Intraocular Muscle Function

IOM function.

To assess the function of the extraocular muscle to assist with diagnosis of strabismus, amblyopia, and other ocular disorders.

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings

  • Normal range of ocular movements in all gaze positions.

Critical Findings and Potential Interventions


(Study type: Sensory (ocular); related body system: Nervous system.) Evaluation of ocular motility is performed to detect and measure muscle imbalance in conditions classified as heterophorias or heterotropias. This evaluation is performed in a manner to assess fixation of each eye, alignment of both eyes in all directions, and the ability of both eyes to work together binocularly. Heterophorias are latent ocular deviations kept in check by the binocular power of fusion and made intermittent by disrupting fusion. Heterotropias are conditions that manifest constant ocular deviations. The prefixes eso- (tendency for the eye to turn in), exo- (tendency for the eye to turn out), and hyper- (tendency for one eye to turn up) indicate the direction in which the affected eye moves spontaneously. Strabismus is the failure of both eyes to spontaneously fixate on the same object because of a muscular imbalance (crossed eyes). Amblyopia, or lazy eye, is a term used for loss of vision in one or both eyes that cannot be attributed to an organic pathological condition of the eye or optic nerve.

There are six extraocular muscles in each eye; their movement is controlled by three nerves. The actions of the muscles vary depending on the position of the eye when they become innervated. The cover test is commonly used because it is reliable, easy to perform, and does not require special equipment. The cover test method is described in this study. Another method for evaluation of ocular muscle function is the corneal light reflex test. It is useful with patients who cannot cooperate for prism cover testing or for patients who have poor fixation.


  • Detection and evaluation of extraocular muscle imbalance.

Interfering Factors

Factors that may alter the results of the study

  • Rubbing or squeezing the eyes may affect results.

Potential Medical Diagnosis: Clinical Significance of Results

The examiner should determine the range of ocular movements in all gaze positions, usually to include up and out, in, down and out, up and in, down and in, and out. Limited movements in gaze position can be recorded semiquantitatively as –1 (minimal), –2 (moderate), –3 (severe), or –4 (total).

Abnormal Findings In:

  • Amblyopia
  • Heterophorias
  • Heterotropias
  • Strabismus

Nursing Implications

Before the Study: Planning and Implementation

Teaching the Patient What to Expect

  • Inform the patient this procedure can assist in evaluating eye muscle function.
  • Review the procedure with the patient. Address concerns about pain and explain that no discomfort will be experienced during the test.
  • Inform the patient that a health-care provider (HCP) performs the test in a quiet room and that to evaluate both eyes, the test can take 2 to 4 min.
  • The study is performed by testing one eye at a time. The patient is given a fixation point such as the testing personnel’s index finger. For pediatric patients, an object, such as a small toy, can be used to ensure fixation.
  • Instructions are given to gaze at and follow the fixation point as it moves. Then the procedure is repeated using the other eye.
  • This procedure is performed first at a distance and then near with and then without corrective lenses. The examiner should determine the range of ocular movements in all gaze positions, usually to include up and out, in, down and out, up and in, down and in, and out.

Potential Nursing Actions

  • Obtain a history of the patient’s known or suspected vision loss; changes in visual acuity, including type and cause; use of glasses or contact lenses; eye conditions with treatment regimens; eye surgery.
  • Advise removal of contact lenses or glasses prior to the study.
  • Explain the importance of keeping the eyes open for the test.

After the Study: Potential Nursing Actions

Treatment Considerations

  • Explain that referral for special therapy to correct the anomaly may be necessary.
  • Referred therapies may include glasses, prisms, eye exercises, eye patches, or chemical patching with drugs that modify the focusing power of the eye.
  • Explain that the chosen mode of therapy involves the process of mental retraining but does not correct vision.
  • Discuss how the chosen therapy is the process by which the brain becomes readapted to accept, receive, and store visual images received by the eye that results in vision correction.
  • Emphasize that therapeutic success is dependent upon the patient being prepared to be alert, cooperative, and properly motivated.

Followup Evaluation and Desired Outcomes

  • Acknowledges the possibility of impaired activity related to vision loss, potential loss of driving privileges, and self-image adjustments related to wearing corrective lenses.

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