How Doctors Test Your Eye Muscles

A Doctor performing an Eye Examination
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Eye muscle testing is done to reveal restricted or abnormal eye movement. This may be due to eye muscle weakness or another issue with functioning and can indicate an optical condition such as strabismus (i.e., being cross-eyed). It may sound like something only done in special cases, but it's actually a preliminary test and an essential part of any comprehensive eye examination.

Your ophthalmologist may also refer to eye muscle testing as extraocular movement testing or ocular motility testing. Here's what you can expect at your appointment.

How Eye Muscle Testing Is Performed

The test itself is simple. Your eye doctor or technician will ask you to sit up straight while you stare at an object in front of you, which is usually a pen, fixation light, or small picture held 12 and 16 inches away.

They will move the object up and down and side to side in an H-shaped pattern.

You are asked to follow the object with your eyes while keeping your head still.

What Your Doctor Is Looking For

In performing eye muscle testing, your doctor will look for the following:

Shaking of the Eyes

Involuntary, rhythmic shaking or wobbling of the eyes characterizes a condition known as nystagmus. The shaking can be horizontal, vertical, or diagonal. In most cases, the condition is present from birth and can be a part of other developmental syndromes.

Nystagmus can be present constantly or exacerbated by certain eye movements. If it's severe enough, visual acuity will suffer as the eyes are constantly moving back and forth.

People with nystagmus can sometimes direct their head or eyes in a certain way that reduces symptoms. This is called a null point.

Misalignment

Your doctor will look to see if one or both eyes is turned in, out, up, or down. This indicates strabismus, and people with the condition are often referred to as "cross-eyed" or "wall-eyed."

Strabismus can be congenital (from birth) or developed later in life. It can also cause double vision (see below). The condition can cause problems with normal depth perception and put one at risk for developing amblyopia ("lazy eye").

Amblyopia begins at a very young age when the eye is not stimulated or used properly. Permanently decreased vision can occur.

Eye Movement Accuracy

"Overshooting" or "undershooting" of certain eye muscles simply means that your eye movement accuracy is off. These signs could point to inherited conditions such as Duane's retraction syndrome, a form of strabismus that affects horizontal eye movement.

Mechanical Restrictions

These are commonly found in traumatic injuries, such as a blow to the eye. The bones that make up the floor of the eye orbit are thin. Blunt trauma to that area can blow out these bones, causing an eye muscle to get trapped or hooked in the bone.

Double Vision

Eye muscle testing can help your doctor determine the cause of double vision, or diplopia, which can occur in one or both eyes. Medical professionals always take double vision seriously as it can be a sign of neurological problems.

Potential muscular causes of double vision include strabismus, myasthenia gravis (a neuromuscular condition causing muscle weakness), a side effect of hyperthyroidism (Graves' disease), and damage to the nerves surrounding eye muscles.

If you experience sudden-onset double vision, see a doctor immediately.

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