Careful screening, measurement should reduce incidence of ectasia

Risk factors for ectasia may exist, but if ophthalmologists carefully screen patients and carefully measure what they're doing, the incidence of this complication of LASIK will be reduced, said Perry S. Binder, MD, Gordon Binder Weiss Vision Institute, San Diego, United States.

"Ectasia is not new," Dr. Binder said, noting that 115 cases have been published in the English literature. "We now are concerned as to why this particular disease entity takes place. There are certain things about what's in the literature that concern me."

He cited a paper (Amoils SP, Deist MB, Gous P, Amoils PM. Iatrogenic keratectasia after laser in situ keratomileusis for less than –4 to –7 D of myopia. J Cataract Refract Surg. 2000;26:967-77) that reported results of 13 eyes in 18 patients in which ectasia developed.

"In 11 of these cases, the topography before surgery was abnormal," Dr. Binder said. "In only one case was there a normal topography in the right eye . . . but if you made the calculations, you would see that this patient had been left with a very thin residual depth well below 250 µm, which probably accounted for this particular patient's complications."

Subsequent to this publication, Dr. Binder said, three other studies that have suggested that an increase in the likelihood of ectasia developing after LASIK is associated with these risk factors: age less than 25 years, residual bed thickness less than 250 µm, corneal thickness less than 500 µm, high myopia, corneal curvatures greater than 47 D, enhancement surgery, and against-the-rule astigmatism.

"Everyone now is fearful: 'If I operate on a patient with these risk factors, I'm going to have a case of ectasia,' " Dr. Binder said. "But there are some perplexing issues in the literature: a case of LASIK in one eye and both eyes developing ectasia; LASIK in both eyes, with only one eye developing ectasia; LASIK in a patient with known keratoconus in both eyes, and only one eye develops ectasia; ectasia after RK, after hyperopic ALK, after a partial flap; ectasia able to be reversed by lowering the IOP. All of these things are telling us that something else is happening in these eyes that we don't know about, and there are many unproven theories as to why we develop ectasia."

When Dr. Binder examined cases in his own database, he found no incidences of ectasia under several different conditions:

• In 117 patients with preoperative corneal thickness less than 500 µm (average, 483 µm) and average follow-up of slightly more than 2 years.

• In 107 patients aged less than 25 years each (average age, 24).

• In 56 eyes with residual beds less than 250 µm (average, 228 µm as measured either at the time of enhancement or calculated based on flap thickness minus the theoretical laser ablation) and a mean follow-up of 27.8 months.

• In 86 eyes with corneal curvature steeper than 47 D and an average follow-up of 30 months.

• In 180 eyes with greater than –8 D of attempted correction (average correction, 10 D) and an average follow-up of 33 months.

• In 67 eyes with more than 2 D of against-the-rule astigmatism and a 2-year follow-up.

"What this tells me is that if you screen your patients and eliminate eyes with abnormal topography, and you measure the cases and know what you're doing, it doesn't mean you're going to get ectasia," he said. "So you can operate on eyes with so-called risk factors, but you're going to have to be very careful and eliminate the family history of keratoconus, atopic diseases, [and] abnormal topography as well."

Of the complications reported in the literature, Dr. Binder said, "The most logical [explanation] is that, because these flaps were never measured, the doctors had achieved very thick flaps and were operating on a much thinner residual bed than they had planned for these particular cases. There were many cases that had abnormal topographies as well, and increased duration of time to create the laser flap causes more dehydration of the stroma, so the laser ablation would be more effective. They may have cut a lot more deeply than they planned on doing."

To reduce the risk of ectasia, he offered these pearls:

• Look for asymmetry between eyes in terms of corneal thickness, in terms of astigmatism, and in terms of the thinnest points of the cornea being well away from the apex.

• Look at differences in best-corrected vision between the two eyes. "You can use the [inferior/superior] ratio and the Klyce keratoconus screening technique for looking at these indices to help warn you that you might be dealing with an abnormal topography," Dr. Binder said.

• Watch out for the flattening below the visual axis that might suggest early blue spot degeneration.

• Watch out for eyes in which a best spectacle-corrected visual acuity of 20/20 cannot be achieved.

The best form of treatment for ectasia is prevention, Dr. Binder said.