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A new digitised screen test for strabismus measurement.
Theo Oltrup1, Marvin Bende1, Celine Henseling1
1Div. Exp. Ophthalmic Surgery and Refractive Surgery, Dept. of Ophthalmology, University Tuebingen, Germany.
Zeitschrift Fur Medizinische Physik
|August 12, 2022
Summary
This study introduces a digital tangent screen test for ocular motility analysis, offering a faster and simpler alternative to traditional methods. The new system achieves high accuracy for squint and gaze direction measurements, with minimal uncertainty.
Area of Science:
- Ophthalmology
- Medical Technology
- Optometry
- Biomedical Engineering
Background:
- Traditional ocular motility analysis, such as the Harms and Hess tests, relies on subjective measurements and can be time-consuming.
- Existing methods often require a light pointer held by the patient, introducing potential variability.
- There is a need for more objective, efficient, and accurate tools for measuring squint angle and gaze direction.
Purpose of the Study:
- To present a novel digitized tangent screen test for ocular motility analysis.
- To evaluate the measurement uncertainty of this new digital system for assessing squint angles and gaze direction.
- To compare the digital test's efficiency and documentation capabilities against conventional methods.
Main Methods:
- Development of a digital tangent screen system using an image beamer, a position sensor for head orientation, and a distance sensor for fixation distance.
- Mathematical modeling to determine the relationship between measured angles and influencing factors on measurement uncertainty.
- Application of the error propagation law to calculate combined standard measurement uncertainties at a test distance of 2.5 meters.
Main Results:
- The digital system achieved a combined standard uncertainty of ≤ 0.43° for squint angle and ≤ 3.13° for gaze direction angle at 2.5m (95% confidence level).
- Individual uncertainties were quantified, with the position sensor contributing the most significantly (1.55°/1.01°).
- The maximum valid test distance for the digital screen test was determined to be 3.8 meters.
Conclusions:
- The digitized tangent screen test is a compact, portable, and efficient tool for ocular motility analysis.
- It simplifies examination procedures and documentation compared to traditional methods.
- While sensor drift affects gaze direction uncertainty, it does not impact squint angle measurements due to the system's inherent principles, offering reliable clinical utility.
