Intra-observer reliability of the Harms tangent screen test

The objective of this study is to evaluate the intra-observer reliability of the Harms Tangent Screen Test (HTS) for ocular motility analysis in eyes with diplopia due to concomitant, paralytic, or restrictive strabismus.

This prospective clinical case study was conducted at the Department of Ophthalmology, Goethe University, Frankfurt am Main, Germany. Squint angles were assessed subjectively in patients aged ≥18 years, presenting with diplopia due to concomitant, paralytic, or restrictive strabismus, using HTS across nine diagnostic gaze positions (0°; 25°). Repeatability was assessed by performing two consecutive measurements per patient by the same examiner. Measurement consistency was evaluated using the intraclass correlation coefficient (ICC) and the 95% limits of agreement (LOA).

A total of 58 patients (46.6% women) with a mean age of 54.0 ± 17.12 years were included. ICCs were highest for the horizontal squint angles of the nine gaze positions (≥0.99), followed by the vertical (0.96-0.99) and the torsional squint angles (0.93-0.98). Mean difference between the two measurements was ≤0.5° for the primary gaze position across all directions. LOA ranged from -3.1°; 2.9° (horizontal), -2.0°; 2.2° (vertical), and -3.6°; 3.1° (torsional). Maximum differences between the two measurements in the primary gaze position were ±8.0° (horizontal), ±5.0° (vertical), and ±6.0° (torsional).

The HTS demonstrates good repeatability across all nine gaze positions in the horizontal, vertical, or torsional squint angles, indicating consistent measurement reliability regardless of gaze position.