Iris Registration
Since the early days of LASIK surgery, improvements have repeatedly been added. One of the biggest has been Wavefront-guided LASIK. Now we have the VISX iris registration, which is an improvement on wavefront technology. It was recently given FDA approval.


/Vision-Eye Care News Articles/ - LOS ANGELES, CA, February 11, 2007 - Many eye surgeons use the wavefront-guided VISX system, which is known as CustomVue. The Iris registration is a hardware upgrade installed on this system.
Wavefront-guided LASIK
It's also called [url=http://www.khannainstitute.com/wavefront.html_Custom LASIK[/url], for good reason.
In the diagnostic stage the wavefront system takes many measurements of each cornea in tiny detail. From these, it makes 3_D maps, which it displays on the system's computer monitor. The information contained in these maps is used to calibrate the laser for treatment.
Nobody else in the world has eyes exactly like yours. These maps are created in such tiny detail that they can't be mistaken for anybody else's, and the laser treatment based on them will be unique to you. It's an entirely customized treatment.
A small Achilles' heel in Custom LASIK
In between the time the eyes are diagnosed and mapped by [url=http://www.khannainstitute.com/custom_lasik.html_Wavefront-guided LASIK[/url], and the time of treatment, if the eyes change at all, the laser needs to be adjusted to match.
Eye movements
When you lie down for your treatment on the patient bed that's part of the wavefront unit, you're moving your eyes from a vertical to a horizontal orientation, and in that change, sometimes the eyes rotate, which is called cyclotorsional movement.
The eyes could make other movements too, in between the mapping stage and the treatment:
The size of the pupil can change if the ambient lighting changes
The head may turn slightly to one side
That means that the measurements done on your eyes while you were sitting will be very slightly wrong now that you're lying down for treatment. The wavefront diagnostic information needs to be slightly modified to align the laser to the eyes' new positions.
Previous ways of aligning treatment
Your eye surgeon needs a reference point for aligning the laser during treatment. In the past there have been two ways of setting the reference point:
1. Manual - with a sterile pen, the eye surgeon made tiny marks on the cornea to indicate where the laser would be focused during treatment. At the time of treatment, he manually positioned the patient's head so as to line the laser up with the marks.
This method was prone to human error at times. Also, the ink used to make the marks was short-lived, drying up after a minute or so.
2. Semi-automatic - The outlines of both the pupil and the iris were used as reference points and with the eyes dilated to enlarge the pupil, tiny marks were manually made outside the iris to indicate where treatment should be focused.
This method took longer, as the eyes had to be dilated, and it also allowed human error to creep in at times.
Automatic iris registration
The outside boundary of the iris does not change, only the inside boundary when the pupil changes size. So [url=http://www.khannainstitute.com/iris_registration.html_iris registration[/url] uses the center of the pupil as the reference point, targeting the laser beam on that center, as it relates to the outside of the iris.
During treatment, the Wavefront software works with two images of your eye:
The pre-operative image contained in the 3-D map
The present-time image as you're receiving treatment
If there's any movement during treatment, it automatically and continuously re-matches the two images to each other, causing the laser to re-target on the prescribed treatment area.
Because of this continual automatic readjustment of the laser, your eye surgeon can treat exactly those areas which his or her diagnostic tests revealed as needing treatment.

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