Phorcides Guided Topographic Ptk Combined With Cross Linking For Keratoconus

The combination of transepithelial topography guided Phototherapeutic Keratectomy (PTK) with Corneal Crosslinking (CXL) is a well-established treatment method for improving corneal topography and hence visual quality in keratoconus. However, what is not well established is the most predictable method for estimating the refractive effect of the PTK.

The Phorcides Analytic Engine uses vector analysis and lens theory to predict the resultant topographic change of the treatment profile and provides a modified refractive correction. This software has shown impressive results in virgin eyes undergoing topography guided LASIK. This study reports 12-month safety and efficacy outcomes of applying this treatment to keratoconus.   

Private Ophthalmology clinic, Brisbane, Australia. 

 Retrospective single centre consecutive case series of all Phorcides treatments performed by 2 surgeons (DG and BC) between January 2020 and December 2023. Alcon WaveLight Contoura treatment plans, Pentacam anterior and posterior surface keratometry and subjective refraction were input to the Phorcides planning software to calculate modified refractive corrections. Transepithelial topography guided PTK was performed and immediately followed by refractively neutral 45-50 um PTK on the Wavelight EX500 excimer laser. An accelerated corneal cross linking protocol was performed on the same day. Postoperative assessments were performed at 1 week, 1 month, 3 months, and 12 months. 

A total of 65 eyes were included. By 12 months, there was an overall flattening of the cornea with an average reduction in KMax of 4.0D. In 30% of eyes, KMax reduced by 5D or more. The mean refractive cylinder reduced by 1.40D, and 20% of eyes had a reduction of 3.00D or more. CDVA improved by 2 or more lines in 42% of eyes, and no eyes lost 2 or more lines of CDVA. No eye showed progression of keratoconus. There were no significant post-operative complications.

Topography-guided PTK combined with cross linking is a safe and effective treatment protocol for keratoconus which is well established in the literature. The use of the Phorcides Analytic Engine has proved to be a useful tool for determining the most appropriate modified refractive correction and can be used in keratoconic eyes. This method removes the estimations often required in refractive topographic treatments, providing the surgeon with more confidence in determining the required refractive correction. This technique provides excellent improvements in both corrected and uncorrected vision compared to cross linking alone and has demonstrated good refractive predictability at 12 months follow up.