Keratomileusis is a form of lamellar refractive surgery intended to alter the refractive status of the cornea and consequently the optical system of the eye, reducing myopia and hyperopia and hence the need of devices used for the optical correction of these ametropias.1
The general principle of lamellar refractive surgery consists of the modification of the central corneal topography hy the removal (eg, myopic keratomileusis in situ) or the accretion (eg, keratophakia) of a certain amount of tissue to the corneal stroma.2 To perform it, a 150-u.m-thick cap of superficial cornea must be resected to expose the stroma and make possible the surgical manipulation at this site.3 Finally, at the end of the procedure, the superficial cornea cap has to be sutured back at its original position. This suturing of the superficial disk is an essential step for the success of the surgery. Every effort is taken to avoid traction, rotation, and/or decentration of this delicate disk which could compromise the final visual acuity of the patient. We have utilized numerous suture techniques with lamellar corneal surgery and concluded that the best postoperative results were obtained with an overlay suture for the fixation of the disk back to the stroma. We called it the "BRA technique" for lamellar surgery, so designated because the suture supports the corneal cap in a manner similar to a woman's brassiere.
THE BRA SUTURE TECHNIQUE
The BEA suture is basically an overlay concept of keeping the disk in place by anchoring the suture in the surrounding nonoperated cornea. Many possible variations are effective as long as the overlay concept is respected.
A 10-0 nylon monofilament on a full curve needle is used, in the following sequence: 1) It is anchored in the cornea by a stromal pass from 9 to 10 o'clock position. 2) An overlay is made 10 to 2 o'clock. 3) A stromal bite extends from 2 to 3 o'clock. 4) An overlay from 3 to 7:30. 5) A stromal pass is made from 7:30 to 6:30. 6) Another overlay extends from 6:30 to 5:30. 7) An intrastromal bite is made from 5:30 to 4:30. 8) A final overlay goes from 4:30 to 9:00 where the suture is tied by a 2-1 knot (Fig 1) which is buried to avoid irritation. A slender spatula is used to smooth and realign the disk, if necessary. One individual additional suture at 12 o'clock or two additional sutures, one at 12 o'clock and another at 6 o'clock positions, should be used by the beginner and/or inexperienced surgeon to stabilize the cap; these sutures must be secured gently and removed within 24 hours to avoid localized traction.
Figure 1: The six basic steps of the suture are shown: (1 ) The 10-0 nylon monofilament is anchored by a stromal pass from 9 to 10 o'clock position. (2) The first overlay Is made from 10 to 2 o'clock position. (3) The stromal pass from 2 to 3 o'clock and the overlay from 3 to 7:30 o'clock position. (4) The stromal from 7:30 to 6:30 o'clock position. (5) The overlay from 6:30 to 5:30 o'clock position and intrastromal from 5:30 to 4:30 o'clock. (6) Overlay from 4:30 to 9:00 where the suture is tied by a 2-1 knot and buried. A slender spatula may be used to smooth and/or realign the disk, before the 12 o'clock fixing suture is placed, when needed.
After surgery, the blepharostat should be gently removed and the lids manually closed. Ideally, the upper lid should be lifted with a spatula and carried over the eye to avoid displacement of the disk.
Every patient is examined the morning after surgery and the suture is then removed. Epithelial healing and normal corneal imbibition pressure secure the disk and avoid displacement from then on. A delay in suture removal may be required in lamellar graft patients and some cases of* keratophakia and reconstructive interlamellar graft (unpublished data).
Early corneal surgeons had a difficult time working with rough sutures and needles available at that time.4 Better quality suture materials and needles now require highly refined surgical techniques to satisfy the high expectations from refractive procedures.
Figure 2: The classic eight-bite running suture still produces folds and decentration of the disk.
Figure 3: Imbalanced suture or localized stress points produce traction folds on the disk.
Figure 4: Rotation of the disk will displace It from its original bed altering the extremely organized lamellar orientation.
Figure 5: Front view of the eye with the suture In place.
The ideal suture technique for lamellar keratoplasties should allow correct centration, perfect positioning of the button, no bare areas of stroma, and no entrance sites for epithelium into the lamellar bed. To achieve these goals while simultaneously avoiding traction or tissue torque, the ideal suture should provide the least number of bites, in addition to being easily performed and removed.
With these objectives in mind, we designed a technique whereby the suture is passed over the disk and attached to the corneal periphery around the disk. A similar type of overlay suture was first used by Elschnig5 and by Zirm,6 who also used the conjunctiva to anchor early keratoplasties.
Currently, a classic eight-bite running suture is usually advocated as the best fixation method7 for suturing the disk over the receptor site at the cornea. This suturing technique requires at least four cardinal sutures of 10-0 nylon to hold the tissue in place and prevent rotation. The definitive eight-bite, antitorque suture is then placed.8 In our experience with the running suture, the eight bites continue to produce folds, rotation, and decentration of the disk (Figs 2-3). Tearing of the periphery of the disk occurs due to the small thickness of the edge. An irregular disk is predisposed to decentration making it virtually impossible to perform the traditional running suture.
It is also important to avoid lateral displacement and decentration of the button while placing the running suture. Usually, the lateral deviation is maximum when the suture forms an isosceles triangle (Fig 2). Under this circumstance, the forces created along the margins of the wound are stronger than those perpendicular to them. The disk tends to slide eccentrically (Fig 4). These forces are increased when the suture is secured with unequal tension or when the suture bites are placed at varying distances from the disk.
Sutures available for ophthalmic surgery are commonly smaller than the needles used and do not fill the tunnel formed within the tissue. Consequently, the suture moves within this tunnel contributing to an additional displacement of the disk.9
Epithelial ingrowth down a suture tract into or beneath the disk10 is less frequent with the BRA suture.
In our experience with more than 300 cases, the BRA suture has shown to be an excellent suture pattern for superficial disk fixation in keratomileusis in situ, keratophakia, reconstructive interlamellar graft, and other lamellar microkeratoplasties using the microkeratome.
The 10-0 or 11-0 nylon suture with a full curve needle offers the advantage of good tensile strength and low tissue reactivity. The full curve needle assists in shorter or precise deep bites with only overlay pressure to secure the corneal superficial disk.
In the first cases, we crossed the BRA suture over the pupil which eventually interfered with the vision. Displacing the crossing point below the pupil allows better vision in the first days, besides preventing suture marks in the optical zone (Fig 5).
The optical recovery depends basically on centration, transparency, optimal refractive correction, and surface regularity. The smoothness and regularity of the superficial corneal disk depend mainly on the equal balance among tension suture lines.
Distinct advantages include the patient comfort and surgical simplicity. The epithelium heals overnight with diminished patient complaints. The BRA suture is usually removed on the 1st postoperative day. However, if the disk does not appear stable, it may be safely removed whenever necessary.
Earlier removal is associated with niinimal scarring, usually present when a continuous suture is used.
A continuous suture cannot be safely removed 24 hours after surgery without the risk of disk displacement. Early removal of the BRA suture resulted from our clinical observation that in spite of a loosened or ruptured suture on the 1st postoperative day, the disk was still adherent and clear. Follow up in these patients was uneventful and patient complaints of foreign body sensation due to the suture were diminished. The slit-lamp microscope appearance remarkably improved when suture removal occurred at an earlier phase.
1. Schwab IR. Refractive Keratoplasty. New York, NY: Churchill Livingstone; 1989:2.
2. Sanders DR. Refractive Corneal Surgery. Thorofare, NJ: SLACK Ine; 1986:XXII.
3. Bores LD, Ruiz LA. Myopic Keratomileusis. Scottsdale, Ariz: LRS Systems Ine; 1988:106.
4. Arruga H. Chirurgie Oculaire. 4th ed. Barcelona, Spain: Massen E; 1964:22-25.
5. Elschnig A. In: Arruga H. Chirurgie Oculaire, 4th ed. Barcelona, Spain: Masson E; 1964:384.
6. Zirm EK. Eine erfolgreiche totale Keratoplastik, v. Graefe's Arch für Ophthalmologie. 1906;64:580-593.
7. Barraquer JI. Keratomileusis for the correction of myopia. Archivos de la Sociedad Americana de Oftalmologia y Optom etria. 1964;5:27-48
8. Bores LD, Ruiz LA. Myopie Keratomileusis. Scottsdale, Ariz LRS Systems Ine; 1988:114-18.
9. Eisner G. Eye Surgery. An Introduction to Operative lech nique. New York, NY: Springer-Verlag, Berlin Heidelberg; 1980:33-43.
10. Schwab IR. Refractive Keratoplasty. New York, NY: Churchill Livingstone; 1987:59.