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LASIK complications1

1999; Elsevier BV; Volume: 106; Issue: 8 Linguagem: Inglês

10.1016/s0161-6420(99)90474-8

1549-4713

Dennis S.C. Lam, Arthur C.K. Cheng, Alfred T.S. Leung,

Intraocular Surgery and Lenses

Although we echo the management of flap complications as described by Gimbel et al, we believe the explanation of perforated flap by corneal curvature accounts for only part of the story. We reviewed our cases and found that those with perforated flaps did not have a particularly steep cornea. For the four consecutive cases we experienced, the mean preoperative keratometry (K) reading was 43.75 D (range, 42.23 D to 44.97 D) in contrast to Gimbel et al’s 46.7 D. Three cases had perforation occur on the second eye, and the K readings of first eye with good result were also similar. Furthermore, all cases received retreatment later on without any problem. All of them had a very smooth procedure with very desirable flap thickness even with the same microkeratome (Automated Corneal Shaper, Chiron) and footplate. These observations suggest that other factors, unique to the time of operation, are responsible for this complication. We have also noticed that the cases clustered together in the same 1-month period and were evenly distributed among all surgeons, which strongly suggests a temporal relationship. Examining each case in detail, we noticed that all perforated buttonholes had a rugged edge on the temporal half and a clean sharp edge on the nasal half. The shape of the buttonhole also varied, but there was no perfect circle and many had a characteristic pointing edge toward the temporal side. We also noticed that the driving motor of the microkeratome was not as powerful as before, and the engineer from the supplier confirmed this. After the microkeratome was serviced and the motor power returned to normal, no further flap perforations were noticed. We believe that suboptimal motor power with reduced driving force of the microkeratome was the key factor for the complications. We hypothesize the mechanism of flap perforation as follows: The microkeratome provides two mechanical actions, a driving force that moves the microkeratome forward and a cutting force provided by the oscillating blade. The smooth incisional interface of the stroma is provided by the continuous slicing action of the oscillating blade. With repeated use, like any other mechanical equipment, the power of the microkeratome is gradually reduced but still sufficient to produce a good flap with a desired thickness in most cases. However, in cases where resistance is increased, either due to a blunted blade or poor oscillation, the blade can be trapped within the stroma and forced to advance without an adequate synchronized oscillatory slicing action. The blade may well be lifted up within the limited space available inside the microkeratome. Subsequently, the blade breaks through the flap, and the central cornea slips under the blade, resulting in a perforated flap. It is the poor slicing action that results in a ragged edge. Now that the resistance is released, oscillation becomes effective again and can re-enter the stroma, leaving a clean sharp edge on the nasal side and complete the flap incision. The whole process is similar to potato skin peeling when one leaves a central island of intact skin after overcoming a point of friction. Even if the flap is not perforated, the resulting flap is likely to be thin. The fact that this complication is more common on the second eye can be explained by the blunting effect on the blade edge after the first incision and the collection of microcrystals and debris after the use of balanced salt solution in the first eye. We therefore advocate a regular routine check and service of the microkeratome to ensure that there is no undue resistance. Because the microkeratome is driven by a constant velocity motor, any increase in resistance is reflected by a corresponding increase in electric current. The newly designed microkeratome with the amperage value displayed like the Hansatome by Chiron, is therefore a welcome addition. It will be an important indication to alert the surgeon about the status of the system. LASIK complications: Authors’ replyOphthalmologyVol. 106Issue 8Preview Full-Text PDF