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Renita Sebastin, Nish Mohith Kurukuti, Eleftherios I Paschalis, Kevin Houston; Force to elevate eyelid and allow blink in magnetic correction of blepharoptosis: preliminary results. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2225.
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© ARVO (1962-2015); The Authors (2016-present)
To measure the force needed to mechanically treat symptoms of severe ptosis. Specifically, this study seeks to use magnetic force to open the eyelid while still allowing voluntary blink control, removing the obstruction of the visual axis, and restoring sight to the ptotic eye(s). These measurements have not been reported previously and are needed for the development of a magnetic levator prosthesis (MLP) (Houston et. al. 2014). The MLP consists of three small magnets embedded in silicone (lid array) attached to the lid with medical adhesive, and a larger magnet, cased in a housing, in a spectacle frame above the eye.
Subjects (n=30) enrolled in this study were required to have ptosis occluding the visual axis in the resting state with no frontalis drive. A force transducer was taped to the eyelid skin of the ptotic eye(s) to pull open the eye nine times per patient. Force measurements were taken from when the eyelid started to open until the interpalpebral fissure (IPF) seemed to be at a natural fully open position. To measure the force that inhibited the patient’s blink, nine magnets of varying strength (4.4g – 52.1g) were individually placed at the brow while the patient wore an array attached to the affected lid. Order of force testing was counterbalanced with double blind methodology.
The sample mean IPF (n=7) when pulled open was 7.29 ± 1.30mm requiring a force of 25.05 ± 8.27g. Figure 1 shows force plotted against IPF in each subject and indicates an overall positive correlation between increasing force and IPF. The average force needed to start opening the eye was 1.66g, which is within the field of a ½” x ½” Neodymium magnet at a distance up to ~20mm. Average force for impedance of spontaneous blink was 30.61 ± 16.15g, and 40.25 ± 12.05g for volitional blink.
Further testing with more subjects will be done to investigate variance due to qualities such as age or gender. The maximum force for this magnet system to allow for blink reanimation and reduce subject discomfort was measured and these values will be used to better fit our patients with the MLP. Forces for blink impedance will also be used to calculate the minimum thickness of the magnet housing on the spectacle frame so that the subject is able to blink naturally while still experiencing consistent unobstructed vision.
This is a 2020 ARVO Annual Meeting abstract.
Figure 1. Each subject’s range of force x IPF for all trials.
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