Holmium laser thermokeratoplasty.
OBJECTIVE
Corneal curvature can be altered by shrinking stromal collagen with a pulsed solid-state holmium: YAG laser in a procedure termed laser thermokeratoplasty.


METHODS
The authors performed laser thermokeratoplasty in 40 human cadaver eyes using a ring pattern of 32 spots, each spot having a diameter of 300 microns.


RESULTS
The amount of induced corneal steepening decreased as ring diameter was increased in 1 mm increments, with 22.2 +/- 3.3 and 3.7 +/- 2.0 diopters (D) of central steepening with diameters of 3 and 7 mm, respectively. Results of histologic examination showed a cone-shaped zone of increased stromal hematoxylin uptake extending posteriorly for 90% of stromal thickness. Energy levels greater than those needed to induce topographic changes produced limited endothelial injury in rabbit corneas and, in some cases, intraocular inflammation. A computerized, finite element model of the globe demonstrated central corneal steepening as a result of heat-induced stromal contraction to a depth of 75% corneal thickness.


CONCLUSIONS
These data support previous studies indicating that central corneal topography can be modified by heating corneal stroma in a controlled fashion with the mid-infrared holmium:YAG laser.
Moreira
H
H
Doheny Eye Institute, Los Angeles, CA 90033.
Campos
M
M
Sawusch
M R
MR
McDonnell
J M
JM
Sand
B
B
McDonnell
P J
PJ
D000818:Animals; D003094:Collagen / Q000648:ultrastructure; D003198:Computer Simulation; D003315:Cornea / Q000601:surgery* / Q000648:ultrastructure; D003319:Corneal Stroma / Q000648:ultrastructure; D004564:Electrocoagulation; D004728:Endothelium, Corneal / Q000648:ultrastructure; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007429:Intraocular Pressure; D053685:Laser Therapy; D008855:Microscopy, Electron, Scanning; D008953:Models, Anatomic; D011817:Rabbits; D014065:Tonometry, Ocular
D003094:Collagen