Refractive surgery innovations drive improvements

November 15, 2011

Advanced technology from Schwind is already shaping the future of refractive surgery, but surgeons can look forward to further refinements and innovations that will offer additional capabilities.

Muscat, Oman-Advanced technology from Schwind is already shaping the future of refractive surgery, but surgeons can look forward to further refinements and innovations that will offer additional capabilities, said Maria Clara Arbelaez, MD.

Excimer laser, eyetracking system

"There is capability to increase the laser's repetition rate [further] and to make the spot diameter even smaller as well as to have additional variations in fluence," Dr. Arbelaez said. "With these modifications it may be possible to decrease ablation time [further], not dramatically, but still by fractions of a second."

To compensate for involuntary eye movement and assure precise delivery of the laser energy, the laser features an advanced eyetracking system. Monitoring of the eye position is done at a rate of 1,050 times per second and the eyetracker has a reaction time of about 0.003 seconds that is fast enough to match the laser's high repetition rate.

The latest generation of the eyetracker compensates for eye movement in six dimensions to take into account dynamic (intraoperative) cyclotorsion as well as linear up/down movement along the z-axis.

"With the high sampling rate of its eyetracker and the platform's ability to compensate actively for the various dimensions of movement, the [laser] optimizes treatment precision and safety," she said.

The laser is also designed with a thermal control system that minimizes heating of corneal tissue intraoperatively and maintains a temperature within safe limits (overall increase <8° C and maximum temperature <40° C, which is the threshold for collagen denaturation). Results from a study using a high-resolution infrared thermographic camera to measure changes in corneal temperature show that in treating myopia up to –9.25 D, the cornea temperature increased by a maximum of less than 4° C and remained below 35° C, Dr. Arbelaez said.

The company is developing technology that will integrate measurements of corneal hydration and refractive index into the ablation plan.

"Typically, a constant refractive index of 1.376 is used in diagnosis and treatment planning for refractive surgery," she said.

"However, the refractive index varies in the corneal layers, increasing from the endothelium through the stroma to the epithelium, and also between patients, being higher in older individuals," Dr. Arbelaez said. "Individualized measurement of refractive index that is used to calculate water content is already possible, and results from initial clinical testing show its promise for improving treatment accuracy that can be expected to reduce enhancement rates."

None of the Schwind devices is approved by the FDA.

FYI

Maria Clara Arbelaez, MDE-mail: drmaria@omantel.net.om

Dr. Arbelaez receives travel fees from Schwind, but has no other financial interest in the company.

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