ASTIGMATISMDefinition
Jessica Conroy, OD, FAAO
Astigmatism
Corneal astigmatism is the difference between the two principle keratometry meridians.
- Low corneal astigmatism is defined as being <2.00D.
- High corneal astigmatism is defined as being >2.50D.
Calculated residual astigmatism is the difference between corneal astigmatism and refractive astigmatism.
Actual residual astigmatism is the amount of astigmatism refractive error present when a contact lens is placed on the eye (i.e., the amount of astigmatism in an over-refraction).1
- Low Residual Astigmatism is defined as being <0.50D.
References
- Bennett ES, Henry VA, Kinoshita BT, Lampa M. Correction of Astigmatism. In Bennett ES, Henry VA. Clinical Manual of Contact Lenses, 5th ed., Wolters Kluwer, Philadelphia, PA, 2020:388–439.