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D. Vazquez, A. Seidemann, H. Altheimer, F. Schaeffel, D. Uttenweiler; Optical Tracking of Head Movement Patterns When Wearing Spectacle Lenses With Different Radial Power Profiles. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3981.
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The aim of this study was to test the comfort and wearability in near vision tasks of non-standard spectacle lenses with an optical tracking system. For this purpose, head movement patterns were analysed for radial refractive gradient (RRG) spectacle lenses with different types of radial symmetric power increase (addition). RRG spectacle lenses are of potential interest in reducing myopia progression.
Ten subjects (>-0.75 D Spherical Equivalent with no optical correction or contact lenses) performed three near vision tasks (reading texts on a computer screen and on a table, handwriting) in 4 different situations: (1) wearing no lens and frame; (2) wearing a trial frame with no lenses; (3) wearing a frame with lenses with a central plano area and a radial continuous symmetric addition; (4) wearing a trial frame with lenses with a central plano area and a radial discontinuous symmetric addition. Linear and angular head movements were analysed with an optical tracking system (OptitrackTM) based on the POSIT algorithm.
The linear and angular resolution of the optical tracking system for head movements ranged between 1 and 2 mm and 1° and 2°, respectively. It was found that a distinct difference existed between the head movement patterns when wearing RRG lenses versus no correction. These differences increased with decreasing object distance of near vision tasks. The angular movements of the head increased up to 50% of its reference values without correction, the subjects strongly bent forward, and the head movements became more irregular during handwriting.
The optical tracking system provided useful data for the characterization of the wearing comfort of RRG spectacle lenses. Head movement patterns were clearly affected by the imposed peripheral defocus and distortions that were generated by this kind of lenses. These results suggest that an extensive analysis of the wearability of RRG lenses should be carried out since the head movement patterns were severely altered during near vision tasks.
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