February 2018

COVER FEATURE

Laser vision correction
Considerations for irregular cornea treatments


by Rich Daly EyeWorld Contributing Writer


Eye undergoing CXL
Source: James Randleman, MD

Surgeons address the complex issue of when to treat—or not treat—patients with suspicious corneas

Among the important considerations for surgeons confronted with irregular corneas are whether and when to treat them.
“This is currently a highly controversial topic,” said J. Bradley Randleman, MD, professor, Department of Ophthalmology, Keck School of Medicine, University of Southern California (USC), and director of cornea, external disease and refractive surgery, USC Roski Eye Institute, Los Angeles.
Dr. Randleman divides such patients between those who have known ectatic disorders, who are being considered for therapeutic ablations to improve their corneal regularity, and those who are presenting for refractive surgery evaluation and are seeking or being offered refractive correction.
“For patients with ectatic corneas, the cornerstone of treatment involves corneal crosslinking (CXL) first with future considerations about therapeutic ablations,” Dr. Randleman said. “For patients with irregular corneas but without a clear ectasia diagnosis, some have advocated for using surface ablation in these patients, but there are also cases in the literature of these patients developing ectasia after surgery, and I do not currently offer treatment to these individuals.”
Instead, he follows the latter group of patients for any evidence of progression.
Renato Ambrósio Jr., MD, PhD, adjunct professor of ophthalmology, Federal University of the State of Rio de Janeiro (UNIRIO), also first distinguishes between refractive and therapeutic patients.
“Treating diseased corneas is a whole different world from enabling patients to be less dependent on spectacles and contact lenses,”1 Dr. Ambrósio said.
Both patients and surgeons need to be educated about the fundamental differences between elective treatments with a refractive purpose and those for the visual rehabilitation of patients with corneal disease, he said.
“For the latter, the education of patients and their families is fundamental to the success of your intervention, as it enables patients to manage their disease better, and it also helps them maintain realistic expectations of what treatment can achieve,” Dr. Ambrósio said. 
Recent developments in refractive technologies including custom ablations, intracorneal ring segments, and CXL have benefits for corneal ectasia and keratoconus, as well as other causes of irregular corneas.
“The paradox is that if the patient does not need surgery, we should avoid or consider it very carefully,” Dr. Ambrósio said. “But when the patient needs surgery, we should do the procedure as soon as possible.”
Although quality of vision is important, refractive independence should not be a priority, he said. Also important is the balance between the eyes, as many cases have significant anisometropia.
The second reason to indicate surgery is related to corneal stability, Dr. Ambrósio said. 
“If there is progression, we should proceed with crosslinking even if the patient retains good corrected vision,” Dr. Ambrósio said. “But the need for corneal imaging for documentation and guiding clinical decisions is a must.”
Dr. Ambrósio said the Belin ABCD Progression Display, which is available on the Pentacam (Oculus, Wetzlar, Germany), has been useful.

Exam keys

In a routine eye exam or a refractive consultation, surgeons should look for risk factors for ectasia—high posterior float, pachymetric progression, or otherwise suspicious appearance for ectatic disease—as constituting a cornea that should be crosslinked, according to David Hardten, MD, director of refractive surgery, Minnesota Eye Consultants, and adjunct professor of ophthalmology, University of Minnesota, Minneapolis.
Dr. Randleman agreed that the detection of progressive corneal ectasia indicates a need for CXL.
“Crosslinking is highly effective at halting progression, but its results are a bit unpredictable in terms of an overall flattening effect or regularization, so I do not recommend using CXL for non-progressive corneas or for patients without clear corneal ectasias,” Dr. Randleman said.
To document progression or understand the high risk for it, Dr. Ambrósio urged characterizing the susceptibility for biomechanical failure of the cornea using advanced corneal imaging, including Placido front surface topography and tomography with Scheimpflug and OCT.
“The latter, OCT, along with very high frequency ultrasound, provides the ability for layered or segmental tomography, providing critical data related to epithelial thickness, for example,” Dr. Ambrósio said.
Biomechanical data also has been useful for making clinical decisions, mainly in borderline cases. 
“In a routine exam, we should always pay attention to the patient’s complaints,” Dr. Ambrósio said. “If the patient notices worsening vision, that fact is a major alert.”

Post-refractive patients

Post-PRK, post-LASIK, and post-SMILE corneas that develop postoperative corneal ectasia should undergo CXL upon diagnosis, Dr. Randleman said.
“The treatment is most effective at halting progression, so if performed early enough the resulting vision loss can be reduced,” Dr. Randleman said.
However, as a prophylactic procedure, this is still controversial, and recent data has found that CXL does not completely prevent ectasia after LASIK,2 Dr. Ambrósio said.
Dr. Hardten checks the topography of post-corneal refractive surgery patients at risk for ectasia annually if they are older and every 6 months in young patients.
Along with routine exams, Dr. Ambrósio asks about the quality of vision and performs wavefront analysis. For progression documentation, he advocates for subtraction maps from the axial curvature, and also from the front and back elevation maps using the respective 8.0-mm best fit spheres for the first measurement.

Post-CXL treatment

Another ongoing debate is the best surgical timing for patients who need CXL and also desire laser vision correction.
“There are valid arguments for simultaneous treatment with excimer laser ablation followed immediately by corneal crosslinking and literature to support the efficacy of this approach,” Dr. Randleman said. “Others, including myself, advocate sequential treatment, with crosslinking first followed by excimer laser ablation only when the patient has stabilized and only if laser treatment would be highly beneficial given the inherent risks and uncertainties that come with ablating an ectatic cornea.”
He urges patients to wait a minimum of 6 months and preferably 12 months after CXL to consider laser treatment.
Dr. Ambrósio underscored the need to understand the patient’s situation, including symptoms, wishes, and demands, as well as efforts to obtain balance between the eyes. He advocates for performing the therapeutic custom surface ablation and CXL in the same day as reported by A. John Kanellopoulos, MD, in the Athens protocol.3 Dr. Ambrósio uses a fast CXL protocol with 18 mW/cm2 for 5 minutes.
When performing therapeutic laser vision correction on eyes also undergoing CXL, Dr. Ambrósio said that the indication is key.
“Less ablation is usually more efficient,” Dr. Ambrósio said. “Customization with topo-guided using either Scheimpflug or Placido is possible, but in some cases, just the PTK is indicated.”
As crosslinking can have continued long-term flattening effects over many years, Dr. Randleman noted that it is important not to be too aggressive with any laser ablation.
“If the surgeon targets emmetropia and the patient continues to flatten over time there will be induced hyperopia,” Dr. Randleman said.

References

1. Ambrósio R Jr. Therapeutic refractive surgery: Why we should differentiate? Rev Bras Oftalmol. 2013;72:85–6.
2. Taneri S, et al. Corneal ectasia after LASIK combined with prophylactic corneal cross-linking. J Refract Surg. 2017;33:50–52.
3. Kanellopoulos AJ. Comparison of sequential vs same-day simultaneous collagen cross-linking and topography-guided PRK for treatment of keratoconus. J Refract Surg. 2009;25:S812–8.

Editors’ note: Dr. Ambrósio has financial interests with Oculus, Alcon (Fort Worth, Texas), Carl Zeiss Meditec (Jena, Germany), and Mediphacos (Belo Horizonte, Brazil). Dr. Hardten has financial interests with Johnson & Johnson (Santa Ana, California) and Avedro (Waltham, Massachusetts). Dr. Randleman has no related financial interests related to his comments.

Contact information

Ambrósio
: dr.renatoambrosio@gmail.com
Hardten: drhardten@mneye.com
Randleman: randlema@usc.edu

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