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Biomedical subjects

C A Puliafito

Publications and source records attributed to C A Puliafito.

At least 109 records · Page 6Linked to original sources

Excimer laser ablation of the lens.

Ablation of the bovine crystalline lens was studied using radiation from an excimer laser at four ultraviolet wave lengths as follows: 193 nm (argon fluoride), 248 nm (krypton fluoride), 308 nm (xenon chloride), and 351 nm (xenon fluoride). The ablation process was quantitated by measuring mass ablated with an electronic balance, and characterized by examining ablation craters with scanning electron microscopy. The highest ablation rate was observed at 248 nm with lower rates at 193 and 308 nm. No ablation was observed at 351 nm. Scanning electron microscopy revealed the smoothest craters at 193 nm while at 248 nm there was vacuolization in the crater walls and greater disruption of surrounding tissue. The craters made at 308 nm did not have as smooth a contour as the 193-nm lesions. The spectral absorbance of the bovine lens was calculated at the wavelengths used for ablation and correlated with ablation rates and thresholds. High peak-power, pulsed ultraviolet laser radiation may have a role in surgical removal of the lens.

Animals↗

Fibroblast radiosensitivity and intraocular fibrovascular proliferation following radiotherapy for bilateral retinoblastoma.

A 5-day-old female patient was found to have large hereditary retinoblastomas in the posterior pole of each eye. The patient received radiation treatment over a 39-day period, with each retina receiving 4600 rad. Two weeks after the complete treatment the tumours had regressed to approximately one-quarter of their original size. By 14 weeks following completion of radiotherapy the patient had developed in each eye extensive iris neovascularisation with progressive closure of the filtration angles, secondary glaucoma, and retinal detachments resulting from fibrovascular proliferation on the retinal surface. Radiosensitivity studies were from separate conjunctival biopsies obtained before and after radiation. These showed a D0 (calculated survival curve parameters, defined in the Methods section) in the exponential growth phase of 110 prior to radiation and a postirradiation exponential growth phase D0 of 70. Karotype studies showed several chromosomal abnormalities following radiotherapy. The clinical course and pathology findings are thought to represent an unusually severe orbital and ocular response to radiation therapy. These findings are consistent with our hypothesis that some patients with hereditary retinoblastoma may have a defect in the accumulation repair of x-irradiation induced DNA damage.

Cell Survival↗

Q-switched neodymium-YAG laser trabeculopuncture in monkeys.

In nine cynomolgus monkeys, trabeculopuncture was performed with a Q-switched neodymium-YAG laser, using a pulse energy of 5 to 7 millijoules and an exposure time of 14 nanoseconds. A penetration into Schlemm's canal was successfully achieved with two to four pulses; this penetration was accompanied by intraocular pressure (IOP) reduction and blood reflux into the anterior chamber. However, after eight days, IOP returned to baseline level, while white tissue was observed gonioscopically to fill in the puncture sites. Histologically, one hour after laser treatment, a blasting effect on the trabecular meshwork was observed with no signs of necrosis. Ater eight days, a hypertrophic scar formed, with the corneal endothelium extending over the scarred surface. At eight weeks and at six months after laser treatment, further shrinkage of the scar and the formation of a membrane over it was evident. Attempts to control scar formation by preventing blood reflux or injecting fluorouracil subconjunctivally for two weeks were unsuccessful. Scar formation at the trabecular puncture site severely limits the applicability of this potentially simple glaucoma treatment.

Animals↗

Cutting efficiency of single shot and burst mode neodymium:YAG lasers.

The efficiency of cutting by single pulses and bursts of two, four, and eight pulses from a Q-switched Nd:YAG laser was determined in a model of a heavy membrane and a loosely floating target. The burst modes cut the targets somewhat more quickly than single shots, but required a marked increase in total energy delivered. Anterior movement of the breakdown zone and posterior displacement of the target explain the energy inefficiency of burst-mode photodisruption.

Humans↗

Excimer laser ablation of the cornea and lens. Experimental studies.

The pulsed ultraviolet excimer laser has been used to produce tissue ablation with a high degree of precision and with minimal thermal damage to adjacent structures. In comparative studies of excimer laser ablation of the cornea and crystalline lens using 193 nm and 248 nm radiation, threshold fluence for corneal and lens ablation was higher at 248 nm than at 193 nm. Ablation of corneal stroma at 193 nm produced the most precise cuts. When examined by transmission electron microscopy, a narrow zone of damaged tissue (0.1 to 0.3 micron) was seen immediately adjacent to the tissue removed by the laser. Ablation with 248 nm radiation produced incisions with ragged edges and with a wider and more severe zone of damage in adjacent stroma. Ultraviolet spectral transmission studies of the corneal stroma showed that absorption is 10 times greater at 193 nm than at 248 nm. The excimer laser was effective in producing well controlled ablation of the crystalline lens in vitro, with effects parallel to those seen in the cornea.

Animals↗

Time-resolved studies of Nd:YAG laser-induced breakdown. Plasma formation, acoustic wave generation, and cavitation.

The use of high intensity ultrashort pulsed laser radiation to produce optical breakdown is an important approach for the surgical treatment of intraocular structures. We have investigated the transient properties of Nd:YAG laser induced breakdown in a saline model using time-resolved spectroscopic techniques. Spatially resolved pump and probe techniques are applied to study the dynamic behavior of the plasma formation, acoustic wave generation, and cavitation processes which accompany the optical breakdown. Measurements of plasma shielding and luminescence indicate that the laser induced plasma forms on a subnanosecond time scale and has a lifetime of several nanoseconds. An acoustic transient is generated at the breakdown site and propagates spherically outward with an initial hypersonic velocity, then loses energy and propagates at sound velocity. Transient heating following the plasma formation produces a liquid-gas phase change and gives rise to cavitation or gas bubble formation. This gas bubble expands rapidly for several microseconds, then slows to reach its maximum size and finally collapses.

Eye↗

Neodymium-YAG laser therapy to the anterior hyaloid in aphakic malignant (ciliovitreal block) glaucoma.

In three aphakic eyes and two eyes with intraocular lens implants (five patients, four women and one man, ranging in age from 65 to 76 years) persistent shallow or flat anterior chamber was observed despite multiple patent laser or surgical iridectomies. In each case direct application of the neodymium-YAG laser (3 to 11 mJ) to the anterior hyaloid face resulted in immediate deepening of the anterior chamber. This deepening was sustained in four of the cases. These results confirm previous observations suggesting that the anterior hyaloid can be the locus of abnormality in aphakic malignant (ciliovitreal block) glaucoma. Neodymium-YAG "hyaloidotomy" may be better than penetrating surgery in such cases.

Aged↗

Neodymium-YAG laser surgery on experimental vitreous membranes.

A Q-switched neodymium-YAG laser was used to cut experimental vitreous membranes in rabbit eyes. We were able to cut vitreous membranes up to 4 mm from the retinal surface using single pulse energies of up to 4 mJ without fluorescein angiographic evidence of retinal injury. When cutting membranes between 1.5 and 3 mm from the retinal surface, injury was documented in five of seven cases. The most frequently observed fundus injury was choroidal hemorrhage. The neodymium-YAG laser may be useful in cutting avascular membranes in the posterior segment of the eye.

Animals↗

Experimental iridotomy with the Q-switched neodymium-YAG laser.

Iridotomies were performed on pigmented rabbits with a Q-switched ophthalmic neodymium-YAG (Nd-YAG) laser and an argon laser. Because short-pulsed Nd-YAG lasers are effective in performing capsulotomies of the crystalline lens, injury to the underlying lens was evaluated by slit-lamp biomicroscopy at various intervals following the iridotomy, and then lenses were examined in vitro with the use of procion yellow, an extracellular dye. Patent iridotomies were produced with one to two pulse applications of the Nd-YAG laser. Focal areas of pigment deposition on the lens capsule and focal lens capsule opacities underlying the iridotomy site were observed, but no inadvertent capsulotomies occurred. Lens injury could be minimized through optimal focusing and energy selection. Minimal hemorrhage occurred with Nd-YAG laser iridotomy; prior treatment with the argon laser was not necessary to achieve hemostasis.

Animals↗

Long-term follow-up of Nd:YAG laser posterior capsulotomy.

A Nd:YAG laser developed for ophthalmic surgery was studied for safety and efficacy in secondary discission of the posterior capsule in aphakic and pseudophakic subjects. The study involves 6,800 subjects, 526 of whom had completed the six-month postoperative course by the time the data base was closed for analysis. Of the 526 subjects who were treated with the laser, 87.8% had improved vision, with 82.9% achieving a visual acuity of 20/40 or better. This result compares favorably with results for the surgically treated population in which only 68.4% experienced improved vision, with 80.2% achieving a visual acuity of 20/40 or better. Approximately four times more surgically treated subjects than laser-treated subjects experienced diminished vision (14.8%). Cumulative complication rates in the laser-treated population were very low (CME 2.3%, secondary glaucoma 3.6%, retinal detachment 0.4%, overall rate 4.8%). Persistent complications (present at the six-month postoperative period) were present at an overall incidence of 2.3%, comprised primarily of CME, 0.2%, retinal detachment, 0.2%, and secondary glaucoma, 0.8%. Only 5.7% of subjects experienced an intraocular pressure (IOP) rise to 30 mm Hg or greater. Return to the preoperative IOP level occurred in 89% of subjects in the first 24 hours to one week. Predictors of IOP rise to 30 mm Hg or greater were determined to be preoperative glaucoma and/or preoperative IOP of greater than 20 mm Hg.

Aged↗

Recurrent isolated sixth nerve palsy in children.

Six children had recurrent sixth nerve palsy the average duration of which was six weeks. One youngster, after several episodes of sixth nerve palsy, had residual esotropia and underwent strabismus surgery. The average interval between recurrences was 1.3 years. Ipsilateral recurrences were a prominent feature. Thus far the recurrences of palsy in this group of patients has not been associated with any identifiable intracranial process. Multiple recurrences in the absence of any recognizable febrile illness clearly suggests that not all "benign" sixth nerve palsies in children are due to postinfectious processes. The etiology of isolated benign sixth nerve palsy remains uncertain. Benign sixth nerve palsy with recurrence may account for a larger percentage of truly "isolated" palsies in otherwise healthy youngsters than has been generally appreciated since several widely quoted papers on this subject have included individuals with multiple neurologic deficits at the time of initial presentation. This report of recurrent palsies for which etiologies were not established should not diminish the concern that there might be an identifiable, serious, cause for sudden onset of sixth nerve palsy in a youngster. The diagnosis of "benign" sixth nerve palsy is one of exclusion that is made retrospectively and only after an adequate period of close observation.

Abducens Nerve↗

Experimental gypsy moth (Lymantria dispar) ophthalmia nodosa.

Ophthalmia nodosa is the nodular granulomatous inflammatory response of ocular tissue to caterpillar hairs. We experimentally simulated this condition by surgically implanting gypsy moth hairs in the rabbit cornea. We were not, however, able to produce ophthalmia nodosa solely by placing cilia in the rabbit cul-de-sac. The experimentally induced inflammation closely resembled human ophthalmia nodosa in both its clinical and histopathologic features.

Animals↗

Plasma formation and shielding by three ophthalmic neodymium-YAG lasers.

Because microplasma formation may provide an energy-absorbing shield that protects the retina from inadvertent injury during neodymium-YAG laser surgery, we studied plasma formation and shielding by three ophthalmic neodymium-YAG lasers (the Q-switched American Medical Optics YAG-100, the mode-locked Meditec OPL-3, and the Q-switched LASAG Sirius Microruptor 2) with three model targets (physiologic saline, 1% sodium hyaluronate, and a cellophane membrane). Plasma formation produced a linear reduction in the transmission of light energy along the beam path in a qualitatively differences. Plasma shielding was similar in both saline and sodium hyaluronate; enhancement of the shield effect occurred only with the cellophane membrane target. Operating the lasers at energy levels far above threshold did not reduce total light transmission significantly. Clinical use should be guided by the principle of employing the minimum energy necessary to cut the target tissue.

Lasers↗

Plasma shielding by Q-switched and mode-locked Nd-YAG lasers.

Q-switched and mode-locked Nd-YAG lasers depend on beam divergence and plasma formation to reduce energy transmission below the retinal damage threshold. In a model system of physiologic saline, we investigated plasma "shielding" and found that plasma formation markedly reduces further energy transmission along the beam path once plasma formation occurs. The protective effect of plasma shielding appears similar for a Q-switched pulse and a train of mode-locked pulses in a physiologic saline medium.

Humans↗