Corneal tissue addition keratoplasty offers another option for keratoconus treatment
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Corneal tissue addition keratoplasty, or CTAK, is a novel intrastromal lamellar keratoplasty technique for the treatment of keratoconus.
Given my long-standing interest in keratoconus, in 2015 I started working with preserved corneal tissue inlays to recontour the irregular keratoconus corneal shape. Early implantations of shaped tissue inlays of various sizes, under an institutional review board protocol, gave excellent improvements in corneal topography; however, visual acuity outcomes were not satisfactory, likely secondary to the graft interface over the pupil. Thus, the procedure has evolved over time into a pupil-sparing intrastromal lamellar inlay (Figure 1). The CTAK tissue itself is prepared from preserved, gamma-irradiated, sterilized, acellular corneal tissue.
Clinical study results
With my co-developers, Drs. Steven Greenstein and John Gelles, and in partnership with CorneaGen and Ziemer, the CTAK lamellar inlay and surgical technique have been refined to give excellent patient outcomes. In a prospective clinical trial of 21 eyes of 18 patients published in the Journal of Cataract & Refractive Surgery, we found that uncorrected visual acuity improved, on average, six logMAR lines, with half of the patients improving more than six lines. Spectacle corrected distance visual acuity improved by approximately three lines. Manifest refraction spherical equivalent decreased from an average of –6.3 D to –1.6 D. Looking at corneal topography descriptors, there was an average flattening of mean central keratometry of 8.4 D, maximum keratometry of 6.9 D and average maximum corneal flattening of 16 D. There was one adverse event, with a channel tear requiring suturing. CTAK has now been used in more than 150 patients by different surgeons who report similar outcomes.
Customization
Importantly, the CTAK inlay can be customized to a particular patient’s topographic and clinical characteristics. By varying inlay thickness, the arc length subtended (up to an almost complete doughnut of 330°) and the radius of curvature, as well as meticulously planning the inlay position, results can be optimized for the patient’s individual corneal topography characteristics, with the goal of restoring as normal a corneal curvature as possible. Using a variety of topographic and tomographic parameters, each CTAK inlay is prepared to custom specifications after final review by the surgeon. The tissue is processed to these specifications by CorneaGen using the Ziemer Z8 femtosecond laser. The surgeon receives the CTAK inlay with the customized dimensions, as well as a suggested surgical plan derived from the individual patient’s topography and tomography characteristics.
CTAK surgical procedure
The first step in the CTAK procedure is marking of the patient’s cornea to assure proper location and placement of the inlay, which is a requirement for optimal outcomes. To guide this, the surgeon receives a planning diagram for each individual patient delineating proper inlay positioning (Figure 2). A full set of CTAK instrumentation has been designed in partnership with Corza to facilitate each step of the procedure. After marking using the appropriate optical zone marker, a properly sized channel is prepared with a femtosecond laser. The depth of placement within the cornea is typically 200 µm.
Source: Peter S. Hersh, MD
The CTAK tissue is sterilely removed from its transport container and irrigated with balanced salt solution (Figure 3). A CTAK dissector is used to fully open the channel. Using placement forceps, the CTAK tissue is advanced into the intrastromal channel. In practice, the gamma-irradiated preserved tissue has some rigidity to it, facilitating placement. Next, the CTAK manipulator can be used to adjust tissue position. At the end of the procedure, the lamellar inlay is smoothed with an applanator over the corneal surface. Typically, no suture is required.
Patient selection
Although CTAK can be used for a wide range of keratoconus patients, an ideal early candidate would have a maximum keratometry of between 50 D and 75 D with the center of the cone within the 6-mm optical zone of the cornea. Corneas with very peripheral steepening should be avoided. Patients with central scarring who do not have good potential visual acuity are not good candidates. In addition, patients with corneal ectasia should be carefully evaluated because of potential risks to the flap. With properly customized inlays, good results can be obtained across the spectrum of mild, moderate and marked keratoconic eyes (Figures 4 and 5).
CTAK brings a new treatment option for our keratoconus patients. Customized tissue preparation and meticulous surgical planning lead to excellent outcomes. Typically, results have been quite satisfying, with happy patients and substantially improved visual function. Having followed patients for 8 years now, the tissue itself seems to be biocompatible with continued clarity over the years.
- Reference:
- Greenstein SA, et al. J Cataract Refract Surg. 2023;doi:10.1097/j.jcrs.0000000000001187.
- For more information:
- Peter S. Hersh, MD, of Cornea and Laser Eye Institute in Teaneck, New Jersey, can be reached at phersh@vision-institute.com.
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