Bruch's Membrane Contributes to the Structural Integrity of the Normal Human Eye

Purpose: To investigate the contribution of the Bruch's membrane and sclera tissues to the overall structural integrity of the ocular wall. Methods: Twenty-three human globes were subjected to biomechanical testing. A piece of sclera measuring 5 × 5 mm was carefully removed at the nasal region, 2 mm away from the optic nerve head. The IOP was increased at approximately 1 mm Hg/s until Bruch's membrane-uvea-retina tissue layer (BMUR) ruptured. Next, strips of sclera and Bruch's membrane-choriocapillaris (BMC) complex were isolated from the superior fundus region. Uniaxial tension tests were performed at a strain rate of 0.01/s and sampling rate of 15 Hz. The tangent moduli of the BMC and sclera at 0.01, 0.02, and 0.03 strains were compared. Results: The rupture pressure of the BMUR was 98.1 ± 21.4 mm Hg. The tangent moduli of the BMC at 0.01, 0.02, and 0.03 strains were 2.96 ± 1.44 MPa, 7.68 ± 1.78 MPa, and 9.43 ± 2.11 MPa, respectively, and the tangent moduli of the sclera at 0.01, 0.02, and 0.03 strains were 1.09 ± 0.80 MPa, 2.72 ± 1.67 MPa, and 5.69 ± 3.27 MPa, respectively. Conclusions: The BMUR was able to sustain a relatively high IOP before rupturing. The uniaxial tensile tests showed that the BMC tangent moduli were about three times of those of the sclera at strains of 0.01 and 0.02. Although the sclera is approximately 47 times thicker, the BMC is still likely to make a significant contribution (3.51% to 9.79% at a strain of <0.03) to the overall structural strength of the ocular wall.