Validity of Novel Microsoft Excel Software for Calculating Surgically Induced Astigmatism

Purpose: To investigate validity and predictability of a new software calculator for surgically induced astigmatism quantification.

Techniques and Methods: A new astigmatic calculator was designed, based on Pythagorean principle and trigonometric functions using Microsoft office excel 2007. Astigmatic magnitude was quantified in diopters and axis direction was depicted in degrees. Calculator was applied, investigated and analyzed on 30 pseudophakic eyes that underwent temporal scleral incision surgery with in the bag intraocular lens implantation. Pre and postoperative anterior corneal curvature was measured with Bausch and Lomb keratometer. Similarities and differences were compared with the existing version 1.1 and 2.1 calculators and statistical analysis was performed using Microsoft excel.

Results: Mean pre and postoperative astigmatic magnitude was calculated as 62.67 (+/- 2.40) and 62.83 (+/- 2.29) diopters. Mean pre and postoperative astigmatic axis was 89.74 (+/- 1.37) and 89.51 (+/- 1.37) degrees. Pearson’s coefficient (r) was calculated as 0.91 and 0.83; coefficient of determinations (R2) was calculated as 0.82 and 0.68 for astigmatic magnitudes and axes respectively. Student chi-square test was used to calculate T values, which were 0.39 and 0.26 for astigmatic magnitude and axis respectively. P value less than 0.05 was considered as statistically significant (p 0.16). Validity was compared with existing surgically induced astigmatism calculators 1.1 and 2.1 versions and predictability was assessed by y=2.83+0.95x for astigmatic magnitude and y=15.28+0.83x equations for astigmatic axis.

Conclusion: Present Microsoft excel calculator application was valid as the values for astigmatic magnitude and axis were comparable with existing SIA calculators and can be used for astigmatic predictability.