title: Re-evaluation of the four prism diopter base-out test.
abstract: The four prism diopter base-out (4 delta BO) test is often recommended for use as an objective assessment of binocular visual function in patients with suspected microstrabismus or central suppression; however, many aspects of the test are unknown. In this series of investigations we evaluated: (1) inter-observer agreement between 2 examiners, using 15 subjects; (2) types of eye movements made and prevalence of the various response types demonstrated in 212 children and 116 adults with normal binocular vision, and 10 children and 4 adults with abnormal binocular vision; and (3) repeatability of test results for 22 subjects evaluated on two separate occasions. In addition, using an SRI Eye-tracker, we documented the eye movements made while testing 2 subjects with small angle strabismus and 4 subjects with normal binocular vision. We found the following results: (1) inter-observer agreement is high; (2) both children and adults exhibit many atypical responses, whether or not they have normal binocular vision; (3) diplopia awareness does not differentiate between subjects with normal and abnormal binocular vision; and (4) 4 delta BO test results are not repeatable. Due to frequent atypical and variable responses in subjects with or without normal binocular vision, we suggest the examiner use caution when making a diagnosis based solely on the 4 delta BO test.
authors.affiliation: Illinois College of Optometry, Chicago.
authors.forename: K A
authors.initials: KA
authors.lastname: Frantz
authors.forename: S A
authors.initials: SA
authors.lastname: Cotter
authors.forename: B
authors.initials: B
authors.lastname: Wick
mesh_terms: D000328:Adult; D002648:Child; D002675:Child, Preschool; D005133:Eye Movements; D006801:Humans; D015588:Observer Variation; D015203:Reproducibility of Results; D013285:Strabismus / Q000175:diagnosis*; D014786:Vision Disorders / Q000175:diagnosis*; D014787:Vision Tests; D015348:Vision, Binocular / Q000502:physiology*