Advances in technology are improving patient outcomes across many areas of eye care, and refractive surgery is no exception. Many improvements have occurred in excimer laser hardware, for example, including eye tracking technology and the capability of creating ultraprecise ablation patterns with more than 100,000 topographic data points.
AT A GLANCE
- In the original Contoura Vision FDA trial, only eyes with perfectly normal topography were included; this did not translate well to clinical practice.
- With the addition of an artificial intelligence component, Contoura LASIK can now treat eyes with complex topographies.
- In a trial including all safe candidates, results with Phorcides Contoura LASIK matched results seen in the FDA trial with highly selective inclusion criteria.
Along with this precision comes an extraordinary amount of data to interpret and convert into the visual results that patients desire, unfortunately requiring time-consuming surgical calculations for each cornea. This challenge, once at the forefront of topography-guided LASIK, is becoming a distant memory, thanks to artificial intelligence (AI) software, which can provide treatment calculations in a matter of seconds, resulting in some of the best LASIK visual outcomes published to date.
EARLY EXPERIENCE WITH TOPOGRAPHY-GUIDED LASIK
Topography-guided LASIK with Contoura Vision on the WaveLight Allegretto Wave Eye-Q or WaveLight EX500 Excimer Laser System (Alcon) made its US debut in November 2015 with high expectations after impressive results in an FDA study.1 Investigators in that study reported that 64.8% of patients achieved 20/16 or better UCVA, as well as statistically significant reductions in glare, light sensitivity, and improvements in overall vision quality as compared with preoperative vision with glasses or contact lenses.2
Unfortunately, these results did not translate to clinical practice, as the FDA study criteria allowed inclusion only of eyes with perfectly normal topography. In other words, the majority of patients in an average clinic would have been excluded. This new LASIK system was capable of remarkable results, but it was too complicated and time-consuming to successfully implement in daily practice.
MEASURING IT ALL
The precise measurement of slight elevations and undulations of each cornea is what gives the Contoura Vision system its great potential, but using it on irregular corneas was difficult because, in these eyes, neither topography nor manifest refraction could fully quantify the total refractive power by itself, and it could take hours to calculate by hand. The Phorcides Analytic Engine (Phorcides) was created to bridge this gap and assist the surgeon in fully harnessing the power of the Contoura Vision technology.
Phorcides uses geographic imaging software, or GIS, to analyze the topography of each cornea and identify visually significant areas of elevation. In geology, a small, elevated mound of material at the base of a larger hill or mountain is termed a talus, and this term has been adapted for describing small elevations seen on corneal topography as well (Figure 1). Each talus is analyzed by the GIS using optical physics to quantify the magnitude and direction of the induced astigmatism as a vector (Figure 2).
Each of these vectors is then entered into the algorithm, along with vectors for anterior corneal astigmatism, posterior corneal astigmatism, and internal lenticular astigmatism, and the program calculates a fully customized AI-recommended treatment in less than 10 seconds.
The ability to simultaneously neutralize all sources of astigmatism and corneal irregularities results not only in better visual acuity, but also in better visual quality. Normalizing the topography reduces higher-order aberrations such as coma (Figure 3) and trefoil, which in turn lessens blur and shadowing.
RESULTS WITH PHORCIDES PLANNED TOPOGRAPHY
With custom wavefront-guided or wavefront-optimized LASIK, generally patients must be counseled that glare and halos may be more prominent at night postoperatively. After Contoura, by contrast, patients have reported less glare than they had experienced preoperatively with their glasses or contact lenses.2
Studies incorporating Phorcides planned topography guidance have yielded some of the best LASIK visual results published to date. In a recent retrospective double-arm study, all eyes suitable for refractive surgery were included for treatment with Phorcides Contoura (PC). The strict inclusion criteria of the FDA Contoura (FC) trial would have accepted only 24% of these eyes for treatment. Despite including a much wider range of regular and irregular astigmatic eyes, treatment with PC resulted in vision at 3 months postoperative that was similar to that with FC; 94% of PC eyes achieved 20/20 uncorrected distance visual acuity (UDVA), compared with 93% of FC eyes, and 63% of PC eyes achieved 20/16 UDVA compared with 69% of FC eyes.2,3 In addition, 37% of eyes that underwent PC treatment had better postoperative UDVA than their preoperative corrected distance visual acuity.3
Looking forward, there are other potential applications for AI in refractive surgery. Phorcides is working on integrating corneal epithelial thickness mapping into its topographic analytic software to produce better PRK results, and the company is exploring how AI could improve power selection for both spherical and toric IOLs.
With highly sophisticated and precise femtosecond and excimer lasers already available today, many of tomorrow’s advances may consist of improvements in AI-guided software to push further the limits of vision correction and ultimately to improve patient satisfaction.
1. Alcon introduces Contoura Vision as first personalized LASIK procedure at American Academy of Ophthalmology annual meeting [press release]. Alcon. November 16. 2015. www.alcon.com/media-release/alcon-introduces-contoura-vision-first-personalized-lasik-procedure-american-academy. Accessed August 11, 2020.
2. US FDA. Allegretto Wave Eye-Q addendum procedure manual T-CAT topography-guided treatments. www.accessdata.fda.gov/cdrh_docs/pdf2/P020050S012d.pdf.
3. Lobanoff M, Stonecipher K, Tooma T, Wexler S, Potvin R. Clinical outcomes after topography-guided LASIK: comparing results based on a new topography analysis algorithm with those based on manifest refraction. J Cataract Refract Surg. 2020;46(6):814-819.