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Comparing a Novel Motorized Push-Up Ruler with Conventional Subjective Methods for Measuring the Amplitude of
Sven Schumayer1,2,3, Jona Laukhuf3, Torsten Straßer2,4
1Faculty Mechanical and Medical Engineering (MME), Institute for Microsystems Technology (iMST), Furtwangen University, Furtwangen, Germany.
Purpose:
Determination of the amplitude of accommodation (AoA) is a clinical technique used in ophthalmology and optometry to assess the eye's ability to focus on near objects. This study compares the reliability of a novel motorized push-up variant with conventional manual push-up and push-down methods for the determination of AoA in 26 emmetropes.
Methods:
The motorized push-up method reduces limitations of the manual methods, such as differences due to varying examiner abilities, ruler placement (forehead, zygomatic bone, spectacle plane), and inconsistent target movement speeds. This is achieved by providing a participant-controlled, constant target movement of 2 cm/s, with the medial zone of the zygomatic bone as the reference point for ruler placement. Additionally, digital image-based and traditional ruler-based AoA measurements were compared. The participants' impressions of the three methods were assessed based on ease of use, confidence in measurement reliability, and comfort of experience, using a questionnaire.
Results:
The comparison of the AoA across the methods revealed no statistically significant differences. However, the concordance correlation coefficient was highest between the motorized and manual push-up method (ρc = 0.72). All methods showed good test-retest reliability with the highest ICC found for the motorized push-up method (0.83), which also had the narrowest limits of agreement interval for accommodative demand (3.22 cm). Beyond digital and ruler-based measurements showed underestimation by both rulers, with a mean bias of 0.3 cm for the motorized ruler compared to about 2.0 cm for the conventional ruler. The questionnaire responses suggest that the motorized version outperforms the manual versions being 5 times more likely to score higher for ease of use and 6 times more likely for confidence in measurement reliability.
Conclusion:
These findings demonstrate that the motorized push-up method effectively measures the AoA, reduces interfering factors, and provides higher reliability without compromising precision, making it a valuable alternative to conventional methods.
