Here at Cohen Eye Institute, we receive a significant amount of referrals that result in corneal collagen crosslinking (CXL) in keratoconic patients. In this edition of Foresight, we will discuss topography guided PRK (TG-PRK) which often follows the crosslinking procedure.
Keratoconus (KC) is a primarily a biomechanical problem. Keratoconus compromises the structural integrity of the corneal lamellae, collagen-based triple helices linked by intramolecular hydrogen bonding.
The goal of CXL is to stabilize the cornea, not to improve vision or partially reverse the disease (although this often occurs). We approach the process in many patients by combining CXL and topography guided PRK for the best results. Our process begins with epithelial debridement (9 mm epithelium removal), transitioning into 30 minutes of riboflavin applied in 2-minute intervals throughout the process. After the 30 minute application, we then examine the cornea for the uptake of riboflavin.
The patient then undergoes UVA exposure to the cornea. We have the patient look up at UV diodes, activating the riboflavin. A bandage lens is placed into the eye, and anti-inflammatory, antibiotic drops are used post-operatively.
Epithelial On Treatment (Transepithelial)
We use the same procedure as our standard CXL but do not remove the epithelial cells. The epithelium has a high absorption coefficient in the UV spectrum and may have Riboflavin absorption issues. At this time, new drug delivery systems are being investigated. This process does have the potential disadvantage of lower increases in corneal rigidity compared to epi-off treatment.
TG-PRK for Keratoconus
The objective of our combined process is to strengthen the cornea and then reduce corneal abberations. TG-PRK is not FDA approved for KC but can be used off-label.
A typical keratoconus patient has steepening inferotemporally, where the cornea is relatively flat. A topography-guided ablation combines myopic and hyperopic treatments based on multiple topographies to reduce corneal irregularity.
TG-PRK is not for everyone. It’s designed for select cases. Dr. Cohen evaluates each patient personally to better understand their unique conditions and the solutions required.