Abstract
Purpose: :
Orthokeratology (Ortho-K) is non-surgical fitting of rigid contact lens to temporarily reduce myopia. Corneal collagen cross-linking (CxL), a new treatment for keratoconus is considered to halt the progression of keratoconus. The hypothesis is that in keratoconus if cornea can be re-shaped & flattened with Ortho-K then subsequent CxL may help retain this improved shape. Our aim was to study whether preoperative Ortho-K combined with CxL works better than standard cross-linking in the treatment of keratoconus.
Methods: :
We prospectively treated 19 known keratoconus patients (age-18-39 years, maximal K<60D, minimal pachymetry 400µ) after randomizing them to CxL alone (Group I, n=10) or CxL combined with pre-operative Ortho-K (Group II, n=9). A custom designed reverse geometry (RVG) rigid gas permeable lens with at least 8mm central corneal touch was worn for 7 nights before CxL in the Ortho-K group. Standard CxL was performed by mechanical debridement of 9mm of central epithelium, followed by application of Riboflavin drops (0.1% Riboflavin in 20% dextran) every 3 minutes for 30 minutes, & exposure to UV-A (3mW/cm2) for 30 minutes with the instillation of riboflavin drops every 5 minutes in between. Refraction, topography, corneal hysteresis, confocal & specular microscopy were performed pre & 6 months post-operatively. The primary outcome was the difference in refractive outcome between the two groups pre & post CxL.
Results: :
In the Ortho-K group, after 1 week of wearing the RVG lens but before CxL treatment we detected minimal change in mean steep K (Dioptres, SD) {baseline- 48.09 (2.28), post-ortho-K 47.86 (2.74), p=0.25} and astigmatism {baseline- 2.94 (1.51), post-ortho-K 3.12 (1.29), p=0.64}.At 6 months post CxL, steep K reduced significantly in both groups from baseline. Astigmatism also reduced but insignificantly from baseline (t-test).Mean pre-op and 6-month post-op, steep K and astigmatism: Group I- Steep K: Pre-51.90(4.3), Post 51.16(4.3), p<0.01- Astigmatism: Pre-5.42(3.24), Post- 5.21(3.59), p=0.57.Group II-Steep K: Pre-48.09(2.28), Post 47.69(2.34) p=0.01-Astigmatism: Pre-2.94(1.51), Post- 2.66(0.94) p=0.27There was no difference in effect in two groups (steep K p=0.3, astigmatism p=0.79) even after correcting for baseline differences in steep K and astigmatism.
Conclusions: :
This exploratory randomized trial suggests that one week pre-operative Ortho-K does not seem to work better than standard CxL in improving the corneal shape & reducing astigmatism in patients with keratoconus.
Clinical Trial: :
www.ISRCTN.org ISRCTN29378493
Keywords: keratoconus • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials