Posters

Repeatability of field averages versus single point measurements of maximal corneal curvature and elevation in keratoconus using a dual scheimpflug-placido topography system

Poster Details

First Author: C.Mehanna LEBANON

Co Author(s):    C. Mehanna   L. Asroui   A. Salloum   R. Shalhoub   C. Roberts   S. Awwad     

Abstract Details

Purpose:

To evaluate the repeatability of keratometric field averages centered on the point of maximum keratometry (Kmax), compared to that of the single point Kmax, in eyes with keratoconus.

Setting:

Department of Ophthalmology, American University of Beirut Medical Center, Beirut, Lebanon.

Methods:

49 eyes of 34 adult patients with keratoconus were evaluated with 3 consecutive scans using the Galilei dual Scheimpflug-Placido system. Eyes were subdivided into those with Kmax50D and those with Kmax>50D. Repeatability of the single point Kmax was compared to that of field averages centered on it, with radii ranging from 0.1mm to 2.0mm. Repeatability was assessed by within-subject standard deviations (Sw), repeatability limits (r), and intraclass correlation coefficients (ICC). The repeatability of the location of Kmax, determined from its coordinates, was also assessed.

Results:

Compared to Kmax, repeatability was improved with a 1.5mm radius field average for eyes with Kmax50D (r=0.99D and r=0.72D, respectively), and a 2.0mm radius field average for eyes with Kmax>50D (r=2.38D and r=1.05D, respectively). Repeatability limits for all radii were worse with Kmax>50D (range: 1.05D to 2.85D) than Kmax≤50D (range: 0.58D to 1.71D). For all eyes, the repeatability limit of the location of Kmax was 0.91mm.

Conclusions:

Field averages centered on Kmax resulted in clinically adequate improvement in repeatability only with radii of 1.5mm or greater, for eyes with Kmax50D. This improvement in repeatability, while providing better specificity, comes at the cost of larger field averages, which can decrease the sensitivity of early keratoconus progression detection. The steepest field average may yield better repeatability than that of a field average centered on the steepest keratometric point.

Financial Disclosure:

receives consulting fees, retainer, or contract payments from a company producing, developing or supplying the product or procedure presented