Keratoconus is a corneal disease that leads to various ocular illnesses such as scarring and thinning and the most common treatment for this disease at this time is Cross Linking. Previously, post-surgical outcomes of cross linking were analyzed using the AK (Amsler- Krumeich) system which didn’t account for posterior corneal surface and corneal thickness. In order to overcome these shortcomings, a new ABCD classification was developed which accounts for anterior (A) and posterior (B) radius of curvature, thinnest corneal pachymetry (C) and distance for best corrected vision (D).
A retrospective study was done using 104 patients who underwent CXL treatment for keratoconus at Wills Eye between 1/2016 and 6/2019. The ABCD values of these patients were analyzed at 1, 3, and 6 months post-op visits Patients who had undergone a previous Lasix surgery were excluded from this study as their cornea might show different post-surgical changes.
Paired T-test analysis showed the A value progressed initially (from 3.6 to 3.88) but improved compared to baseline by 6 months. This A value roughly correlates to Kmax value and this improvement from baseline matched up with what was seen in previous studies. The B (posterior measurements) and C (thickness) values also increased significantly at 3 months and showed regression by 6 months, but was still progressed when compared to baseline.
A, B and C all initially progressed post-operatively and then regressed. However, at 6 months post operatively, the A values improved compared to baseline measurements while the B and C values did not. Thus it seems as if CXL surgery is able to improve keratoconus in the anterior cornea but is not as effective in the posterior cornea. Having this data is helpful in evaluating post-operative patients. Seeing an initial regression in the B and C value should not be a concern as it seems that they stabilize later than the A value; it does not mean that the CXL surgery was unsuccessful.
Patel, Sonali; Vadhar, Neil; and Syed, Zeba, "ABCD progression post crosslinking for Keratoconus" (2021). Phase 1. Paper 13.