Poster P20 - Mechanics Testing of Eye Muscle to Understand Tissue Properties and Behavior

Introduction: Limited data exists on the mechanical properties of eye muscles and many of these studies are outdated or use outdated data. Additionally, most studies focus on skeletal muscles, which are stiffer than eye muscles and have large variance in mechanical properties. Regardless of this, common trends can be observed within existing datasets of muscle tissue tests. The purpose of this study is to determine if these common trends also exist among eye muscle and to obtain quantifiable, repeatable data on eye muscle properties. The data obtained will be invaluable for advanced medical applications, providing insights into the mechanical behavior of eye muscles and potentially informing the development of new treatments or interventions.

Materials and

Methods: Uniaxial tensile testing and creep tests were performed using the BioTester (CellScale). For uniaxial tensile testing, the displacement control was utilized with a linear ramping rate of 1000um/ 60 seconds. For the creep tests, the machine was set to a force control mode with the force magnitude at 300 mN. The ramping duration is 10s, holding for 300s, and then unloaded for 300s. Stress, strain, young’s modulus, strain rate, and equilibrium viscosity were calculated from raw data collected. These values were averaged, with the stress and strain being averaged across the linear elastic region, and standard deviation was calculated to see if the results would be consistent with the protocol test data.

Results, Conclusions, and Discussions: Results
The eye muscle samples creep tests showed mostly consistent Young’s modulus with each other and the previous chicken muscle tests across its three trials There are some variances in the calculated values for these eye muscle creep tests with young’s modulus of 100.98 ± 43.49, strain rate of 0.00015 ± 7.04E-06, and an equilibrium viscosity of 179439.02 ± 6468.37. Considering standard deviation, the value range of the Young’s modulus for eye muscle is consistent with the protocol chicken muscle testing results (118.24 ± 12.71).

Discussion
Consistent testing results between the protocol and eye muscle samples were achieved. This information can be used to help quantify the mechanical behavior of eye muscle for several clinical applications, for example in the case of strabismus surgery where surgeons are guessing about the eye muscle forces to either remove or loosen eye muscle for lazy eye correction. When looking at the results of a similar study finding viscoelastic properties of monkey eye muscles, we can see a similar trend in force vs. displacement in the linear region of the creep test. While the displacements are not the same for each force, the trend is very similar to that seen in this study, these differences can be attributed to the study using live samples and this study using ex vivo samples.

Conclusion
The results of this study showed consistency within results between protocol testing and eye muscle sample testing. This data is valuable and up to date with current testing methods to allow for access to more accurate mechanical properties of eye muscles. With this knowledge accessible, it would provide significant information for physicians to be able to provide better clinical planning and execution for eye muscle related surgeries and therapies.

Acknowledgements (Optional): Dr. Linxia Gu, Yingnan Zhai (Phd)