Surgical incision alters the swelling response of the human cornea

The ocular characteristics and responses were examined in patients who had undergone extracapsular cataract extraction (ECCE), intracapsular cataract extraction (ICCE) and penetrating keratoplasty (PKP) in one eye only. In each of the three groups, corneal sensitivity (the inverse of corneal touch threshold), oxygen uptake rate, and endothelial cell density were lower in the operated eye than in the normal healthy fellow eye. For the subjects as a whole, the differences in ocular characteristics between the two eyes were proportional to the angular size of the corneal incision, with ECCE patients (33 degrees incision) showing the least differences and PKP patients (360 degrees incision) showing the greatest differences. Five patients from the ICCE group were subjected to an osmotic stress test. There was no statistically significant difference in the corneal swelling response between the operated eye (5.1%) and the unoperated eye (4.7%), indicating that surgically induced scar tissue does not restrict the swelling properties of the cornea. When subjected to a hypoxic stress test, all three groups manifested less corneal edema in the operated eye (ECCE -0.7%, ICCE -4.0%, and PKP -3.3%). The reduction in hypoxic corneal swelling could not be attributed to removal of the crystalline lens since a similar reduction was seen in the PKP group who had phakic eyes. The corneal swelling response correlated inversely with the corneal touch threshold and directly with epithelial oxygen uptake, but did not correlate with endothelial cell density.(ABSTRACT TRUNCATED AT 250 WORDS)