Comparison Of Epithelium-Off Hypo-Collagen Cross Linking And Oxygen Assisted Epithelium On Iso-Collagen Cross Linking In Keratoconus In Corneas Thinner Than 400 Microns Excluding The Epithelial Thickness : A Randomized Comparative Trial

In corneas thinner than 400 microns, after the epithelial debridement hypo-CXL has been used with suboptimal outcome. Epithelium on Iso-CXL has limitation of lesser penetration of riboflavin as well as oxygen. Oxygen supplementation in epithelium off CXL in published human studies has shown better outcome.

Only single published non comparative study with oxygen supplementation in epithelium on CXL showed better outcome without any complications. Hence we planned a study comparing epithelium off hypo-CXL versus epithelium on Iso-CXL with increased riboflavin penetration with 0.01% benzalkonium chloride and oxygen supplementation to know which technique can be preferred in eyes where corneal thickness is less than 400 microns. 

The study was conducted at  Dr Rajendra Prasad Centre For Ophthalmic Sciences, AIIMS, New Delhi. A sample population (n=40), willing to give consent will undergo pentacam and patients with pachymetry values of 400 microns to 430 microns will undergo preoperative ASOCT. Those candidates with thickness less than 400 microns excluding the epithelial thickness will be selected and randomized by computer generated randomization protocols and will be divided into two groups of 20 patients each. 

First group will undergo epithelium on accelerated iso-osmolar CXL (UVA 9mW/cm2 for 10min) with 0.01% benzalkonium chloride under increased oxygen concentrations (100%) delivered with the help of corneal oxygen goggles. Second group will undergo epithelium off accelerated hypo-osmolar CXL under normal atmospheric oxygen concentrations. The patients will then be followed up at 1week, 1month, 3months and 6months to obtain specific parameters. The parameters so obtained would then be analyzed using Stata 12.1 software.

Inclusion Criteria for the study were:

1)Progressive keratoconus 

2)Age more than 16years 

3)Corneal thickness less than 400microns excluding the epithelial thickness on ASOCT but more than 400microns including epithelial thickness

The parameters in both the group were analysed using stata 12.1 software. The parameters in both the group showed comparable change with stability of the disease with no further progression of keratoconus. However pain score in epithelium on group was much less compared to epithelium off group.

Epithelium off accelerated CXL causes pain, photophobia and transient reduction in vision for few weeks post operatively and need for bandage contact lens use and risk of infective keratitis .This can be avoided with epithelium on accelerated CXL with 0.01% benzalkonium chloride and oxygen supplementation as it is as effective as epithelium off hypo-CXL at normal atmospheric oxygen tension in corneas thinner than 400 microns excluding the epithelial thickness.