State of the art SBK with a microkeratome

Key Points

Early in my experience with thin flaps, I expected more striae and dislocations, but found just the opposite. The thin flap adheres better and stretches to fit more precisely back on the stromal bed, especially with a good stretching technique (see tip).

The meniscus myth

But after looking more carefully at anterior segment Visante OCT images (Carl Zeiss Meditec), I realized that my microkeratome - at the time, the Moria LSK One and more recently, the Moria One Use-Plus SBK - is actually cutting flaps that are as planar in shape as the IntraLase femtosecond laser flaps. The microkeratome flap shallows (not deepens) only slightly in the far periphery as it nears its tapered edge.

The new OCT technology provides valuable information, but it is not yet sensitive or high resolution enough to reproducibly measure flap thickness in all meridia or even along one complete meridian. In our tests, a skilled technician attempting to place the cursor at the exact same location five times in a row obtained flap thickness measurements that differed by as much as 32 µm, with a standard deviation of 9.5 µm, whether the flap was made with the FS laser or with the One Use-Plus SBK microkeratome. With this kind of variability, it would be easy to mistakenly identify either a microkeratome or a femtosecond flap as a "meniscus" flap.

If we use these OCT images more appropriately for a qualitative assessment of flap shape, we see that, at least with a longitudinal translational model, microkeratome flaps are just as planar in shape as IntraLase flaps. It is possible that compression-type pivot microkeratomes do make meniscus-shaped flaps, but the idea that all microkeratome flaps are always meniscus shaped is simply a myth, or at least significantly overstated.