The Effect of The Changes in Cylinder Power and Axis of Toric Soft Contact Lenses on Vision of Astigmatic Subjects

Purpose: To investigate the effect of higher cylindrical power and axis misalignment of toric SCL in mild and moderate astigmatism on visual acuity, contrast sensitivity, visual satisfaction, and vision acceptability. Methods: 20 astigmatic participants underwent randomized experimental trial for the following conditions on different days: full cylinder power, higher cylindrical power by 0.5D, and higher cylindrical power by 1.0DC. Axis was also misaligned by -10 and +10degree for each cylinder power alteration. Baseline and outcome variables were assessed using: Snellen chart for visual acuity, Pelli-Robson Chart for contrast sensitivity, and VAS scale for visual clarity, satisfaction and vision acceptability. Results: Overcorrecting cylinder power resulted in significant effect (p<0.05) on all variables. Overall, higher cylindrical power by 1.0DC had stronger statistical evidence (p<0.01) than 0.5DC. There was no significant difference between the mild and moderate astigmatism groups, except for the visual acuity when higher cylindrical power by 0.5 D was implemented. Misalignment by both +10° and -10° had a significant effect on all variables, except contrast sensitivity. Conclusion: Toric SCL with higher cylindrical power by 0.5DC and 1.0DC as well as misalignment of 10° had a significant effect on visual acuity, contrast sensitivity, clarity, satisfaction, and vision acceptability in patients with mild to moderate astigmatism.