Ivis Excimer Laser Tomography Raytracing-Driven Corneal Remodelling In Stable Keratoconus

The iVis excimer laser (iRES) system uses the tomographic data from a preoperative corneal tomographic measurement to plan and execute tomography derived raytracing-driven corneal remodelling for irregular corneas.  All other laser platforms convert topographic or tomographic data into corneal wavefront data and ablate a wavefront correction not a direct topographic or tomographic correction.  We describe the outcome of tomographic raytracing-driven corneal remodelling using the iRES laser and its planning software (CIPTA) in stable keratoconus.

Adelaide University and Ashford Advanced Eye Care

Keratoconus cases were observed for disease stability, either spontaneously achieved or post-corneal collagen crosslinking. An exploratory planning of a possible ablation targeted at corneal remodelling to regularise the corneal surface was undertaken. Cases with a calculated likely thinnest post-operative pachymetry of less than 400 microns were excluded. This minimum pachymetry was to allow corneal collagen crosslinking should any ablation destabilise previously stable cornea.Transepithelial ablations were carried out ,followed for 3 and 6 months with refractive and tomographic measurements.If there was sufficient corneal thickness to allow inclusion of a correction for the pre-operative sphere equivalent in the ablation, it was included.

19 eyes were treated in 17 patients.  3 month and 6 month follow up was undertaken with the following results, 16 eyes reaching the 6 month point to date.  Mean (SD) preoperative logMAR UAVA of  0.85 (0.33) improved to 0.36 (0.29) at 6 months.  DCVA (logMAR) improved from 0.23 (0.19) to 0.05 (0.12).  Refractive cylinder improved from a mean (SD) 5.75D (2.22) to 3.14D (2.05) with a mean (SD) of 3.92 (3.15) improvement in lines of UAVA .  The mean (SD) improvement in lines of UCVA in eyes with sphere equivalent refractive data included in the ablation was 5.42 (2.88).

No corneas have demonstrated instability with follow-up of 6 months.  No complications have been encountered

Tomography derived ray tracing-driven excimer laser regularisation of keratoconic corneas using the iVis laser was safe and effective in this cohort.   This strategy is different to other excimer lasers, employing corneal wavefront data in their topographic or tomographic treatments. It led to gains of between 3 and 4 lines of unaided vision, on average, increasing to between 5 and 6 lines in cases where sufficient corneal thickness allowed inclusion of refractive sphere equivalent correction in the ablation