Laser sclerostomy ab interno using continuous wave and pulsed lasers in a rabbit model.
OBJECTIVE
This experimental study was designed to find an optimal combination of parameters for a gonioscopic ab interno approach to laser sclerostomy.


METHODS
Laser sclerostomy ab interno was performed delivering the laser energy via a slit lamp and a gonioscopic contact lens to the iridocorneal angle. The laser energy is required to be well transmitted by the cornea and at the same time to be maximally absorbed by the sclera at the iridocorneal angle. For local enhancement of absorption the sclera was stained with the biocompatible dyes Fluorescein (absorption maximum at 480 nm) and Methylene blue (absorption maximum at 668 nm) applied by iontophoresis. A continuous-wave (cw)-Argon laser and a cw-dye laser produced relatively long pulses (200 ms) at wavelengths matching with these respective maxima. Additionally a pulsed dye laser emitting shorter pulses (2 microseconds) was successively adapted to the wavelengths of the two maxima. In some cases a Q-switched Nd: YAG laser had to be used for perforation of Descemet's membrane. A total of 44 rabbit eyes was treated to compare the results for these four different laser/dye combinations.


RESULTS
While no successfull perforation of the sclera could be achieved using the cw-dye laser with scleral staining by Methylene blue, the intraoperative success rate ranged between 59% and 75% for the other three laser/dye combinations. Histological examinations of the eyes on the first postoperative day showed smaller thermal necrosis zones, but more often fibrin reactions when using the shorter pulse length. Although we often found iris adherences to the internal fistula ostium, no major complications were observed.


CONCLUSIONS
Further improvement of intraoperative success rates is needed, before clinical application of the approach can be considered.
Wetzel
W
W
University Eye Hospital Kiel, Clinic for Ophthalmology, Germany.
Scheu
M
M
D000818:Animals; D003315:Cornea / Q000601:surgery; D005901:Glaucoma / Q000601:surgery; D006068:Gonioscopy; D007498:Iris / Q000601:surgery; D053685:Laser Therapy / Q000379:methods*; D008954:Models, Biological; D010030:Ostomy; D011817:Rabbits; D012590:Sclera / Q000473:pathology / Q000601:surgery*; D012599:Sclerostomy