An Overview of Cycloplegic Refraction

Situations in Which Eye Dilation Is Necessary

Girl wearing glasses looks at a molecular structure.

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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 myopia, hyperopia, 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.

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, and at the same time these drops also cause the pupils to dilate for a dilated examination. However sometimes the doctor might have you back for a cycloplegic refraction because certain drops are better for this specific exam.  

Cycloplegic refraction is performed to ascertain the cause of a refractive error without any adjustment of the focus by the person being tested.

For example, when a doctor performs refraction without cycloplegic eye drops, there could a conscious or unconscious influence on the readings by the patient. Sometimes the patient may be subconsciously over-focusing. This may make someone appear more nearsighted or less farsighted than they actually are. 


Sometimes when people come in for an eye examination, things are not always what they seem. An example of this that occurs with fluctuating prescriptions.

Let's say that a person comes into a doctor's office. The examination goes smoothly and a new prescription for eyeglasses is made. A few days later, the person comes back in claiming that the glasses helped a little but that the eyes are extremely tired and the glasses "did not seem right." 

Upon hearing the news, the doctor rechecks the prescription by performing regular refraction. However, this time around, the patient is able to see 20/20 through a variety of lens powers.

In instances like this, the doctor will realize that the patient was indeed farsighted but had a large amplitude of accommodation. This means that the patient was able to compensate for the farsightedness by adjusting the accommodation (strong ability to focus) of the eye.

Cycloplegic drops paralyze the focusing muscles of the eye and prevent the accommodating reflex by which focus is automatically adjusted. Doing so ensures a more accurate diagnosis and prescription.

While the drops can cause short-term blurriness and light sensitivity, it allows the doctor to measure the entire amount of farsightedness. The doctor can then measure the true refractive error and adjust the prescription accordingly.


Cycloplegic drops are not needed by everyone searching for a new pair of eyeglasses. They are used for a very specific purpose in those with a large amplitude of accommodation. There are three groups of people that cycloplegic refraction may benefit:


A cycloplegic refraction is often performed on children. Children have the 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.


Presbyopia is a condition that affects all of us around the age of 40 to 45. It is when 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, symptoms may develop much earlier (a condition referred to as pre-presbyopia). They will be unable to focus quickly from near to far distance or be unable to focus properly at night. The best way to isolate the problem is for the doctor to perform cycloplegic refraction.

LASIK Candidates

People who decide to have laser vision correction (LASIK) or other refractive surgery must undergo 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.

Side Effects

Cycloplegic eye drops do tend to sting for a few seconds when first applied to the eye. Depending on the type of drop used, they can cause blurriness and light sensitivity for several hours. Some people may even continue to have blurriness the next day.

Protective disposable sunglasses are typically provided to prevent squinting and discomfort as well as to protect the eye from sun damage.

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.

If undergoing a procedure involving cycloplegic eye drops, be sure to bring someone with you to drive you home. Do not use heavy machinery or cutting utensils until your vision has completely normalized.

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