Wednesday, September 9, 2009

Abstract: Lasik study (cough, choke)

If you didn't notice the date of this study or the word 'wavefront', you might be forgiven for having assumed it came straight out of the Dark Ages of LASIK in the 90s when the only thing anybody (well, any ophthalmologist) knew or cared much about was UCVA and BCVA after surgery.

I know the profession has made considerable progress since then in recognizing the significance of things like vision quality and ocular surface pain. So what gives here?

I don't know whether to laugh, cry or bust someone's chops (I'm inclining to the latter, I'm afraid) when I read in a study of this scope a dry eye rate of 0.18%. I recalculated it to make sure the decimal was in the right place.

You are seriously claiming to have seen no more dry eye in your patients than DLK?

You have got to be kidding me.

How'd you measure dry eye? ("Quick, stick a Schirmer strip in there while the anaesthetic drop is still sloshing around.")

The real explanation of course is in the abstract: "Complications were tabulated using all available data." In a study stating a dry eye rate far lower than almost any recent research would put it by almost any measure of dry eye symptoms and/or signs, I can only conclude that dry eye data was unavailable for the majority of these patients because no one bothered to gather it.

One-month outcomes of wavefront-guided LASIK for low to moderate myopia with the VISX STAR S4 laser in 32,569 eyes.
Schallhorn SC, Venter JA.

J Refract Surg. 2009 Jul;25(7 Suppl):S634-41.

PURPOSE: To determine the safety and efficacy of wavefront-guided LASIK for the correction of low to moderate myopia, as performed by surgeons employed by Optical Express, a large corporate provider.

METHODS: Data were extracted from the Optical Express central database on 22,900 patients (42,143 eyes) who underwent primary LASIK to treat low to moderate myopia and/or astigmatism. All treatments used a wavefront-guided ablation profile and had a refractive target of emmetropia. Outcomes were evaluated using 1-month follow-up data, which were available for 32,569 eyes of 17,713 patients (77% follow-up). Complications were tabulated using all available data.

RESULTS: The mean manifest spherical equivalent (MSE) was reduced from -2.97 +/- 1.33 diopters (D) (range: -0.37 to -6.00 D) to -0.03 +/- 0.29 D (range: -3.50 to +4.50 D) 1 month after surgery. Ninety-four percent of eyes were within 0.50 D of the intended correction, and the correlation coefficient of the attempted versus achieved MSE was 0.96. Uncorrected visual acuity (UCVA) of 20/20 or better was achieved in 92% of eyes; 99% of eyes achieved UCVA of 20/40 or better. Among patients who had bilateral laser vision correction, 98% achieved 20/20 uncorrected binocular vision. Average best spectacle-corrected visual acuity (BSCVA) improved slightly 1 month after surgery (mean change: +0.01 logMAR). There were 210 (0.67%) eyes that lost 2 or more lines of BSCVA; however, all eyes were 20/40 or better. Intraoperative complications occurred in 25 eyes (0.06%; 1:1686), and postoperative complications occurred in 210 eyes (0.64%; 1:155). The most common complications were dry eye (n=58; 0.18%; 1:562) and mild diffuse lamellar keratitis (grade 1 or 2) (n=58; 0.18%; 1:562).

CONCLUSIONS: Wavefront-guided LASIK can safely and effectively correct low to moderate myopia, as demonstrated by 1-month postoperative visual outcomes from a large number of patients.

2 comments:

Teri said...

I, too, find this study hard to believe. Is there any way I can read the entire paper? I am curious as to how they measured the so-called "complications."

It is well-established that dryness is a very common side effect of Lasik, whether or not you develop chronic dry eye disease. It is standard operating procedure for surgeons to have patients using OTC drops (like Refresh Plus) prior to and after surgery. Isn't it?

I wonder if they simply gave patients a survey at their one-month follow-up appointments and asked them if they were experiencing dryness. Most people probably wouldn't even know that their discomfort was due to dryness. I didn't. I didn't realize that the gritty, grainy, burning sensation was because my eyes were dry.

And basing the sweeping conclusion that the surgery is "save and effective" on a one-month follow-up is ridiculous given that the eye hasn't even healed by then. How are the patients doing at six months? One year? Two years? How many are using rewetting drops and how often are they using them, etc.

This is infuriating. I guess my last question is what kind of journal is the "Journal of Refractive Surgery"? Is is peer-reviewed? Does it require its articles to follow any kind of rigorous scientific standards? Does it have a section for letters? Maybe we should write a letter to the editor citing the studies that contradict this one and listing the weaknesses in these author's methods.

Teri

Rebecca said...

Teri, I suppose they used data from patients over a very long period of time including the years when they really didn't bother to assess this, let alone assess it in a way likely to produce solid data. I think back to my experience in 2001. No one was even talking about dryness then except as relates to the immediate postop period.

Yet in a study covering this many patients, one of the very most valuable pieces of information would have been complications and side effects. I think that saying they used all available information on complications, and yet they produced that low of a figure, reflects poorly both on the authors and on the journal.

JRS is a peer reviewed journal. I used to subscribe. Personally I consider it more of an industry cheerleader than a medical journal. I used to run across good studies periodically, but also many that I feel sure would not pass the standards for more highly rated ophthalmology journals. I remember at one point a couple of years ago reviewing several years worth of JRS studies looking for anything on LASIK and dry eye. They were very, very few and far between. It was stunning to me, considering it is universally accepted to be the most common complication of LASIK and LASIK has the lion's share of refractive surgery, which is the subject of the journal.