Purpose: The purpose of this study was to analyze the reliability of the fixation preference test (FPT) in the detection of amblyopia, and to determine interexaminer agreement.
Methods: Eighty patients whose visual acuity could be tested objectively and had a horizontal misalignment of more than 10 prism diopters were enrolled. The best corrected visual acuity (BCVA) and orthoptic findings were all recorded. Non-preferred eye in primary position and fixation preference grade were assessed independently by two masked experienced examiners. The primary outcome measures were reliability of FPT in terms of its correlation with BCVA and interexaminer agreement.
Results: There was no significant correlation between fixation preference grades and interocular visual acuity difference as well as the type and amount of deviation, the presence of fusion, stereopsis, anisometropia, and previous strabismus surgery for none of the examiners (p > 0.05 for all). Sensitivity was 52.0% for examiner 1 and 54.0% for examiner 2 while specificity was 50.0 and 46.7%, respectively. Interexaminer agreement was 76.7% (p < 0.001) for all patients.
Conclusions: FPT is widely used in children particularly when the visual acuity cannot be determined in an objective manner. The test may not be accurate and reliable in the detection of amblyopia and also in predicting the visual acuity difference between both eyes, even though it was found to show a high degree of agreement between examiners. In conclusion, it should be kept in mind that the reliability of FPT may be limited and the results should be interpreted with caution and be supported by other tests.
Keywords: Amblyopia; Fixation preference test; Interexaminer agreement; Strabismus.