According to a recent study published in the Journal of Refractive Surgery, improving astigmatism control in refractive lens surgery is related to several factors such as limbal incision size, patient age, meridian and magnitude of corneal astigmatism or intraocular pressure. The study is titled “Influence of Ocular Features and Incision Width on Surgically Induced Astigmatism After Cataract Surgery.“
The development of a certain degree of astigmatism is expected during cataract surgery, but improved surgery techniques in recent decades have resulted in decreased incision widths to control surgically induced astigmatism (SIA). However, how SIA can be minimised remains clinically relevant.
In order to identify which factors associate with surgically induced astigmatism (SIA) following phacoemulsification, Shu-Wen Chang from the Department of Ophthalmology at Far Eastern Memorial Hospital in New Taipei City, Taiwan along with colleagues conducted phacoemulsification with a 2.2-mm in 248 eyes and with 2.75-mm in 357 eyes, with superior limbal incision. They then measured preoperative axial length, anterior chamber depth, corneal curvature, and intra-ocular pressure.
At 1 day, 1 week, and 1, 2, and 3 months after surgery, the investigators measured corneal curvature and intraocular pressure. Using the Alpins method, the investigators calculated surgically induced astigmatism, corneal flattening, and torque. Furthermore, they assessed the effect of preoperative corneal astigmatism meridian on surgically induced astigmatism before surgery. Moreover, they examined the differences in SIA between the two groups (2.2-mm versus 2.75-mm), and potential correlations between SIA and corneal astigmatism, anterior chamber depth, axial length, age, and intraocular pressure before surgery.
At 1 week, the results showed that surgically induced astigmatism, corneal flattening, and torque were smaller in the 2.2-mm group than in the 2.75-mm group. However, these differences were not achieved in other study time-points.
In both groups, higher corneal astigmatism before surgery, older age, and narrower anterior chamber depth were all statistically related with higher surgically induced astigmatism. The group who had 2.75-mm phacoemulsification had a clearer effect of astigmatism meridian on surgically induced astigmatism. Compared to the 2.2-mm group, the 2.75-mm group had a greater surgically induced astigmatism associated with shorter axial length and lower intraocular pressures.
Based on these results, Shu-Wen Chang and colleagues believe that “reducing limbal incision width and considering patient age, the meridian and magnitude of corneal astigmatism, anterior chamber depth, axial length, and intraocular pressure, and adjusting the flattening component of SIA input for toric intraocular lens power calculation could potentially improve the astigmatism control in refractive lens surgery.”
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