December 2007

 

REFRACTIVE SURGERY

 

High-pressure vacuum during LASIK


by Matt Young EyeWorld Contributing Editor

   

Elongation of vitreous body, increasing axial length were two trends identified when evaluating effects of high pressure

LASIK A new study details the high-pressure vacuum affects upon the eye that are associated with LASIK procedures Source: Perry S. Binder, M.D.

By now, LASIK surgeons are well aware that vacuum causes at least temporary ocular changes, such as a spike in IOP for its duration. But in a large series of patients, researchers have now detailed more precisely what happens to the cornea during high-pressure vacuum. “Review of the literature as to the effects of vacuum by the microkeratome suction ring on ocular structures demonstrates no consensus,” according to lead study author Richard M. Davis, M.D., Department of Ophthalmology, University of South Carolina, Columbia, S.C. “Our study has conclusively shown compression of the anterior structures with elongation of the vitreous body and a trend of increasing axial length.”

Although Dr. Davis noted that the clinical significance of this is still unknown, such as the risk of rhegmatogenous retinal detachment, the findings should help ophthalmologists better understand the vacuum effects upon their patients and perhaps ultimately make more informed decisions as to whom they operate on.

Vacuum effects

In Dr. Davis’ study, 69 eyes (39 patients) scheduled for LASIK underwent analysis. A-scan ultrasonography was used to measure anterior chamber depth, lens thickness, vitreous body, and axial length. Patients were measured before and during placement of a Hansatome microkeratome suction ring (Bausch & Lomb, Rochester, N.Y.) on their eyes. “Our study represents the largest number of living volunteer patients where ultrasonography has been performed in vivo to measure changes in ocular structures during vacuum by a microkeratome suction ring,” Dr. Davis noted. During suction, the length of the anterior chamber decreased by –0.06 mm and corneal thickness decreased by –0.14 mm. Meanwhile, the vitreous body increased in length by 0.25 mm. A trend toward increasing axial length also was demonstrated. “We have illustrated the changes to be more complex than previously reported as the anterior and posterior structures respond differently to high vacuum, making the axial length measurement less illuminating,” Dr. Davis reported. “Although the clinical significance has yet to be determined, biomechanical deformation by a rapid sequence of compression and decompression associated with LASIK theoretically may increase the risk of vitreoretinal pathology.”

LASIK unquestionably has become a popular procedure, in no small part due to its safety and efficacy. But for Dr. Davis, questions still remain about retinal detachment. Dr. Davis noted the yearly incidence of phakic idiopathic rhegmatogenous retinal detachment is only 6.1 to 9.1 per 100,000 people (or 0.0061 to 0.0091%). That’s for all refractive errors. But, he noted, in one study of 1,554 LASIK eyes with a mean spherical equivalent of –13.52 D, the rate of detachment was 0.25%. In another study of 3,009 LASIK eyes with a mean spherical equivalent of –13.77 D, the rate was 0.36%. Lower risk has been reported with lower myopia but at rates still higher than the general population. “Fortunately, no study has conclusively shown a cause and effect relationship with rhegmatogenous retinal detachment and LASIK,” Dr. Davis wrote.

Not a danger

Dr. Davis’ results make sense to William Trattler, M.D., director, Cornea, Center for Excellence in Eye Care, Miami. “You are using a vacuum to increase the pressure of the eye, and structural changes are expected,” Dr. Trattler said. “I’m not sure if that’s anything surprising.” LASIK fact

But Dr. Trattler said that more than a decade of experience with LASIK has demonstrated that the procedure does not appear to increase the risk of a retinal detachment. He still acknowledges the potential risks of retinal holes, tears, and other problems surrounding the creation of the LASIK flap. “It is interesting that LASIK patients, who are commonly nearsighted, have a higher risk of retinal problems,” Dr. Trattler said. “But whether they have surgery or not, they are still at risk for a retinal holes or detachment.”

Dr. Trattler recalled one patient scheduled for LASIK surgery at his clinic. The patient delayed surgery, and the day after she was originally scheduled to undergo LASIK, she suffered a retinal detachment. “The timing was bizarre,” Dr. Trattler said. “If she had actually undergone the LASIK procedure as scheduled, she would have blamed LASIK for the retinal detachment.” And perhaps Dr. Trattler would have wondered about that, too. Dr. Trattler’s understanding about myopia’s relation to retinal detachment is correct, though. Dr. Davis’ study did report that “axial myopia is the most common risk factor in nontraumatic rhegmatogenous retinal detachment with a refractive error from –1.00 to –3.00 D having a four-fold increased risk.” Further, he noted that those with greater than –3.00 D have close to 10 times the risk of having a detachment.

Editors’ note: Dr. Davis has no financial interests related to his study. Dr. Trattler has no financial interests related to his comments.

Contact Information

Davis: 803-434-7062, rdavis@gw.mp.sc.edu

Trattler: 305-598-2020, wtrattler@earthlink.net

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