NOV 07, 2012
This experimental study found that using a femtosecond laser to produce thin flaps with optimized side-cut angles minimizes corneal biomechanical strain in LASIK procedures.
The authors explored the biomechanical effects of laser flap creation on human donor corneas, demonstrating and quantifying three important principles: (1) corneal strain is predominantly due to the vertical side cut and not the horizontal lamellar cut, (2) thin flaps produce less strain than thick flaps, and (3) angulating side cuts to produce a stromal flap diameter greater than the epithelial diameter can decrease the strain.
They divided 42 organ-cultured human corneas into a control group and three investigative groups, each undergoing different incision types at both 90- and 160-μm depth using a femtosecond laser. In the first group, typical LASIK flaps were created; in the second group, only the bed was cut (delamination); and in the third group, side cuts alone were affected. Corneal strain was measured using radial shearing speckle pattern interferometry before and after treatment following an increase in hydrostatic pressure from 15.0 to 15.5 mmHg and again after one week of incubation in culture medium.
The control group showed a degree of displacement related to the depth of cut, with strain increasing by 9 percent at 90 μm and 32 percent at 160 μm. Similar changes were observed with side cuts at the same depths. With delamination, strain increased 5 percent following both cut depths.
The authors conclude that in the future it may be possible to prevent haze pharmacologically and thereby eliminate the most significant complication of surface ablation. Until then, with this finding that thin-flap LASIK causes only insignificant mechanical changes and with other investigations demonstrating that patient recovery is equivalent after thin-flap LASIK to that following conventional LASIK, and much more rapid than after PRK, these results support the clinical trend toward creation of thinner flaps.