A Proposal for the Use of a Fixed Low-Energy Selective Laser Trabeculoplasty for Open Angle Glaucoma.

Selective laser trabeculoplasty (SLT) has been in routine clinical use for over 20 years with millions of patients successfully treated and a low rate of clinically significant complications. The procedure requires the clinician to manually position the laser beam on the trabecular meshwork using a gonioscopy lens and to titrate the SLT laser energy based on the amount of pigmentation in the angle, as well as the observation of small bubbles produced by the laser effect. We propose that SLT energy titration is unnecessary either to achieve intraocular pressure (IOP) reduction or to minimize potential side effects. Ample evidence to support our proposal includes multiple clinical reports demonstrating comparable levels of IOP reduction resulting from different laser energies, a large variety of energy and other laser parameters used in commercially available SLT lasers, and the nature of the laser-induced changes in the trabecular meshwork tissue with respect to energy. Despite these variations in laser parameters, SLT consistently reduces IOP with a low complication rate. We propose that using low fixed energy for all patients will effectively and safely lower patients' IOP while reducing the complexity of the SLT procedure, potentially making SLT accessible to more patients.

Energy Dose-Response in Selective Laser Trabeculoplasty: A Review.

PRCIS: A literature review of selective laser trabeculoplasty (SLT) energy dose-response found no definitive relationship between intraocular pressure (IOP) reduction with respect to total or pulse energy, race, pigmentation, or application pattern. PURPOSE: SLT is a safe and effective treatment for lowering IOP. Although evidence is mounting for the advantage of its use as a first-line treatment for IOP reduction, the SLT procedures in use vary widely. The purpose of this literature review was to investigate whether there were any relationships between SLT energy and efficacy for lowering IOP in the published literature. METHODS: A literature review was undertaken that included studies in which energy levels required for successful SLT treatment were investigated: in general, with respect to angle pigmentation, race or ethnicity, and treatment arc extent. RESULTS: There was no indication that higher (or lower) energy used in the treatment leads to greater (or less) IOP reduction. Similar results were obtained regarding the level of trabecular meshwork pigmentation. Race was not found to be associated with altered dose response in SLT. There were indications that treating the full 360 degrees, as opposed to smaller arcs, could be beneficial for more IOP reduction. IOP reduction from SLT was found to be similar to that provided by topical medications. CONCLUSIONS: The optimal energy level of SLT needed for IOP reduction has not yet been definitively established, with all reported pulse energies resulting in similar IOP reduction. Furthermore, similar lack of conclusive findings exists regarding optimal SLT energy dosage for use in different races and degrees of trabecular meshwork pigmentation. This parameter and each of the abovementioned factors requires further research.

Automated Direct Selective Laser Trabeculoplasty: First Prospective Clinical Trial.

Purpose: Direct selective laser trabeculoplasty (DSLT) is a rapid, noncontact automated procedure performed directly through the limbus without gonioscopy. In this first nonrandomized clinical trial we assessed its safety and ability to reduce intraocular pressure (IOP). Methods: Fifteen patients (15 eyes: 10 with open-angle glaucoma [OAG], 4 with ocular hypertension, and 1 with pseudoexfoliation glaucoma), naive or after medication washout, with an IOP ≥22 mm Hg, underwent DSLT by irradiation with 100 or 120 sequential noncontact 532-nm, Q-switched laser shots (0.8-1.4 mJ) automatically applied during 1.5 or 2.3 seconds on the limbus, guided by image analysis and eye tracking. Results were assessed at 1 and 3 hours, 1 day, 1 week, and 1, 3, and 6 months. Results: The mean ± standard deviation baseline IOP (mm Hg) in all eyes was 26.7 ± 2.3. At 1, 3, and 6 months, this value was significantly reduced to 21.7 ± 4.2 (by 18.1%), to 20.8 ± 2.5 (by 21.4%), and to 21.5 ± 4.1 (by 18.8%), respectively. In six patients treated with 1.4 mJ/shot, the mean IOP at 6 months decreased from 26.7 ± 3.2 to 19.3 ± 2.0 (27.1%, P = 0.03). There was a significant reduction in hypotensive medications (from 1.6 ± 1.0 to 0.4 ± 0.7, P = 0.03). No serious adverse events occurred. Conclusions: Automated DSLT appears to be an effective and safe noncontact, rapid modality for reducing IOP in patients with OAG. Higher energy usage led to better results. Translational Relevance: Studying laser transmission through sclera enabled laser irradiation of the trabeculum without gonioscopy.

Non-contact direct selective laser trabeculoplasty: light propagation analysis.

Selective laser trabeculoplasty (SLT), used to treat glaucoma and ocular hypertension, requires the use of a gonioscope placed on the cornea to visualize and irradiate the trabecular meshwork (TM). Alternatively, non-contact direct SLT (DSLT) irradiates the TM through the overlying tissues. Here we analyze this innovative procedure using analytical modeling and Monte Carlo simulations to quantify the laser energy reaching the TM through the overlying tissues. Compared with energy launched from the laser, DSLT energy transmission to the TM is 2.8 times less than SLT, which verifies the efficacy of non-contact DSLT given the lowest reported effective SLT energies.

Improving the efficiency of an optical parametric oscillator by tailoring the pump pulse shape.

The conversion efficiency of an optical parametric oscillator is reduced by energy consumption during build-up of signal and idler intensities and due to back-conversion effects. By tailoring the pump pulse temporal shape, we are able to improve the conversion efficiency by minimizing build-up time and back-conversion. Simulations predict a significant improvement in 1064 nm to 4000 nm idler conversion by using a double-rectangular temporal shape rather than using a simple Gaussian pulse. Experimental results qualitatively verify the effect resulting in a 20% improvement of a rectangular pulse over a Gaussian pulse.

Subsurface photodisruption in human sclera: wavelength dependence.

BACKGROUND AND OBJECTIVE: Approximately 105 million people worldwide have glaucoma, and approximately 5 million are blind from its complications. Current surgical techniques often fail because of scarring of the conjunctival tissue, Tenon's tissue, or both. Femtosecond lasers can create highly precise incisions beneath the surface of a tissue, as previously demonstrated in the transparent cornea. Because the sclera is a highly scattering subsurface, photodisruption has not been previously possible. MATERIALS AND METHODS: To overcome scattering, a laser operating at 1,700 nm was used to make subsurface cuts in human sclera in vitro via photodisruption. RESULTS: Sub-10-microm width incisions were created beneath the surface without collateral tissue effects, something not possible with shorter wavelengths used to date in corneal applications with the femtosecond laser. CONCLUSION: Completely subsurface photodisruptions can be accomplished in human sclera in vitro. In vivo studies are required to evaluate the potential use of this technology for scleral applications.

High precision subsurface photodisruption in human sclera.

BACKGROUND AND OBJECTIVES: Femtosecond pulses can generate high precision subsurface photodisruption in transparent tissues, such as the cornea. We used femtosecond laser technology to demonstrate early proof of concept for high precision subsurface photodisruption in the translucent sclera. This technique may ultimately enable novel surgical procedures for the treatment of glaucoma and/or presbyopia. STUDY DESIGN/METHODS AND MATERIALS: Microjoule femtosecond pulses from two different sources, 1060 and 775 nm, were used to make subsurface incisions in human sclera in vitro. Scleral tissue was dehydrated to improve translucency at these wavelengths. The beam was focused to a 1.5 (775 nm) or 5 microm spot size (1060 nm) and scanned below the tissue surface at various depths to produce four incision patterns. RESULTS: Photodisruption on the backsurface of the sclera was achieved without damage to overlying tissue. Several types of intrascleral incisions were made, including transcleral channels and grooves for scleral implants. CONCLUSIONS: High precision, subsurface scleral photodisruption can be achieved in vitro for a variety of intrascleral incisions. Further studies are required to determine if this technique is applicable in vivo for actual surgical applications.