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BACKGROUND: The holmium:YAG laser shrinks stromal collagen and changes corneal refractive power, reportedly without recurrent or persistent epithelial defects, stromal necrosis, or damage to the epithelium and endothelium observed with some other thermokeratoplasty techniques. METHODS: We studied the safety of the holmium:YAG laser using various patterns and energy densities after treating 12 poorly sighted eyes, two immediately prior to corneal transplantation and 10 followed for a mean period of 90 days (range, 60 to 180 days). Visual acuity, intraocular pressure and inflammation, central corneal endothelial cell density and thickness, and intraocular structures of the eye were indices evaluated regularly. Patients were also assessed for specific symptoms during the post-operative period. RESULTS: There were no problems with epithelial healing and no stromal necrosis or evidence of endothelial damage; no significant differences were noted in any of the endothelial cell indices examined. A mean change in corneal curvature of 1.10 diopter (D) was achieved, but varying amounts of regression of this effect was noted. CONCLUSIONS: Holmium:YAG laser thermal keratoplasty appears to be safe over a follow up of up to 180 days. Corneal refractive changes on the order of 1.05 D can be achieved using the parameters employed in this study. Whether or not larger, persistent corneal refractive change can be achieved with a holmium:YAG laser remains to be determined. [J Refract Surg. 1995,11:358-365.]

A THC:YAG laser (thulium, holmium, chromium-doped YAG crystal) was used to create thermal sclerostomies in 21 glaucomatous eyes of 19 patients. The laser is a long-pulsed (300 µsec), compact, self-contained, solid state laser operating in the near infrared (2.1 µ). A 1-mm conjunctiva) stab incision was made 12 mm away from the sclerostomy site to allow entry of a specially designed 22-gauge (712 µ) optic probe that delivers energy at a right angle to the long axis of the fiber. Probe insertion produced minimal disturbance of the conjunctiva. Pulse energies of 80 mJ to 120 mJ were used with a repetition rate of 5 pulses/second. Total energy levels to produce full-thickness sclerostomies ranged from 1.4 to 4.8 J. Subconjunctival 5-fluorouracil injections were administered in 15 eyes. At 3 months the mean intraocular pressure of successful cases (16) was 14 mmHg (range, 9 to 22 mmHg). Of successful cases, the mean intraocular pressure at 6 months was 13 mmHg (range, 2 to 22 mmHg). Five cases failed within the initial 3 months, and 3 additional cases failed by 6 months. The authors conclude that this full-thickness sclerostomy technique may simplify filtering surgery without anterior chamber instrumentation and with minimal conjunctiva) trauma.

A newly developed compact (40 kg), self-contained contact Neodymium:YAG laser produces high-peak, high-energy (800 mJ/pulse), short (1.0 millisecond) pulses with 1 to 3 pulses/exposure. Energy is delivered via a 320- µm cleaved quartz fiber optic probe. Cyclophotocoagulation was performed in five eyes of three medium-sized Dutch-pigmented rabbits. The eyes received exposures of 1 to 3 pulses/exposure. Energy delivered ranged from 100 to 800 mJ/pulse. Histopathology revealed ciliary body disruption and hemorrhage with no damage to overlying sclera. When used for transscleral cyclodiathermy in the rabbit, the laser created significant ciliary body disruption with minimal scleral injury.

We present our research into a pulsed xenon lamp source for the treatment of psoriasis and other skin disorders. Various filtering techniques, lamp configurations, power supply configurations and delivery systems are discussed. Comparisons are made to existing treatment modalities. Cryogen cooling of the treatment site is discussed.

Chromium-sensitized and thulium- and holmiumdoped YAG lasers (THC:YAG laser) were used to create a nasal bony ostium in the area of the lacrimal sac fossa in four fresh frozen bisected human cadaver heads. The lasers - long pulsed (300 milliseconds), compact, self-contained, and solid state - operate in the near infrared (2.1 urn). The opening was created by passing the 320-micrometer laser fiber across the canalicular system. Pulse energies of 250 to 900 mJ were used with a repetition rate of 5 to 15 pulses per second. Energy levels ranging from 1.25 to 9 W produced a full-thickness bony ostium approximately 3 to 4 mm in diameter. Silicone tubing was then threaded through the superior and inferior canaliculus system in the standard fashion. This technique may simplify conventional dacryocystorhinostomy as well as endonasal laser dacryocystorhinostomy procedures.

A new method to create filtering tracts ab interno or ab externo which may eventually prove useful in eyes with poorly controlled glaucoma is described. Fiberoptics of 200 µm diameter, with either cleaved or 500 µm ball lens tips, were coupled to the output of an argon gas laser emitting a number of radiation lines in the ultraviolet (333 to 363 nm) wavelengths. This system was used to perforate the corneoscleral limbal tissue of enucleated bovine eyes with a small number of laser applications to create a filtering fistula. Corneoscleral limbal perforation with a 200 µm cleaved fiber required 0.6 to 1.1 J total energy, delivered with a laser power of 0.5 W, or greater, for 0.1 second. With a 500 µm ball lens fiber tip a tract of nearly 0.5 mm diameter was created, requiring 5.1 to 10.4 J total energy, delivered with a laser power of 2.0 W, or greater, for at least 0.1 second. The energy required for perforation from the external surface to the anterior chamber was the same as the energy required for ab interno perforation.

Fluorometric studies have been made with modified slit-lamp microscopes. These instruments offered considerable versatility in modifying experimental parameters, but were seldom optimized in terms of detector and illuminator apertures, filter band-pass characteristics, detection system, light-source stabilization, or optical resolution. Improper control of these parameters can result in artifacts which override useful information. A new fluorophotometer for ocular research has been designed that utilizes an optical system, which eliminates the need for a contact lens. An effort was made to optimize both the axial resolution and the minimum detectable signal. The characteristics of standard barrier filters and excitation filters were examined and compared with photomultiplier sensitivity curves. It was necessary to use double filters in order to reduce artifacts due to excitation light that was not rejected by the barrier filter. In order to optimize the signal-to-noise ratio, a photon counting detection system was used. A dark current equivalent to 3 X 10(-10) g/ml allows a useful detection range of 1 X 10(-10) g/ml.