DEPTH PREDICTABILITY OF STROMAL POCKETS IN THE POSTERIOR CORNEA

Purpose, To evaluate the predictability of the depth of stromal pocket s made in the posterior cornea for the excision of anterior or posteri or lamellar corneal buttons with a planned thickness. Methods, Stromal corneal pocket dissections were created in human eye bank eyes by mak ing a peripheral arcuate keratotomy incision at 60, 80, or 95% of cent ral pachymetry and creating a pocket from the bottom of the incision a cross the cornea. Pocket depth was measured by pachymetry immediately after surgery and by light microscopy. Results. Mean achieved central pocket depth differed by 0.03+/-0.03 mm from the intended depth. Varia tion in depth across the pocket decreased from 0.07+/-0.02 mm for pock ets made at 60% of the intended depth to 0.05+/-0.01 mm for pockets ma de at 80(ro depth, and 0.04+/-0.02 mm for pockets made at 95% depth (p < 0.01). Pachymetric and histological measurements of relative pocket depth averaged 64+/-9% and 73+/-7%, respectively, for pockets made at 60% of the intended depth, 82+/-7% and 86+/-3% for pockets made at 80 % depth, and 91+/-7% and 92+/-3% for pockets made at 95% depth. The di fference between pachymetric and histological relative pocket depth me asurements decreased with deeper pocket depth (p < 0.01). Conclusions. In the posterior cornea, stromal pockets can be created to within 30 mu m from the intended depth. Variation in depth throughout the pocket decreases with deeper pocket depth. Pachymetry is a reliable method t o check the achieved pocket depth during surgery, the accuracy of pach ymetry readings improves with deeper pocket depth.