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New thermal keratoplasty procedure for presbyopia, hyperopia avoids pitfalls
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Optimal keratoplasty, an improved thermal laser technique that addresses presbyopia and hyperopia, may become the treatment of the future due to its temporary effect on unstable refractive disorders, according to a specialist.
“In the aging eye, both presbyopia and hyperopia are progressive conditions. An office-based, noninvasive procedure that can safely, quickly and easily be performed repeatedly as patients’ visual improvement needs change over time is the ideal solution. Not only is there a rationale for it, but there is the potential for a very large market, comparable to that of noninvasive laser skin procedures, botulin toxin and dermal filler injections,” Harry Glen, MD, said in an interview with Ocular Surgery News.
Refractive surgeons traditionally perform operations that produce permanent results and therefore do not need to be redone. They may be accustomed to thinking that a re-treatment results from a substandard outcome or a complication.
“It is in their DNA, it seems, to dismiss any elective procedure that reminds them of either of these scenarios,” Glen said.
Harry Glen
However, even procedures such as LASIK cannot prevent the need for corrective lenses permanently, because young myopic patients will require spectacles once they age and become presbyopic. Therefore, a lack of interest in an elective procedure that is deemed to be temporary should not restrain ophthalmologists from performing these more patient-friendly treatments, Glen said.
The procedure
Optimal keratoplasty (Opti-K, NTK Enterprises) entails the use of a thulium fiber laser operating at 1.93 µm wavelength with 150 ms pulse duration and variable power ranging up to approximately 3 W. The laser light is transmitted through a sapphire applanation window, which cools the corneal surface, thereby reducing the heating by the laser at the epithelial level to below the threshold of about 60°C at which thermal damage occurs. However, the temperature rise within the stroma is sufficient to cause corneal shape change. The epithelium is left intact, and the resulting heat-affected zone extends to approximately 100 µm (0.1 mm) within the anterior stroma.
“These technical characteristics are important to understand how Opti-K successfully avoids the land mines of its predecessors, laser thermal keratoplasty and conductive keratoplasty, by enabling the corneal epithelium and basement membrane to remain intact,” Glen said. “By preserving this all-important barrier, there appears to be no fibrotic wound healing and the patient is left comfortable, able to see instantly and return to active life without delay.”
The laser procedure lasts less than 3 seconds per eye. Prior to the procedure, a drop of anesthetic is placed in each eye. A lid speculum can be used, but most surgeons who have become confident with the procedure no longer use one, Glen said. A drop of water is used to hydrate the corneal surface, and a cone-shaped interface unit with a sapphire window for applanation is positioned on the eye and centered over the pupil. An appended suction ring enables secure attachment to the bulbar surface, and once applied, the laser handpiece, containing 16 ocular fibers, is docked onto the cone. Laser energy is irradiated for 2.5 seconds, resulting in two concentric rings of eight spots, 0.5 mm in diameter, placed at 6 mm and 7.2 mm from the pupillary centroid.
“Topographically, this procedure produces a patent-pending rosette-shaped pattern of alternating steeper and flatter sectors, a kind of multifocal cornea that is optimal for both near and far vision improvement in hyperopic presbyopes. Emmetropes achieve improvement in their near vision without losing clarity in their distance vision,” Glen said. “This effect is instantaneous and independent of pupil size. Patients are amazed at how well they see immediately after this rapid, pain-free procedure. Postoperative discomfort is minimal. A low percentage of patients in our clinical trial had just a very mild foreign body sensation, which disappeared within a day.”
Clinical studies
Opti-K is currently undergoing a U.S. Food and Drug Administration clinical trial. So far, 10 eyes of 10 patients with low to moderate hyperopic presbyopia were treated and have reached 18 months of follow-up.
“We had no adverse events or clinically significant changes in astigmatism, tear osmolarity, IOP, corneal thickness, endothelial cell density, ocular aberrations or contrast sensitivity,” Glen said.
A larger study of two groups of patients with hyperopic presbyopia (65 eyes of 35 patients) and emmetropic presbyopia (63 eyes of 33 patients) was conducted at a single center in the Bahamas.
Retention of functional presbyopic correction averaged 2 years in emmetropes and 18 months in hyperopes. Retention of functional distance correction in hyperopes averaged 2 years.
“Although regression of effect is normally reported over time, a re-treatment restores the initial outcome and can be performed at any time the patient elects to do so,” Glen said.
Patient neuroadaptation to the multifocality produced by Opti-K occurred immediately after treatment without clinically significant loss of contrast sensitivity.
Patients are currently being treated in Italy, France, Germany, the Bahamas and Bermuda. Preliminary results of a study conducted by surgeons in Italy have also been encouraging, Glen said. – by Michela Cimberle