The value of the Terry keratometer in predicting postoperative astigmatism.

The Terry keratometer was used immediately before and immediately after cataract surgery. The results were compared with keratometry readings taken before surgery and readings taken on the morning of the first postoperative day. The mean preoperative cylinder in 27 eyes was 1/2 diopter less than that measured prior to the start of surgery. Preoperative readings and readings obtained prior to the start of surgery differed by more than 1 diopter in 37% of eyes. The keratometer readings obtained at the end of the surgery in 63 eyes were flatter than those obtained on the first postoperative day. Forty-four percent of the intraoperative cylinder readings differed from postoperative readings by more than 2 diopters. The factors which can produce errors with the use of this instrument include changes in intraocular pressure, the effect of the lid speculum, rectus suture tension, the alignment of the eye with respect to the keratometer , and user experience.