Perilimbal sclera mechanical properties: Impact on intraocular pressure in porcine eyes

Abstract

There is extensive knowledge on the relationship of posterior scleral biomechanics and intraocular pressure (IOP) load on glaucomatous optic neuropathy; however, the role for biomechanical influence of the perilimbal scleral tissue on the aqueous humor drainage pathway, including the distal venous outflow system, and IOP regulation is not fully understood. The purpose of this work is to study the outflow characteristics of perfused porcine eyes relative to the biomechanical properties of the perilimbal sclera, the posterior sclera and the cornea. Enucleated porcine eyes from eleven different animals were perfused with surrogate aqueous at two fixed flow rates while monitoring their IOP. After perfusion, mechanical stress-strain and relaxation tests were conducted on specimens of perilimbal sclera, posterior sclera, and cornea from the same perfused eyes. Statistical analysis of the data demonstrated a strong correlation between increased tangent modulus of the perilimbal sclera tissues and increased perfusion IOP (R2 = 0.74, p = 0.0006 at lower flow rate and R2 = 0.71, p = 0.0011 at higher flow rate). In contrast, there were no significant correlations between IOP and the tangent modulus of the other tissues (Posterior sclera: R2 = 0.17 at lower flow rate and R2 = 0.30 at higher flow rate; cornea: R2 = 0.02 at lower flow rate and R2<0.01 at higher flow rate) nor the viscoelastic properties of any tissue (R2 ≤ 0.08 in all cases). Additionally, the correlation occurred for IOP and not net outflow facility (R2 ≤ 0.12 in all cases). These results provide new evidence that IOP in perfused porcine eyes is strongly influenced by the tangent modulus, sometimes called the tissue stiffness, of the most anterior portion of the sclera, i.e. the limbus.

Trabecular Meshwork Motion Profile from Pulsatile Pressure Transients: A New Platform to Simulate Transitory Responses in Humans and Nonhuman Primates

“…The well-recognized force-displacement relationships may explain the reduction in the time constant in response to increasing baseline pressures. The increased stiffness with an increasing tension or load is a behavior that occurs in many ocular tissues [28][29][30][31]. At a higher baseline IOP, the force-displacement curve is steeper, and thus, the recoil speed at unloading is faster, which leads to a reduced time constant, as seen in our study.…”

Measurement of the Elastic Modulus of Cornea, Sclera and Limbus: The Importance of the Corneal-Limbus-Scleral Biomechanical Unit

“…Episclera is a dense layer of collagen found in bundles that run circumferentially around the eye and merge with the underlying stroma [17]. They prevent radial enlargement of the sclera due to increases in internal pressure in the eye by limiting "hoop strain" preventing "blow out" failure of the globe [21][22][23]. It merges with the superficial layer of the limbus and therefore should have a similar modulus to that layer.…”

Microinvasive Glaucoma Surgery: A Review of Schlemm’s Canal-Based Procedures

“…46 The complete mechanism of the formation of this residual resistance is not fully known. What is known, however, is that the segmental AH outflow, 47 perilimbal tissue biomechanics, 48 and the aqueous veins are factors contributing to this mechanism. 49 In a healthy eye, the IOP is nearly 16 mmHg, while pressure in the episcleral veins is 7-8 mmHg.…”