[Measurement of the Strength of Human Musculus Orbicularis Oculi Using Video Analysis]

Introduction Current methods to measure the of strength of the musculus orbicularis oculi are limited by high proneness to examiner error or by their complex and impracticable set-ups. Our aim was to develop a simple and practicable method to measure eye lid power via video analysis. Methods 50 healthy subjects were included. A deformable single use lid speculum was used. Forced maximum lid closure was recorded via a video slit lamp. Analysis of the video data was performed with open source tracking software. The maximum and minimum distances of the inserted lid speculum were detected. The rigidity and mechanical characteristics of the lid speculum were tested separately. In this way, lid power could be determined by analysis of the maximum compression of the lid speculum. To explore the impact of age and sex on eye lid power, Pearson's correlation coefficient was evaluated. ICC (intra class correlation) was analysed as a measure of reliability. Results In three repeated measurements in 9 subjects, an ICC of α = 0.91 was detected. With 50 healthy subjects, the range of lid power was 0.62 - 4.72 N. No correlation was found between the age of the subjects and eyelid power (Pearson's correlation coefficient = 0.054). A weak correlation was found between the sex of the subjects and eyelid power. For female subjects, the mean power was 1.82 N and for male subjects 2.58 N (Pearson's correlation coefficient = 0.428). Discussion A test series of 50 healthy subjects exhibited a wide range of lid power. The wide range makes it difficult to distinguish between pathological and normal eyelid power. The major application field of the method may therefore be in inner-individual measurements of known eyelid pathologies, such as paresis of the facial nerve or ocular myasthenia.