OBL formation in LASIK

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Dr Kanellopoulos describes a study in which the quantitative differences in the presence and extent of opaque bubble layer in flaps created with a femtosecond laser with a wider venting canal design and its predecessor design have been compared.

Although no serious complication has been described by its occurrence, it may temporarily obscure the pupil image that most excimer laser trackers use. It may additionally interfere with iris architectural landmarks reading that some excimer laser trackers use for cyclorotation compensation, and finally, may even obscure the patient fixation target.

A second group of 36 patients (72 eyes), previously treated for bilateral primary myopic or hyperopic femtosecond-assisted LASIK in our centre using the 'narrow canal' design, was selected to match group A and to form the reference group B in regard to flap diameter distribution. In addition to the 1.3 mm wide canal, the canal line separation in group B of patients was sparser, and specifically, 4.0 μm.

In all procedures - performed by the same surgeon (AJK) - the LASIK flap was created with the Alcon/WaveLight (Alcon Surgical, Fort Worth, Texas, USA) FS200 femtosecond laser, and subsequent excimer ablation was provided by the Alcon/WaveLight EX500 excimer laser.6

The common femtosecond laser flap settings for both groups were as follows: stromal bed cut spot separation, 8 μm; line separation, 8 μm; side cut bed separation, 5 μm; line separation, 3 μm; side cut angle, 70°; bed cut pulse energy, 0.80 μJ; side cut pulse energy, 0.80 μJ; canal spot separation, 4.0 μm; hinge angle, 45°.