Comparison Of Demarcation Line (Dl) Depth After Accelerated Transepithelial Corneal Cross Linking (Acc Tecxl) Using Hpmc Riboflavin Versus Riboflavin With Vitamin E Tpgs

TECXL uses riboflavin solutions containing permeability enhancers e.g. benzalkonium chloride (BAK), to allow the hydrophilic riboflavin to penetrate the lipophilic epithelium. Vitamin E-TPGS (D-tocopheryl polyethylene glycol succinate)  has also been established to be an effective permeation enhancer across biological barriers. VE-TPGS also  protects biological membranes from free radical damage  which may be beneficial since oxygen free radicals are generated in CXL. DL depth after CXL is often considered a surrogate marker for the effectiveness of the CXL procedure. The purpose of this study was to compare the DL depth in patients with progressive keratoconus (KCN) undergoing Acc TECXL with HPMC riboflavin versus Vit E TPGS riboflavin.

Prospective, randomized, interventional, study conducted at the Cornea Services of a tertiary care institute in India.

Thirty two eyes of 32 patients with progressive KCN were randomized into two equal groups and subjected to Acc TECXL using either HPMC riboflavin (0.25 % riboflavin,1.2 % HPMC, 0.01% BAK) [Group I]  or Vit E TPGS riboflavin (0.1% riboflavin, Vit E TPGS) [Group II]   . Inclusion criteria: i) Age > 16 years ii) Minimum corneal thickness (MCT)  > 360 µ on Scheimpflug imaging iii)K max < 65 D iv) KCN grade 1-3 by Belin ABCD classification. Exclusion criteria: i) previous history of CXL ii) pregnant or lactating women. All patients underwent TECXL with 9mW/cm² X 10 minutes of UV A exposure (total fluence 5.4 J/cm²) . DL depth was measured at 6 weeks following the procedure, on Casia 2 (Tomey ,USA) Swept Source OCT (SSOCT).

Mean age, Kmax,  MCT, uncorrected and corrected distance visual acuity (UDVA and CDVA) at baseline  for group I ( 23.2 ± 6.1 years, 56.5D ± 5.9 D, 460.4 ± 33.9 µ, 0.7 ± 0.3 log MAR, 0.3 ± 0.2 logMAR respectively) and group II (22.6 ± 4.9 years, 55.6D ± 5.9 D, 447.4 ± 32µ, 0.8 ± 0.4 log MAR, 0.3 ± 0.1 logMAR respectively) were comparable ( all p’s >0.05). DL depth for group II (Vit E TPGS riboflavin) was significantly deeper (177 ± 26 µ) than for group I (HPMC riboflavin) (150 ± 26 µ)(p=0.01). The DL was seen at a depth of 32 % and 39.6% of the baseline MCT in groups I and II respectively. In the Vit E TPGS group CDVA at 3 months (0.2 ± 0.1 logMAR) was significantly better (p=0.02) as compared to baseline; it was unchanged in the HPMC group.

Vit E TPGS supplemented riboflavin solution resulted in a significantly deeper demarcation line  and improved CDVA at 3 months  as compared to HPMC riboflavin when used for accelerated TECXL. DL depth seen with both solutions was however less than that reported for conventional epithelium off protocols. Long term evaluation of Vit E containing riboflavin is warranted to assess its  potential benefits .