What is a thick flap? (Posted: jan 2005)

A thick flap is a flap which is in fact cut significantly thicker than the microkeratome was programmed for.

What causes a thick flap? (posted: jan 2005)

Microkeratome accuracy tolerances are not that good, according to the medical literature. Flap thickness can vary by 20% or more from the programmed thickness. (However, it is much more usual for a flap to be thinner than programmed than thicker than programmed.) Anatomical features may affect the probability of a thick flap.

What does it mean for the patient? (posted: jan 2005)

A thick flap, in and of itself, may not be a problem - up to a point. Excessively thick flaps will affect the visual outcome irrespective of whether they cause any other problems. But the two main worries of a thick flap (well, OUR two main worries) are as follows: (1) the increased risk of ectasia, particularly if the cornea has been penetrated deeper than was felt to be safe; (2) the risk posed by having a retreatment without determining the flap thickness. If the surgeon simply assumes the flap to be the thickness it was programmed to be, and then goes back in and removes more tissue which he thinks takes the residual stroma near to the safe threshold, he could in fact be surpassing that threshold and placing the patient at greatly increased risk of ectasia.

How is a flap measured? (posted: jan 2005)

Flap thickness cannot be measured accurately with any equipment that is in common use in ophthalmologists' or optometrists' offices. It can be measured with confocal microscopy or Artemis VHF digital ultrasound. The latter analyses the features of the epithelium, flap and stroma in great detail.