As cornea specialists, we’ve all been there. You’re sitting across from a patient with keratoconus who has come in for a consultation for corneal crosslinking (CXL). You methodically review the exam findings and diagnostic testing with the patient and recommend CXL. You explain that the CXL procedure is meant to stabilize, halt or, as I explain to my patients, “freeze” disease progression. Inevitably, the patient’s next question is often, “Once you freeze my keratoconus, how will you improve my vision?” The patient will often share that he cannot see well with eyeglasses or soft contact lenses or that he cannot tolerate his scleral lenses any longer. He would like to know about other options for refractive surgery.
The reality is that our mild and moderate keratoconus patients and even stable post-CXL severe keratoconus and keratectasia patients deserve to have access to refractive surgery options. Below, I will share three refractive surgery strategies to consider with keratoconus patients.
1. PHAKIC IOL SURGERY WITH ICL
As a cornea specialist, I routinely perform CXL on several patients per week. When I have a patient who is seeking refractive surgery, I most often offer lens-based refractive surgery.
Most keratoconus/ectasia patients are younger and pre-presbyopic; therefore, implantation of an implantable collamer lens (ICL) allows for the patient to hold onto accommodation. Most (though not all) keratoconus patients will require toric ICLs.
Due to the irregularity of the cornea, ICL is very good in the correction of refractive error but it is not perfect. I warn my patients that ICL surgery will vastly improve vision but that there will likely be a requirement for postoperative glasses to improve/perfect their vision. This expectation should be set with patients early on and repeated often. I have found that the majority of my pre-presbyopic keratoconus patients are so thrilled with their post-CXL, post-ICL vision that they choose not to utilize glasses postoperatively. They often feel that their vision is excellent and does not require improvement.
It is also important to explain that any residual refractive error post-ICL surgery can only be corrected with eyeglasses/contact lenses and we are unlikely to have corneal refractive surgery as an option as we would for patients with normal corneas.
Keep in mind that not all keratoconus patients have the appropriately sized anterior and posterior chamber to house an ICL. Careful attention should be paid to anterior and posterior chamber measurements. I use biometry, topography and high frequency ultrasound to confirm sizing of ICLs for every ICL candidate. While keratoconus patients are often myopic (and even highly myopic), this does not necessarily mean that the anterior/posterior chambers are large enough. Some of these patients may have shorter than average axial length and smaller anterior chamber but have high myopia simply due to higher Ks produced by corneal ectasia/keratoconus.
2. REFRACTIVE LENS EXCHANGE
If the patient’s anterior chamber is not within the range to house an ICL, then refractive lens exchange (RLE) can be considered.
For patients with keratoconus or keratectasia who are stable post-CXL and presbyopic, I recommend RLE with Light Adjustable Lenses (LALs, RxSight). LALs are excellent monofocal, customizable, IOLs that can have toricity after being adjusted postoperatively with the Light Delivery Device. LAL is FDA-approved to treat + or -2.00 D of sphere and up to 2.00 D of astigmatism. I have successfully corrected up to 3.5 D of astigmatism with LALs and +/-3.00 D of sphere.
Also, many keratoconus patients suffer from high myopia (due to elevated Ks). Luckily, LALs come in low diopters, as low as +4.0 D. Since LALs are adjustable not only with regards to astigmatism but also spherical equivalent, we can treat the LAL to provide excellent vision for even higher myopes.
No toric IOLs are available in the United States lower than +5.0 D, and these only correct up to about 4.11 D of astigmatism at the corneal plane. Therefore, LALs are very valuable for high myopes with astigmatism who are hoping to be spectacle-free to some degree after RLE. According to RxSight, 16.7% of patients choose distance vision in both eyes (requiring magnification for intermediate and near activities), and 79.6% choose blended vision with a goal of complete spectacle freedom.1
The LALs are customizable, and patients love hearing that their input is paramount to the process of determining their final vision. Patients love having this level of control. Still, the surgeon must explain that there are potential limitations with keratoconus cornea irregularity. LALs are the only light-adjustable IOLs available to provide customizable vision. But, with a highly irregular cornea, even LALs may not be able to deliver 100% perfection to the patient. It is important to explain to the patient that with fixed, monofocal toric IOLs, there is not often the opportunity for vision improvement with corneal refractive surgery.
3. PHOTOREFRACTIVE KERATECTOMY AND CXL
A final strategy to improve vision for keratoconus patients is with simultaneous topography-guided, epithelium off, photorefractive keratectomy (PRK) and CXL, also known as the Minneapolis Protocol for the Treatment of Keratoconus,2 which is being developed by Mark Lobanoff, MD. Initially, A. John Kanellopoulos, MD, described the Athens protocol,3 which is the simultaneous application of topography-guided partial PRK to reduce larger amounts of corneal irregular astigmatism followed by immediate CXL. A maximum of 50 microns of tissue is removed with this protocol, and corneal thickness must be more than 400 microns for the patient to be a candidate. The goal of the Athens protocol was to strive to improve BCVA.
I recently spoke to Dr. Lobanoff on his approach to performing PRK and CXL simultaneously as opposed to CXL followed by PRK 2-3 years later, which is a more commonly performed sequence. The reasoning for inferior results with sequential PRK after years of stability after CXL is that PRK will remove corneal fibers that were strengthened by the previous CXL. If PRK is performed first followed by immediate CXL, the epithelium only needs to be removed once, creating more safety and convenience for the patient. With PRK occurring first then CXL next, all of the strengthened crosslinked corneal fibers will be created with CXL and then remain, creating a stable refractive result. Finally, with PRK, one is able to reduce the irregularity of the keratoconic cornea, thus improving the BCVA after the procedure.
Dr. Lobanoff’s approach is to use topography-guided PRK with the use of Phorcides, a clinical decision support software, with an effort to correct as much of the sphere and cylinder of the refractive error as possible. Dr. Lobanoff removes more than 50 microns of tissue, sometimes as much as 150 microns. Extremely efficient CXL follows immediately after the PRK with a new device that Dr. Lobanoff is developing called the C2 device. The C2 is a cone-shaped device that suctions to the eye near the limbus, then floods riboflavin fluid into the chamber above the cone-shaped cornea, allowing for the cornea to be equally submerged in riboflavin for 5 minutes. Then, the device extracts the riboflavin fluid and fills the chamber with 100% oxygen with pressure. Meanwhile, the ultraviolet light is emitted from the top of the device, so that there is a continuous flow of oxygen, creating continuous CXL reaction in a very efficient manner.
Dr. Lobanoff says that all of the patients in his series have experienced improved uncorrected VA and BCVA. About 30% of these patients have even achieved 20/20 or better binocular UCVA. And, almost 4 years after the combined procedure, none of the patients have had keratoconus progression.
CONCLUSION
While we previously felt we could only help keratoconus patients by halting progression of their disease, we now have multiple options to improve their vision with regards to refractive surgery. We must continue to educate our colleagues and patients of these modalities to give our keratoconus patients the opportunity to improve their UCVA and BCVA going forward. OM
References
1. RxSight PMCS-002 Clinical Outcomes of Patients Bilaterally Implanted with LAL.
2. Zhao H, Hammond P, Lobanoff M. Improving Outcomes for Crosslinking Keratoconus Eyes: Results of the New Minneapolis Protocol for the Treatment of Keratoconus Eyes. Paper presented at: 2020 ASCRS Virtual Annual Meeting; May 16-17, 2020.
3. Kanellopoulos AJ. Management of progressive keratoconus with partial topography-guided PRK combined with refractive, customized CXL - a novel technique: the enhanced Athens protocol. Clin Ophthalmol. 2019;13:581-588. Published 2019 Apr 2.
