Yoshiko Takesue

Ultraviolet Solid-state Laser (213-nm) Photorefractive Keratectomy

BACKGROUND The pulsed ultraviolet 213-nm solid-state laser has been demonstrated as an alternative to the gas argon-fluoride 193-nm excimer laser for photorefractive keratectomy (PRK). The authors studied the clinical course and histopathologic changes occurring in rabbit corneas after PRK with a 213-nm solid-state laser. METHODS The 213-nm output of neodymium:YAG frequency-quintupled laser was used to create 5-mm optical zone ablations in seven pigmented rabbit corneas. The radiant exposure was 250 mJ/cm2 delivered through a computer-controlled scanning delivery system with a spot size of 0.5 mm. The target ablation was 4.0 diopters with an estimated ablation depth of 40 microns. A clinical estimate of corneal epithelial healing and stromal haze was made at intervals over the 3-month study period. Animals were killed immediately after ablation, or at 10 days, 1 month, or 3 months after ablation. Corneal tissue was preserved for light microscopy and transmission electron microscopy at each study interval. RESULTS All corneas re-epithelialized within 10 days postoperatively. Anterior stromal haze was clinically visible at 3 days, increased until approximately 1 month, and then gradually decreased over the succeeding 2 months. Residual subepithelial haze was visible at 3 months. Results of histopathologic study documented normal epithelium healing over time; the basement membrane retained its regular thickness and hemidesmosomes were abundant at 3 months. The anterior stroma had an increased number of fibroblasts at 10 days, many of which remained until 1 month. A mild, transient, cellular reaction occurred throughout the thickness of the stroma and the endothelium. CONCLUSION Using the 213-nm ultraviolet solid-state laser with a scanning delivery system, PRK shows a similar clinical course and histopathologic findings to the 193-nm excimer PRK study in rabbits. It is a clinically viable procedure for refractive surgery and requires further human clinical trails to determine its efficacy.

Comparative photodynamic effect of rose bengal, Erythrosin B, and dihematoporphyrin ethers on lens epithelial cells

The proliferation of residual lens epithelial cells (LEC) is responsible for reopacification of the lens capsule and loss of visual acuity after cataract surgery. Photodynamic therapy (PDT) using Di-Hematoporphyrin Ether (DHE) was shown to kill cultured LEC. We studied 2 synthetic photodynamic drugs: Rose Bengal (RB) and Erythrosin B (EB) to determine the minimal PDT parameters. LEC located on the anterior capsule of freshly explanted rabbit lenses were subcultured for the following studies: (1) Dye uptake was evaluated by cellular fluorescence. The minimum concentrations for RB and EB after 1 minute of exposure were 1 (mu) g/ml, and 50 (mu) g/ml; (2) Cytotoxicity was evaluated by reculturing the cells, and was detectable with concentrations of 200 (mu) g/ml RB or 2000 (mu) g/ml EB; (3) The PDT effect was evaluated using concentrations of 1 to 25 (mu) g/ml of RB and 1 to 2000 (mu) g/ml of EB. The minimum parameters for PDT of cultured LEC were 0.5 (mu) g/ml of RB and 10 (mu) g/ml of EB with a 60 second 0.5 W/cm2 irradiation using a 514.5 nm Argon laser. To mimic the in vivo setting, LEC attached to the anterior lens capsule were incubated with EB to evaluate dye uptake. The minimum parameters were 100 (mu) g/ml and 7 minutes of exposure. RB was found most effective and may be useful, but EB was found safer and has potential for conjugation with LEC antibodies for the prevention of secondary cataracts.

Measuring ocular characteristics after gel injection adjustable keratoplasty (GIAK) in the rabbit

Gel Injection Adjustable Keratoplasty (GIAK) is a refractive surgery procedure which uses an ocular ring implant made of a polyethylene oxide hydrogel to cause a refractive change in the cornea. Unlike laser photo refractive keratectomy, GIAK does not interfere with the central cornea because the ring lies around the optical axis. Thus, vision can be assessed immediately after surgery. Our in vivo study was designed to quantify GIAKs effects on tissues, the biocompatibility of the polymer and in the process investigate which ocular changes in the rabbit model can be monitored with precision using current technology. Thirty-two young rabbits underwent a delamination in one eye, 22 of which were injected with a new polymeric gel. Corneal topography, keratometry, pachymetry, and tonometry were performed on both eyes for up to 105 days. All corneas flattened with growth. In GIAK animals, we found an average flattening of 6.51 +/- 1.23 diopters (p < 0.0001) relative to the fellow eye. No statistically significant regression over the 102 days was observed. Intraocular pressure dropped slightly by 0.69 +/- 1.21 mmHg (p equals 0.025), a clinically insignificant value, while no significant change was detected in corneal thickness. Keratometry can be tracked in rabbits after GIAK surgery from POD 1. Measuring unoperated fellow eyes allows for the effects of surgery to be assessed without bias from growth. Using this protocol, GIAK was shown to be stable. It was more difficult to draw conclusions from pachymetry, tonometry, and topography data.

Noncontact laser penetrating keratoplasty: in-vivo comparative evaluation in rabbit and cat

With their inherent precision and avoidance of tissue deformation, non-contact laser trephines may minimize graft postoperative astigmatism. Laser-cut corneal button geometry surpassed handheld and equaled Hanna and Krumeich vacuum held trephines, without significant endothelium or wound healing differences for linear cuts between laser and metal blades. To compare the laser with metal trephines, we performed 8 mm diameter grafts on 12 rabbits and 12 cats. A new laser system, using an advanced pulsed HF laser coupled to a computer controlled optical delivery system and equipped for quasi-instantaneous simultaneous 8-point corneal marking (200 ns) for precise suture placement at the 5.5 to 10.5 mm diameter and rapid corneal trephination (approximately equals 6 sec), or a new disposable sterile vacuum-assisted Hessburg-Barron (HB) trephine was used in each procedure. Circumferential keratotomies were more accurately and more easily performed with the laser. No statistical differences were found in wound strength and healing. The laser produced a slightly lower astigmatism. These initial results suggest the safety of HF laser corneal marking-trephination and its potential for PK procedures in humans.

Laser scleral buckling: a new method to treat retinal detachment

Scleral indentation was induced in cadaver eyes by shrinkage of scleral collagen fibers using a pulsed solid state Ho:YAG (2.1 micrometers ) laser with fiber optic delivery. Applying Ho:YAG laser radiation permits control of the amount of laser induced buckling effect by selecting laser treatment parameters such as beam spot, radiant exposure, and number of pulses. With treatment using 11.3 +/- 1.2 J/cm2 laser radiant exposure and 5 pulses, laser induced scleral shrinkage affected only the external two-thirds of scleral tissue. No thermal damage or disruption was observed in subjacent retinal pigment epithelium, chorioid, or retina. Coupling of two appropriately selected lasers may allow laser induced scleral buckling and transscleral retinal photocoagulation using the same laser probe for retinal reattachment surgery.

Corneal reshaping using a pulsed UV solid-state laser

Replacing the gas ArF (193 nm) excimer laser with a solid state laser source in the far-UV spectrum region would eliminate the hazards of a gas laser and would reduce its size which is desirable for photo-refractive keratectomy (PRK). In this study, we investigated corneal reshaping using a frequency-quintupled (213 nm) pulsed (10 ns) Nd:YAG laser coupled to a computer-controlled optical scanning delivery system. Corneal topographic measurements showed myopic corrections ranging from 2.3 to 6.1 diopters. Post-operative examination with the slit-lamp and operating microscope demonstrated a smoothly ablated surface without corneal haze. Histological results showed a smoothly sloping surface without recognizable steps. The surface quality and cellular effects were similar to that of previously described excimer PRK. Our study demonstrated that a UV solid state laser coupled to an optical scanning delivery system is capable of reshaping the corneal surface with the advantage of producing customized, aspheric corrections without corneal haze which may improve the quality of vision following PRK.

Laser sclerectomy and 5-FU controlled-drug-release biodegradable implant for glaucoma therapy

Laser sclerectomy, a simple filtering procedure performed to alleviate high intraocular pressure in glaucoma patients, was taught to offer longer lasting effect and therefore improve the patients outcome when compared with the standard trabeculectomy procedure. Recent clinical trials have shown that this was not the case and pharmacologic wound healing modulation is also required with this new procedure. Five-Fluorouracil (5-FU) is useful as an adjunct treatment for glaucoma filtering surgery. However, efficacy depends upon maintaining sustained drug levels, currently achieved by repeated daily injection of the drug for several weeks. To overcome this limitation, we designed a biodegradable implant for the sustained release of 5-FU. After laser sclerectomy, the implant is inserted through the same 1 mm wide conjunctival snip incision and positioned below the open channel. Implantation takes less than a minute. The implant releases the drug for over 15 days and totally biodegrades in less than 100 days. The combined laser surgery and implantation procedure show great potentials for the treatment of glaucoma.