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Biomedical subjects

J A Zuclich

Publications and source records attributed to J A Zuclich.

16 recordsLinked to original sources
PubMed2001

Retinal damage induced by red diode laser.

Widespread use of compact, low-cost diode lasers (pointers and illuminators) has ushered in an era where large numbers of the general public are accidentally or deliberately exposed to low-power laser radiation. The objectives of this study are both to determine the primate retinal lesion threshold for exposure to 650 nm diode laser radiation and to examine the risks of retinal damage from low-level (sub-threshold) ocular exposures. To this end, the ED50 and ED10 damage thresholds, their fiducial limits, and the slopes of the probability vs. dose curves have been examined in detail. In addition to conventional fundoscopy, exposed eyes were examined by confocal scanning laser ophthalmoscopy, fluorescein angiography, and histopathology at both the light and electron microscopic levels in attempts to discern tissue disruption following exposures below the ophthalmoscopic ED50 threshold dose. These alternative observation techniques did not identify detectable tissue disruption following exposures below the ophthalmoscopic lesion threshold dose.

Animals↗
PubMed1995

Retinal effects of ultrashort laser pulses in the rabbit eye.

PURPOSE: To evaluate the effects of ultrashort laser pulses from femtoseconds to nanoseconds on the retinas of live rabbit eyes and to determine the energy requirements for visible lesion development. METHODS: The retinal effects of laser exposures were examined for laser exposures with pulsewidths ranging from 4 ns to 90 fs, with visible wavelengths of 532 nm for durations > 5 ps and 580 nm for durations < 5 ps. The authors examined and scored all laser impact sites in the retina ophthalmoscopically--with fundus photography and with fluorescein angiography--to identify evidence of visible laser effects. RESULTS: The laser energy required for retinal minimal visible lesions was found to be slightly less for pulsewidths < 5 ps and varied from 5 microJ at 4 ns to 1.1 microJ at 90 fs for the 1-hour ophthalmoscopic reading. Lesions from higher energy pulses (7 to 120 microJ) were examined at all pulsewidths. For 90-fs high-energy pulse delivery, an increased intensity of retinal lesions and the development of several subretinal hemorrhages were demonstrated at peak energies of 30 microJ. Fluorescein angiography was found to be much more sensitive as an indicator of retinal damage for both femtosecond pulsewidths. CONCLUSIONS: The low energies required for visible lesion production in live rabbit eyes raise new questions surrounding ultrashort pulse propagation in ocular media, energy deposition at the retina, and mechanisms limiting retinal damage from ultrashort laser pulses.

Animals↗
PubMed1993

Probability-summation model of multiple laser-exposure effects.

A probability-summation model is introduced to provide quantitative criteria for discriminating independent from interactive effects of multiple laser exposures on biological tissue. Data that differ statistically from predictions of the probability-summation model indicate the action of sensitizing (synergistic/positive) or desensitizing (hardening/negative) biophysical interactions. Interactions are indicated when response probabilities vary with changes in the spatial or temporal separation of exposures. In the absence of interactions, probability-summation parsimoniously accounts for "cumulative" effects. Data analyzed using the probability-summation model show instances of both sensitization and desensitization of retinal tissue by laser exposures. Other results are shown to be consistent with probability-summation. The relevance of the probability-summation model to previous laser-bioeffects studies, models, and safety standards is discussed and an appeal is made for improved empirical estimates of response probabilities for single exposures.

Humans↗
PubMed1992

In situ measurements of lens fluorescence and its interference with visual function.

Irradiation of the primate lens by near-ultraviolet wavelengths results in a blue fluorescence, which can be an intraocular source of veiling glare. This study quantitated the fluorescence intensity as a function of exciting intensity and wavelength. As the exciting wavelength was increased from 360 to 430 nm, the decreasing fluorescence intensity (for equal radiant exposures) was partially offset by a shift in the fluorescence spectrum to wavelengths of greater luminous efficiency so the luminance of the lens fluorescence remained approximately constant. The measured luminance of the lens fluorescence was high enough to imply degradation of visual function as a result of reduced contrast of the retinal image. To obtain an objective measure of visual deficit associated with the fluorescent glare, the visual evoked potential (VEP) elicited by counterphased sine-wave gratings was recorded while the subject eye was continuously exposed to the 413 nm emission from a krypton laser. The VEP amplitude was reduced in the presence of the exciting laser even at levels defined as "safe" (ie, where exposure levels are insufficient to induce an acute ocular lesion). Because the direct glare effect of the exciting radiation was negligible in this experiment, the VEP response loss is attributed to the effect of the lens fluorescent glare.

Animals↗
PubMed1989

Ultraviolet-induced photochemical damage in ocular tissues.

Exposure to ultraviolet (UV) lasers may result in pathology to either the cornea, lens or retina of the primate eye. The particular combination of exposure parameters (wavelength, peak power, pulsewidth, pulse repetition rate, and total energy delivered) determines the primary target tissue(s) in each instance. The effect may be acute or chronic, and the implicated damage mechanism may be categorized as photochemical, photoablative or thermal. This paper summarizes a number of specific cases where UV laser radiation affected one or more of the ocular tissues, describes the nature of the pathologies, and indicates what is known about the damage mechanism in each case. Ranges of exposure parameters where each ocular tissue is the most sensitive are defined. The cornea is most sensitive via a photochemical damge mechanism in the 260- to 280-nm range, where the threshold dose is approximately 5 mJ cm-2. For near-UV wavelengths (320-400 nm), different target molecules absorb the radiation and are susceptible to less efficient photochemical damage mechanism yielding corneal thresholds in the range of 10-100 J cm-2. However, we report acute cataract induction following exposure to a 337-nm nitrogen laser at 1 J cm-2 when the energy is delivered in a 10-ns pulse. Further, with longer pulsewidths (approximately 1 s) of comparable wavelength, retinal lesions were induced when 0.28 J was delivered to the eye. The data suggest that the acute lens effect is the result of a thermal mechanism, whereas the UV-induced retinal lesions result from a photochemical insult to the photoreceptors. Data presented include the action spectra for far- and near-UV-induced ocular damage, the pulsewidth and total energy dependencies of ocular thresholds, cumulative effects of repeated exposures, and repair or recovery rates.

Animals↗
PubMed1985

Ocular effects of pulsed Nd laser radiation: variation of threshold with pulsewidth.

This study of retinal damage thresholds in the rhesus monkey eye investigated the effects of Nd:YAG laser radiation at four pulsewidths; 4, 30, and 200 ns, and 10 microseconds. The thresholds for induction of minimal ophthalmoscopically visible lesions for the four pulsewidths were 158, 326, 170, and 425 microJ, respectively, incident at the eye in single-pulse exposures. The data are interpreted to imply a flat trend of threshold with pulsewidth over the range of pulsewidths examined, in agreement with maximum permissible exposures quoted in existing laser safety standards. This finding is in contrast with the hypothesis of an anomalous trend of increasing threshold with decreasing pulsewidth which was suggested for the nanosec-microsec pulsewidth range based on the sparse data base previously available.

Animals↗
PubMed1984

Corneal damage induced by pulsed CO2 laser radiation.

Corneal damage thresholds were determined in Dutch Belted rabbits following CO2 laser radiation with pulse widths of 1.7, 25 and 250 ns. The threshold values for corneal clouding found for the 3 cases were 0.33, 0.54 and 0.18 J/cm2, respectively. These results are in accord with expectations based on a thermal-damage mechanism, with no evidence of acoustic shock or other mechanisms contributing to the observed damage for the exposure parameters used in this study. The data support the suggested maximum permissible exposure levels for short-pulse far-infrared laser radiation as quoted in current laser safety standards.

Animals↗
PubMed1984

Ultraviolet induced damage in the primate cornea and retina.

This paper presents a review of ultraviolet induced corneal effects which have been observed in the primate eye. Data discussed include the action spectra for far- and near-UV induced corneal damage, the pulsewidth dependence and oxygen dependence of near-UV corneal thresholds, and recovery rates of corneal epithelial damage following ultraviolet induced cell lethality. In addition, retinal photoreceptor damage induced by near-UV radiation is described.

Animals↗
PubMed1984

Effect of non-mode-locked ultraviolet laser radiation (334 nm) on the retina.

The eyes of three rhesus monkeys (Macaca mulatta) were exposed to non-mode-locked ultraviolet (UV) radiation at 334 nm. The beam incident at the corneal plane had a diameter of approximately 2.0 mm and a maximum power of 45-50 mW. Each eye received nine exposures with exposure times ranging from 0.1 to 8.0 s. The animals were euthanized at various times following exposure so that the eyes were examined at approximately 1 h and 1, 2, 5, 7, and 14 d post-exposure. Histologic lesions were primarily seen involving photoreceptors, and were qualitatively similar regardless of duration of exposure; although quantitatively more damage was seen at sites exposed for 4.0 to 8.0 s. The results indicate that retinal sensitivity to UV laser light is a wavelength effect, rather than due to laser mode-locking which was present in an earlier study but absent in this study.

Animals↗
PubMed1980

Retinal lesions due to ultraviolet laser exposure.

The morphologic appearance of retinal lesions induced by 325 nm radiation from a helium cadmium laser is described. The damage is limited primarily to the outer retinal layers with only minimal or moderate retinal pigment epithelial changes. The lowest radiant exposure to produce a light microscopic lesion was 0.15 J/cm2, which is about a factor of two below the ophthalmoscopic threshold.

Animals↗
PubMed1976

Ocular damage induced by near-ultraviolet laser radiation.

A quantitative study was conducted of ocular damage thresholds in the rhesus monkey eye from krypton, argon, and nitrogen laser radiation. Corneal and lenticular thresholds are reported for various laser beam parameters. Corneal damage was found to occur following incident energy doses of approximately 60 to 70 Joules per square centimeter (J./cm.2) for pulsewidths ranging from 250 musec to 120 sec. The results are consistent with a photochemical damage mechanism. With certain exposure parameters, cataracts were induced with lower energy doses than required to cause corneal damage. The lenticular thresholds, however, appear to be consistent with a thermal rather than a photochemical mechanism. Corneal and lenticular hazards of near-ultraviolet (near-UV) lasers are discussed in terms of existing safety standards for laser radiation.

Animals↗
PubMed1975

Protein triplet states.

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Electron Spin Resonance Spectroscopy↗