Choosing the location of corneal incision based on preexisting astigmatism in phacoemulsification

Abstract

Purpose: To investigate the best location of clear-cornea incision in phacoemulsification, depending on preexisting corneal astigmatism.

Design: Randomized clinical trial and noncomparative interventional case series.

Methods: A total of 574 patients in five stages were assigned to the following incisions: superior or temporal (n = 89), superior (n = 141), superior or superior plus relaxing (n = 102), nasal or temporal (n = 156), and incisions based on applying conclusions of preceding and current studies (n = 86). Visual acuity, refraction, biomicroscopy, keratometry, and videokeratography (Fourier analysis) were performed before and after phacoemulsification and intraocular lens implantation (3.5-mm incision). main outcome measures: Corneal refractive and surface regularity index change between preoperative and 6-month postoperative examination. Visual acuity at 6 months.

Results: In patients without corneal astigmatism, corneal changes induced were greater in superior than temporal incision. After a superior incision (preoperative steep axis at 90 degrees), a shift of the axis 90 degrees away was less likely with at least 1.5 diopters of astigmatism. A perpendicular relaxing limbal incision decreased corneal changes. Nasal incision induced greater corneal change than temporal incision (preoperative steep axis at 180 degrees). A shift of this axis 90 degrees away was more likely with astigmatism < 0.75 diopters in temporal incision and < 1.25 diopters in nasal incision.

Conclusions: Superior incision is recommended with at least 1.5 diopters of astigmatism and steep axis at 90 degrees. Temporal incision is recommended with astigmatism < 1.5 diopters and steep axis at 90 degrees, negligible astigmatism, or astigmatism < 0.75 diopters and steep axis at 180 degrees. Nasal incision is recommended with at least 0.75 diopters of astigmatism and steep axis at 180 degrees.