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PurposeTo evaluate and compare the biomechanical properties of the eye bank-prepared and surgeon prepared Descemet stripping automated endothelial keratoplasty (DSAEK) tissues.MethodsIn this laboratory study, corneal tissues for research were randomly allocated in the following groups: a) surgeon-cut DSAEK and b) eye bank-prepared (pre-cut and pre-loaded) DSAEK. Endothelial cell loss (ECL), immunostaining for tight junction protein ZO-1, elastic modulus, and adhesion force were investigated.ResultsECL was not found to be significantly different between surgeon-cut DSAEK (7.8% ±6.5%), pre-cut DSAEK (8.6% ±2.3%), and pre-loaded DSAEK (11.1% ±4.8%) (P = 0.5910). ZO-1 was expressed equally across all groups. Surgeon-cut DSAEK grafts showed a significantly higher elastic modulus compared to pre-cut and pre-loaded DSAEK groups (P = 0.0047 and P < 0.0001, respectively). Adhesion force was significantly greater in the surgeon-cut DSAEK compared to pre-cut (P < 0.0001) or pre-loaded DSAEK groups (P = 0.0101).ConclusionThe laboratory data on the biomechanics of DSAEK grafts suggests that surgeon-cut DSAEK grafts present higher elastic modulus and adhesion force compared to eye bank-prepared DSAEK grafts.

Purpose To explore the effect of age on corneal biomechanical properties following corneal cross-linking (CXL). Methods A total of 12 pairs of human eye-banked corneas (24 corneas, from 14 females and 10 males) were used in the study. The mean donor age was 48.5 years (ranging from 26 to 71 years). Corneas were divided into three age groups: A (26–41 years), B (42–57 years) and C (58–71 years), with four pairs in each group. For each pair, the right corneas were cross-linked using accelerated CXL with UVA (10 mW/cm2) and riboflavin, while the left corneas served as controls and were not exposed to either UVA irradiation or riboflavin. The corneal elastic modulus of the anterior, mid and posterior corneal stroma was measured using nanoindentation. Results The difference in the corneal elastic modulus following CXL was significant in the anterior (p = 0.00002) and mid stroma (p = 0.001); however, the difference was not significant in the posterior stroma (p = 0.27) when compared to control corneas. The corneal elastic modulus of the anterior stroma increased by 178.44% in Group A, 119.7% in Group B and 50.73% in Group C compared to control corneas. For the mid stroma, the elastic modulus increased by 47.35% in Group A, 25% in Group B and 24.56% in Group C. No differences were observed in the posterior stroma between age groups. Conclusions Corneal elasticity showed a greater response to CXL in the younger group compared to older groups. CXL treatment showed effectiveness in enhancing stromal strength, and the effect was concentrated in the anterior and mid stroma with minimal impact on the posterior stroma in all age groups.

Under physiological conditions, the cornea is exposed to various enzymes, some of them have digestive actions, such as amylase and collagenase that may change the ultrastructure (collagen morphology) and sequentially change the mechanical response of the cornea and distort vision, such as in keratoconus. This study investigates the ultrastructure and nanomechanical properties of porcine cornea following incubation with α-amylase and collagenase. Atomic force microscopy (AFM) was used to capture nanoscale topographical details of stromal collagen fibrils (diameter and D-periodicity) and calculate their elastic modulus. Samples were incubated with varying concentrations of α-amylase and collagenase (crude and purified). Dimethylmethylene blue (DMMB) assay was utilised to detect depleted glycosaminoglycans (GAGs) following incubation with amylase. Collagen fibril diameters were decreased following incubation with amylase, but not D-periodicity. Elastic modulus was gradually decreased with enzyme concentration in amylase-treated samples. Elastic modulus, diameter, and D-periodicity were greatly reduced in collagenase-treated samples. The effect of crude collagenase on corneal samples was more pronounced than purified collagenase. Amylase was found to deplete GAGs from the samples. This enzymatic treatment may help in answering some questions related to keratoconus, and possibly be used to build an empirical animal model of keratoconic corneas with different progression levels.

There has been a lot of interest in accurately characterising corneal biomechanical properties under intraocular pressure (IOP) to help better understand ocular pathologies that are associated with elevated IOP. This study investigates the novel use of Line-Field Optical Coherence Tomography (LF-OCT) as an elastographic tool for accurately measuring mechanical properties of porcine corneas based on volumetric deformation following varying IOPs. A custom-built LF-OCT was used to measure geometrical and corneal surface displacement changes in porcine corneas under a range of IOPs, from 0–60 mmHg. Corneal thickness, elastic properties and hysteresis were calculated as a function of pressure. In addition, the effects of hydration were explored. We found that the elastic modulus increased in a linear fashion with IOP. Corneal thickness was found to reduce with IOP, decreasing 14% from 0 to 60 mmHg. Prolonged hydration in phosphate buffered saline (PBS) was found to significantly increase the elastic modulus and corneal hysteresis. Our study demonstrates that LF-OCT can be used to accurately measure the elastic properties based on volumetric deformation following physiological pressures. Furthermore, we show that prolonged hydration in PBS has a significant effect on the measured corneal properties.

The micromechanical behaviour of the cornea is important for understanding and modelling of many ocular disorders. Whereas inflation testing has been utilised to determine the bulk mechanical properties of the cornea under physiological pressures, micromechanical testing has been limited to unpressurised corneal samples. In this study the micromechanical properties of pressurised porcine corneas were determined using oscillatory nanoindentation coupled with a custom inflation method. Inflation was conducted in phosphate buffered saline (PBS) and tissue culture (TC) solutions. The shear storage modulus (G′) and shear loss modulus (G”) was determined for corneas inflated corneas with PBS and TC. Central corneal thickness (CCT) was monitored during the inflation (0–60 mmHg). Elastic modulus (E) was also calculated and quantitatively mapped for corneas. The results showed that G′ at 15 mmHg was 86.18 ± 16 kPa and 88.86 + 13.54 kPa inflated by PBS and TC respectively. These values increased 3.2 times in an approximate linear relationship to 60 mmHg. G″ at 15 mmHg was 12.5 ± 2.5 kPa and 13.54 + 1.9 kPa inflated by PBS and TC respectively. G″ increased 1.9 times in an approximate linear relationship to 60 mmHg. No significant change was noticed in viscoelastic properties of corneas inflated by TC for 4 h whereas 4 h of hydration on PBS affected the mechanical properties. The central corneal region was found to be stiffer than in peripheral region. Mapping of elasticity revealed a symmetrical distribution of properties that varied with inflation. Our method has potential for measurement of viscoelastic properties of corneas in conditions where there have been localised changes in mechanical properties such as keratoconus.