Posters

Sectorial thickness progression index: a fixation-independent parameter for the detection of keratoconus

Poster Details

First Author: C.Mehanna LEBANON

Co Author(s):    L. Asroui   J. Khalil   L. El Zein   S. Awwad           

Abstract Details

Purpose:

To determine whether sectors of corneal thickness progression, centered around the thinnest point in the cornea, as well as differences between diametrically opposite sectors, are effective at differentiating corneas with keratoconus from normal corneas.

Setting:

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

Methods:

One-hundred seventy-three keratoconic eyes and 117 normal eyes that were imaged and categorized using the Galilei dual Scheimpflug-Placido system, were included. Maps of corneal thickness progression centered on the thinnest point were obtained, with each point on the map representing the speed of thickness progression from the center, to that point. 15-degree sectors, with radii of 0.5mm, 1.0mm, and 2.0mm, were analyzed. The sectors with the greatest mean thickness progression were identified for every radius. Additionally, the greatest difference in means between diametrically opposite sectors was determined. The area under the receiver operator curve (AUROC) was determined for each outcome.

Results:

For sectors with the greatest mean thickness progression, the AUROC, sensitivity, specificity, and optimal cut-off values were 0.988, 96.5%, 99.1%, and 12.92µm.mm-1 for a radius of 0.5mm, 0.994, 98.3%, 99.1%, and 24.81µm.mm-1 for a radius of 1.0mm, and 0.997, 96.0%, 98.3%%, and 50.23µm.mm-1 for a radius of 2.0mm. An index combining all the sectors, the Sectorial Thickness Progression Index (STPI), was effective at identifying 100% of keratoconic eyes, with a 0% false positive rate. Diametrically opposite sectors with the greatest difference in thickness progression had AUROCs of 0.940, 0.936, and 0.966 for radii of 0.5mm, 1.0mm, and 2.0mm, respectively.

Conclusions:

Sectors of corneal thickness progression, at different radii, as well as differences between diametrically opposite sectors, were effective at discriminating between normal and keratoconic corneas. The STPI is a promising diagnostic approach that offers the advantage of being independent of fixation or of corneal vertex location, and able to detect small regional abnormalities.

Financial Disclosure:

None