We investigated the use of ultrashort pulsed (femtosecond) laser technology
in corneal refractive surgery, When compared to longer pulsewidth nanoseco
nd or picosecond laser pulses, femtosecond laser-tissue interactions are ch
aracterized by significantly smaller and more deterministic photodisruptive
energy thresholds, as well as reduced shock waves and smaller cavitation b
ubbles. We utilized a highly reliable all solid state femtosecond laser sys
tem for all studies to demonstrate practicality in real-world operating con
ditions. Contiguous tissue effects were achieved by scanning a 5-mu m focus
ed laser spot below the corneal surface at pulse energies of approximately
2-4 mu J. A variety of scanning patterns was used to perform three prototyp
e procedures in animal eyes; corneal flap cutting, keratomileusis, and intr
astromal vision correction. Superior dissection and surface quality results
were obtained for lamellar procedures (corneal flap cutting and keratomile
usis), Preliminary in vivo studies of intrastromal vision correction sugges
t that consistent refractive changes can also be achieved with this method.
We conclude that femtosecond laser technology may be able to perform a var
iety of corneal refractive procedures with high precision, offering advanta
ges over current mechanical and laser devices and techniques.