February 2012

 

INTERNATIONAL

 

International outlook

Lenticule may beat LASIK in the dry eye arena


by Matt Young EyeWorld Contributing Editor

 

John Vukich, M.D.

Femtosecond lasers continue to find new applications in ophthalmology. In this article we learn from three experts that precision intrastromal refractive surgery may preserve corneal sensation and offer an improved safety profile for dry eye symptoms.The anatomical basis for this potential benefit certainly makes sense, but the clinical difference, if any, has yet to be carefully studied. What is clear is that corneal refractive surgery continues to be an active area for the application of new technology. It seems possible that femtosecond lasers may someday compete with LASIK, and we will continue to watch for further reports on this promising new treatment.

John Vukich, M.D., international editor

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SMILE procedure gears up to improve corneal sensation after refractive procedures

Whiskered man

Dr. Shah's YouTube video is simple enough: It shows a straightforward SMILE (small incision lamellar extraction, Carl Zeiss Meditec, Jena, Germany) procedure to the tune of some Eastern music. For that, Rupal Shah, M.D., New Vision Laser Centers, Vadodara, India, received more than 7,000 hits and counting. SMILE, which has received regulatory approvals outside of the U.S., is an entirely femtosecond refractive procedure, involving the excision of a lenticule from stroma with a femtosecond laser. It is extracted through a small incision, and no excimer laser is needed. "I thinkSMILEis very attractive, both for doctors and patients," said Dr. Shah. "Patients love the idea of not having a flap in the eye, which could possibly be one reason why they are looking for alternatives. A lot of eye surgeons watch the YouTube videos because they are evaluating whether to incorporate it into their practice."

One point that surgeons and patients should consider carefully is SMILE's impact on dry eye, or more importantly, the lack thereof. "The reason why corneal sensation is reduced after LASIK is that the corneal nerves are cut, especially in the nasal-temporal regions," Dr. Shah said. "InSMILE, because of the small incision, and at the superior position, fewer nerves are cut, which certainly should make a difference to the corneal sensation and consequent dry eye."

While the jury is still out on SMILE's evidence-based impact on dry eyeas more prospective studies are neededadvocates are convinced that the procedure will be a boon to those with this condition, and would-be sufferers too.

Corneal sensation quickly recovered

Dan Z. Reinstein, M.D., medical director, London Vision Clinic, London, believes SMILE will make refractive surgery available to people previously classified as unsuitable for LASIK, based on pre-existing dry eye conditions. "We are effectively preserving the natural neural arc systems that control the production of three components of the tear film: mucin, water, and oil," Dr. Reinstein said.

He explained the nerves supplying the cornea run along its surface. With SMILE, the lenticule is removed from beneath where the nerves run, while the capand its nervesremain intact. "We have measured corneal sensation on a Cochet-Bonnet aesthesiometer," Dr. Reinstein said. "The normal range is 45-55. By 1 month, [SMILE patients] are back to 60normal. For LASIK patients, it takes 6-12 months for corneal sensation to reach that level [again]. SMILE changes the landscape of the post-op recovery for the patient."

Dr. Reinstein emphasized that while LASIK is a fast procedureincluding the visual recovery aspectdry eye sensations remain long after the procedure is over. "Using artificial tears for several times a day for up to a year in LASIK patients happens," Dr. Reinstein said. "It's not a big price to pay from going blind to being able to see. But it's a heck of a nuisance."

The procedure will help patients and also doctors, he said. "The greatest drag on post-op follow-up requirements that the surgeon needs to provide for patients is with respect to dry eye," Dr. Reinstein said. "On the internet, LASIK-ruined-my-life types of websites are about dry eye sensation. Now, a procedure that can get around this major side effect is a massive advance for everyone."

Phantom pain: Disappearing for good?

Ilpo S. Tuisku, M.D., Ph.D., Helsinki University Eye Hospital, Finland, is optimistic about the procedure as well. His Ph.D. thesis was on the topic of corneal nerves in refractive surgery and dry eye. Perhaps most importantly, he found that LASIK dry eye is a spectrum of disease states, which he divided into four categories: 1) neuropathic epitheliopathy, 2) tear fluid instability, 3) real aqueous tear deficiency due to nerve damage, 4) and neuropathic pain (phantom pain). Dr. Tuisku has found that most patients improve with respect to the first three categories of dry eye 6-12 months after LASIK. "But neuropathic pain is more complex," Dr. Tuisku said.

Regeneration of nerves can take 5 years, and the nerves regenerate differently than before, leading to what Dr. Tuisku calls "aberrant nerve fibers." "As nerve fibers grow back into the flap, they branch out," Dr. Reinstein said. "There tend to be more nerve endings than originallydouble or triple nerve endings. Now a breeze of wind across the eye will feel like three times the amount of breeze, causing a sensation that the eyes are very dry."

Patients cannot differentiate these sensations from normal dry eye symptoms, Dr. Tuisku said. "Doctors don't see any findings," he said. "The cornea looks clear and there are no signs of dry eye and still these patients complain, maybe 1 year after LASIK surgery."

Asked whether he thinks SMILE could provide a solution to this problem, Dr. Tuisku replied favorably, but stopped short of vouching for the procedure.

"SMILE is totally different from LASIK," he said. "We spare more nerves. We make a small incision. In LASIK, when we do the flap and there's a hinge, we cut 90% of the nerves. Some comparative, prospective studies comparing femtosecond laser LASIK and SMILE should be done."

Clinically, Dr. Shah already has seen SMILE benefits over LASIK in terms of dry eye. "I have personally treated several patients on whom I would not have done LASIK, because of dry eye, with SMILE, and they are extremely happy and grateful," Dr. Shah said. Of course, there are drawbacks with any procedure, and SMILE is not immune to these. The procedure is not available for hyperopia, Dr. Shah noted. "There is also no customization possibility at the moment. The treatments are already optimized for spherical aberrations though."

Editors' note: Drs. Reinstein and Shah have financial interests with Carl Zeiss Meditec. Dr. Tuisku has no financial interests related to this article.

Contact information

Reinstein: +44 020 7224 1005, dzr@londonvisionclinic.com
Shah: +91 265 3058 603, rupal@newvisionindia.com
Tuisku: ilpo.tuisku@helsinki.fi

Related articles:

Up-and-coming technologies may be key for management of dry eye by Ellen Stodola EyeWorld Staff Writer

PRK no better than LASIK for dry eye patients by Faith A. Hayden EyeWorld Staff Writer

Guide your patients toward better gel and ointment use by Vanessa Caceres EyeWorld Contributing Editor

Diagnosing dry eye by Michelle Dalton EyeWorld Contributing Editor

Impact of dry eye on patient satisfaction by Jena Passut EyeWorld Staff Writer

Lenticule vs LASIK in the dry eye arena Lenticule vs LASIK in the dry eye arena
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