gms | German Medical Science

In-vitro examination of morphology of flap thickness and stromal bed after LASIK in swine eyes.

The microkeratomes Carriazo-Pendular (Schwind), Hansatome (Bausch&Lomb), MK-2000 (Nidek) and Amadeus (AMO) were used for cutting flaps, n = 13 each, on freshly enucleated swine eyes and synthetic eye-models. The flap thickness of swine eyes was determined using a non-contact, confocal optical distance measuring device (CHR 150N, Jurca) and also of eye-models using a mechanical thickness measuring device (Käfler). The morphology of the stromal bed was examined by photography, light-microscopy, scanning electron microscopy and confocal optical distance measurements.

The optical/mechanical flap thickness measurements showed an average difference compared to the adjusted thickness of +11±14 / +0±0 μm (Carriazo-Pendular), -3±27 / +90±0 μm (Hansatome), -4±7 / +80±0 μm (MK-2000) and -35±5 / +40±0 μm (Amadeus). Histology showed no mechanical damage and smooth, slightly undulating surfaces in all microkeratomes. In scanning electron microscopic examination, the stromal surface was found to be more homogeneous and smoother in the case of the microkeratome Amadeus, followed by Hansatome, MK-2000 and Carriazo-Pendular. Average roughness of the ablation surface was 0.29±0.06 μm (Carriazo-Pendular), 0.27±0.05 μm (Hansatome), 0.23±0.04 μm (MK-2000) and 0.22±0.06 μm (Amadeus).

The stromal bed showed in all cases only a slight roughness, which seems to be acceptable for the clinical outcome. However, the more critical point are larger amounts of differences in flap thickness compared to the adjusted thickness. There were also remarkable differences between mechanical and optical measurements of flap thickness.