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The Prism Adaptation Study (PAS)

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details. Identifier: NCT00000121
Recruitment Status : Completed
First Posted : September 24, 1999
Last Update Posted : September 17, 2009
Information provided by:
National Eye Institute (NEI)

Brief Summary:

To determine whether the preoperative use of prisms in eyeglasses can improve the outcome of surgery for acquired esotropia, a type of strabismus.

To determine whether patients who respond to prism adaptation by developing a new stable angle of -deviation have a better surgical result than do patients who do not respond to prism adaptation.

To determine whether patients who respond to prism adaptation are more accurately corrected by operating for the prism-adapted angle or the original angle of deviation.

To determine the usefulness of certain input variables (e.g., age at the time of surgery, size of the deviation, visual acuity, binocular function, refractive error) in predicting which patients are more likely to benefit from prism adaptation.

Condition or disease Intervention/treatment Phase
Esotropia Device: Prisms in Eyeglasses Phase 3

Detailed Description:

Acquired esotropia (crossed eyes that develop after a child reaches the age of 6 months) accounts for 25 percent of all patients with misaligned eyes. Surgery to correct esotropia is done primarily to attain functional use of the two eyes together. The cosmetic aspect of the surgery is secondary. In 40 to 50 percent of cases, more than one operation is needed to accomplish the primary goal, and in some cases even three and four operations are needed.

Preliminary studies from two eye care centers reported that the use of prisms on eyeglasses for about a month before surgery led to good results after a single operation in more than 90 percent of patients. These uncontrolled preliminary studies pointed to the need for a multicenter, randomized, controlled clinical trial designed to prove or disprove scientifically the beneficial effect of prisms.

The Prism Adaptation Study was a double randomization trial involving 286 patients. Three-fifths of the patients were randomly selected for prism adaptation before surgery. Of the patients who responded to the prisms, one-half were randomly selected to have surgery based on the amount of prism required to stabilize the deviation, and the other half had surgery based on the amount of esotropia originally measured. Patients who did not respond to the prisms also had surgery based on the amount of esotropia measured, as did the two-fifths of the patients who did not undergo prism adaptation.

Patients were examined postoperatively at 1 week, 1 month, 3 months, 6 months, and 1 year. An independent examiner, masked to the treatment assignment, evaluated the patient at the 6-month followup. The results were analyzed to determine whether the outcome was better in patients who underwent prism adaptation or in those who underwent conventional treatment. Because the examiner did not know what type of treatment a patient had received, he or she would have no bias in evaluating the results.

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Study Type : Interventional  (Clinical Trial)
Allocation: Randomized
Primary Purpose: Treatment
Study Start Date : March 1984
Actual Study Completion Date : May 1989

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Information from the National Library of Medicine

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Ages Eligible for Study:   3 Years and older   (Child, Adult, Older Adult)
Sexes Eligible for Study:   All
An eligible male or female must have been age 3 years or older (adults were included) and must have had esotropia that occurred at age 6 months or older, with no history of previous eye muscle surgery.
Layout table for additonal information Identifier: NCT00000121    
Other Study ID Numbers: NEI-20
First Posted: September 24, 1999    Key Record Dates
Last Update Posted: September 17, 2009
Last Verified: September 2009
Keywords provided by National Eye Institute (NEI):
Additional relevant MeSH terms:
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Ocular Motility Disorders
Cranial Nerve Diseases
Nervous System Diseases
Eye Diseases