Reviewed by Mark Lobanoff, DO
Can combined topography-guided PRK/CXL for keratoconus be a viable option to provide positive patient outcomes? The answer is yes, according to Mark Lobanoff, DO, who explained the hows and whys of the procedure.
The advent of collagen cross-linking (CXL) has been a big breakthrough for patients with keratoconus. However, as Lobanoff pointed out, stopping the disease process using CXL is not enough. “If stopping the progression is all we’re doing, we’ve permanently locked the cornea into an irregular shape that affects the patient’s long-term vision,” said Lobanoff, who has a private practice in St Louis Park, Minnesota.
A slow and steady story
A. John Kanellopoulos, MD, introduced the Athens Protocol to enhance the effect of CXL by limiting the application of the protocol to corneas thicker than 400 μ. This treatment, as Lobanoff explained, was intended to be therapeutic and non-refractive with the removal of 50 μ of tissue.
Eric Donnenfeld, MD, and his colleagues took a step forward and worked to address both topography and refractive error and perform CXL. In patients who had been treated with CXL 2-3 years previously, he and his colleagues performed topography-guided photorefractive keratectomy (PRK) to improve vision. When they performed PRK and CXL simultaneously, rather than performing PRK after CXL, they found better results, Lobanoff recounted.
Sequential vs Simultaneous PRK
An advantage of PRK performed sequentially is that the cornea will flatten with CXL treatment; however, this flattening can be unpredictable, Lobanoff pointed out. The disadvantage of sequential PRK is that corneal fibers that have been reinforced by CXL are removed.
“With PRK performed concurrently, the patient undergoes surgery to remove the epithelium and all reticular fibers remain,” Lobanoff said. “However, there is variability in the CXL and corneal curvature.”
Lobanoff performed a study in which he planned topographic PRK treatments using the Phorcides platform and corrected corneal topography and as many spheres and cylinders as possible. During this procedure he removed approximately 100 μ of tissue to 150 μ in rare cases.
He always uses hypotonic riboflavin to achieve corneal swelling before the CXL procedure is performed, especially in cases with thin corneas.
The importance of an accurate CXL procedure cannot be overemphasized when dealing with thin corneas that are about to undergo tissue ablation. Lobanoff has created a device to prevent riboflavin drops from dripping onto stiff corneas during application. By depositing the riboflavin on the stiffened cornea, the area that needed it most was exposed to it for the shortest time possible, he explained.
To keep the riboflavin on the corneas for a longer period, he initially used the Lensar laser patient device, sucked it up to the eye and created a well filled with riboflavin to cover the cornea and not s ‘flow out. This resulted in even distribution of riboflavin and faster penetration into corneal tissue.
He used an accelerated CXL approach using 18 mW/cm2 and shorter pulsed treatment times (i.e. 2 minutes on, 1 minute riboflavin, and 1 minute off), and explained that the pulsed therapy was used with the accelerated model because the reactive rate limiting during the CXL procedure is oxygen in the corneal tissue. The results showed that the preoperative uncorrected vision improved from 20/300 to 20/40 after the operation, in contrast to the uncorrected visual acuities (VA) of 20/100 and 20/80 respectively after the Donnenfeld procedure. , Lobanoff said.
The preoperative and postoperative remotely corrected VAs were 20/40 and 20/25, respectively, in contrast to the 20/50 preoperatively corrected and 20/30 postoperatively corrected VAs in Donnenfeld’s study. Both studies showed the same decrease in maximum K values.
“All patients in my study had improved uncorrected VA and best-corrected VA,” Lobanoff said. “In addition, 30% of patients achieved an uncorrected binocular VA of 20/20 or better; 76% of eyes gained more than 2 lines of best-corrected vision. Above all, 2 years after CXL, the keratoconus had not progressed.
“I believe early treatment of mild form keratoconus gives better results,” Lobanov continued. “Many patients with mild form keratoconus achieve 20/20 uncorrected vision. I believe that combination therapy is a very viable option for these patients.
However, Lobanoff noted, careful progression is important. “We have to have a great CXL. We need better saturation,” he explained. “I believe in using accelerated CXL with supplemental oxygen. We also needed improved software. Phorcides was originally designed for use in primary blank eyes.
Lobanoff said he’s been working on a variation of this for keratoconus and a device that attaches to the eye by suction and is filled with riboflavin. “Once full saturation is reached, 100% oxygen can be pumped in at high pressure and UVight applied continuously through the highest oxygen level,” he concluded.
Mark Lobanoff, DO
Email: [email protected]
This article is adapted from Lobanoff’s presentation at the 2022 American Society of Cataract and Refractive Surgery Annual Meeting in Washington, DC. He is a consultant for Alcon, Bausch & Lomb and Phorcides.