Understanding Posterior Human Sclera
Authors: Geraghty, B., Abass, A., Eliasy, A., Jones, S.W., Rama, P., Kassem, W., Akhtar, R., and Elsheikh, A.
Journal: Journal of Biomechanics
Publication Date: Jan 2020
Contour map of thickness variation at 25 µm intervals on a developed scleral surface for (a) average data obtained from all sclerae tested, and (b) represents the locations of thickness measurements. Colour bar values are presented in micrometres (µm). The map centre represents the posterior pole. Maps continue to the anterior foramen edge. S = superior direction, I = inferior direction, N = nasal direction, T = temporal direction, ONH = optic nerve head.
Summary:
The human eye is a complex organ, and understanding its biomechanics is essential for treating various eye conditions. Our research focuses on the sclera, the white outer layer of the eye that maintains its shape and protects it from injury. Specifically, we aimed to simplify the process of determining the material properties of the sclera, which can help researchers study ocular biomechanics more efficiently.
We conducted experiments on five human donor sclerae, aged between 36 and 72 years, inflating them with internal pressure using a custom-built inflation rig. We then measured the displacements of the sclera using a laser beam and two cameras. Afterwards, we created detailed computer models of each sclera and used an inverse finite element procedure to determine the material properties for each region.
Our method proved effective in determining the material properties of the sclera, with a maximum error of only 17.5 micrometres between our computer models and the actual measurements. We found that the stiffness of the sclera gradually decreases from the equator to the posterior region at low-stress levels. However, at higher stresses, the difference in stiffness between adjacent regions became less apparent and statistically insignificant.
We believe that our research will make it easier for other scientists to study ocular biomechanics, as our method simplifies the process of determining the material properties of the sclera. This could, in turn, lead to improved understanding and treatment of various eye conditions, such as glaucoma, which is a leading cause of blindness worldwide.
In conclusion, our study demonstrates how inflation testing combined with inverse modelling can effectively characterise regional material properties of the human sclera. While our results showed variations in material properties between specimens, we expect that age could be a contributing factor behind these differences. Future research will aim to characterise the variations in scleral tissue properties with age and medical history.