[Detection and diagnosis of small ocular misalignment with the Purkinje reflex pattern method]

Application test for an automatic classification strategy for ocular alignment data for the detection of ocular misalignment in strabismic patients.

Photographic Purkinje Reflection Pattern Evaluation was used a) with a handheld device for the detection and measurement of ocular misalignments in near fixation (group 1, n = 64 strabismic patients) and b) with a stationary device for the detection and measurement of ocular misalignments in near fixation (group 2, n = 38 patients) and in distance fixation (group 3, n = 36 patients). The orthoptic diagnoses were mostly primary and secondary microtropia with manifest angles of strabismus from naught or 0.25 degrees to 3-4 degrees, with maximum angles up to 6-9 degrees. The ocular alignment data were classified using the computer based strabismus index procedure. This strategy relies on thresholds derived from means and standard deviations in orthotropic control populations. In this way the data sets were classified automatically as "no referral" or "referral". In addition, an automatic diagnosis of the type of misalignment was given and the results were compared to the orthoptic gold standard.

The sensitivity for the detection of a manifest ocular misalignment was a ca. 80% in group 1 and 2, and 90% in group 3, with specificities from 90% to 100%. All manifest angles of strabismus larger than 1 degree were correctly classified as "referral". There was good agreement between the diagnoses of the type of misalignment in most cases. Discrepancies were observed with very small ocular misalignments or with incomplete data sets, or they could be explained by a switch of fixation. The amount of the misalignment varied markedly as compared to the orthoptic measurement in a number of cases.

The examination allows for a detection of small manifest ocular misalignments with a very high sensitivity. The deviated eye and the type of the misalignment in the primary position are evaluated automatically by a data base computer algorithm. The differences between the measured angles of strabismus indicate that the photographic examination conditions and the orthoptic simultaneous prism and cover test conditions are not exactly alike. Purkinje Reflection Pattern Evaluation represents a step towards an examiner-independent measurement of the angle of strabismus.