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Manual approach is a simple way to perform LASIK centration
An inexpensive system may be more reliable than automated eye-tracking devices.
---The Assisted Intraoperative Manual Eye-tracker (AIME II) is a simple, inexpensive manual system that can help surgeons achieve perfect centration in LASIK.
ROME – Centration in laser in situ keratomileusis (LASIK) can be achieved with the aid of a simple, inexpensive manual system, called an Assisted Intraoperative Manual Eye-tracker (AIME II), devised by Prof. Mathias Zirm, MD, of Innsbruck University. He discussed the device here at the Rome ’99 meeting.
“Even slight decentration in refractive laser surgery has very serious consequences on visual acuity, and once the damage is done, there is no other solution than keratoplasty,” Prof. Zirm said.
Prof. Zirm said he does not believe that an automated eye-tracker is always the best answer. “Although today automated eye-trackers are safer than they used to be, they are still very expensive. In a much easier and cheaper way, we can achieve the same, or even better, results,” he said.
The AIME II system
---The AIME II system consists of a ring-mark in the ocular of the microscope, staining of the cornea and sclera, and a corresponding suction ring.
The system consists of a crossed ring mark in the ocular of the microscope, a staining marker for the cornea and sclera and a suction ring.
At the beginning of surgery, the patient is asked to fixate on the red light of the laser. “In this situation,” Prof. Zirm explained, “the centration on the light is the best possible, as the eye is still untouched and the cornea is naturally moist.”
The second step is to stain the cornea with the marker, drawing a 12-mm diameter ring around the cornea with three rays, at the 12-o’clock position, 6-o’clock position and temporally.
The 12-mm diameter mark corresponds to the diameter of the suction ring. “The inside diameter of the keratome we use is exactly 12 mm,” Prof. Zirm said. “With a different size keratome, all the measurements will, of course, be modified.”
At this point, the flap is cut and opened and the stromal bed is well centered in the optical zone.
During ablation, the crossed ring, which is marked on the ocular of the microscope, is visible against the eye. Adjusting it to correspond to the suction ring diameter and to the rays that are marked on the cornea, the surgeon will be able to keep the ablation perfectly centered. Even minimal movements of the eye will be immediately detected.
“The only thing is that you need a firm hold on the eye,” Prof. Zirm said. “If your hand is shaky, better rely on an automated eye-tracker.”
Completing the operation
---Rotation of the globe during excimer laser surgery causes an elliptical treatment zone.
After laser ablation, Prof. Zirm washes the cornea with a rinsing cannula of his own design and applies a soft contact lens to allow safe and accelerated reattachment of the flap without fold formation.
The instrumentation for AIME II is designed by Geuder GmbH, of Heidelberg, Germany.
For Your Information:
- Prof. Mathias Zirm, MD, can be reached at Fallmerayerstrasse 3, A-6020 Innsbruck, Austria; (43) 512-581860; fax: (43) 512-5722501; e-mail: office@zirm.net. Dr. Zirm has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Geuder GmbH, manufacturers of the instrumentation for AIME II, can be reached at Hertzstrasse 4, D-69126 Heidelberg, Germany; (49) 06221-3066; fax: (49) 06221-303122.