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D. J. Russell, I. W. Porter, K. L. Cohen; Astigmatism After Bimanual Phacoemulsification. Invest. Ophthalmol. Vis. Sci. 2008;49(13):378.
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© ARVO (1962-2015); The Authors (2016-present)
To determine astigmatic changes after bimanual, microincision phacoemulsification.
12 patients over age 60, with cataracts, no other eye disease, and BCVA >20/80 were enrolled. Pre-operative manifest refraction and video keratoscopy were recorded. Two limbal paracentesis incisions were made at 10 and 8 or 2 and 4 o’clock, using a 1.2 x 1.4 mm trapezoid blade, followed by phaco. Then, a 2.75 mm keratome incision in between was made to allow injection of a pcIOL into the capsular bag. One 10-0 nylon suture closed this incision and was removed at 1 week. To our knowledge, induced astigmatism using this surgical technique has not been reported. All tests were repeated postoperatively. Astigmatism (diopters) was compared pre-operatively and postoperatively.
Mean refractive astigmatism decreased from preoperative to postoperative. Mean preoperative refractive astigmatism was 0.95 +/-0.61, and mean postoperative refractive astigmatism was 0.83 +/-0.62. Surgically induced astigmatism calculated by vector analysis was 0.78 +/- 0.49. The refractive axis was 180° +/- 15° in 8/12 preoperative, and in 9/12 postoperative. Topographic astigmatism showed minimal increase from preoperative to postoperative. Mean preoperative topographic astigmatism was 1.53 +/- 0.49, and mean postoperative topographic astigmatism was 1.67 +/- 0.51. Surgically induced astigmatism calculated by vector analysis was 0.56 +/- 0.43. The preoperative topographic axis was 180° +/- 15° in 9/12, and postoperative in 6/12. The amount of the flat meridian did not change with 42.42 +/- 1.56 preoperative and 42.25 +/- 1.15 postoperative.
Bimanual, microincision phaco allows cataract surgeons to operate through smaller incisions than allowed by coaxial phaco. This advantage could theoretically reduce the induced astigmatism caused by surgery. Unfortunately, in the United States small incision IOLs are not available to fit through 1.2 mm x 1.4 mm trapezoidal incisions. Therefore, widening of one of the incisions or a third larger incision needs to occur for implantation of the IOL. The results of this study demonstrate that the induced astigmatism is small and comparable to previously reported data. Induced astigmatic changes are not different from previously reported data on coaxial phaco. The refractive cylinder was decreased compared to the topographic cylinder, and this may have clinical implications for postoperative uncorrected visual acuity.
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