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Which combination of procedures would be your best choice to provide vision improvement in patients with progressive keratoconus?
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The Athens protocol
Cross-linking combined with excimer laser partial PRK may offer stable, reliable, improved visual rehabilitation, in addition to potentially increased biomechanical strengthening.
We have shown that same-session partial topo-guided PRK with CXL is more effective than sequential PRK after earlier CXL in a large comparative case series. The refractive effects of the combined, same-day treatment were impressive: The majority of patients obtained a corrected distance visual acuity of 20/40.
This procedure, known today as the Athens protocol, has evolved since we introduced it to include, sequentially, a 7- to 7.5-mm phototherapeutic keratectomy to remove 50 µm of epithelium, topography-guided partial PRK with cyclorotation compensation, application of mitomycin C for 20 seconds and, last, the higher fluence CXL procedure.
The most challenging part of the Athens protocol is the design of the excimer laser ablation pattern. As this is not a refractive procedure, the priority is the maximal “normalization” of the irregular anterior corneal surface that the thinned cornea permits. Therefore, the aim of the design is dual: to reduce the large curvature of the cone area and to attempt to “relocate” the steeper cornea area to a more central location by steepening the flattened central cornea next to the cone. We do this by combining a myopic ablation component with a hyperopic ablation component corresponding to the “antipode” of the cone. The purpose of this second “hyperopic” component is to create an artificial “elevation” gradient to the cone diagonal location. Together, these two different keratomileusis patterns result in dramatic reduction of corneal asymmetry, correlating clinically with the postoperative marked CDVA increase.
Of course, this may not be absolutely necessary in patients who had or can tolerate rigid gas permeable and/or scleral contact lenses. It has proven nevertheless in our hands to be the most stable, predictable tool in addressing severe visual morbidity associated with moderate to advanced keratoconus, leading to long-term stability and good visual rehabilitation.
A. John Kanellopoulos, MD, is from LaserVision Eye Institute, Athens, Greece. Disclosure: Kanellopoulos reports he is a consultant for Alcon, Allergan, Avedro, Optovue and Zeiss.
Triple or quadruple procedure
There are two basic options to correct irregularity and improve vision: laser correction and intracorneal ring segment (ICRS) implantation. Today we know that ICRS alone does not halt disease progression, and combination with cross-linking is advisable. After ICRS implantation, I wait a minimum of 1 day to perform CXL to evaluate the effect of ICRS and to check if we need to change the location or the thickness of the rings.
If there is still significant corneal irregularity at the 6-month control after ICRS plus CXL, I perform topography-guided transepithelial PRK (topo-guided PRK). We have a large experience with ICRS and generally can predict the results we are going to obtain with ICRS in individual patients. We know that even with the thickest ICRS, we can achieve a regularization between 7 D and 9 D in the difference between the minimum keratometry and maximum keratometry in the cornea at 3 mm. With CXL, we can provide a refractive correction of approximately 1.5 D, and with the topography-guided treatment, performed 6 months later, we can also provide about 5 D of correction. We presented this treatment for the first time with the name of “triple procedure,” namely ICRS + CXL + topo-guided PRK.
Another triple procedure consists of implanting a phakic toric IOL (ICL/EVO toric, Staar Surgical) after ICRS plus CXL. Patients with ICRS and CXL still have a refractive defect, and if the anterior chamber is 2.8 mm wide, a posterior chamber phakic toric IOL might be the most appropriate treatment, leading to significant improvement in best corrected visual acuity.
Our latest study evaluated the results of fine-tuning with topo-guided PRK in addition to the ICRS + CXL + toric ICL procedure to correct residual irregularity, with a target refraction of –2 D. We can call this a “quadruple procedure.” The biggest problem here is the difficulty in refracting for phakic IOLs in advanced, irregular patients. If the patient cannot be refracted, we may plan to regularize the cornea with topo-guided PRK first and then implant the ICL.
Efekan Coskunseven, MD, is from Dünyagöz Eye Hospital, Istanbul, Turkey. Disclosure: Coskunseven reports he is a consultant for Mediphacos.