The aim of this study is to detect the safety and effectiveness of contact lens assisted corneal cross linking in managing progressive keratoconus with thin corneas CACXL was done for 40 eyes of 30 of keratoconic patients presented to cornea outpatient clinic in Kasr Alainy teaching hospital The UDVA ,BDVA KMAX, thinnest corneal thickness pre-operative and 9 months postoperatively and the endothelial cell count was measured preoperative and 3 months postoperative Demarcation line was measured after 1 month by using ASOCT There was statistical significant difference in UDVA and BDVA, there was stabilization of Kmax there was decrease in endothelial cell count but not statistically significant According to results the procedure seems to be effective and safe un managing progressive keratoconus.

Corneal collagen cross linking showed effective results in stabilizing progressive keratoconic corneas. It is the only treatment that halts progression of keratoconus, It was first described in 1998 by Spoerl et al . A major limitation of the procedure that it cannot be used in corneas with pachymetry less than400 micrometers based on the fact that an irradiance of 0.37 mW/cm2 has been found to be cytotoxic for the endothelial cell layer. Since the absorption coefficient for the human corneas is 70 cm-1 and the intended surface irradiance is 3.0 mW/cm2, the 0.37 mW/cm2 irradiance is reached at 300 microns depth. In a 400 microns thick cornea saturated with riboflavin, the irradiance at the endothelial level is 0.18 mW/cm2, which is a factor of 2 smaller than the damage threshold. Therefore, the 400 microns limit is considered to be a safe limit to protect the endothelium and intraocular structures from the hazards of UV irradiation 12 However , the patients with advanced ectasia who are desperately in need for cxl , are the same ones who have thin corneas often below the threshold which is considered to be safe for CXL treatment However further studies with longer follow up and larger numbers of cases are needed to confirm our findings.

Inclusion Criteria:

• Age from 18 to 35years old Mild , moderate and severe keratoconic patients with a corneal thickness from 360-400 µm at the thinnest location .

Exclusion Criteria:

• • Previous corneal surgeries such as rings or crosslinking.

  • Patients with stromal corneal scar.
  • Other ocular pathology such as glaucoma or iridocyclitis.
  • Patient with systemic diseases that likely affects wound healing such as insulin dependent diabetes mellitus.
  • Patients with collagen vascular diseases, autoimmune or immune deficiency diseases.
  • Pregnant or nursing women.
  • Patients taking the following medications ; isotretinoin, amiodarone, sumatriptan.
  • Other corneal pathology rather than keratoconus