FEB 26, 2014
By Liliana Werner, MD, PhD
Cataract/Anterior Segment
This experimental study found that femtosecond lasers produce capsulotomies with irregular edges compared to manual-performed capsulotomies.
The authors used light and scanning electron microscopy to examine the microanatomic edge structures of anterior lens capsule specimens derived from 30 manual and 30 femtosecond laser–assisted capsulotomies.
They found several types of irregularities along the capsulotomy edge, including a prominent demarcation line along the cutting edge, tags and bridges, microgrooves, and valley- and mountain-like structures.
The authors say that tags and bridges could not be related to the laser beam steering because they assumed that the laser cuts perfectly regular patterns. Therefore, they believe that the tags and bridges are caused by minimal torsional movements of the eye, which they observed during surgery, even with the eye fixated by limbal–conjunctival suction of the patient interface. They say this effect may be reduced when a liquid immersion interface is used and by reducing pulse energies.
They add that the most likely reason for the straying is the design of the patient interface. All femtosecond laser–assisted lens removal procedures were performed with a rigid, curved patient interface, which applanates the cornea. They say that pressing the cornea against a rigid surface with a curvature different from the cornea's natural shape causes deformations of the cornea, resulting in unwanted folds in the posterior surface.
They note that a major finding in this study was the clear demarcation line in the femtosecond laser–assisted capsulotomy edges, which confirms an effect of the laser on the surrounding tissue. This demarcation line could be the result of this expanding cavitation bubble in combination with the chosen relatively high pulse energy of 15 mJ, which might lead to displacement of cells and destruction of cell nuclei close to the cutting edge.
They say that by lowering the pulse energy and/or using a liquid immersion/soft interface, the demarcation line, and therefore the impact on surrounding tissue, may be reduced. Further studies of the relationship between pulse energy, patient interface design and capsule burst strength will help elucidate the optimum parameters for laser capsulotomy.