Fine-tuning of the crosslinking procedure is producing better end results for patients.
This article was reviewed by Karolinne M. Rocha, MD, PhD
The changes to the eye caused by ectasia are profound and comprehensive—with shape, structure, strength, and sight affected.
In advanced disease, the changes in corneal shape are marked and the clinical findings are visible during slit-lamp evaluation. The corneal structure is affected extensively by significant epithelial hyperplasia that fills the space and compensates for the characteristic stromal loss.
Biomechanical changes occur early in the disease process and are essential for determining the corneal geometric and optical properties. Finally, progressive disruptions in sight are manifested clearly by the worsening of the point spread function on topographic evaluation, according to Karolinne M. Rocha, MD, PhD, assistant professor of ophthalmology, and director, corneal and refractive surgery, Storm Eye Institute, Medical University of South Carolina, Mount Pleasant, SC.
The goal in keratoconus is treatment with crosslinking (CXL) as early as possible when progression becomes evident. The epi-off procedure is the current gold standard treatment with proven efficacy and more than 10 years of follow-up.
The classic Dresden protocol, Dr. Rocha recounted, is application of 0.1% riboflavin-5-phosphate with 30 minutes of soaking and 20% dextran during a 30-minute exposure time to 370 nm of ultraviolet (UV) A light with an irradiance of 3 mW/cm2.
“The three main components of the CXL procedure are riboflavin, UV light, and the drug,” she noted. “The stromal availability of all the components impact the efficacy of the CXL procedure.”
Dr. Rocha demonstrated the structural changes in the collagen fibers that occur following the epi-off procedure. In contrast, the epi-on CXL procedure can be performed in patients with a corneal thickness less than 400 μm. This procedure is advantageous in that it improves patient comfort with more rapid return to normal daily activities and reduces the risk of infection, she explained.
However, a meta-analysis of epi-on techniques reported inconsistent efficacy.
“Studies reported improved maximum keratometry values, but in some cases keratoconic progression was evident,” she said.