VARIABILITY IN CORNEAL THICKNESS BEFORE, DURING, AND AFTER RADIAL KERATOTOMY

BACKGROUND: Precision in radial keratotomy requires accurate pachymetr y for safety and efficacy. We evaluated the location, timing, and exte nt of changes in corneal thickness between those determined by preoper ative measurement in the clinic and those determined by pre-incision a nd post-incision measurement in the operating room. METHODS: Sixty eye s of 37 patients had ultrasonic pachymetry measurements of the central and paracentral cornea taken in the clinic 20 minutes before each pat ient underwent radial keratotomy, The pachymetry was repeated intraope ratively immediately before and, in a subset of 17 eyes, immediately a fter incisions were made, and the readings were compared. RESULTS: The thinnest of the four paracentral readings measured just prior to plac ing the radial keratotomy incisions was located temporally in 92% of t he eyes and inferiorly in 8%. Corneas progressively thinned from clini c to surgery by an average of 7 +/- 12 mu m centrally and 10 +/- 18 mu m temporally, Additional thinning of 13 +/- 14 mu m centrally and 22 +/- 23 mu m temporally occurred during surgery. CONCLUSION: The thinne st paracentral corneal region measured in an eye was not always locate d in the same quadrant preoperatively and intraoperatively. During the time of incision placement, significant corneal thinning had occurred at each incision site. Individual variations in corneal thickness bet ween that measured preoperatively and that measured during surgery cau tions against the use of clinic readings for diamond knife settings du ring radial keratotomy.