Mixed Astigmatism in Refractive surgery

Noel Alpins

Meeting:  2015 RANZCO


Date:      -

Session Title: Oculoplastic/Refractive Surgery/Cataract Rapid Fire

Session Time:      -

Purpose: To investigate refractive mixed astigmatism outcomes using cross-cylinder ablations.

Method: A retrospective analysis was performed on 315 eyes having undergone refractive laser surgery for mixed astigmatism on the ViSX STAR S4 IR system. The treatments were based on cross-cylinder ablations with a plano/positive cylinder at 5.0-9.0mm and plano/negative cylinder at 6.5×6.0mm ablation zone. No spherical component was required. Outcomes were assessed 4 weeks postoperatively.

Results: Preoperative mean refractive cylinder was 2.65 +/- 1.19D and 0.55 +/- 0.46D postoperatively. The mean corneal astigmatism preoperatively was 2.43 +/- 1.20D preoperatively and 0.98 +/- 0.71D postoperatively. The mean target induced astigmatism vector (TIA) was 2.55D arithmetically and 1.20D x 4 vectorially. The surgically induced astigmatism vector (SIA) was 2.49D arithmetically and 1.00D x 6 vectorially. The difference vector (DV) was 0.71D arithmetically and 0.20D x 172 vectorially. The Magitude of Error (M of E) was -0.06 +/- 0.74D. The Correction Index (CI) 0.89. The arithmetic Angle of Error (A of E) was 0.28 +/- 12.24 degrees. 91% had an unaided visual acuity of 6/6 or better and 95% had an unaided visual acuity of 6/12 or better.

Conclusion: Using cross-cylinder ablations to correct mixed astigmatism in refractive laser surgery is safe and effective, utilising the minimum amount of ablated tissue with the technique employed.