Maximum angle of horizontal strabismus consistent with true stereopsis.

Area of Science:

• Ophthalmology
• Vision Science
• Clinical Research

Background:

• Strabismus significantly impacts visual development and function.
• Accurate assessment of stereopsis in strabismus is crucial for treatment planning.

Purpose of the Study:

• To evaluate stereoacuity tests in patients with horizontal strabismus.
• Determine the maximum horizontal strabismus angle for true stereopsis.
• Assess the rate of false-positive results with different tests.

Main Methods:

• Prospective study of 186 patients (age ≥5) with constant horizontal strabismus.
• Stereoacuity measured using Titmus Fly, Animals, Circles, original Preschool Randot, and Frisby tests.
• Defined false-positive results (>20 prism diopters [PD]) and true-positive results based on established criteria.

Main Results:

• False-positive rates varied: Titmus Fly (6%), Animals (10%), Circles (35%), Randot (10%).
• No false-positive results occurred with the Frisby test.
• True stereopsis was absent in patients with >10 PD deviation; threshold may be as low as 4 PD.

Conclusions:

• Titmus tests (Fly, Animals, Circles) have limitations due to monocular clues.
• Frisby test is valuable for rapid presence/absence assessment of stereopsis.
• New Preschool Randot test quantifies stereopsis; true stereopsis is rare with horizontal deviation >4 PD.