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Biomedical subjects

J Mellerio

Publications and source records attributed to J Mellerio.

At least 19 recordsLinked to original sources
PubMed1991

Temporal variations in the ionic transport across rabbit retinal pigment epithelium.

The potential difference (PD), short circuit current (SCC) and resistance (R) of rabbit retina-retinal pigment epithelium-choroid-sclera preparations were measured in a modified Ussing chamber. The rabbits were kept in 14 hour light/10 hour dark cycle conditions for 14 days: tissues were taken for measurement at 1.5, 6, 13, 20 and 23 hours after the start of the fifteenth light period. Significant variations in PD and SCC were observed 6 hours into the light cycle while the resistance remained constant during the test period. When in a second experiment the fifteenth light period was replaced by darkness, the highest PD and SCC values recorded occurred 12 hours after the time when the light period should have started in the normal light/dark cycle. In a third experiment the fifteenth light period was replaced by darkness and the retina was removed. There were variations in the PD and SCC as in the second experiment but the SCC peak was reduced in amplitude. From these preliminary studies it is suggested that these variations may be circadian in origin and may be related to variations in retinal function.

Animals↗
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↗
PubMed1987

Yellowing of the human lens: nuclear and cortical contributions.

The geometry of the cortex and nucleus of excised human lenses was determined by photography and dissection. Samples of the cortex and nucleus were measured spectrophotometrically to allow determination of light loss through the whole lens and the light loss per unit pathlength. It was concluded that the reduction of short wavelength light transmission with increasing age is due to two processes; first, the nuclear pathlength remains constant but there is increased pigment deposition; second, the pigment concentration does not change in the cortex but the pathlength increases.

Adult↗
PubMed1987

Retinal detachment following Nd:YAG posterior capsulotomy.

Five hundred and eighty-two patients who underwent Nd:YAG laser posterior capsulotomy at Moorfields Eye Hospital were reviewed retrospectively. Twelve patients (2 per cent), nine of whom were previously myopic, subsequently developed rhegmatogenous retinal detachment. Comparison with other studies suggests there is no greater risk of retinal detachment associated with Nd:YAG laser capsulotomy than with surgical discission. The relevance of the damage mechanisms of Nd:YAG lasers are discussed.

Eye Diseases↗
PubMed1984

Retinitis pigmentosa: a quantitative study of the apical membrane of normal and dystrophic human retinal pigment epithelial cells in tissue culture in relation to phagocytosis.

The phagocytic capabilities of both normal and dystrophic human retinal pigment epithelial cells were assessed by challenging cultures with both non-biological and biological particles. Cells from either source ingested both carbon particles and latex microspheres. Quantification of the phagocytic process in relation to microspheres showed that uptake was linear over an 8 h period and the rate was dose-dependent. All cultures phagocytosed rod outer segments from a variety of species, but excluded bacteria. By using bovine rod outer segments labelled with [H3] choline both normal and dystrophic cells were still accumulating label 24 h subsequent to challenge; however, this technique had significant problems. The introduction of any particulate matter into the culture medium resulted in changes in the apical membrane of the recipient cells. Such responses were quantified in terms of apical projections per unit area. Counts were always greater in cells challenged with biological material even if the material was not engulfed.

Aged↗
PubMed1980

Ocular physiology.

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Aqueous Humor↗