Smaller suction ring of Moria keratome works for shallow orbits of Asian eyes

Study found that fewer than 1% of Asian patients’ eyes required a minicanthotomy to accommodate the ring.

SAN GABRIEL, Calif. — The Carriazo-Barraquer (Moria SA; Doylestown, Pa.) microkeratome is an appropriate microkeratome for laser in situ keratomileusis (LASIK) in Asian eyes, according to a prospective analysis of 596 Asian eyes.

"Fewer than 1% of patients (four eyes) required minicanthotomy for the microkeratome pass, despite generally smaller Asian lid aperture," said Steven Ma, MD, a high-volume refractive surgeon in private solo practice here who caters to the Asian community. The incidence of buttonholes in the study was also a low 0.2% (one eye), and the incidence of microkeratome-related epithelial defects was fewer than 2% (eight eyes).

Dr. Ma has used various microkeratomes in the past; however, he finds the Carriazo-Barraquer the most suitable for Asian eyes.

"It has a smaller suction ring than other microkeratomes," Dr. Ma said. "Asian patients have shallow orbits and tend to have narrower lid fissures." As a result, with larger suction rings a minicanthotomy must often be performed.

Furthermore, he said, patients who undergo LASIK usually expect only a topical anesthetic. But a canthotomy requires an anesthetic by injection to the eyelids. "This can be fairly inconvenient and painful for some patients," Dr. Ma said.

Dr. Ma also favors the Carriazo-Barraquer because "it is the only microkeratome that allows the surgeon to choose the hinge location of the flap for LASIK." Moreover, "I feel this microkeratome creates very consistent flaps," he said. "Even in challenging situations where the lid aperture is too small with other microkeratomes, I can still create the flap that I need for LASIK with the Carriazo-Barraquer."

Surgical steps

Dr. Ma performed LASIK in all 596 eyes (approximately 300 patients) during the months of June and July 2000. Preoperatively, patients received one drop of Ciloxan (ciprofloxacin HCl, Alcon) in each eye, as well as topical proparacaine. A Lieberman pediatric lid speculum is also employed. "In cases where there is a very small lid aperture, I open the lid speculum to the maximum initially, then I extend the opening slightly about 2 or 3 minutes later," Dr. Ma said.

During suction ring placement, for which ring size depends on the patient's preoperative keratometry, "the globe needs to be proptosed by using the lid speculum to push down to the orbit," Dr. Ma said. To ensure good suction, Dr. Ma always uses a Barraquer tonometer. He also uses the manual turbine of the Carriazo-Barraquer microkeratome with a 130-µm head.

"According to the manufacturer, this head should produce a 160-µm flap," Dr. Ma said. "In a small study of about 30 eyes, we found that the flap thickness actually produced is about 160 µm with a standard deviation of 20 µm. This is certainly an acceptable range."

Prior to the microkeratome pass, the cornea is lubricated with Refresh Plus (carboxymethylcellulose 0.5%; Allergan). "The forward pass of the microkeratome is about 4 seconds," Dr. Ma said. For the reverse pass, however, "the turbine is shut off, and sometimes the suction is placed on low vacuum." Such maneuvers "minimize any torsion of the flap on the backward pass and minimize flap displacement during surgery," he said.

Dr. Ma also dries both the fornix of the conjunctiva and the flap edge before lifting it. After making sure that the stroma hydration is even, excimer laser ablation is started.

The smaller dimensions of the Moria Carriazo-Barraquer microkeratome are appropriate for the generally smaller lid apertures and shallower orbits of Asian patients, according to Dr. Ma, whose practice serves a largely Asian patient base.

Good visual results

None of the study eyes lost more than two lines of best-corrected visual acuity at final preop visit, even those with flap complications.

Overall, study results "were better than I anticipated," Dr. Ma said. "Certain microkeratomes when used in this population may require minicanthotmy at a rate of as high as 10%." In addition, "clinically, I found that flap thickness was fairly consistent with the Carriazo-Barraquer microkeratome and that the stromal bed was fairly smooth, even prior to ablation," Dr. Ma said. The flaps also healed "very quickly. In all eyes, the flaps cleared within 24 hours."

Because Asian eyes have tighter lid aperture, "I found that having a superiorly hinged flap helps, because you have a lesser incidence of flap displacement," Dr. Ma said. "My concern with a nasally hinged flap is that it requires increased drying time after LASIK for the flap to settle."

In a separate study, the investigators found that, in general, myopia is worse in Asian eyes than in non-Asian eyes. "The mean refraction spherical equivalent for Asian eyes is about –6 D, whereas in non-Asian eyes, it is only about –3 D," Dr. Ma said. Therefore, "I think it is more critical in Asian eyes that you use an instrument that will produce a consistent flap thickness, so you can better estimate how much cornea you have for treatment."

Dr. Ma believes the Carriazo-Barraquer microkeratome is "great for all eyes, not just Asian ones. It is a very versatile microkeratome." He cautions, however, that surgeons not automatically use a microkeratome bundled with an excimer laser as the only microkeratome of choice. "Despite the financial incentive, it might not be in patients' best interest," Dr. Ma said.

For Your Information:

• Steven Ma, MD, can be reached at 316 E. Las Tunas Dr., San Gabriel, CA 91776; (626) 285-3039; fax: (419) 793-3233. Dr. Ma has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any company mentioned.