[Factors modifying postoperative astigmatism after no-stitch cataract surgery]

One of the main advantages of the no-stitch technique in cataract surgery is that induced astigmatism occurs less frequently than with any other procedure and stabilizes within a very short time postoperatively. The resultant high wound strength enabled us to alter the incision parameters in an attempt to identify those which influenced postoperative astigmatism, the ultimate goal being to improve the prognosis of the expected astigmatism. Since the influence of tunnel width and incision length and shape were well known, we investigated the influence of incision depth and site and that of various parameters in a prospective randomized and controlled clinical trial.

The study included 256 eyes with a 7-mm tunnel incision as examined in 256 patients. The following subgroups of 27 eyes each were investigated: primary incision depth of 300 microns versus 500 microns, limbal incision versus scleral incision, scleral incision in the 12 o'clock position versus temporal scleral incision, and limbal incision in the 12 o'clock position versus temporal limbal incision. In another group the influence of age, IOP, axial length of the globe, preoperative astigmatism, corneal diameter, and postoperative astigmatism as measured by the keratometer were all assessed using Spearman's correlation coefficient.

Temporal incisions made 2 mm posterior to the limbus resulted in induced astigmatism of 0.64 +/- 0.22 D 6 months postoperatively, which was less than after incisions in the 12 o'clock position (0.98 +/- 0.40 D). Induced astigmatism was highest after limbal incisions in the 12 o'clock position (1.31 +/- 0.60 D), yet was less if a temporal limbal incision was made (0.84 +/- 0.52 D). Incision depth did not have significant influence on induced astigmatism. Of the parameters, age (Spearman's correlation coefficient after 4 weeks 0.34; P = 0.002; after 6 months 0.28; P = 0.01), and preoperative astigmatism (Spearman's correlation coefficient after 4 weeks 0.28; P = 0.01; after 6 months 0.27; P = 0.01) had a significant influence on postoperative astigmatism.

These findings indicate that induced astigmatism was highest after limbal incisions in the 12 o'clock position and lowest after scleral incisions in the temporal position. Age and preoperative astigmatism were also found to influence induced astigmatism significantly. All of these factors have to taken into account to minimize postoperative astigmatism.