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Sequential epi-on cross-linking, topography-guided PRK show good results
PRK was performed at least 3 months after CXL, when corneal topography and refraction had stabilized.
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Topography-guided PRK improves vision in keratoconus patients after corneal cross-linking, according to a study published in Journal of Cataract and Refractive Surgery.
“Our study is the largest U.S. series investigating the safety and efficacy of these combined procedures. It is an eye opener for many ophthalmologists who were not familiar with this sequence of treatment and will now be able to tell keratoconus patients that they have options available for improving vision,” Alanna Nattis, DO, first author of the study, told Ocular Surgery News.
Unlike in other studies previously performed in Europe or Asia, the two procedures were performed sequentially, and a modified epithelium-on cross-linking protocol was used.
Selective, tissue-sparing technique
CXL was first developed in the late 1990s, gradually adopted internationally in the early 2000s and approved by the FDA in 2016. It is recognized worldwide as an effective method to halt the progression of keratoconus but has limited effect on functional vision. Among vision-enhancing options, such as intracorneal ring segments or phakic lenses, topography-guided PRK appears to be the best match because it reshapes the cornea, reducing the ectasia and smoothing out the irregularities that lead to high-order aberrations and astigmatism.
“Topography-guided laser ablation is a highly selective, tissue-sparing technique that removes about one-third less tissue than wavefront-guided ablation. It collects and analyzes 20,000 data points, as compared with wavefront-guided ablation, which collects only 1,000 points,” Nattis said.
Two groups of patients were included in the study. Of 56 patients (62 eyes), 34 had both topographic and refractive treatment and 28 had treatment of topographic irregularities only. In the first group, the total refractive error was corrected whenever the cornea was thick enough to achieve this goal safely. In corneas that were at risk for ablating below the 300 µm safety threshold, some residual error was left, aiming at correcting cylinder before sphere. The WaveLight EX500 excimer laser (Alcon) was used for the ablation.
PRK was not performed in this study before the cornea had achieved and maintained refractive and topographic stability for at least 3 months after CXL. The time between CXL and PRK ranged between 4 months and 10 months.
“This might differentiate us from other studies performed previously, where topography-guided PRK and CXL were performed simultaneously. In our group, we believe that waiting is important because the cornea undergoes remodeling after CXL, which continues for a variable length of time. PRK treatment done when the cornea is still unstable will result in unwanted changes later on,” Nattis said.
Proactive approach to disease
Corneal cross-linking was performed using a modified epi-on technique.
“We rolled a cotton-tipped applicator over the cornea to create small erosions on the epithelium and improve riboflavin penetration. Then we applied a riboflavin solution every 2 minutes for 1 hour or more, until corneal saturation was achieved. UV light was delivered for 5 minutes at a 365 nm wavelength and a fluence of 15 mW/cm2, using the CCL-Vario 365 system (Peschke Trade),” Nattis said.
A gain in corrected distance visual acuity (CDVA) of one line was observed after CXL, with a slight decrease of astigmatism and myopia and a mean reduction of maximum keratometry by –0.20 D.
“After PRK, the patients treated for refractive error had significant visual acuity improvement, with a mean [uncorrected distance visual acuity] gain of three lines and a mean CDVA gain of two lines. At 6 months, 93% of these patients had CDVA of 20/40 or better. Spherical equivalent and astigmatism improved significantly as compared with the non-refractive group. The steepest K decreased by 3.40 D,” Nattis said.
Visual improvement was not as great in the non-refractive group, but patients felt more comfortable with contact lenses and reported improved quality of vision.
“This was most likely due to the smoothing effect of topography-guided PRK and to the decrease of high-order aberrations,” Nattis said.
The combined option of CXL and PRK has allowed cornea specialists to become more proactive with the treatment of keratoconus patients and is allowing ophthalmologists, optometrists and opticians to work synergistically, Nattis said.
“When progressive keratoconus is diagnosed now, we can tell our patients that there is something we can do immediately to halt the disease,” she said. “None of us would think twice before performing CXL. And PRK is a further option we can offer to make them see better, without the need for corneal transplantation.” – by Michela Cimberle
- Reference:
- Nattis A, et al. J Cataract Refract Surg. 2018;doi:10.1016/j.jcrs.2018.05.020.
- For more information:
- Alanna Nattis, DO, can be reached at Lindenhurst Eye Physicians and Surgeons, 500 W. Main St., Suite 210, Babylon, NY 11702; email: asn516lu@gmail.com.
Disclosure: Nattis reports no relevant financial disclosures.