Corneal minimized-volume ablation with accelerated CXL appears promising for keratoconus

In this prospective pilot study, the authors investigated the safety and efficacy of corneal minimized-volume ablation with accelerated crosslinking in eyes with keratoconus.

Study design

A total of 25 eyes of 25 consecutive patients with keratoconus were recruited to undergo transepithelial photorefractive keratectomy (tPRK) with a "minimized volume" treatment algorithm using the Schwind AMARIS 750 excimer laser platform (Schwind eye-tech-solutions GmbH). Simultaneous accelerated corneal crosslinking (CXL) was performed with continuous ultraviolet A radiation of 30 mW/cm² was used for 3 to 4 minutes. All patients were either intolerant of rigid contact lenses or unable to wear them for other reasons. Patients were included irrespective of whether the keratoconus was stable or progressive but with strongly subjective vision complaints. Patients with any significant corneal scarring were excluded.

Corrected and uncorrected distance visual acuities, manifest refraction, corneal curvature, surface irregularity, higher-order aberrations (HOA) and endothelial cells were assessed over a minimum 6-month follow-up period.

Outcomes

The mean Kmax in this cohort was 55.26 D. Mean duration of follow-up was approximately 8 months. The corrected and uncorrected distance visual acuities (logMAR) improved from 0.24 and 1.12 to 0.07 and 0.45, respectively (P<0.01). Spherical equivalent (SE) improved from -6.50 D to -2.75 D (P<0.001) despite the fact that the attempted correction in SE was only -2.25 D. Likewise, mean preoperative refractive cylinder was −2.91 and improved to −1.38 (P=0.04), even though the mean attempted correction was only 55% of astigmatism.  

There was a significant reduction in higher-order aberrations, along with significant improvement in corneal surface morphological indices. No significant change was found in posterior corneal curvature or endothelial cell density.

Limitations

This was a small cohort in which duration of follow-up was less than 1 year. Seven of the 25 patients were under the age of 18. Longer follow-up data would be important in ascertaining the longevity of this procedure's effects. Additionally, there was no control group in which CXL alone was performed in order to assess the additional efficacy of adding tPRK in this combined procedure.

Clinical significance

Corneal minimized-volume ablation combined with accelerated cross-linking, or an "updated Athens protocol" as dubbed by the authors, was safe and effective in improving visual function in patients with keratoconus. The functional improvement appears in large part to be related to a significant reduction in HOAs, especially coma and astigmatism, as well as an improvement in the ocular modulation transfer function.