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Biomedical subjects

F Docchio

Publications and source records attributed to F Docchio.

At least 19 recordsLinked to original sources
PubMed1996

Vitreous laser absorption following fluorescein angiography in diabetic patients.

BACKGROUND: Sodium fluorescein staining of the vitreous following fluorescein angiography may interact with laser photocoagulation. METHODS: We evaluated the laser absorption by fluorescein in the vitreous when photocoagulation is performed following fluorescein angiography in 15 eyes of nine diabetic patients. Axial fluorescein concentration in the vitreous was measured by a scanning vitreal fluorophotometer. The amount of light absorbed by the fluorescein within the vitreous was calculated according to the Lambert-Beer law. RESULTS: The mean fluorescein concentration ranged from 2.93 ng cm-3 to 105.16 ng cm-3 at 1 h after injection of fluorescein and from 8.03 to 188.56 ng cm-3 after 4 h. Maximum laser absorption at 488 nm ranged from 6.79% (after 1 h) to 14.53% (after 4 h); at 514.5 nm it ranged from 0.96% to 2.14%; at 532 nm it ranged from 0.03% to 0.07%. At lambda > 550 nm, laser absorption was found to be negligible. CONCLUSIONS: In order to optimize the effect of photocoagulation, especially during long photocoagulation sessions, argon blue laser (488 nm) should be avoided following fluorescein angiography. Argon green laser (514.5 nm) should be used within 1 h after fluorescein injection. Frequency-doubled Nd:YAG laser (532 nm), krypton laser (647 nm) or semiconductor diode laser (810 nm) may be used at any time.

Absorption↗
PubMed1993

Refractive hazards of intraoperative retinal photocoagulation.

The refractions of a laser beam during transpupillary and endo-ocular intraoperative retinal photocoagulation as it passes through vitreous substitutes, with varying refractive indexes, were investigated with the use of mathematical algorithms and ray tracers. The following modifications and potential hazards were noted: 1) deviations of the laser beam (unlikely, however, to cause target error when surgery is properly conducted); 2) variations in laser-beam diameter and power density (up to 60%), easily leading to retinal underexposure or overexposure; and 3) asymmetry in beam distribution at the target site, leading to non-uniform retinal photocoagulation. Proper surgical techniques must be adopted before and during intraoperative photocoagulation to minimize retinal hazards. The relatively short distance between the endolaser probe and the retina means that fewer undesirable refractions occur with endo-ocular photocoagulation than with transpupillary indirect intraoperative photocoagulation.

Algorithms↗
PubMed1992

Interactions between light and vitreous fluid substitutes.

To determine the interactions between light and vitreous fluid substitutes, we studied the absorption and fluorescence properties of the following fluids that are commonly used in vitreoretinal surgery: Ringer's solution, balanced salt citrate-buffered solution, balanced salt bicarbonate-buffered solution, hydroxypropyl methylcellulose ophthalmic solution, hyaluronate sodium, perfluorocarbons, silicone oil, and fluorosilicone oil. The absorption spectra for all the fluids peaked in the UV-C (reference range <280 nm) and UV-B (reference range from 315 to 280 nm) regions of the spectrum, with little or no absorption in the visible region of the spectrum (from 400 to 700 nm). Emission of almost all of the fluids occurred mainly in the 300- to 360-nm region, with fairly low-quantum efficiency. The limited light absorption properties of the fluids calls for caution during transpupillary and intraocular laser photocoagulation to avoid excessive retinal damage, mainly when the laser power is increased during treatment. Transmission of incoherent light (environmental and ophthalmic artificial light) through highly transparent vitreous fluid substitutes may lead in time to dangerous light exposure, particularly in aphakic eyes. The emitted fluorescence in these fluids generates a minimal risk of long-term damage.

Absorption↗
PubMed1991

Study of laser damage to injection-molded diffractive intraocular lenses.

A study of the probability of damage induced in two implant quality injection-molded diffractive intraocular lenses by a commercial Q-switched Nd:YAG laser is presented. The damage thresholds of the diffractive intraocular lenses (0.10 mJ at 10% probability, 0.24 mJ at 50% probability, and 0.90 mJ at 99% probability) did not differ significantly from those of other poly(methyl methacrylate) lenses manufactured with the same technology. These low values (compared to those of other lens types) suggest that care should be taken during laser capsulotomy in eyes implanted with refractive lenses, with special attention given to power losses at the target site due to diffraction effects.

Laser Therapy↗
PubMed1991

Age-related changes in the fluorescence of melanin and lipofuscin granules of the retinal pigment epithelium: a time-resolved fluorescence spectroscopy study.

The photophysical properties of purified populations of melanin and lipofuscin granules from human retinal pigment epithelium, and their changes with donor age, have been investigated using high-sensitivity time-resolved fluorescence spectroscopy techniques with picosecond gating capabilities. The overall fluorescence intensity of both melanin and lipofuscin granules clearly increased with increasing donor age, the increase being most marked for melanin. In all granule populations the fluorescence decays were multiexponential with subnanosecond and nanosecond decay components. The resultant time-integrated and time-gated spectra also exhibited marked age-variations for each type of granule. Young melanin showed spectral patterns similar to those of bovine melanin, while a yellow-orange fluorescence band appeared in melanin samples from older age groups. Lipofuscin granules exhibited a blue, a yellow and an orange band whose relative amounts were age-related. The results demonstrate the potential of time-resolved techniques for discriminating fluorophores in vitro and in situ, and have confirmed results previously obtained using extraction techniques. Furthermore, the ability of this technique to identify and quantify individual fluorophores within granules may provide an important insight into the origin and development of lipofuscin within the retinal pigment epithelium and ultimately into the mechanisms of age-related retinal diseases.

Adolescent↗
PubMed1990

Age-related changes in the morphology, absorption and fluorescence of melanosomes and lipofuscin granules of the retinal pigment epithelium.

The morphological and spectral characteristics of purified populations of melanosomes and lipofuscin granules from the human retinal pigment epithelium (RPE) were studied with respect to donor age. All melanosome and lipofuscin fractions exhibited the typical ultrastructural appearance associated with these granules. Absorption profiles of both melanin and lipofuscin granules demonstrated an increased optical density of the granules with increasing age. The former was associated with an overall increase of melanin within the granules. Melanosomes were weakly fluorescent; emission in the blue decreased with increasing age while emission in the red increased. The fluorescent intensity of lipofuscin granules increased with age. These results provide support for the concept that melanogenesis is occurring within the human RPE throughout life and that pigment granules within the RPE undergo age-related modifications during life.

Adolescent↗
PubMed1990

Comprehensive study of damage to intraocular lenses by single and multiple nanosecond neodymium: YAG laser pulses.

The results of an extensive study of the probability of damage induced in implant quality intraocular lenses (IOLs) by a commercially available nanosecond Nd:YAG photodisruptor are presented. These results were compared with the morphology of damage seen on scanning electron microscopy. The differences in the shape of the damage probability curves derived for the different lens groups demonstrate that a single threshold value does not characterize the threshold for IOL damage. We suggest that a standard method using a clinical photodisruptor be used by all workers to derive these curves for all IOLs in clinical use. The clinical relevance of our findings is emphasized.

Lasers↗
PubMed1989

Ocular fluorometry: principles, fluorophores, instrumentation, and clinical applications.

Ocular fluorometry is rapidly evolving as a versatile technique for research and diagnosis in ophthalmology. The main reasons for this increasing success are 1) the ideal characteristics of the eye as an optical device for excitation of tissue fluorescence and for the detection of the fluorescent emission; 2) the development of novel fluorometric techniques, including differential and time-resolved fluorescence spectroscopy; and 3) the increasing use of coupling geometries with high-resolution and high spatial selectivity. Both endogenous and exogenous fluorophores are of interest to ocular fluorometry. The most significant among endogenous fluorophores are the fluorescing pigments of the lens and of the retinal pigment epithelium (RPE). The nature, topography, and fluorescence properties of such pigments depend on age and pathology and on the level of light exposure. Exogenous fluorophores of interest are both intentionally induced and unintentionally accumulated drugs (some of which are phototoxic). Laser-based fluorometric techniques play a leading role in ocular fluorometry. The peculiar properties of the laser for the excitation of fluorescence make this source a favorite candidate for ocular fluorometry both in vitro and in vivo.

Eye Diseases↗
PubMed1989

Time-gated fluorescence spectroscopy of the tumor localizing fraction of HpD in the presence of cationic surfactant.

Time-gated fluorescence spectroscopy was performed on the tumor localizing fraction (TLF) of HpD in buffer at different concentrations of cationic surfactant. This technique obtains emission spectra with programmable delay relative to the excitation pulse. According to the measured fluorescence decay-time constants (approximately 0.7, approximately 3 and approximately 15 ns) three gates were considered, delayed by 0, 5 and 18 ns, respectively, to evaluate the contribution of the emitting molecular species to the spectra. Simultaneous to these measurements, fluorescence decay waveforms and time-integrated spectra were also detected. In buffer and in detergent micelles the fluorescence spectra are given by the superposition of the emission of the different molecular species present in the solution, and no appreciable interaction among the chromophores is observed. On the contrary, in the pre-micellar range of the surfactant, evidence for the existence of an energy transfer mechanism was found. This effect seems to be related to the configurational state of the TLF polymeric chains and depends on the relative TLF/surfactant concentration.

Cetrimonium↗
PubMed1988

Nd:YAG laser photodisruption: an experimental investigation on shielding and multiple plasma formation.

In an ocular model plasmas were induced by Q-switched, commercially available Nd:YAG lasers that operated in low order or fundamental mode. Plasma shielding was measured and analysed in relation to energy input, number of plasmas and plasma evolution. Near breakdown threshold, attenuation or shielding of the laser beam resulting from absorption and scattering by the plasma is low and is characterized by high variability from shot to shot. More importantly, shielding does not increase when multiple plasmas are formed, possibly due to a competitive mechanism between these plasmas. Further evidence of this mechanism was obtained from measurement performed using a streak camera. The effectiveness of shielding is scarcely changed by an increase in the cone angle of the incident radiation. In the light of these experiments and other published data, safety guidelines for the clinical use of the Nd:YAG laser have been formulated.

Absorption↗
PubMed1988

Intraocular lens damage from Nd:YAG laser pulses focused in the vitreous. Part I: Q-switched lasers.

The damage resulting from laser-induced optical breakdown and plasma formation on or near an intraocular lens (IOL) has been well described, but there is another form of damage, not associated with optical breakdown, that can harm an IOL. The parameters that lead to this damage were investigated. Polymethylmethacrylate IOLs were irradiated by a Q-switched Nd:YAG laser beam focused so that plasmas were formed well clear of the IOL. Damage was induced in the volume of plastic through which the laser beam passed and was cumulative, not being visible until several laser pulses had passed through the lens. The number of pulses required to produce damage varied inversely with the distance between the IOL and the site of plasma formation. This damage is most likely to occur clinically when vitreous structures are targeted in the pseudophakic eye.

Humans↗
PubMed1988

A new form of damage to PMMA intraocular lenses by Nd:YAG laser photodisruptors.

The damage that Nd:YAG laser radiation can cause to plastic (PMMA) IOLs during pseudophakic capsulotomy is well documented in the literature. This damage is the result of direct plasma action on the lens material. We report here another form of damage to PMMA IOLs which is more subtle and does not result from plasma action in the plastic. Even when the irradiance within the IOL is well below the threshold for optical breakdown, the PMMA can be damaged if irradiated by many laser pulses. This subthreshold damage is therefore cumulative. Its importance, likelihood of occurrence and ways to minimise this are considered.

Dose-Response Relationship, Radiation↗
PubMed1988

Shielding properties of laser-induced plasmas in ocular media irradiated by single Nd:YAG pulses of different durations.

Shielding of laser pulses by plasmas generated in ocular media has been experimentally investigated using single Nd:YAG laser pulses of different durations, ranging from several nanoseconds (ns) to a few tens of picoseconds (ps), both in saline solution and extracted calf vitreous. At the respective threshold radiant exposures for breakdown in saline (259 mJ/cm2 for 7 ns, 20.5 mJ/cm2 for 220 ps and 4.7 mJ/cm2 for 30 ps pulses) the single pulse energy transmission is found to be about 74% for 7 ns, 55% for 220 ps and 50% for 30 ps, thus showing that shielding of laser-induced plasmas is more effective for shorter pulses than for longer pulses. Moreover, the decrease in transmission with increasing radiant exposure is faster in the picosecond case than in the nanosecond case. These results show that direct irradiation of the retina is, to some extent, present especially near threshold. In the case of picosecond pulses, a comparison with published results indicates that shielding between subsequent pulses in a train is likely to occur only to a very limited extent.

Culture Media↗
PubMed1987

Nd:YAG laser irradiation of an eye model: experimental analysis.

This work reviews a series of experiments performed on an eye model to study physical effect relevant for a safe and effective use of the Q-switched Nd:YAG laser in ophthalmic microsurgery. The breakdown probability per laser pulse has been found to depend exponentially on the reciprocal laser field. This indicates that, as in transparent solids, electron avalanche ionization is likely the main mechanism for optical breakdown in liquids. Shielding of the retina, by the laser-induced plasma, is not very effective, but an appreciable degree of shielding is present, in burst operation, even after membrane disruption. A backscattered beam, which presents the typical properties of stimulated Brillouin scattering, has been observed in the eye model, with a threshold of approximately 5 X 10(9) W/cm2. This beam, which presents an irregular spatial structure with peaks of irradiance well above the average value, may produce damage of the internal wall of the cornea.

Eye↗
PubMed1986

A study on the possible involvement of nonlinear mechanism of light absorption by HpD with Nd:YAG laser.

The purpose of this study was to investigate whether excitation of porphyrin could be related to nonlinear mechanisms of absorption of porphyrin itself or of the medium in which porphyrin is embedded. This possibility was proposed as an explanation for results of previous experiments where a Nd:YAG laser was used. An MS-2 sarcoma transplanted into the hind pad of BALB/c mice was used as the experimental tumor model. Mice were given HpD i.v. (25 mg/kg) 24 h before exposure to light delivered from an IR laser (1,060 nm). Since at dose-rates ranging between 600 and 1,200 mW/cm2 the thermal effect tended to mask the nonlinear effect, the temperature of the limb of mice was kept cold by running water. Irradiation performed under cooling conditions did not show any tumor growth inhibition. Experiments in vitro performed on HT-29 cells by a continuous wave (CW) or pulsed (Q-switch) Nd:YAG laser indicated no appreciable difference in DNA synthesis between irradiated and nonirradiated cells. Our results did not evidence nonlinear mechanisms of absorption by HpD with Nd:YAG laser both in CW and pulsed (nanosecond range) modes. Whether this effect should occur, in any case it is unlikely to be suitable to induce a photodynamic effect due to its low efficiency. Nd:YAG laser could induce a heating related effect, which can improve the therapeutic efficacy of PDT.

Animals↗
PubMed1984

In situ evaluation of the functional state of chromatin by means of Quinacrine Mustard staining and time-resolved fluorescence microscopy.

A pulsed laser microfluorometer with high spatial and temporal resolution was employed to study the functional state of chromatin, using Quinacrine Mustard as the fluorescent probe. Corresponding segments of polytene chromosomes of embryo suspensor cells of Phaseolus coccineus and parenchymal cells of Helianthus tuberosus, in phases not involving DNA synthesis, were selected as models. The fluorescence decay time turned out to be a discriminating parameter for the chromatin fractions of differing functional engagement. The results were interpreted on the basis of a different accessibility of the DNA to the intercalating agent, as a result of the different structural situation of the chromatin. This fact determines modifications of the energy transfer rates between dye molecules in different quantum efficiency conditions, which results in variations of fluorescence decay times.

Chromatin↗
PubMed1984

The time-dependent behaviour of hematoporphyrin-derivative in saline: a study of spectral modifications.

Hematoporphyrin-Derivative (HpD), a widely-used tumor-specific photosensitizer, is a complex mixture of porphyrins whose composition has yet to be clarified. This paper reports on the behaviour of HpD in saline. From a spectroscopic point of view, the fresh solution is characterized by two main absorption peaks, attributable to monomeric and dimeric forms. With aging, a new porphyrin species (NPS) appears. To define the NPS, absorption, excitation and emission spectra were measured in different conditions and time-resolved fluorescence measurements were also performed. This species exhibits an absorption/excitation peak at 405 nm, an emission peak at 575 nm and a fluorescence decay time of approximately 3.5 ns. Its formation is strongly influenced by many environmental factors: in particular, gases diluted in the solution, temperature, pH and concentration. The presence of Oxygen and a pH value outside the 6-8 range may be considered inhibiting factors. The NPS seems to be quite important in the understanding of HpD tumor-specificity, since the presence of an emission band similar to the NPS one seems to be favoured in tumor cells as compared with normal cells.

Hematoporphyrin Derivative↗