A new Tomographic Method of Staging/Classifying Keratoconus: The ABCD Grading System

Abstract

Purpose: To incorporate advanced corneal imaging into a new keratoconus classification system that utilizes posterior curvature, thinnest pachymetry, and best-corrected distance vision (CDVA) in addition to standard anterior parameters. Materials and methods:A total of 672 eyes of 336 normal patients were imaged with the Oculus Pentacam HR. Anterior and posterior radius of curvature measurements were taken using a 3.0 mm zone centered on the thinnest area and corneal thickness was measured at the thinnest point. Mean and standard deviations were recorded and anterior data were compared to the existing Amsler-Krumeich (AK) classification. Results:A total of 672 eyes of 336 patients were analyzed. Anterior and posterior values were 7.65 ± 0.236 mm / 6.26 ± 0.214 mm respectively and thinnest pachymetry values were 534.2 ± 30.36 um. Comparing anterior curvature values to AK staging yielded 2.63, 5.47, 6.44 standard deviations for stages 1, 2, and 3 respectively. Posterior staging uses the same standard deviation gates. Comparative pachymetric values yielded 4.42, and 7.72 standard deviations for stages 2 and 3 respectively. Conclusion:A new keratoconus staging system incorporates posterior curvature, thinnest pachymetric values, and distance visual acuity in addition to the standard anterior curvature and consists of stages 0 to 4 (5 stages), closely matches the existing AK classification stages 1 to 4 on anterior curvature. The new classification system by incorporating curvature and thickness measurements based on the thinnest point, as opposed to apical, better reflects the anatomic changes in keratoconus.

Reliability analysis of successive Corvis ST® measurements in keratoconus 2 years after accelerated corneal crosslinking compared to untreated keratoconus corneas

“…The crosslinking group (CXLG) consisted of 20 KC corneas of 16 KC patients who underwent epithelium-off accelerated CXL (9 mW/cm 2 , 10 min, 5.4 J/cm 2 ) two or more years ago with the Avedro KXL® system (Avedro, Waltham, MA, USA) using riboflavin VibeX Rapid™ 0.1% solution (Avedro, Waltham, MA, USA). Diagnosis of KC was based on clinical features such as corneal hemosiderin deposition known as a Fleischer ring, Vogt striae, corneal thinning on the slit lamp examination, and/or tomographic abnormalities as detected within the Belin/Ambrósio-enhanced ectasia screening display within the Pentacam® HR software (high resolution (HR), Oculus, Wetzlar, Germany) [ 16 , 17 ]. KC progression was defined as an increase in corneal astigmatism ≥ 1 diopter (D), and/or an increase of maximal keratometry (Kmax) ≥ 1 D and/or a decrease of corneal thickness of 30 µm within 1 year.…”

Corneal Surface Elevation and Thickness in Relation to the Fit of Rigid Contact Lenses in Keratoconus and After Corneal Cross-Linking

“…Keratoconus was graded from 0-to-4 according to the "A, B, C, D" staging system advocated by Belin et al and fully explained elsewhere. 28 Patient's self-assessment of the comfort experienced during contact lens wear was evaluated on a 0-to-5 visual analogue scale (where 0=very poor, 1=poor, 2=not good, 3=satisfactory, 4=good and 5=very good) like those proven useful in pain studies. 29,30 In addition, each patient recorded the total number of hours their lenses were worn each day, at 1 week, 3 and 6 months.…”

Keratoconus: Diagnosis and Staging

“…9). 26 Of the newer proposed classification/staging systems, the ABCD seems to have the widest acceptance, yet the AK systems, despite its significant limitations and lack of clinical utility, remain the most commonly used in articles and presentations.…”