Waterjet microkeratome shows clean cuts in animal eyes

Water microjet used to create hinged corneal incision concludes preclinical testing.

EDISON, N.J. – A microkeratome that uses a waterjet instead of a blade has completed preliminary testing in animals and will soon be tested in human blind-eye subjects, according the developer.

The waterjet device, created by Medjet Inc., based here, could provide an alternative to LASIK, said Eugene Gordon, PhD, the CEO of Medjet and developer of the device.

Two devices are being developed by Medjet. The first uses sterile water microjets to cut a hinged flap in the cornea as the first step in LASIK. The other would eliminate the need for a laser by using the same waterjet device to perform the corneal shaping normally done by a laser in LASIK.

First announced in 1994, the waterjet microkeratome has recently been successfully tested on animals with no complications, according to Medjet.

Tissue loss

---Early version of Medjet waterjet microkeratome illustrating its size. It is oriented to produce superior hinges.
With a blade-based microkeratome, shredding of tissue is unavoidable, Dr. Gordon said, making it more difficult for the flap to heal. One of the goals of animal testing of his device was to determine the amount of tissue lost during the procedure.

“Using several independent techniques, we were able to demonstrate that with human eyes and in pig eyes one can operate this device with zero erosion, so that there is no tissue lost,” Dr. Gordon said.

“Erosion of tissue by the waterjet need not occur despite vigorous claims to the contrary by others,” he continued. “The issue has been resolved unambiguously at Medjet by several types of experiments on human and porcine corneas. The waterjet tissue separation, in contrast to blade cuts, is a blunt dissection that is cleaner, produces a significantly smoother surface and removes no tissue.”

The high speed of the waterjet scan contributes to the uniformity of the cut in the cornea. Cutting at a speed of 15 mm per second or more, the amount of tissue loss is virtually zero, Dr. Gordon said. When the speed is lower, tests have shown that a non-uniform layer of tissue is eroded, he said.

“If you look at the collagen fibrils after LASIK, the fibrils are congealed,” said Joseph P. Calderone Jr., MD, FACS, ophthalmologic consultant to Medjet. “There’s lots of damage where the blade went. When we do a waterjet cut, the collagen fibrils are pristine.”

Problems with blades

One of the reasons Medjet developed the water microkeratome technology was to help surgeons avoid problems that occur with blade microkeratomes. Blade microkeratome complications can include non-planar cuts giving the flap a wedged, rippled or striated shape, making it difficult for it to heal correctly. Also, epithelium, metal chips from the blade and oil from the gears on the device can get onto the stromal bed and underside of the flap. Dr. Gordon said he hopes the new waterjet will resolve these complications.

“The waterjet device eliminates all of those problems,” Dr. Gordon said. “It makes good cuts every time. The flaps are uniform in thickness. The thickness is within a few microns of the chosen value.”

Planar cuts

---Newer version. The magnetically held applanation template is transparent, facilitating alignment and allowing viewing of the cut. The applanation diameter is adjusted up to 11 mm by turning the knurled knob. The template is removed for sterilization. Different templates allow choice of flap thickness ranging upward from 100 µm. The scleral chuck footprint is circular with a diameter of 18 mm.

An advantage of the waterjet is that its cut is planar, minimizing refractive errors arising from a non-uniform flap cross-section.

The waterjet device has a scleral chuck containing an applanating surface and is held firmly to the eye with partial vacuum. The applanating surface comes into contact with the apex of the anterior corneal surface and flattens it so that it is planar in the area of contact. The force of the waterjet beam is so slight, the tissue of the cornea is undisturbed.

“In this case the stromal bed is left perfectly clean,” Dr. Gordon said. “There’s no need to clean it or to clean the back of the flap because it’s free of epithelium, free of oil, free of blade chips and so on.”

Dr. Gordon said the device is able to cut flaps of up to 11 mm diameter, larger than standard microkeratome flaps with a maximum of 8 mm to 8.5 mm diameter. The range of the measured flap thickness has a standard deviation of 4 µm, which is mostly measurement error, Dr. Gordon said.

For vision correction, using a second cut after the flap is lifted, an accurately shaped lenticule is removed, according to Dr. Gordon.

The next step

Now that preclinical testing is complete, the company will next test the device on human blind eye subjects, Dr. Gordon said. Findings from those reports will be sent to the Food and Drug Administration (FDA).

“After that we’re going to do a study which we’ve been asked to do by the FDA called an ‘ease of use’ study,” Dr. Gordon said. “It really has to do with the doctor’s perception of how easy it is to use the device and how easy it is to use on a patient.”

Medjet plans to introduce the waterjet technology at the meeting of the American Society of Cataract and Refractive Surgeons in April and have it for sale by October.

For Your Information:

• Joseph P. Calderone Jr., MD, FACS, can be reached at 2 South Ave. East, Cranford, NJ 07016 U.S.A.; (908) 276-3030; fax (908) 276-3174; e-mail: eyegolf@worldnet.att.net. Dr. Calderone has a direct financial interest the product mentioned in this article. He is a paid consultant for Medjet Inc.
• Eugene Gordon, PhD, is CEO of Medjet Inc., 1090 King George Post Rd., Ste. 301, Edison, NJ 08837 U.S.A.; (732) 738-3990; fax (732) 738-3984; e-mail: egordon@medjetinc.com.