Effect on Astigmatism of the Location of Clear Corneal Incision in Phacoemulsification of Cataract

Abstract

PURPOSE: To investigate the refractive results of clear corneal incision performed at the steepest meridian of pre-existing corneal astigmatism. METHODS: One hundred eighty-two patients with astigmatism >0.75 diopters (D) were evaluated. Superior, temporal, nasal, supe rotemporal, or superonasal clear corneal incisions were performed at the steep meridian. Refraction, visual acuity, and topography values were evaluated, and changes in surgically induced astigmatism were calculated by vector analysis using the Fourier formula. Paired t test was used to compare mean values. RESULTS: Postoperative cylinder va lues showed minor changes in all groups, except the nasal group. Nasal incision increased preoperative cylinder from 1.13 D to 1.83 D 6 months after surgery. Temporal and supe rotemporal incisions resulted only in small astigmatic changes. Conversely, superior, superonasal, and nasal incisions induced more pronounced astigmatism. CONCLUSIONS: Performing clear corneal incision for phacoemulsification of cataract at the steep meridian resulted in small changes with temporal incisions, whereas nasal incisions resulted in higher surgically induced astigmatism. [J Refract Surg. 2007;23:515-518.]

Effects of steep meridian incision on corneal astigmatism in phacoemulsification cataract surgery

“…An incision on the preoperative steep meridian resulted in insignificant torsion in all incision groups. Altan-Yaycioglu et al 3 evaluated the refractive results of CCIs performed at the steepest meridian in cases of astigmatism greater than 0.75 D. They conclude that the change was small with temporal incisions, whereas nasal incisions resulted in higher SIA. Kohnen et al 11 found that the induced corneal astigmatism was 0.47 D with temporal CCIs and 1.55 D with nasal CCIs.…”

“…Kohnen et al 11 found that the induced corneal astigmatism was 0.47 D with temporal CCIs and 1.55 D with nasal CCIs. Altan-Yaycioglu et al 3 performed vector analysis using J0 and J45 for statistical comparison. However, this method is limited because each vector component has different implications for different steep meridians.…”

“…Previous studies have obtained power vector values using a Jackson (J) cross-cylinder of power J0 at the 180-degree meridian and a Jackson cross-cylinder of power J45 at the 45-degree meridian. 3 In this method, corneal flattening is expressed differently according to the meridian. For example, flattening the cornea along the 180-degree meridian is expressed as an increase in the J0 component, whereas flattening along the 90-degree meridian is expressed as a decrease in the J0 component.…”

“…2 Superior corneal and scleral incisions are reported to induce greater corneal changes than temporal incisions. [3][4][5] Analysis of SIA requires the conversion of net astigmatism to orthonormal components in dioptric space. Previous studies have obtained power vector values using a Jackson (J) cross-cylinder of power J0 at the 180-degree meridian and a Jackson cross-cylinder of power J45 at the 45-degree meridian.…”

Expected effects of surgically induced astigmatism on AcrySof toric intraocular lens results

“…astigmatism (SIA) to select the correct toric IOL and calculate the optimum angle of placement Surgically induced astigmatism is a known consequence of creating the incision necessary for cataract removal and IOL implantation. 7,8 Because corneal astigmatism is a vector quantity (comprising a magnitude and a direction), simply adding and subtracting astigmatism values will not yield useful information. The amount of astigmatism to be corrected at the time of surgery must be the vector sum of the preoperative corneal astigmatism and any SIA.…”