A Critical Evaluation of Refractive Outcomes Following LASIK for Moderate to High Astigmatism Using Two Excimer Laser...

To calculate the surgically induced astigmatism (SIA) following LASIK and identify any association between SIA and the target induced astigmatism (TIA) at 1 year postoperatively.

The SIA was calculated using the TIA and residual astigmatism values for [A] myopic astigmatism and [B] mixed astigmatism treated with either the [I] WaveLight Allegretto EyeQ 400-Hz (Alcon Laboratories, Inc. Fort Worth, TX) or [II] Schwind Amaris 750S (Schwind eye-tech-solutions, Kleinostheim, Germany) platforms. The TIA and corresponding SIA results were analyzed using various techniques.

Key findings were the negative SIA power (y₁) was significantly correlated with negative TIA power (x₁) and sine of the TIA axis (x₂) as follows: [A] I, y₁= 0.829x₁-0.403x₂-0.325 (F = 87.76, r = 0.804, P < .001, n = 127); II, y₁= 0.891x₁-0.037x₂-0.192 (F = 240.06, r = 0.901, P < .001, n = 119) and [B] I, y₁= 1.063x₁+0.233x₂+0.411 (F = 990.99, r = 0.881, P < .001, n = 61); II, y₁= 1.029x₁-0.115x₂+0.322 (F = 270.12, r = 0.908, P < 0.001, n = 111). The sine of negative SIA axis (y₂) was significantly correlated with negative TIA power (x₁) and TIA axis (x₂) as follows: [A] I, y₂ = 0.951x₂-0.007x₁+0.008 (F = 446.58, r = 0.950, P < .001, n = 127); II, y₂ = 0.856x₂+0.007x₁+0.105 (F = 277.18, r = 0.912, P< .001, n = 119) and [B] I, y₂ = 0.953x₂+0.009x₁+0.075 (F = 362.6, r = 0.963, P < .001, n = 61); II, y₂ = 0.977x₂-0.004x₁+0.002 (F = 2910.9, r = 0.990, P < .001, n = 111).

The predicted SIA power was up to 12% less than expected in cases of -6.00 diopters cylinder treated for myopic astigmatism using the Allegretto platform. The mean predicted angle of error (the angle between the SIA and TIA axes) was less than 4°, increasing to 12° for against-the-rule astigmatism. The Allegretto platform tended toward a clockwise axis rotational error, whereas the Amaris platform tended toward the opposite. [J Refract Surg. 2017;33(2):104-109.].