Eyeworld

EW CORNEA 94 September 2017 by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer manifest refraction, or on Scheimp- flug between the two procedures. Similar morphologic changes and a pronounced demarcation line were apparent in both groups postopera- tively. The investigators concluded that the accelerated CXL procedure, having similar outcomes to standard CXL treatment, appeared to be more beneficial to patients and surgeons. 3 "Everyone has a different cor- neal thickness, so I think we have to take it one step at a time. When you look at our studies, it is difficult to decrease the time and increase the intensity to get these effects in keratoconus patients," Dr. Kohnen said. "So far, we have only used ri- boflavin, but we may not only have to treat with riboflavin in the future. There is a whole range of molecules coming out for use in CXL. There will be other modalities. Using accelerated CXL, we see almost the same wound healing and epithelial closure as with the standard proto- col. We also use contact lenses after the procedure. I can't see a downside of this accelerated procedure at the moment. It is shorter and has good efficacy. And whenever we can re- duce treatment time in ophthalmic surgery, it is a good thing. However, we have yet to know the exact dos- age for optimal treatment." EW References 1. Raiskup F, et al. Corneal collagen crosslink- ing with riboflavin and ultraviolet-A light in progressive keratoconus: Ten-year results. J Cataract Refract Surg. 2015;41:41–6. 2. Horovitz RNC, et al. Crosslinking: an updat- ed and effective insight. Rev Bras Ofthalmol. 2015;74:119–123. 3. Tomita M, et al. Accelerated versus conven- tional corneal collagen crosslinking. J Cataract Refract Surg. 2014;40:1013–1020. Editors' note: Dr. Kohnen has no finan- cial interests related to his comments. Contact information Kohnen: kohnen@em.uni-frankfurt.de Old data The Dresden protocol involves an epi-off approach of 3 mW/cm 2 for 30 minutes at a dose of 5.4 J/cm 2 using 0.1% riboflavin every 1–2 minutes. The 10-year outcomes of CXL using this protocol in 34 eyes (24 patients) with progressive keratoconus treated from 2000 to 2004 showed a reduc- tion in K-values of about 1–2 D. The long-term reduction in astigmatism was 2 D. Corrected distance visual acuity showed an increase of rough- ly 1–2 logMAR. The investigators concluded that CXL was effective and achieved long-term stabilization of the condition. 1 Accelerated crosslinking is based on the Bunsen-Roscoe law of reciprocity, which states that the photochemical effect is directly pro- portional to the total energy dose, whereby the dose is the product of intensity and the duration of expo- sure. There are a number of different CXL protocols 2 that have led up to the accelerated CXL use of higher intensity and shorter treatment time. Accelerated CXL uses 30 mW/ cm 2 for a 3-minute duration. "CXL treatments went from 3 mW/cm 2 for a duration of 30 min- utes to 30 mW/cm 2 for 3 minutes. There are also higher intensity devices that use different intensi- ties. Ex vivo experiments with pigs tested the biomechanics of acceler- ated crosslinking and saw corneal stiffening at intensities up to 40–50 mW/cm 2 and decreased stiffening at intensities from 3–18 mW/cm 2 , possibly due to intrastromal oxy- gen diffusion capacity or increased oxygen consumption," Dr. Kohnen explained. A recent study that implement- ed accelerated corneal crosslinking corroborated Dr. Kohnen's out- comes. It compared conventional and accelerated CXL in 48 eyes of 39 patients, of which 18 eyes had conventional CXL with a 30-minute riboflavin presoak and 30 minutes of 3 mW/cm 2 UVA, while 30 eyes had accelerated CXL with a 15-minute riboflavin presoak and 3 minutes of 30 mW/cm 2 UVA. After 1 year, no significant differences in postopera- tive changes were seen in corrected or uncorrected visual acuity, in the central concentric zones from 0.0 mm to 2.0 mm, and 2.0 mm to 6.0 mm. The mean spherical equivalent, maximum keratometry, and simulated keratometry were not significantly changed, while mean central corneal thickness decreased significantly from 470 µm before treatment to 450 µm after treatment (P=.473). In a second retrospective study comparing 29 keratoconus patients treated using the Dresden protocol and 29 using the accelerated CXL protocol, Dr. Kohnen revealed that both treatments were equally effec- tive. Dr. Kohnen took two Scheimp- flug measurements per patient both pre- and postoperatively, which stood out compared to studies in the existing literature that only take one measurement. According to the regression analysis, progression of keratoconus was significant in both study groups preoperatively, with an increase in D-value in the Dresden cohort (P=.01) and in the acceler- ated cohort (P=.033). Postoperative data showed an improvement in all observed keratoconus indices, including D-values, pachymetry, Kmax, and ISV, in both study groups with progression stagnating in the accelerated cohort (P=.771 for D-value) and regressing slightly in the Dresden cohort (P<.01 for D-val- ue). Increased corneal density was evident on imaging up to 12 months after treatment. "In Frankfurt, we have changed to the accelerated CXL procedure from the original Dresden treatment protocol. There are small advantag- es in favor of the Dresden protocol compared to the accelerated proto- col, but further studies are required for direct comparison of both meth- ods, as are greater patient numbers," Dr. Kohnen said. "Keep in mind that this was only a retrospective from cases that were operated using stan- dard protocol a couple of years ago, compared to our current accelerated CXL patients. This new approach proved safe, and I think that with the shorter treatment time with higher intensity, 18 minutes versus 60 minutes, we can vastly reduce the time for CXL." New studies in patients with progressive keratoconus undergoing accelerated crosslinking demonstrate benefits of the technique C orneal collagen crosslink- ing (CXL) is a non-invasive surgical treatment modali- ty for corneal ectasia, such as keratoconus, pellucid marginal degeneration, and cases of post-LASIK ectasia, that combines the use of liquid riboflavin (vitamin B2) and the controlled application of UVA light on the surface of the eye to strengthen the cornea and eliminate ectasia. Treatment of ecta- sia is difficult mainly due to progres- sive corneal thinning and irregular astigmatism, with CXL representing the only real option to slow or halt its progression and avoid corneal transplantation. Results from studies in patients with progressive keratoconus treated with a new accelerated crosslinking approach demonstrated high safety and comparable results for K-values, uncorrected distance visual acuity (UCDVA), corrected distance visual acuity (CDVA), refraction, corneal biomechanics, and side effects to those obtained using the standard Dresden protocol for corneal cross- linking, while greatly reducing the treatment time. In a session at the 2017 ASCRS•ASOA Symposium & Congress, Thomas Kohnen, MD, professor and chair, Department of Ophthalmology, Goethe University Frankfurt, Germany, reported on the results he obtained from two new studies. New data In a retrospective study of 12 pa- tients with progressive keratoconus, Dr. Kohnen and his team examined corneal densitometry 3 months after accelerated-pulse epithelium-off CXL treatments, as measured by Scheimpflug imaging with the Pentacam HR (Oculus, Wetzlar, Germany), noting an increase in corneal densitometry, particularly in the anterior stromal layer, within Saving time with accelerated crosslinking Presentation spotlight For more on crosslinking and current research, see this month's Feature section.

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