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Biomedical subjects

C A Puliafito

Publications and source records attributed to C A Puliafito.

At least 91 records · Page 5Linked to original sources
PubMed1989

Transscleral cyclophotocoagulation using a contact laser probe: a histologic and clinical study in rabbits.

Transscleral photocoagulation of the ciliary body was achieved in pigmented rabbits using a sapphire probe delivery system coupled to a commercial surgical continuous-wave Nd:YAG laser. This contact technique was found to be effective in reducing intraocular pressure (IOP); greater treatment energies were associated with a more prolonged reduction in IOP, and also correlated with a greater degree of histologic damage to the ciliary body. Treatment energies of 0.8-1.0 Joules produced substantial disruption of the ciliary body. This technique is easy to learn and offers ease in control and placement of the coagulation spots.

Animals↗
PubMed1989

Indocyanine green videoangiography of choroidal neovascularization.

Choroidal neovascular membranes often are poorly defined on fluorescein angiography because of rapid or indistinct fluorescein leakage or because of blockage of hyperfluorescence by overlying hemorrhage, lipid, turbid fluid, or pigment. Indocyanine green (ICG) is a high protein-bound dye with peak absorption (805 nm) and peak fluorescence (835 nm) in the near infrared portion of the spectrum. At these wavelengths, penetration through overlying pigments is increased. Using an infrared videoangiography system, the authors obtained ICG angiograms of 32 eyes with suspected choroidal neovascularization. Compared with fluorescein angiography, ICG improved visualization of the choroidal circulation and enhanced visualization of some membranes that were poorly defined with fluorescein. In addition, after clearance of the dye from the retinal and choroidal circulations, ICG remained in and around the neovascular tissue. The authors conclude that ICG videoangiography may aid in the evaluation of selected patients with poorly defined membranes on fluorescein angiography.

Adult↗
PubMed1989

Femtosecond optical ranging of corneal incision depth.

Excimer laser ablation has been proposed as a technique for keratorefractive surgery. Clinical acceptance of linear-incision laser keratectomy may depend on the availability of a method for accurately and noninvasively monitoring incision depth during the ablation process. We have developed a femto-second optical ranging technique for measurement of corneal incision depth. This technique uses nonlinear optical cross-correlation to determine the time-of-flight of an ultrashort laser pulse between the anterior corneal surface and the bottom of the keratectomy incision. Longitudinal and transverse resolution are estimated to be 5 micron and 10 micron, respectively.

Animals↗
PubMed1988

Infrared laser bone ablation.

The bone ablation characteristics of five infrared lasers, including three pulsed lasers (Nd:YAG, lambda = 1,064 micron; Hol:YSGG, lambda = 2.10 micron; and Erb:YAG, lambda = 2.94 micron) and two continuous-wave lasers (Nd:YAG, lambda = 1.064 micron; and CO2, lambda = 10.6 micron), were studied. All laser ablations were performed in vitro, using moist, freshly dissected calvarium of guinea pig skulls. Quantitative etch rates of the three pulsed lasers were calculated. Light microscopy of histologic sections of ablated bone revealed a zone of tissue damage of 10 to 15 micron adjacent to the lesion edge in the case of the pulsed Nd:YAG and the Erb:YAG lasers, from 20 to 90 micron zone of tissue damage for bone ablated by the Hol:YSGG laser, and 60 to 135 micron zone of tissue damage in the case of the two continuous-wave lasers. Possible mechanisms of bone ablation and tissue damage are discussed.

Animals↗
PubMed1988

Infrared laser surgery of the cornea. Studies with a Raman-shifted neodymium:YAG laser at 2.80 and 2.92 micron.

Tissue absorption lengths for infrared radiation at 2.8 to 3.1 micron are very short due to strong absorption by water. Corneal ablation using pulsed lasers at these wavelengths can potentially produce incisions similar in quality to cuts produced by excimer lasers at 193 nm. The authors have used 8-ns pulses at 2.80 and 2.92 micron, generated by a Raman-shifted neodymium:YAG (Nd:YAG) laser, to make slit-like incisions in bovine and human corneas. At 2.8 micron, etch depth per pulse increases sigmoidally from 0.15 micron at 390 mJ/cm2 to 3.8 micron at 2200 mJ/cm2. No ablation occurs at fluences below 250 mJ/cm2. Light and transmission electron microscopy show smooth-walled incisions bordered by a thermally damaged region that varies in width from 1.5 micron at 600 mJ/cm2 to 10 micron at 2200 mJ/cm2. The small amount of tissue damage produced at low fluences suggests that infrared ablation may be useful in keratorefractive surgery.

Animals↗
PubMed1987

Semiconductor laser endophotocoagulation of the retina.

Laser endophotocoagulation is an important technique in vitreoretinal surgery. We performed successful retinal endophotocoagulation in the eyes of Dutch-belted rabbits, using high-power phased-array semiconductor lasers, emitting at 808 and 817 nm. The laser itself measured 25 X 30 X 21 mm, was air cooled, and was portable. At a treatment power of 100 mW, uniformly white photocoagulation lesions were seen at exposure durations of 0.2 to 1.0 s. Lesions were similar in appearance to argon laser photocoagulation lesions, as determined by ophthalmoscopy and fluorescein angiography. Thin-section histologic examination of acute lesions revealed injury localized to the outer retina; chorioretinal scar formation was noted ten days after photocoagulation. To our knowledge, this study is the first in which therapeutically useful lesions were produced using a diode laser and demonstrates the feasibility of using these highly efficient and compact laser sources for ophthalmic photocoagulation.

Animals↗
PubMed1987

High-speed photography of excimer laser ablation of the cornea.

We have used laser-based high-speed photography to investigate excimer laser ablation of the cornea. Photographs of the ablation plume were obtained 500 ns to 150 microseconds after incidence of a 193- or 248-nm excimer laser pulse on the surface of the cornea. Ejection of material from the cornea begins on a time scale of nanoseconds and continues for 5 to 15 microseconds following the excimer pulse. At 193 nm the ablation plume resembles a burst of smoke, and individual particles are too small to be optically resolved with our apparatus. At 248 nm the plume resembles a spray of larger, discrete droplets. Material is ejected from the cornea at supersonic velocity but decelerates rapidly; the velocity for the first 500 ns following the excimer pulse averages 400 m/s at 193 nm. Plume size and velocity increase with increasing fluence.

Animals↗
PubMed1987

Quantitative and ultrastructural studies of excimer laser ablation of the cornea at 193 and 248 nanometers.

Excimer laser radiation at 193 nm and 248 nm was used to create linear etch perforations of enucleated calf corneas. The etch depth per pulse was determined for various exposures, and specimens were examined by light and transmission electron microscopy. Compared to 248 nm, excimer laser ablation at 193 nm was found to have a lower threshold for onset of ablation, less increase in etch depth per pulse at increasing fluences, and less structural alteration in adjacent cornea. For 193 nm, structural alterations were minimal, confined to an area less than 0.3 micron wide, and did not increase with increasing fluence. These studies suggest that clinical strategies for excimer laser refractive surgery will employ the 193-nm wavelength, with fluence chosen depending on surgical strategy. Ablation exposures above 600 mJ/cm2 at 193 nm may give the most repeatable etch depth.

Animals↗
PubMed1987

Interferometric technique for investigation of laser thermal retinal damage.

We describe a new technique for investigating laser-tissue interactions based on the use of an interferometric laser exposure pattern. A Michelson interferometer is used to generate a sinusoidal fringe exposure pattern. The periodicity of the fringe pattern may be adjusted from macroscopic dimensions to a scale of microns without the need for an imaging plane. Since fringe pattern periodicity is more adjustable and directly measureable than laser spot size, this technique offers significant advantages for studying the effects of thermal damage and diffusion in the irradiated tissue. In addition, the comparison of tissue response with theoretical models is simplified since the sinusoidal fringe pattern is itself an eigenfunction of the thermal diffusion equation. This technique is demonstrated for argon laser photocoagulation in the rabbit retina. Exposures at durations comparable to the thermal relaxation time produced spatially confined lesions, while those at much longer durations resulted in significant diffusion of the thermal damage beyond the primary targeted regions. The role of thermal diffusion can thus be assessed directly from the ophthalmoscopic and histologic appearances of the lesions. This technique can be employed to study thermal diffusion and other transport phenomena occurring in laser-tissue interactions for a variety of laser sources and tissue targets.

Animals↗
PubMed1987

Unscheduled DNA synthesis following excimer laser ablation of the cornea in vivo.

The amount of unscheduled DNA synthesis (UDS) produced in the cells adjacent to excimer laser ablations in the cornea was compared for 193-nm and 248-nm laser wavelengths. UDS is interpreted to indicate the process of excision repair of pyrimidine dimers formed in DNA. 193-nm laser ablation did not produce a statistically significant difference in the amount of UDS as compared to a negative control (diamond-knife corneal incision). However, 248-nm laser ablation did produce a highly statistically significant difference in the amount of UDS as compared to both the negative control (P < 0.001) and the 193-nm laser irradiation (P < 0.001). Other forms of DNA damage (single-strand DNA chain breaks and DNA-protein crosslinks) are not measurable by UDS and need to be investigated in the evaluation of the oncogenic potential of 193-nm laser ablation.

Animals↗
PubMed1986

Vitreous changes after neodymium-YAG laser photodisruption.

We investigated physicochemical changes in the vitreous body after photodisruption with a Q-switched neodymium-YAG laser. In vivo proton nuclear magnetic resonance imaging techniques were employed to assess alterations in the vitreous of irradiated rabbit eyes. Measurements of proton relaxation times (T1 and T2), viscosity, and chromatographic spectra were made in vitro on irradiated bovine and rabbit vitreous, and circular dichroism measurements were used to study changes in an irradiated sodium hyaluronate solution. Statistically significant changes in T1, were observed immediately after irradiation, but the small magnitude and reversibility of those changes, combined with the fact that the other measurements detected no changes, suggest that neodymium-YAG laser photodisruption does not have a direct deleterious effect on the structural integrity of the normal vitreous body.

Animals↗
PubMed1986

Corneal endothelial injury in rabbits following excimer laser ablation at 193 and 248 nm.

We performed a morphologic investigation of the corneal endothelium following in vivo excimer laser ablation at 193 and 248 nm in rabbit eyes. Control experiments were performed in eyes with incisions of similar depth made with a diamond surgical knife, and normal control eyes were studied in parallel. We found that 193-nm excimer laser incision to 90% of corneal depth produces endothelial alterations similar to those seen underlying diamond knife incisions of similar depth. Scanning electron microscopy revealed an incisional ridge and endothelial cellular edema; endothelial cell loss was not observed. In contrast, 248-nm ablations of similar depth and energy density revealed loss of underlying endothelial cells and a surrounding zone of severe cellular damage.

Animals↗