Creating a Full-thickness Choroidal Incision: An Ex Vivo Analysis of Human and Porcine Tissue Contraction Dynamics

Purpose: We hypothesized that the elastic nature of the choroid leads to tissue contraction following a full-thickness, sharp incision. Furthermore, we sought to quantify, measure, and compare tissue contraction in ex vivo porcine globes and human globes of various ages using predetermined variables. Method: A full-thickness, ex vivo choroidal incision was performed in either pig (n-97) or human (n = 30) specimens. Variables included trephine diameter (1.5, 2.0, or 2.5 mm) versus a straight surgical blade, and temperature (1.7 degrees-4.4 degrees vs. 36.6 degrees F). Central centripetal and surround centrifugal tissue contractions were measured. Mean percentage tissue contraction was assessed as a ratio of trephine diameter to final tissue contraction measured immediately following each incision using a standardized device. Results: For trephination in pig specimens, centripetal contraction ranged from 38% to 50% with a mean of 44%. Centrifugal contraction was approximately 15%. Human choroidal contraction was 39% and 15%, respectively, with a statistically significant inverse relationship to age (R-2-0.35, P <= 0.01). Asymmetric contraction was noted when incisions were closer to choroidal attachment sites to the sclera, such as near vortex ampullae. Linear incisions resulted in contraction that correlated with incision length (R-2-0.35, P <= 0.001). Conclusions: A full-thickness choroidal incision results in significant tissue contraction. For circular incisions, the centripetal contraction approaches 50% of the original incision size. For linear incisions, the contraction corresponds directly with incision length. In human specimens, there is less contraction with advancing age.