LASIK technique: is a large flap better?

Postop advantages include better adherence, greater corneal stability and rapid re-epithelialization during healing.

ByLucio Buratto, MD

Since its creation in 1949 by José Barraquer in Bogota, Colombia, keratomileusis has been modified considerably, resulting in the current, safe and very precise technique of laser in situ keratomileusis (LASIK) with a superior hinge.

The modern LASIK technique has two basic steps: the lamellar cut, which makes a flap with the microkeratome for access to the underlying stroma, and the refractive “cut” or ablation of the exposed stroma made with the excimer laser.

Flap quality

The quality of the lamellar cut is of the utmost importance because it creates the flap. For good surgical results, the flap must have a smooth and uniform cut surface, be uniformly deep, be well-centered on the pupil, have a regular diameter suitable for the refractive ablation and be attached by a hinge that has sufficient extension.

To date, surgeons have been making a 7- to 8-mm diameter flap, but in my opinion a larger diameter is better, and I prefer a diameter of 9 to 10 mm.

Intraop advantages of large flap

Numerous advantages accompany a flap with a large diameter. With the 7- to 8-mm flap diameter, the hinge is close to the area that is ablated, which necessitates protective measures for the hinge during ablation. With a 9- to 10-mm flap, on the other hand, the corneal hinge lies further from the rays of the excimer and is thus protected from the laser ablation. No special retracting instrument has to be used to protect the hinge, and this saves surgical time. In addition, the absence of retracting instruments prevents interference with the eye tracking system.

Also, with the hinge lying far from the center of the ablation, a better quality ablation can be expected because the in situ stroma can be kept dry during the laser sculpting. This too saves time because drying sponges do not need to be used.

The area available for the myopic, the astigmatic and especially the hyperopic ablations is larger, allowing for a large intrastromal optical and blend zone. And at the end of the surgery, the large flap repositions easily. I have found that patients are more comfortable during the surgery, and they appreciate the shorter operating time.

With the large diameter flap, LASIK is easy to perform in special cases, such as eyes that have had penetrating keratoplasty, radial keratotomy, astigmatic keratotomy, intracorneal ring removal or other procedures.

Postop advantages of large flap

The advantages of the large flap continue in the postoperative stage. Adherence of the large flap to the underlying tissue is better because of the larger area (38.5 mm² area for a 7-mm flap compared with a 70.7 mm² area for a 9.5-mm flap). This improved flap adhesion gives greater corneal stability, and flap displacement, either spontaneously or if the patient rubs the eye, is highly unlikely.

Also, the circumference of the scar that occurs from Bowman’s to Bowman’s is larger. During healing, re-epithelialization is rapid because the new epithelium forms in the peripheral area. Because the hinge is positioned superiorly instead of nasally and the lamellar cut has a larger diameter, epithelium is injured only peripherally, and patients have only minimal foreign body sensation postoperatively.

Disadvantages of large flap

Disadvantages exist with every technique, but fortunately they are not major with the large diameter flap. Disadvantages that have been noted include the possibility of bleeding because the cut is close to the limbal vessels. Furthermore, experience is required to obtain a good quality cut with the existing design of the microkeratome and its blade, and the cut must be automatic to ensure that the large cut surface is uniform and regular. It also is more difficult to raise the flap if enhancement is needed.

Technically, it is difficult to obtain a large diameter cut, and a microkeratome of the latest generation — a suitable ring and fitted with a very sharp blade — is required. The microkeratome also must have an automated movement that provides a constant, uniform speed without stops, to produce a smooth cut. At this time, the only instrument that has the necessary characteristics is the Hansatome, produced by Bausch & Lomb Surgical (Claremont, U.S.A.). A surgeon with this instrument in hand is in the best position for making a large diameter flap with a superior corneal hinge for the best possible surgical results.

For Your Information:

Lucio Buratto, MD, can be reached at Centro Ambrosiano di Microchirurgia Oculare, Piazza Republica, 21-20124 Milan, Italy; +(39) 02-6361191; fax: +(39) 02-6598875. Dr. Buratto has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.