UCLA researchers have developed a software-based digitizer for Hess Screen Test (HST) charts that automates extraction of gaze misalignment measurements across the visual field, converting paper charts into precise numerical eye-angle data. The system is faster, more repeatable, and more scalable than manual annotation. IOVS
The Hess Screen Test is used clinically to assess binocular misalignment by having patients fixate at grid points and drawing lines between gaze positions on a paper chart. While the HST yields quantitative misalignment information overall, extracting exact numerical values for each tested gaze point is done manually—this is time-consuming, variable between raters, and limits large-scale or longitudinal studies. There is a need for a more objective, rapid, and reproducible method to digitize HST charts. IOVS
The approach involves scanning or imaging the paper HST chart, applying image processing to correct for rotation, segment the relevant color markings, remove grid overlays, and detect intersections of drawn gaze lines at gaze fixation points. A custom corner detector identifies the positions of gaze lines, which are then converted to horizontal and vertical eye angles using the tangent-scale of the HST chart. The system includes a graphical user interface to allow manual correction if needed. In testing with charts from patients with sagging eye syndrome, the software digitizes an HST chart in about 20 seconds versus ~5 minutes manually, with small errors in angle estimates. IOVS
Much faster quantification: chart digitization takes ~20 seconds vs ~5 minutes manually. IOVS
Improved repeatability and consistency in measurement. IOVS
Produces numerical angle data (horizontal/vertical) for each gaze fixation point. IOVS
Reduces human error and variability. IOVS
Supports large-scale analysis of binocular misalignment (e.g. across many patients or repeated over time). IOVS
Clinical ophthalmology: diagnostic clinics using HST to assess and monitor ocular misalignments.
Research studies examining binocular alignment disorders (e.g. sagging eye syndrome, strabismus) or tracking changes over time.
Telemedicine or remote screening settings where paper HST charts are used and digitization improves accessibility.
Automated ophthalmic data analysis pipelines.
Integration into electronic medical records and analytics for large patient populations.
Method tested with 19 patient HST charts (from patients with sagging eye syndrome). IOVS
Automated extraction was fully accurate in many charts; some required minor manual corrections. IOVS
Error margins versus manual: ~0.6° horizontal, ~0.5° vertical, ~0.9° overall in gaze angle. IOVS
Publication: Image Processing for Digitization of Hess Screen Test (HST) Charts. ARVO IOVS, 2024, Vol. 65, 1146. DOI: 10.1167/iovs.65.7.1146 IOVS