The effects of the extraocular muscles on eye impact force-deflection and globe rupture response

There are over 1.9 million eye injuries per year in the United States, with blunt impacts the cause of approximately one-half of all civilian eye injuries. No previous experimental studies have investigated the effects of the extraocular muscles on the impact response of the eye. A spring-powered blunt impactor was used to determine the effects that the extraocular muscles have on the force-deflection and injury response of the eye to blunt trauma. A total of 10 dynamic impact tests were performed at 8.2+/-0.1m/s on five human cadaver heads. With the extraocular muscles left intact, the average peak force was found to be 271+/-51N at 7.5+/-0.9mm posterior translation; with the muscles transected, the average peak force was 268+/-26N at 7.6+/-1.3mm of posterior translation. From the data available from this study, the peak impact force and overall amount of translation during the impact are not affected by the extraocular muscles. Additionally, from the data presented in this study, the eyes with the extraocular muscles left intact do not rupture with a different injury pattern or display an increased risk for rupture than the eyes with the extraocular muscles transected. Therefore, it is believed that the effect of the extraocular muscles is not sufficient to drastically alter the response of the eye under dynamic impact. This information is useful to characterize the boundary conditions that dictate the eye response from blunt impact and can be used to define the biofidelity requirements for the impact response of synthetic eyes.