Placement of a hard contact lens on an irregular cornea provides a smooth anterior surface, helping the clinician to determine the contribution of the surface irregularity to vision loss.
Evaluation of the mires projected onto the cornea during keratometry and Placido disk–based topography can help distinguish irregular astigmatism (distorted mires) due to ocular surface irregularity from regular corneal astigmatism (clear but oval mires).
Corneal topography and tomography can give the clinician accurate data on corneal power, elevation, and thickness that are useful in diagnosis and surgical planning.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.