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The effect of incisions for cataract on corneal curvature
John C Merriam1, Lei Zheng, Joanna E Merriam
1Edward S Harkness Eye Institute, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA. jcm5@columbia.edu
Purpose:
To determine the magnitude and duration of change on the horizontal and vertical meridians of the cornea after five different incisions for cataract.
Design:
Retrospective comparative interventional study of five commonly used incisions for cataract surgery: extracapsular cataract extraction (ECCE), 6-mm superior scleral tunnel (6Sup), 3-mm superior scleral tunnel (3Sup), 3-mm temporal scleral tunnel (3Temp), and 3-mm temporal corneal incision (3Cor).
Participants:
A total of 662 cases with preoperative regular astigmatism, measured with keratometry.
Methods:
The mean net change on each meridian was computed at 1 day, 1 week, 2 weeks, 1 month, 1.5 months, 2 months, 4 months, 6 months, and 12 months and at succeeding 6-month intervals after surgery. Best-fit parameters were calculated for the observed changes in the horizontal and vertical keratometry values after each incision. To determine when the cornea stabilized, average change on the horizontal and vertical meridians was compared with an estimate of the accuracy of keratometry measurement.
Main Outcome Measures:
The pattern of change on the horizontal and vertical meridians and time for the cornea to stabilize after each incision.
Results:
The initial and final net changes after a superior incision decrease with length. A sigmoid equation describes the course of the changes on the horizontal and vertical meridians after the superior incisions. The changes after the temporal incisions depend linearly on time after surgery. Considering the uncertainty of keratometry, the corneal meridians stabilized 4.5 months after ECCE, 1.2 months after 6Sup, and 0.3 months after 3Sup. No significant change was detected on the horizontal and vertical meridians after 3Temp and 3Cor.
Conclusions:
The magnitude and the duration of keratometric change on the horizontal and vertical meridians of the cornea depend on the length and location of the incision. Within the limits of measurement error, no significant change in corneal curvature was detected after either small temporal incision.
