Comparative Performance Analysis of Corneal Characteristics During Extended Hypothermic Storage in XTRA4 and Optisol-GS

Purpose: To compare endothelial cell morphometry, corneal thickness, and transparency of donor corneas during extended hypothermic storage in XTRA4 and Optisol-GS. Methods: Mate donor corneas were stored in XTRA4 or Optisol-GS at 2 to 8°C for up to 28 days. Endothelial cell density, coefficient of variation (CV), and hexagonality (HEX) were evaluated by specular microscopy. Central corneal thickness (CCT) was measured by Optical Coherence Tomography (OCT). Endothelium quality, stromal edema, and Descemet folds were graded by slit lamp using defined grading scales. Results: Endothelial cell density, CV, and HEX were similar between cohorts through day 21 ( P > 0.05); however, HEX was higher in the XTRA4 group on the final day ( P = 0.03). Endothelial cell viability was comparable at all time points ( P > 0.05). Initial stromal thickness averaged 520 ± 38 μm (XTRA4) and 502 ± 28 μm (Optisol-GS), with no difference through day 7 ( P > 0.05). Beyond day 7, XTRA4 corneas were significantly thinner (all P < 0.05). Stromal thickness increased over time in both cohorts ( P < 0.05), with a smaller Δ in XTRA4 (15 ± 19 μm) versus Optisol-GS (158 ± 54 μm). Edema scores were similar at baseline (median = 1), although Optisol-GS trended higher by day 21 ( P < 0.001). Descemet folds were fewer in Optisol-GS initially by 1 grade ( P < 0.01) but became more severe than XTRA4 after day 14 (all P < 0.01). Conclusions: XTRA4 preserves the corneal endothelium similarly to Optisol-GS for up to 14 days while maintaining consistently thinner corneas for up to 28 days. This antiswelling property may improve eye bank logistics and support future laboratory and clinical studies toward extending hypothermic storage beyond the current 14-day limit.