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

PurposeTo investigate the contribution of the Bruchs membrane and sclera tissues to the overall structural integrity of the ocular wall. MethodsTwenty-three human globes were subjected to biomechanical testing. A piece of sclera measuring 5 x 5 mm was carefully removed at the nasal region, 2 mm away from the optic nerve head. The intraocular pressure was increased at approximately 1 mmHg/s until Bruchs membrane-uvea-retina-tissue layer (BMUR) ruptured. Next, strips of sclera and Bruchs 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. ResultsThe rupture pressure of the BMUR was 98.1 {+/-} 21.4 mmHg. 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. ConclusionThe BMUR was able to sustain relatively high IOP before rupturing. The uniaxial tensile tests showed that the BMC tangent moduli were about 3 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 7.42% at strain <0.03) to the overall structural strength of the ocular wall.