EyeWorld Weekly News
Volume 10, Number 44 November 28, 2005

http://www.eyeworld.org/ewweek.php?id=395#2

Wavefront-guided LASIK and fractional clearance

The optical zone/pupil ratio (fractional clearance, FC) has a significant impact on HOA induction after wavefront-guided LASIK, according to a study to be published in the December issue of the Journal of Cataract & Refractive Surgery. The study, “Influence of pupil and optical zone diameter on higher order aberrations after wavefront-guided myopic LASIK,” examined 27 myopic eyes of 19 patients. It was authored by Jens Bühren, M.D.; Christoph Kühne, M.D.; and Thomas Kohnen, M.D. Goethe University, Frankfurt am Main, Germany. They wrote that the ratio of optical zone to pupil was higher correlated with HOA induction after wavefront-guided LASIK than pupil diameter alone. The change in HOA root mean square and primary spherical aberration (Z 4, 0) was significantly correlated with FC, according to the study. If the optical zone [OZ] was 16.5% larger than the pupil (FC=1.17), only half of the amount of HOA is expected to be induced as if the OZ equaled the pupil, Dr. Bühren wrote. In contrast, an OZ that was 9% smaller than the pupil (FC=0.91) resulted in an HOA induction of 50% higher as at FC=1, according to the study. All patients underwent uneventful wavefront-guided LASIK using a Zyopix laser (Bausch & Lomb, Rochester, N.Y.)

http://www.lasermyeye.org/keratoscoop/c ... hives.html

Read The Lone Dog's articles.

http://www.envisioneyecenter.com/lasik_risks.html

"Night Glare is common in nearsighted individuals even before any refractive procedure is performed, but increases almost immediately in the healing process and is more common when only one eye is treated. Typically, 6 months after both eyes have been treated, only 2% of patients still experience significant night glare that interferes with their night driving. Severe night glare can impair vision in all reduced lighting conditions producing blurriness, ghosting, or halos. Patients with large pupils and severe myopia and/or significant astigmatism are at greater risk for night glare."

From the FDA website, "When is LASIK not for me?"


http://www.fda.gov/cdrh/LASIK/when.htm


Large pupils. Make sure this evaluation is done in a dark room. Younger patients and patients on certain medications may be prone to having large pupils under dim lighting conditions. This can cause symptoms such as glare, halos, starbursts, and ghost images (double vision) after surgery. In some patients these symptoms may be debilitating. For example, a patient may no longer be able to drive a car at night or in certain weather conditions, such as fog.

From the American Academy of Ophthalmology website:

http://www.aao.org/education/library/re ... /lasik.cfm

Summary Recommendations for LASIK
Issued March 28, 2002

Patient Examination

In determining suitability, a baseline eye evaluation should include:

Manifest and cycloplegic refraction
Measurement of intraocular pressure
Slit-lamp biomicroscopy
Tear film evaluation
Corneal topography
Evaluation of preoperative corneal thickness
Dilated fundoscopic examination
Measurement of scotopic pupil size

Somebody should report Dr. Stephen Slade and Dr. Richard Linstrom and anyone else who operates on patients with large pupils to the AAO for violating AAO guidelines.

From the ASCRS Eye Surgery Education Counsil website, LASIK Patient Screening Guidelines:

http://www.lasikinstitute.org/LASIK_Pat ... lines.html


• Measurement of pupil size in dim and room light. Pupil size is an important factor in counseling a candidate about night vision and planning the appropriate laser vision correction strategy.



I suppose Slade and Lindstrom are both members of ASCRS, too. They should be ostracized.

Even the insurer, OMIC, requires pre-op pupil measurement.

http://www.omic.com/products/bus_produc ... %20app.rtf


PATIENT SELECTION

As part of the independent evaluation, the surgeon must personally examine the patient’s eyes and ocular adnexa, perform a slit lamp exam, and carefully review topographies, pupil size, pachymetry, refractive stability, eye health history, and prior records.


Notice it said "the surgeon must personally examine the patient's eye..."

From the Federal Trade Commission website:

http://www.ftc.gov/bcp/conline/pubs/health/lasik.htm

Take the following measurements:
The curvature of your cornea and your pupils. You may be rejected if your pupils are too large.

http://www.eyeworld.org/article.php?sid=2813

EyeWorld
November, 2005

Large pupils lead to night vision problems, physicians suggest

Excerpt:

While some studies have suggested pupil size has little to no effect on nighttime vision post-refractive surgery, some ophthalmologists point to new evidence that there is a correlation.
“If you compare patients of the same prescriptions, the larger the pupil size, the bigger the chance that they’re going to have more night vision problems,” said William B. Trattler, M.D., Center for Excellence in Eye Care, Miami.
To back up his assertion, Dr. Trattler performed his own studies, one of which included 119 myopic eyes that underwent LASEK or PRK with either a standard VISX (Advanced Medical Optics, Santa Ana, Calif.) Star S3 or S4 laser.
Using a Larson Glarometer, he found that the radius of starbursts was greater in patients with large pupils compared with those in patients with small ones. Dr. Trattler presentedthe results at the most recent ASCRS•ASOA Symposium & Congress. The Larson Glarometer does not have a corporate manufacturer yet. It was developed and is distributed by Bruce Larson, M.D., Hinsdale, Ill.
Meanwhile, James Salz, M.D., clinical professor of ophthalmology, University of Southern California, Los Angeles, also believes large pupils can lead to night vision complaints after refractive surgery.
“The larger the pupil size, the greater the aberrations will be,” said Dr. Salz.

I like the quote below. As I've always said, taking a wavefront scan at 6 mm or 6.5 mm on a patient with pupils 7 mm or larger is like weighing a 250 lb. woman on a scale that only goes up to 150 lbs.

http://www.escrs.com/Publications/Eurot ... gators.pdf

"Aberrometry depends on pupil diameter, as well. HOAs disturb vision increasingly with increasing pupil diameter."

FDA Ophthalmic Devices Panel meeting
August, 2002
Dr. George Pettit is speaking on behalf of ALCON for approval of it's wavefront guided platform.

http://www.fda.gov/ohrms/dockets/ac/02/ ... 3883t1.doc

DR. PETTIT: Just to follow up a little bit on an earlier question. This is George Pettit from Alcon.

I think Dr. Matoba asked the question about the pupil sizes and were the patients informed. Given this high-level expectation, it's important to note that the optical zone was 6.5mm and we informed all patients considering being in the trial that if their natural pupil was larger than 6.5mm, even with this new technology, there was a potential risk for them to have night vision symptoms. So we tried to bring their expectations more in line.

http://www.crstodayarchive.com/03_archive/0503/17.html

Cataract & Refractive Surgery Today
May, 2003

Spherical Aberration and Its Symptoms

Theories on why it occurs and how new technology may address the problem.

BY MARIA REGINA CHALITA, MD, AND RONALD R. KRUEGER, MD, MSE

Excerpt:

SYMPTOMS CORRELATED WITH SPHERICAL ABERRATIONS
Standard laser refractive surgery performed on patients with large scotopic pupil sizes is associated with nighttime vision problems such as halos.12 The increased amount of higher-order aberrations after standard LASIK is consistent with the relatively common patient comment, “I can read 20/20, but my vision is not as good as it was before.”13


We analyzed 105 eyes that underwent LASIK correction and correlated their symptoms with higher-order aberrations. Our analysis of optical symptoms and measured aberrations for a scotopic pupil size showed a statistically significant correlation between higher-order aberrations and glare (P=.041) as well as starburst (P=.004). When we broke down these aberrations into individual Zernike components, spherical aberration was the predominant cause, with a statistically significant correlation to glare (P=.010) and starburst (P=.014). Halos seemed to be associated with spherical aberration for the scotopic pupil size (P=.053). Table 1 shows the relationship of spherical aberration and coma with patients’ symptoms.

SPHERICAL ABERRATION PREVENTION AND CORRECTION
Surgeons must exercise care when treating eyes with larger scotopic pupils, especially if the procedure is expected to induce higher levels of spherical aberration (patients with large pupils will experience more symptoms with higher levels of spherical aberration). Customized laser ablations attempt to minimize these symptoms by more effectively avoiding laser-induced spherical aberrations.
The ideal ablation profile for correcting refractive error without generating spherical aberration is to reshape the cornea with a lesser radius of curvature in the midperiphery rather than in the center. This difference in asphericity corrects the spherical aberration of the eye, because the flatter surface will cause less refraction of the peripheral rays.14

EyeWorld
January, 2001

Inside LASIK

Alphagan pupils: Getting high marks in the glare of the LASIK spotlight

"The patient has the benefit of having a slightly dilated pupil in the dark, but keeps it from going out beyond the 5- or 6-mm margins, where distortions and aberrations occur. With use of the drug, McDonald reports an average pupil diameter of less than 4.5 mm, with an average decrease of 2 to 3 mm in those with large pupils. "What happens is [that] people with bigger pupils get more response, which is ideal," McDonald said."

Read the entire article at:
http://www.eyeworld.org/article.php?sid=1682

Scott MacRae, MD on the importance of pupil size:

https://www.urmc.rochester.edu/pr/news/story.cfm?id=245

Excerpts:


"Ophthalmologist Scott MacRae, M.D., professor of Ophthalmology and Visual Science at the University of Rochester Medical Center, recently studied the role of a patient’s pupil size in determining a patient’s outcome from the surgery. In a study of 340 patients, he found that generally the larger a patient’s pupils, the more likely that person is to have a problem with laser vision correction.

He reports that if a surgeon treats a large enough swath of the eye for such patients, those imperfections are minimized. His study shows that it’s essential that doctors treating patients with large pupils consider creating an especially large treatment zone.

He found that doctors must be especially careful when using a laser to correct vision on people whose pupils are large. If physicians treat too small an area of the cornea, patients are likely to have a problem when their eyes are most dilated – at night. Pupil size is especially critical if a person is extremely near-sighted.

To understand the problem, think of a window washer who should clean an entire window even when the inside blind is partway down. When the blind goes up, a person looking through the window wouldn’t get a clear view unless the previously covered section of the window was washed too. Likewise, MacRae says, surgeons must treat a large part of the cornea so that when the pupil widens, the entire pupil transmits light clearly.


“Oftentimes I’ll have a patient who is initially upset because I won’t treat them, but they become grateful as they realize that we’ve done what is best for them in the long run,” he says. “When the pupil dilates, aberrations can be troubling. You have to be really careful. Patients need to be wary of surgical centers that trivialize these issues.”