Comparison of rabbit and human corneas stored in Optisol-GS: changes in stromal sodium.

PURPOSE

To evaluate the hydration, and the levels of free, total and bound sodium in fresh rabbit corneal stromas and also those preserved for up to 21 days in Optisol-GS. The effect of epithelial removal on stromal sodium and hydration parameters was also evaluated. Trends in stromal hydration and sodium environment were compared to results we previously obtained using human eyes stored under identical conditions.

METHODS

Stromal hydration was evaluated thermogravimetrically. A sodium-specific electrode and an atomic absorption spectrophotometer were used to determine the amounts of free and total stromal sodium, respectively. In one cornea of each pair, the epithelium was removed prior to placement in the storage media. After 3, 7, 14 or 21 days at 4 degrees C, corneas were removed from the Optisol-GS, at which time sodium and hydration measurements were obtained.

RESULTS

With an intact epithelium, the hydration of the rabbit stromas was elevated significantly at each day of storage compared to fresh corneas. Free and total sodium levels of rabbit stromas did not differ statistically from fresh values, however the bound sodium values did increase during storage. In the absence of the epithelium, the stromal hydration and sodium content (free, total and bound) were significantly elevated and the increase was much greater than in corneas stored with an intact epithelium. These findings differ from those we measured previously using human tissue.

CONCLUSIONS

Rabbit corneas responded differently from human corneas to storage in Optisol-GS. The hydration levels increased to a greater level in rabbit than human corneas under both storage conditions. The trends in amounts of both free and total sodium were similar between the species, although the absolute amounts differed. The largest discrepancy was observed in the amount of bound sodium, with the rabbit corneas experiencing large increases not documented in the human tissue. These results suggest that direct comparisons of stromal hydration and ionic environment between the species should be approached with caution.