ABCD Grading System Useful in Monitoring Post-CXL Corneas

Keratoconus of eye
Macro eye photo.
Investigators review a grading system for evaluating corneal parameters after corneal crosslinking, depending on the cone location.

Among patients with keratoconus, no differences were observed in postoperative corneal crosslinking (CXL) response between different cone locations in the ABCD grading system, except an earlier recovery of the parameter D in peripherally located cones, according to results of a study published in the Journal of Optometry.

The investigators prospectively evaluated postoperative results of corneal parameters and the ABCD grading system, depending on the cone location, in 30 eyes of 25 adult patients with keratoconus (mean age, 26.3±5.9 years; 72% men), who received CXL treatment at a tertiary eye center between 2018 and 2020. 

The team examined patients’ eyes at the baseline and at 3, 6, and 12 month visits following CXL, including visual acuity and Scheimpflug tomography. They classified patients into 2 groups based on X-Y coordinates of maximal keratometry, a central and paracentral cones group (within the central 5 mm corneal zone) and a peripheral cones group (outside the central 5 mm corneal zone).

The investigators found that parameter A (anterior radius of curvature) remained stable and parameter B (posterior radius of curvature) and parameter C (corneal thickness) showed significant increases in both groups postoperatively. For parameter D (best corrected distance visual acuity), they observed stability in the peripheral keratoconus group and improvement at 12 months in the central and paracentral keratoconus group.

“The ABCD grading system could be a useful tool in assessing the efficacy of corneal cross-linking, as it is more detailed and incorporates anterior and posterior curvature, thickness measurements, and visual acuity; however a longer follow-up period is needed for more accurate information about halting the [keratoconus] of different cone locations,” report the researchers.

They highlighted that visual acuity/parameter D was significantly better in the central and paracentral keratoconus group and noted that the study was limited by the small sample size.


Krolo I, Kasumović A, Matoc I, Sabol I, Radman I, Ratković M. The ABCD grading system in assessment of corneal cross-linking effect in keratoconus with different cone locations. J Optom. Published online October 4, 2021. doi:10.1016/j.optom.2021.09.002