This article is more than 5 years old. Information may no longer be current.
Iris registration to become standard of care for laser, surgeon says
The most careful manual markings cannot compare to the accuracy of iris registration technology, according to one refractive surgeon.
Click Here to Manage Email Alerts
|
The accuracy of iris registration will help make the technique the standard of care for all patients who undergo wavefront-guided laser refractive surgery, according to Douglas D. Koch, MD.
Dr. Koch presented a comparison of the accuracy of manual measurements and iris registration during a media day hosted by Advanced Medical Optics.
He reported on a series of 64 eyes of 40 patients treated with Visx WaveScan iris registration; the eyes were also marked manually to compare the accuracy of the two methods.
Dr. Koch said he marked the eyes at the 6 o’clock position and temporally and then aligned them under the laser, just as he would with a normal laser treatment without iris registration.
“What’s really interesting is that even though I’ve marked these eyes and I’m meticulous about marking … we had a range of errors up to 6.6° in rotation from my marks to the actual registered image,” he said.
Inconsistency explained
The observed discrepancies left Dr. Koch and colleagues to consider reasons for the inaccuracies.
“When the patients sit in the WaveScan, their heads might not be perfectly vertical, and this might not be noticed by the examiner,” Dr. Koch said. “There might be some cyclorotation during marking as the patient fixation varies.”
The right eye tends to be off in one direction, he said, and the left eye in the other.
In this study, iris registration proved to be a more accurate alternative to eye marking, he said.
“Each eye is different in the cyclorotation,” he said. “The process can break down at any point along the way, from the wavefront measurement through the marking process to the moment of stepping on the laser pedal.”
Comparing alignment methods
Dr. Koch and colleagues performed a retrospective analysis to compare results with iris registration to manual alignment. They compared a series of Fourier-driven PRK surgeries without iris registration performed between September 2004 and May 2005 to a series of Fourier-driven ablation with iris registration performed from June 2005 to July 2005.
“These are early results because we have 1-month follow-up in the latter group,” he said.
Dr. Koch said 78 eyes were treated without iris registration and 20 with iris registration.
He said that while results were comparable for uncorrected acuity at the 20/40 level, there was a statistically significant difference for the 20/20 level, with 60% of the eyes treated without iris registration achieving this compared with 90% of those treated with iris registration.
“What this tells us is that with the use of iris registration, the PRK eye heals much more quickly and achieves excellent vision much more rapidly,” he said.
Dr. Koch said that there were two other benefits noted with iris registration. “Regarding refractive accuracy, the spherical equivalents were comparable, but there was a trend for a lower standard deviation in eyes treated with iris registration. In addition, there was faster recovery of best corrected vision in the iris registration eyes.”
Potential benefits
“Patients are regaining their vision more quickly, not only uncorrected but now best corrected as well,” Dr. Koch said. “I think the more precise alignment of the measured wavefront to the actual wavefront that’s delivered to the patient’s eye makes a clear difference.”
More accurate cyclotorsional alignment leads to improved astigmatic correction, which yields better uncorrected visual acuity, Dr. Koch explained. Improved pupil alignment helps create more accurate spherical correction, which also helps better uncorrected acuity, he said.
Combined, the elements of iris registration give better correction of higher-order aberrations, he said. This should improve both uncorrected and best corrected vision.
“I think there will prove to be fewer enhancements and of course happier patients,” he said. “Iris registration is for all patients, and it’s going to be a standard of care, or at least of the best care, in a short period of time.”
Lack of capture rate
Despite the accuracy of iris registration, Dr. Koch said he is still having some trouble capturing blue eyes.
He said he formerly had a lack of capture rate of about 25% of the blue eyes he treats. However, he said that he now captures nearly all eyes. Dr. Koch credits his improved capture in blue eyes to a combination of persistence and a suggestion from Marc Odrich, who said to capture eyes before lifting the flap or removing the epithelium. This has made capture at the time of treatment much more likely.
Dr. Koch said he continues to treat eyes that cannot be captured. “I align them to my marks, and so I am providing the patient with the same standard of care that I’ve always provided,” he said. “I’m just not able to give them the newest [technology].”
For Your Information:
- Douglas D. Koch, MD, can be reached at Baylor Vision, 6550 Fannin, NC 205, Houston, TX 77030; 713-798-6443; e-mail: dkoch@bcm.tmc.edu. Visx on occasion pays Dr. Koch’s expenses to present data at meetings.
- Advanced Medical Optics can be reached at 1700 E. St. Andrew Place, Santa Ana, CA 92799; 800-449-3060; fax: 866-872-5635; Web site: www.amo-inc.com.
- Daniele Cruz is an OSN Staff Writer who covers all aspects of ophthalmology.