17100 Contact lens fitting after corneal CXL Varsha Rathi Somasheila I Murthy L V Prasad Eye Institute, Hyderabad, India The authors have no financial interest to disclose

Introduction Keratoconus is a bilateral progressive, asymmetric, non-inflammatory ectatic disorder of the cornea that results in high irregular astigmatism resulting in reduced vision Management of keratoconus Arrest progression with CXL Improve vision with glasses, contact lenses and surgery Effectiveness of CXL with the help of ultraviolet A and the photosensitizer riboflavin to arrest the progression of keratoconus and ‘freeze’ the cornea with resultant flattening of the central corneal curvature, improvement in the best-corrected visual acuity, reduction in sim k values is known

Introduction Contact lenses especially rigid gas permeable (RGP) lenses can be considered in improving vision and the selections of RGP lens parameters is mainly dependent on the severity and morphology of the cone Corneal topography helps in determining the severity and morphology It is of interest to study how the contact lens fitting relationship changes after this procedure Purpose: To evaluate the rigid contact lens fitting following CXL

Materials & Methods Retrospective observational study Patients who underwent CXL and presented to contact lens clinic from January, 2008 to July, 2011 were reviewed Comprehensive eye examination Corneal topography with Orbscan IIz before and after CXL Inclusion criteria - Patients who had pre and post CXL contact lens usage Diagnostic Contact lens fitting method based on topography data Trial continued till an acceptable dynamic and static fit achieved Acceptable dynamic fit - well centered lens on cornea, exhibited post blink movement of 1.5 to 2.0 mm and stable in all directions of gaze movements Acceptable static fit - a minimal central fluorescein clearance to minimal central bearing and edge clearance of 0.4 to 0.6 mm Over CL refraction was done once the lens fit was found to be acceptable to finalize the contact lens power

Static fit This photograph shows central This photograph shows a pooling of fluorescein with contact lens after CXL in keratoconus patient This photograph shows a fluorescein pattern of 3 point touch after CXL in keratoconus patient

Statistical analysis Descriptive statistics was used to describe patient demographics and paired test was used to compare the pre and post collagen cross linking data on refraction, visual acuity and contact lens parameters. The statistical significance was kept at p<0.05

Results n= 34 eyes of 27 patients Male 23 Mean age 19.4 ± 4.3 years, range (range, 11- 26 years) Diagnosis - Keratoconus (n=32 eyes) Pellucid marginal degeneration (PMCD=1 eye) Post LASIK ectasia (n=1 eye) One patient had keratoconus associated with vernal keratoconjuntivitis Vogt’s striae (n= 19 eyes), Fleischer’s ring (n= 27 eyes), apical scar pre-operatively (n=7eyes) Mean duration between the surgery and contact lens use =2.53 months (range: 1-5 months) One third of the patients started wearing contact lens one month following the surgery

Pre and postpost-operative refraction, corneal topography and contact lens parameters Variables Pre-operative Post-operative p value Refraction_ sphere -4.16 ± 4.77 -4.11 ± 4.32 0.278 Refraction_cyl -4.36 ± 3.16. -3.54 ± 2.51 0.261 BSCVA 0.50 ± 0.37 0.52 ± 0.36 0.751 Sim K_max 56.12 ± 5.44 57.31 ± 4.87 0.233 Sim K_min 50.26 ± 4.64 51.4 ± 5.05 0.099 Contact lens Base Curve 6.99 ± 0.41 6.92 ± 0.38 0.103 Power -5.15 ± 2.86 -5.63 ± 3.03 0.133 Visual acuity with CL 0.07 ± 0.09 0.09 ± 0.18 0.556 Average daily wear 10.31 ± 1.35 10.25 ± 2.01 0.884 Central fit (3 point-touch vs central pooling) n=(24, 10) n=(30, 4) 0.146 Best spectacle corrected visual acuity - BSCVA

Keratoconus – CL after CXL Same lens Different lenses continued n=12 eyes n=20 eyes Pre Post Pre Post Sim k 51.63 ± 4.37 52.6 ±4.88 49.47±4.75 51.43±5.05 55.85 ± 4.95 56.49 ±4.46 57.12±5.83 57.31 ±4.31 Base curve 6.97 ±0.42 7.00±0.41 6.88 ±0.35 Diameter 9.07 ±0.35 9.18 ±0.48 9.18 ±0.47 visual acuity 0.09±0.09 0.05 ±0.07 0.06±0.09 0.05 ±0.07 3 point touch 9 10 13 18 Central pooling 3 2 7 2

Complications Central corneal haze after CXL n= 31 eyes ( no significant difference in BCVA) Post CXL CL intolerance n=1 eye The central fitting has changed in 12 (35%) eyes. Among them change from central pooling to 3 point touch was seen in 9 eyes and from 3 point touch to central pooling was seen in 3 eyes (p=0.146)

Results and discussion The change in the contact lens fit indicates the changes in the shape of the cone after CXL Our study describes RGP contact lens fitting following CXL and results show that RGP contact lens can be fitted in these eyes immediately after the healing of the cornea As evident from our study one could use patients own RGP contact lens or similar parameter lens in the absence of significant changes in the corneal topography With higher Sim k values, the base curve of the lenses changed compared to when the patients continued using their own lenses