Energy levels and probe placement in contact transscleral semiconductor diode laser cyclophotocoagulation in human cadaver eyes
J. S. Schuman, R. J. Noecker, C. A. Puliafito, J. J. Jacobson, G. J. Shepps and N. Wang
Morse Laser Center, Howe Laboratory of Ophthalmology, Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, MA.
We investigated the effects of semiconductor diode laser contact
transscleral cyclophotocoagulation in human cadaver eyes by gross
examination, light microscopy, and scanning electron microscopy to
determine optimum clinical treatment parameters. Irradiation was performed
using a continuous-wave semiconductor diode laser with a fiber-optic probe.
At 1.0 to 1.25 mm posterior to the limbus, spots were centered on the pars
plicata by gross examination. Exposures of less than 2 J produced no
visible damage. A 2- to 3-J exposure produced mild whitening of the ciliary
processes, while 4- to 5-J exposures created more intense whitening of the
pars plicata. Energies higher than 5 J frequently produced explosive tissue
damage. Light microscopy of tissue treated with 1.8 to 6 J at 1.0 to 1.25
mm posterior to the limbus revealed coagulation necrosis of the
nonpigmented and pigmented epithelium, with evidence of thermal coagulation
of the ciliary stroma and stromal vasculature. Coagulation necrosis was
more intense with longer exposure times. We found the optimum parameters
for contact transscleral diode laser cyclophotocoagulation in cadaver eyes
to be 3 to 4.5 J of energy delivered with the anterior edge of the probe
1.0 to 1.25 mm posterior to the limbus.
