Investigation of mechanical strength and structure of corneal graft-host junction.

Dehiscence is a common complication of corneal transplant surgery involving separating the graft from the host eye. The present article aims to investigate fundamental insights into the mechanical and structural aspects of the graft-host junction (GHJ) of a graft that survived in a patient for 13 years after penetrating keratoplasty (PK). Additionally, it adopts the sutur retention strength (SRS) test procedure defined in ISO:7198-2016 and aims to provide a comprehensive test protocol to study the biomechanics of the GHJ in extracted PK buttons. A 9 mm corneal button with GHJ was extracted from a 46-year-old patient who underwent PK 13 years back. The strength of the GHJ was quantified using the SRS test. Corresponding control results were obtained from the SRS tests of a corneoscleral button with no history of any refractive procedure. Birefringence, histological, and scanning electron microscopy (SEM) imaging were used to visualize the microstructural details of the GHJ. The strength of the GHJ was observed to be ten times lower than the native cornea. Histopathological features, such as fragmented Bowman's layer, and fibrosis with a clear demarcation line between host and graft tissue, were observed at the GHJ, suggesting a weak bond across the GHJ. The low strength of the GHJ in PK indicates the high susceptibility of the GHJ towards wound dehiscence.

Intraoperative collagen imaging of sutured cornea: A way towards managing post-penetrating keratoplasty astigmatism.

The birefringent nature of the human cornea plays an important role in comprehending its structural behavior in both diseased and surgical conditions. During corneal transplantation, irregular astigmatism is a common post-surgical complication that depends on the characteristics of suturing. Four human cadaver corneas are subjected to an in-vitro model of a typical full-thickness penetrating keratoplasty (PK) procedure using 16 simple interrupted 10-0 vicyrl sutures. The birefringence of these four corneas is analyzed using digital photoelasticity and compared with the control cornea (without PK). It is found that the sutures and their mutual interaction influence the morphology of the peripheral birefringence of the cornea. The findings of the present investigation are pertinent to intraoperative suture management during PK. Results suggest conserving the typical diamond-shaped morphology of peripheral birefringence would ensure uniform distribution of sutures. Therefore, birefringence imaging could be useful in suture management to ensure proper apposition of the graft-host junction, thus minimizing the risk of irregular astigmatism.

Investigation of microstructural failure in the human cornea through fracture tests.

Fracture toughness of the human cornea is one of the critical parameters in suture-involved corneal surgeries and the development of bioengineered mimetics of the human cornea. The present article systematically studied the fracture characteristics of the human cornea to evaluate its resistance to tear in the opening (Mode-I) and trouser tear mode (Mode-III). Tear experiments reveal the dependency of the fracture behavior on the notch size and its location created in the corneal specimens. The findings indicate lamellar tear and collagen fiber pull-out as a failure mechanism in trouser tear and opening mode tests, respectively. Experimental results have shown a localized variation of tear behavior in trouser tear mode and indicated an increasing resistance to tear from the corneal center to the periphery. This article demonstrated the complications of evaluating fracture toughness in opening mode and showed that the limbus was weaker than the cornea and sclera against tearing. The overall outcomes of the present study help in designing experiments to understand the toughness of the diseased tissues, understanding the effect of the suturing location and donor placement, and creating numerical models to study parameters affecting corneal replacement surgery.