Cycloplegic Refraction

Children's Eyewear. Christina Kilgour

What is refraction?

Refraction is a process your eye care professional 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 myopiahyperopia, and astigmatism.

During a comprehensive eye examination, your doctor uses refraction to determine how much power is needed to bring your eyes to normal, perfectly focused vision

A cycloplegic refraction is a procedure used to determine a person's complete refractive error by temporarily paralyzing the muscles that aid in focusing the eye. Cycloplegic eye drops are used to temporarily paralyze or relax the ciliary body, or focusing muscle, of the eyes. When a cycloplegic refraction is performed, the doctor is trying to find out what the full refractive error is without any influence of the person being tested. For example, when a doctor 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 would someone need a cycloplegic refraction?

Sometimes when people come in for an eye examination, things are not always what they seem. An example of this that occurs in all eye care practices is the case of the fluctuating prescription.

Let's say that a person came into the office. The examination went smoothly and a new prescription for eyeglasses was determined and the new glasses were made. Well, a few days later the patient came back in complaining that while the glasses helped a little, her eyes still felt extremely tired and the glasses just did not seem right.


The doctor then checks the prescription again by performing a refraction. However, this time, the doctor found that the patient could actually see 20/20 through a variety of lens powers. The doctor determined that this patient was indeed farsighted, but also had a very large amplitude of accommodation. This means that the patient can focus a very large amount and is able to compensate in some instances for her farsightedness. This sounds like a good thing but when a person has to compensate that much and hold it for an extended period of time, it ends up being exhausting for them. 

This ability to over-focus during an eye exam can lead to inaccurate results and glasses that do not work. When this occurs, the doctor has to find a way to control the person's ability to accommodate. A careful refraction can help accomplish this. However, the best way to do this is to install a cycloplegic eye drop. The drop temporarily paralyzes 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 doctor to measure the entire amount of farsightedness. The doctor can then measure the 'true' refractive error.

There are three main types of patients that doctors like to perform a cycloplegic refraction:

  • Children  - A cycloplegic refraction is often performed on children. Children have an ability to accommodate 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 a doctor performs a cycloplegic refraction, they can be confident they are measuring the full prescription.
  • Adults experiencing pre-presbyopia - Presbyopia is the condition that affects all of us around age 40-45. We begin to lose our ability to focus on near objects. This is why people over 40 are often using reading glasses or wearing a bifocal. However, in some people, they experience a lot of symptoms during pre-presbyopia. They are unable to focus quickly from near to distance and back and are easily frustrated. It also causes night time driving symptoms as well. The best way to isolate the problem is for the doctor to perform a cycloplegic refraction.
  • LASIK - People that have decided to have laser vision correction or other refractive surgery must undergo a cycloplegic refraction. This is performed to ensure that their accommodation does not interfere with the results. The surgeon needs to know exactly how much of the person's vision problem to correct with the laser.

Do cycloplegic eye drops have any side effects?

Cycloplegic eye drops do tend to sting for a few seconds when instilling them into the eye. 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. Cycloplegic eye drops can also cause an acute angle closure glaucoma attack in people with very narrow angles. Your eye doctor will check to make sure you are not at risk for glaucoma before instilling the eye drops.

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