To best identify patients at risk, clinicians should follow a specific criteria that takes into account baseline refraction and topography measurements, according to a research team who outlined their  findings at the American Society of Cataract and Refractive Surgery (ASCRS) 2021 meeting in Las Vegas. 

Patients who present with at least 2 D of refractive astigmatism, or who have 1 D to 2 D of against the rule (ATR, 60 ˚ to 120 ˚), refractive astigmatism should be referred for further evaluation and corneal topography, the study shows. 

The recommendations follow a retrospective analysis of the baseline manifest refraction of 1020 eyes with keratoconus that have not undergone previous corneal surgery. Based on Pentacam® (Oculus) metrics (maximum, steep, flat, and mean keratometry), the team divided patients into 3 groups based on the axis of astigmatism: with the rule (WTR, 0 ˚ to 30 ˚, 150 ˚ to 180 ˚), ATR (60 ˚ to 120 ˚), and oblique astigmatism (120 ˚ to 150 ˚, 30 ˚ to 60 ˚). 

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The study shows the average manifest refraction of all eyes was sphere of -2.2D, and cylinder of 3.2D. Patients younger than 20 years were commonly found to have ATR (37%) and oblique (32%) astigmatism, respectively. 

Topography metrics show Kmax, Ksteep, Kflat, Kmean, and Kastig were 58.0±0.6 D, 50.6±0.4 D, 46.8±0.4 D, 48.0±0.4 D, and 3.8±0.2 D, respectively. In eyes with Kmax <50D, Kastig was 2.0±0.2D, and average Ksteep <45D, the report explains.

Researchers advocate for additional consideration for patients with at least 2 D of corneal astigmatism in the hopes that this would empower general eyecare practices to offer a low-cost screening approach.

Disclosure: Multiple study authors declared affiliations with the biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.  


Greenstein S, Wawrzusin P, Hersh P, Gelles J, Ando A, Garvey N. Refraction and keratometryin keratoconus: a proposed screening algorithm. Poster presented at: 2021 ASCRS Annual Meeting; July 2021; Las Vegas, NV. Abstract 76244. 

This article originally appeared on Ophthalmology Advisor