As a practicing optometrist, Dr. W. answers thousands of patient questions a year. Many questions are in regards to eye examinations and what eye doctors are really looking for. Over the next few days Dr. W. will explain what goes on in the eye exam. In Part 2 of the Eye Exam Explained series, he explains the muscles of the eye.
An eye exam consists of much more than simply determining if a patient needs glasses or not. Assessment of eye muscle movements is an essential component of a complete eye exam.
There are six muscles responsible for movements of the eye itself. Figure 1 is a schematic representation of these muscles. Movement of these so-called extraocular muscles allow your eye to move up, down, left, right and rotate. The muscles of the eye also play a major role eye alignment. Symptoms such as double vision and headaches may result from eye muscle dysfunctions.
The Broad H Test
An eye doctor will always check the integrity and efficiency of these muscles by having you follow (with your eyes) a penlight or other small object in the general shape of an “H.” This test is called the “broad H test” and is useful in diagnosing deficiencies in movement. The doctor is looking for restrictions of movement or differences of movement between the two eyes as the patient looks in extreme gazes.
The Cover Test
Eye alignment is one of the most important assessments in an eye exam. When we view objects at a distance our eyes must be perfectly aligned in order to experience a single clear image. When we view near objects (at a distance of 16 inches or so) our eyes must converge or come together a bit. The cover test is usually performed at distance and near. The eye doctor will have you look at objects and alternatively cover each eye then swing the cover paddle back and forth to look for small deviations in alignment. Deviation of the eyes and the tendency to deviate are noted.
What conditions is the eye doctor looking for?
Some of the most common conditions of the eye muscles that can be detected with the broad H test or cover test are:
Strabismus – eye turn
Amblyopia – lazy eye
Saccadic deficiency – inability for eyes to track properly
Convergence insufficiency – inability to converge up close
My goal as a doctor is to provide the best possible vision to everybody. I want to empower my patients with knowledge and understanding regarding their eyes. Evaluation of eye alignment and ocular motility are essential components in the formal eye examination. Stay tuned for further articles explaining what happens during the eye exam.