Influence of age on ocular biomechanical properties in a canine glaucoma model with ADAMTS10 mutation

<div><p>Soft tissue often displays marked age-associated stiffening. This study aims to investigate how age affects scleral biomechanical properties in a canine glaucoma model with <i>ADAMTS10</i> mutation, whose extracellular matrix is concomitantly influenced by the mutation and an increased mechanical load from an early age. Biomechanical data was acquired from <i>ADAMTS10-</i>mutant dogs (n = 10, 21 to 131 months) and normal dogs (n = 5, 69 to 113 months). Infusion testing was first performed in the whole globes to measure ocular rigidity. After infusion experiments, the corneas were immediately trephined to prepare scleral shells that were mounted on a pressurization chamber to measure strains in the posterior sclera using an inflation testing protocol. Dynamic viscoelastic mechanical testing was then performed on dissected posterior scleral strips and the data were combined with those reported earlier by our group from the same animal model (Palko et al, IOVS 2013). The association between age and scleral biomechanical properties was evaluated using multivariate linear regression. The relationships between scleral properties and the mean and last measured intraocular pressure (IOP) were also evaluated. Our results showed that age was positively associated with complex modulus (p<0.001) and negatively associated with loss tangent (p<0.001) in both the affected and the normal groups, suggesting an increased stiffness and decreased mechanical damping with age. The regression slopes were not different between the groups, although the complex modulus was significantly lower in the affected group (p = 0.041). The posterior circumferential tangential strain was negatively correlated with complex modulus (R = -0.744, p = 0.006) showing consistent mechanical evaluation between the testing methods. Normalized ocular rigidity was negatively correlated with the last IOP in the affected group (p = 0.003). Despite a mutation that affects the extracellular matrix and a chronic IOP elevation in the affected dogs, age-associated scleral stiffening and loss of mechanical damping were still prominent and had a similar rate of change as in the normal dogs.</p></div

Light microscopic evaluation and scanning electron microscopic analysis of horse eyes following deep anterior lamellar keratectomy

Objective To describe the technique of deep anterior lamellar keratoplasty (DALK) with Descemet's membrane (DM) exposure in horse eyes. Also, to compare the efficacy and safety of viscodissection and big-bubble techniques for DALK. Animals studied Thirty-four ex vivo horse eyes. Procedure Deep anterior lamellar keratoplasty was performed in 34 ex vivo horse eyes. Two groups (Group V - viscodissection - 2% sodium hyaluronate; Group A - air - big-bubble) of 17 eyes were studied. Other than the substance used, the surgical technique was similar for both groups. Nonperforated eyes were submitted for light microscopic histologic evaluation and scanning electron microscopic (SEM) analysis. Results Group V - Perforations occurred in 18% of the eyes during surgery. Light microscopy revealed exposure of DM in 28% of the eyes with mean thickness of the remaining stroma being 70.4μm. Group A - Perforations occurred in 42% of the eyes. Light microscopy revealed exposure of DM in 60% of the eyes with mean thickness of the remaining stroma being 23.3μm. No significant differences in safety, efficacy and thickness of the remaining stroma (including all eyes or excluding those with DM exposure) were observed. SEM of the surgical site revealed a more even surface in those eyes with DM exposure compared to eyes with thicker remaining stroma in both groups. Conclusions We describe two DALK techniques (viscodissection and big-bubble) for use in horses. No significant differences in safety, efficacy and thickness of the remaining stroma were observed. However, a nonsignificant trend toward the big-bubble technique being more efficacious but less safe was observed. © 2012 American College of Veterinary Ophthalmologists

DMA parameters of the posterior sclera.

<p>Specimens from the affected (n = 15, squares) and normal (n = 10, triangles) groups were measured at six frequencies and two preloads (solid markers: preload at 0.1 N; open markers: preload at 0.04 N). <b>A:</b> Complex Modulus; <b>B:</b> Loss Tangent.</p

Relationship between age and biomechanical parameters from inflation and infusion testing.

<p><b>A.</b> Tangential strains from the circumferential cross-section at 15 mmHg (Tc_15) in the posterior sclera decreased with age in the affected group (R = -0.764, p = 0.027, n = 8). <b>B.</b> Normalized ocular rigidity significantly increased with age in the normal group (R = 0.906, p = 0.034, n = 5). <b>Legend:</b> affected dogs (red circles); normal dogs (gray triangles).</p