegic refraction is often performed on children. Children have the ability to accommodate/focus a great deal. Also, children tend to focus at a close range and are unable to control their focusing when they are supposed to be looking at a far distance during an examination. When an optometrist performs a cycloplegic refraction, they can be confident they are measuring the full prescription.
Are There Side Effects?
Depending on the type of cycloplegic drop used, sometimes they have the temporary side effect of leaving the patient blurry for several hours. The patient could experience blurred vision even into the next day. Because cycloplegic eye drops also dilate the pupil, it will make the patient light sensitive for a few hours and protective sunglasses should be worn for comfort outdoors.