Astigmatism Correction Strategies

Definitions and Axis Orientation

With-the-rule (WTR) astigmatism has the steepest corneal meridian oriented vertically (approximately 90 degrees), while against-the-rule (ATR) astigmatism has the steepest meridian oriented horizontally (approximately 180 degrees) 1, 2

Low to moderate astigmatism (less than 3.00 diopters) can be corrected with soft toric contact lenses or rigid gas-permeable contact lenses 3, 4
Full cylindrical correction may not be needed initially, especially in adults, and substantial changes in axis or power are poorly tolerated in patients with previously uncorrected or partially corrected astigmatism 5
High astigmatism (3.00 diopters or more) can be corrected effectively with rigid gas-permeable and hybrid contact lenses, and bitoric or back-surface toric contact lens designs minimize corneal bearing and improve centration for greater amounts of corneal astigmatism 4, 6
Custom-designed soft toric contact lenses provide good centration, flexible wear schedules, and improved comfort, and rigid gas-permeable scleral lenses (diameter >17mm) are an option for high and/or irregular astigmatism, particularly with anisometropia 4, 6

Adults with astigmatism may not accept full cylindrical correction in their first pair of eyeglasses, and gradual correction may be better tolerated 5
Regular astigmatism has uniform curvature in each meridian with principal meridians 90 degrees apart, while irregular astigmatism (seen in keratoconus, corneal scarring, and post-surgical corneas) varies at different corneal points and cannot be fully corrected with spherocylindrical lenses 1, 2, 7, 8