Visual disruption using the thermal lensing effect in the human eye: pilot study.

At select wavelengths, near infrared (IR) light is absorbed in the preretinal media of the eye. This produces small transient increases in temperature that temporarily alter the local index of refraction. If the IR exposure is sufficiently high, a momentary reduction in the focusing power of the eye can be induced through an effect known as thermal lensing.

Micro-patterned drug delivery device for light-activated drug release.

Background: The primary goal of this study was the fabrication, long-term stability, and measured release of a marker dye from a micro-patterned drug delivery device using (i) mechanical puncture and (ii) photodisruption with an ophthalmic Nd:YAG laser.

Materials And Methods: A drug delivery device was made from a transparent bio-compatible polymer. The device consisted of two 2.

Changes in morphology and optical properties of sclera and choroidal layers due to hyperosmotic agent.

Light scattering in the normally white sclera prevents diagnostic imaging or delivery of a focused laser beam to a target in the underlying choroid layer. In this study, we examine optical clearing of the sclera and changes in blood flow resulting from the application of glycerol to the sclera of rabbits. Recovery dynamics are monitored after the application of saline.

Variation of fluorescence in tissue with temperature.

Background And Objective: Previous studies demonstrated a decrease in fluorescence intensity as tissue temperature increased. In vitro samples were increased from room temperature and in vivo canine liver from body temperature. This study investigated variations in fluorescence intensity with temperatures starting at 14°C and compared in vivo and in vitro results for consistency.

Perfusion in hamster skin treated with glycerol.

Background And Objective: The objective of this article is to quantify the effect of hyper-osmotic agent (glycerol) on blood velocity in hamster skin blood vessels measured with a dynamic imaging technique, laser speckle contrast imaging (LSCI).

Study Design/materials And Methods: In this study a dorsal skin-flap window was implanted on the hamster skin. The hyper-osmotic drug, that is, glycerol was delivered to the skin through the open dermal end of the window model.

Trends in retinal damage thresholds from 100-millisecond near-infrared laser radiation exposures: a study at 1,110, 1,130, 1,150, and 1,319 nm.

Background And Objectives: Retinal damage thresholds from 100-millisecond exposures to laser radiation for wavelengths between 1,100 and 1,350 nm have never previously been established. We sought to determine the retinal damage threshold for 100-millisecond exposures of near-infrared (NIR) laser radiation wavelengths at 1,110, 1,130, 1,150, and 1,319 nm. These data were then used to create trends for retinal damage thresholds over the 1,100-1,350 nm NIR region based upon linear absorption of laser radiation in ocular media and chromatic dispersion of the eye.

First-order model of thermal lensing in a virtual eye.

An ABCD beam-propagation method was used to build a first-order mathematical model of a thermal lens effect from a near-infrared laser beam in water and ocular media. The model was found to fit experimental z-scan data best when the thermo-optic coefficient dn/dT of liquid water at 292 K was -4.46x10(-5) K(-1).

Thermal lensing in ocular media exposed to continuous-wave near-infrared radiation: the 1150-1350-nm region.

Ocular damage threshold data remain sparse in the continuous wave (CW), near-infrared (NIR) radiation region save for the 1300-nm area that has been investigated in the past several decades. The 1300-nm ocular damage data have yielded unusual characteristics where CW retinal damage was observed in rabbit models, but never in nonhuman primate models. This paper reviews the existing 1300-nm ocular damage threshold data in terms of the fundamental criteria of an action spectrum to assist in explaining laser-tissue effects from near-infrared radiation in the eye.

Histological and modeling study of skin thermal injury to 2.0 microm laser irradiation.

Background And Objective: Qualitative and quantitative gross histopathologic studies of skin damage were performed at 48 hours after irradiation with a 2.0 microm thulium CW laser to determine the mechanisms of laser effects in the skin under various exposure conditions.

Study Design/materials And Methods: Pig skin lesions were created at, below and beyond the threshold irradiation conditions for grossly apparent thermal lesions.

Use of hyperosmotic chemical agent to improve the laser treatment of cutaneous vascular lesions.

A method is presented for decreasing radiant exposures required for photocoagulation of cutaneous blood vessels using a hyperosmotic agent applied to skin prior to laser irradiation. The 50% probability for a given radiant exposure (RE50) to result in photocoagulation of vessels classified by type (arteriole, venule) and diameter was determined following direct (subcutaneous) laser irradiation of 84 vessels in a dorsal skin preparation pretreated with glycerol. Values were compared against results without glycerol pretreatment.

Corneal minimal visible lesion thresholds for 2.0 microm laser radiation.

To support refinement of the ANSI Maximum Permissible Exposure safety limits, a series of experiments were conducted in vivo on Dutch Belted rabbit corneas to determine corneal minimum visible lesion thresholds for 2.0 microm continuous-wave laser irradiation. Single pulse radiant exposures were made at specified pulse durations of 0.

Effect of pigmentation density upon 2.0 microm laser irradiation thermal response.

Yucatan mini-pigs with predominantly dark skin have been used to determine skin safety standards for infrared (IR) wavelength irradiation due to its anatomical similarity to all human skin. It has generally been argued that water is the principle absorber in the IR-B band and melanin has relatively low absorbance. To accept dark pigmented damage thresholds for skin with various melanin densities, it is necessary to investigate the potential role of melanin in producing skin injury as characterized by an erythermal response.

Modeling thermal damage in skin from 2000-nm laser irradiation.

An optical-thermal-damage model of the skin under laser irradiation is developed by using finite-element modeling software (FEMLAB 3.1, Comsol, Incorporated, Burlington, Massachusetts). The general model simulates light propagation, heat generation, transient temperature response, and thermal damage produced by a radically symmetric laser beam of normal incidence.

Design and development of a computer-assisted retinal laser surgery system.

Since the mid-1980s, the development of a therapeutic, computer-assisted laser photocoagulation system to treat retinal disorders has progressed under the guidance of Dr. Welch, the Marion E. Forsman Centennial Professor of Engineering, Department of Biomedical Engineering, the University of Texas at Austin.

Dependence of calculus retropulsion on pulse duration during Ho: YAG laser lithotripsy.

Background And Objectives: The purpose of this study was to investigate the effect of optical pulse duration on stone retropulsion during Ho:YAG (lambda = 2.12 microm) laser lithotripsy.

Study Design/materials And Methods: A clinical Ho:YAG laser with pulse durations was employed to fragment calculus phantoms and to evaluate stone phantom retropulsion.

Porcine skin ED50 damage thresholds for 2,000 nm laser irradiation.

Background And Objectives: To gain refinement in safe-exposure limits, indicated by the maximum permissible exposure (MPE) limits, the minimum visible lesion thresholds for three spot sizes (5-15 mm) and four exposure durations (0.25-2.5 seconds) were determined for the skin at 2,000 nm continuous wave laser irradiation.

Urinary calculus fragmentation during Ho: YAG and Er:YAG lithotripsy.

Background And Objectives: We tested Ho:YAG and Er:YAG laser ablation of human urinary calculi to determine if Er:YAG is a more efficient lithotripsy device.

Study Design/materials And Methods: Ablation efficiency of Ho:YAG and Er:YAG lasers was tested at varying energy settings, ranging from the damage threshold to clinical energy setting associated with Ho:YAG laser. Stones of known composition (calcium oxalate monohydrate (COM), cystine, and uric acid (UA)) were irradiated.

Review of laser fibers: a practical guide for urologists.

Holmium:YAG lithotripsy requires transmission of optical energy using laser fibers. Optical fibers may be subjected to severe angular deflection and bending during flexible nephroscopy or flexible ureteronephroscopy. Irradiation of a deflected fiber in a tight bending radius may produce fiber failure and consequent irradiation of the ureteroscope, with risk of instrument damage and patient injury.

Quantitative phase-contrast imaging of cells with phase-sensitive optical coherence microscopy.

We describe a method for en face phase-contrast imaging of cells with a fiber-based differential phase-contrast optical coherence microscopy system. Recorded en face images are quantitative phase-contrast maps of cells due to spatial variation of the refractive index and (or) thickness of various cellular components. Quantitative phase-contrast images of human epithelial cheek cells obtained with the fiber-based differential phase-contrast optical coherence microscopy system are presented.

Morphological changes in blood vessels produced by hyperosmotic agents and measured by optical coherence tomography.

Optical tissue clearing by hyperosmotic chemical agents significantly increases light depth penetration in skin and may improve light-based therapeutics such as laser treatment of cutaneous vascular lesions. A feasibility study was conducted to evaluate the potential role of optical clearing by glycerol in laser treatment of cutaneous vessels. Optical imaging was performed to investigate the morphological effects of glycerol on blood vessels of skin.

Preliminary biocompatibility experiment of polymer films for laser-assisted tissue welding.

Background And Objectives: The purpose of this study was to examine the impact of a polymer film for liquid solder strength reinforcement on the short term healing of a wound closed by laser-tissue soldering.

Materials And Methods: Full thickness incisions created on the dorsum of Sprague-Dawley rats were closed by laser-tissue soldering: albumin solder with Indocyanine Green (ICG) dye was inserted between the incision edges and photothermally coagulated with a diode laser. A poly(DL-lactic-co-glycolic acid) (PLGA) polymer film was implanted subcutaneously in the bottom of the incision (controls had no film).

Infrared imaging of 2-D temperature distribution during cryogen spray cooling.

Cryogen spray cooling (CSC) is used in conjunction with pulsed laser irradiation for treatment of dermatologic indications. The main goal of this study was to determine the radial temperature distribution created by CSC and evaluate the importance of radial temperature gradients upon the subsequent analysis of tissue cooling throughout the skin. Since direct measurement of surface temperatures during CSC are hindered by the formation of a liquid cryogen layer, temperature distributions were estimated using a thin, black aluminum sheet.

Dynamic impedance measurements during radio-frequency heating of cornea.

Hyperopia affects approximately 25% of the population. The aim of different heating modalities for the treatment of hyperopia is to steepen the central curvature of the cornea. Conductive keratoplasty (CK) involves the placement of radio-frequency (RF) lesions around a 7-mm-diameter ring concentric with the pupil of the eye.

Tissue welding with biodegradable polymer films-demonstration of acute strength reinforcement in vivo.

Background And Objectives: To demonstrate, in vivo, acute strength reinforcement benefits of polymer film patches.

Study Design/materials And Methods: Full thickness incisions created in a dorsal skin flap of Sprague-Dawley rats were closed by laser-tissue welding: albumin solder was topically applied to the incision on the dermal surface, and a poly(lactic-co-glycolic acid) (PLGA) polymer film placed on the solder as a patch (controls had no film). Breaking strength was tested acutely (15-20 minutes after sacrifice).

Erbium: YAG laser lithotripsy mechanism.

Purpose: We tested the hypothesis that the mechanism of long pulse erbium:YAG laser lithotripsy is photothermal.

Materials And Methods: Human urinary calculi were placed in deionized water and irradiated with erbium:YAG laser energy delivered through a sapphire optical fiber. Erbium:YAG bubble dynamics were visualized with Schlieren flash photography and correlated to acoustic emissions measured by a polyvinylidene fluoride needle hydrophone.