According to Mark Lobanoff, DO, earlier treatment also can mean the best possible results for patients.
Reviewed by Mark Lobanoff, DO
Can combined topography-guided PRK/CXL for keratoconus be a viable option to provide positive results for patients? The answer is yes, according to Mark Lobanoff, DO, who explained the whys and hows of the procedure.
The advent of collagen cross-linking (CXL) was a great advance for patients with keratoconus. However, as Lobanoff pointed out, halting the disease process using CXL is not enough. “If halting progression is all we do, we have permanently locked the cornea into an irregular shape that affects the patient’s vision over the long term,” said Lobanoff, who is in private practice in St Louis Park, Minnesota.
A slow, steady history
A. John Kanellopoulos, MD, introduced the Athens protocol to improve on the effect of CXL by limiting application of the protocol to corneas thicker than 400 μ. This treatment, as Lobanoff explained, was intended to be therapeutic and not refractive with the removal of 50 μ of tissue.
Eric Donnenfeld, MD, and colleagues took a step forward and worked to address both the topography and refractive error and perform CXL. In patients who had been treated with CXL 2 to 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 sequentially performed PRK is that the cornea will flatten with the CXL treatment; however, that flattening can be unpredictable, Lobanoff pointed out. The disadvantage of sequentially performed PRK is that the corneal fibers that were strengthened by CXL are removed.
“With simultaneously performed PRK, the patient undergoes 1 surgery to remove the epithelium and all the cross-linked 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 the corneal topography and as much sphere and cylinder as possible. During this procedure, he removed from about 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 in the presence of thin corneas about to undergo tissue ablation. Lobanoff created a device to prevent the drops of riboflavin from running off steep corneas upon application. By dropping the riboflavin on the steepened cornea, the area most needing riboflavin was exposed to it for the shortest possible time, he explained.
To keep the riboflavin on the corneas for a longer period, he originally used the patient device from the Lensar laser, suctioned it to the eye, and created a well filled with riboflavin to cover the cornea and not run off. This resulted in even distribution of the riboflavin and faster penetration into the corneal tissue.
He used an accelerated CXL approach using 18 mW/cm2 and shorter pulsed treatment times (ie, 2 minutes on, 1 minute of riboflavin, and 1 minute off), and explained that pulsed treatment was used with the accelerated model because the rate-limiting reactant 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 postoperatively in contrast with the respective uncorrected visual acuities (VAs) of 20/100 and 20/80 after Donnenfeld’s procedure, Lobanoff said.
The corrected distance VAs preoperatively and postoperatively were 20/40 and 20/25, respectively, in contrast with corrected VAs of 20/50 preoperatively and 20/30 postoperatively corrected in the Donnenfeld study. Both studies showed the same decrease in the maximum K values.
“All patients in my study had improved uncorrected VA and in best-corrected VA,” Lobanoff said. “In addition, 30% of the patients achieved 20/20 or better binocular uncorrected VA; 76% of the eyes gained over 2 lines of best-corrected vision.” Importantly, by 2 years after CXL, the keratoconus had not progressed.
“I believe that earlier treatment of forme fruste keratoconus yields better results,” Lobanoff continued. “Many patients with forme fruste keratoconus achieve uncorrected 20/20 vision. I believe that the combined treatment is a very viable option for these patients.”
However, Lobanoff noted, careful progression is important. “We must have excellent CXL. We need better saturation,” he explained. “I believe in the use of accelerated CXL with supplemental oxygen. We also needed improved software. Phorcides was designed originally for use in primary virgin eyes.”
Lobanoff said he is working on a variation of this for keratoconus and a device that attaches to the eye via suction and is filled with riboflavin. “Once full saturation has been achieved, 100% oxygen can be pumped in at high pressure and UVight applied continuously through the higher level of oxygen,” he concluded.
Mark Lobanoff, DO
This article is adapted from Lobanoff’s presentation at the American Society of Cataract and Refractive Surgery’s 2022 annual meeting in Washington, DC. He is a consultant for Alcon, Bausch & Lomb, and Phorcides.