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Biomedical subjects

P Rol

Publications and source records attributed to P Rol.

At least 19 recordsLinked to original sources
PubMed2003

Plant sterols lower LDL cholesterol without improving endothelial function in prepubertal children with familial hypercholesterolaemia.

In adults with familial hypercholesterolaemia (FH), cholesterol lowering with statins has been shown to improve the endothelial function, a hallmark of early atherogenesis. Currently, therapeutic options for treating high cholesterol levels in FH children are limited. Plant sterols safely and effectively reduce serum cholesterol concentrations by inhibiting cholesterol absorption. Therefore, we evaluated the effect of plant sterols on cholesterol and vascular function in prepubertal children with FH. We included 41 children (5-12 years old) with FH in a double-blind crossover trial using spreads containing 2.3 g of plant sterols (mainly sitosterol and campesterol) per 15 g spread and a placebo spread for a 4-week period, separated by a 6-week washout period. Lipid levels and endothelial function were assessed after both 4-week treatment periods. Endothelial function was assessed as flow-mediated dilation (FMD) of the brachial artery using a wall tracking system. Data were compared to those of 20 healthy controls. Intake of 2.3 g plant sterols per day decreased total cholesterol (-11%) and low-density cholesterol (-14%) as compared to placebo spread in FH children. FH children treated with placebo spread were characterized by an impaired FMD compared to healthy control children (7.2% +/- 3.4% versus 10.1% +/- 4.2%, p < 0.005). However, the reduction of LDL in FH children did not improve FMD (placebo: 7.2% +/- 3.4% versus plant sterols: 7.7% +/- 4.1%). In conclusion, the present study shows a clear reduction of LDL cholesterol by plant sterol treatment. However, short-term plant sterol treatment does not improve the endothelial function in FH children.

Brachial Artery↗
PubMed2001

Rhodopsin-mediated blue-light damage to the rat retina: effect of photoreversal of bleaching.

PURPOSE: Acute white-light damage to rods depends on the amount of rhodopsin available for bleaching during light exposure. Bleached rhodopsin is metabolically regenerated through the visual cycle involving the pigment epithelium, or photochemically by deep blue light through photoreversal of bleaching. Because photoreversal is faster than metabolic regeneration of rhodopsin by several orders of magnitude, the photon catch capacity of the retina is significantly augmented during blue-light illumination, which may explain the greater susceptibility of the retina to blue light than to green light. However, blue light can also affect function of several blue-light-absorbing enzymes that may lead to the induction of retinal damage. Therefore, this study was conducted to test whether rhodopsin and its bleaching intermediates play a role in blue-light-induced retinal degeneration. METHODS: Eyes of anesthetized rats and mice that did or did not contain rhodopsin were exposed to green (550 +/- 10 nm) or deep blue (403 +/- 10 nm) light for up to 2 hours. Rats with nearly rhodopsinless retinas were obtained by bleaching rhodopsin in animals with inhibited metabolic rhodopsin regeneration-that is, under halothane anesthesia. In addition, Rpe65(-/-) mice that are completely without rhodopsin were used to test the susceptibility to blue-light damage of a rodent retina completely devoid of the visual pigment. Effects of illumination on photoreceptor morphology were assessed 24 hours or 10 days thereafter by morphologic and biochemical methods. RESULTS: Exposure to blue light resulted in severe retinal damage and activation of the transcription factor AP-1 in rats. In contrast, green light had no effect. When rhodopsin was almost completely bleached by short-term green-light exposure while metabolic regeneration (but not photoreversal) was prevented by halothane anesthesia, blue-light exposure induced distinct lesions in rat retinas. When both metabolic rhodopsin regeneration and photoreversal of bleaching were almost completely inhibited, blue-light exposure caused only very moderate lesions. When mice without rhodopsin were exposed to blue light, no damage occurred, in contrast to wild-type control mice. CONCLUSIONS: Short time exposure to blue light has deleterious effects on retinal morphology. Because damage was observed only in the presence of the visual pigment, blue-light-induced retinal degeneration is rhodopsin mediated. Absorption of blue light by other proteins is not sufficient to induce light damage. Photoreversal of bleaching, which occurs only in blue but not in green light, increases the photon-catch capacity of the retina and may thus account for the difference in the damage potential between blue and green light.

Animals↗
PubMed2000

Transpupillar laser phototherapy for retinal and choroidal tumors: a rational approach.

BACKGROUND: The physical laws are considered that need to be taken into account for optimal photothermal treatment of solid and vascular tumors, as well as other vascular anomalies of various etiology of the retina and choroid. Optimal irradiation therapy should take into account the distribution of both radiant and thermal energy in tumors, such as retinoblastomas, malignant melanomas and vascular malformations. Strict confinement of the extent of photothermal damage is critical since such pathological entities are frequently located close to the macula or optic nerve head. METHODS: A formal treatment of the optical quantities related to these requirements is presented. In this analysis we emphasize the following topics: Arrhenius' law, the kinetics of protein denaturation, the electromagnetic radiation field, wavelength, laser pulse duration (exposure time), optical properties of tissue, photocoagulation and thermotherapy. RESULTS: Generally, the conditions are best fulfilled when using radiation in the near-infrared range of the electromagnetic spectrum, such as that emitted from the diode (810 nm) and Nd:YAG (1064 nm) laser, because of the good optical penetration properties of this radiation in tissue. The xenon arc lamp was a very effective and particularly appropriate energy source for such purposes, and its withdrawal from the world market may have been untimely. Short wavelength sources of radiation, such as the argon ion (488, 514 nm) or the frequency-doubled Nd:YAG (532 nm) laser, are unsuitable for the irradiation of large vascular structures, as they have poor penetration depths. However, for vascular formations with a short path length (1 mm or less), short wavelength sources appear to be the most appropriate choice. Optical coupling of radiant energy to the eye by means of indirect ophthalmoscopic systems or contact lenses to the eye is crucial. Strong positive lenses may lead to severe constriction of the laser beam which leads to high irradiance within the anterior segment, increasing the chances of it being damaged; with negative contact lenses, such as the -64 D Goldmann type, this danger is reduced. CONCLUSIONS: Photothermotherapy is not without risk unless the temperature field can be well adapted to the tumorous structure, as temperature elevations outside a small therapeutic range that affect vital structures are considered to be a risk factor.

Absorption↗
PubMed2000

[Protein-condensation diseases--molecular basis of cataract formation].

There are reasons to classify a number of apparently disparate diseases as "condensation" (or molecular aggregation) diseases. Examples of such condensation diseases include the late phase of diabetes mellitus, Alzheimer's disease and others. With an expanding knowledge, the list of these diseases is likely to increase. We shall describe the underlying common mechanisms, the aim being to find anticataractogenic drugs based on this insight. The common, most important denominator of various clinically differing condensation diseases derives from the interaction of the macromolecules which is in part attractive and in part repulsive. Aggregation resp. clumping of the macromolecules of the crystalline lens, the reasons for light scattering, may be prevented by introducing a number of molecules of various designs into the original macromolecular complex which reduce the tendency of aggregation. Cataract inhibitors of this category may be regarded as effective if they are able to increase the time constant of the normal aging process (i.e. the increment of scatter) by about 20%.

Age Factors↗
PubMed1999

[The electroretinogram (ERG) of the mouse: normal values, optimal stimulation and recording].

PURPOSE: The electroretinogram (ERG) is an appropriate method to evaluate the retinal function in a variety of animal models. In this study we present suitable conditions of stimulation and recording in the dark-adapted mouse. METHODS: Mice (n = 15) were dark-adapted during 14 hours and anesthetized with a single intraperitoneal injection of xylazine/ketamine. Pupils were dilated and a d.c.-silk-silver electrode or a AgCl-contact-lens electrode was placed on the cornea. The electroretinogram (ERG) was obtained by Ganzfeld stimulation over a range of 6 log units of intensity (8 x 10(-2) - 8 x 104 cd/m2). Intensity, duration and the interval of the light stimuli were varied separately. RESULTS: Reproducible values of the intensity-response functions are obtained for the a-, b- and c-waves of the ERG under well controlled adaptation- and stimulus-conditions. C-wave amplitudes are best evaluated using d.c.-recording and a stimulus duration of 4 seconds. The position of the d.c.-silk-silver electrode on the cornea can affect the ERG-amplitudes. Using a contact-lens electrode, the recorded b-wave amplitudes are on average 20% below those recorded with a centrally positioned d.c.-silk-silver electrode. Stimulus-intervals of at least 60 seconds are recommended at high intensities. CONCLUSIONS: An unequivocal assessment of retinal function requires reproducible ERG-values over a wide range of intensities. To obtain these, well controlled and standardized experimental conditions are required.

Animals↗
PubMed1999

High-definition true-colour television for use in minimally invasive medical procedures.

Endoscopes are key elements in the application of minimally invasive medical procedures. Thereby, image quality, ease of application and safety are of decisive importance for the user. This communication is primarily concerned with aspects relating to image quality. Standard television technology is presently used in endoscopes for image presentation purposes. It is however shown, that the inherent optical quality of most endoscopes exceeds the performance of standard TV. Accordingly, a special purpose advanced digital television system exhibiting true colour performance has been developed. Since endoscopic images usually are circular, its aspect ratio is quadratic with a spatial resolution of 1000 x 1000 pixels. It has furthermore a temporal resolution of 1 to 30 Hz noninterlaced and a contrast resolution of 56.6 dB. The design and performance of the system is documented.

Endoscopes↗
PubMed1999

Biconcave contact lenses: a critical analysis of their optical properties.

BACKGROUND AND OBJECTIVE: The purpose of this experiment was to compare biconcave contact lenses with other contact lenses already used for observation and irradiation of the retina and choroid. MATERIALS AND METHODS: The optical performance of different biconcave lenses is described in terms of magnification, resolution, and field of view. The optical properties of the eye were taken into account using the Gullstrand's model of the human eye. RESULTS: The performance of biconcave contact lenses represents a compromise between that of Goldmann's and wide angle indirect contact lenses. An upright image, with good peripheral image quality and an intermediate field of view is characteristic of such design. In addition, laser irradiation with large spot sizes is less hazardous when using such negative contact lenses compared to positive lenses of the same absolute refractive power. CONCLUSIONS: Biconcave contact lenses qualify as a complement to planoconcave lenses for chorioretinal observation and irradiation tasks. For the same magnification factor, the field of view is smaller than that obtained with indirect contact lenses but the image degradation in the periphery of the retina is reduced.

Contact Lenses↗
PubMed1997

[Rigid endoscope with Gradient-index lenses. Preliminary studies].

PURPOSE: Endoscopes for use in ophthalmology can be manufactured in dimensions smaller than 0.89 mm. MATERIALS: Gradient-index lenses that give a higher resolution than fiber bundles can be miniaturized down to 0.35 mm. RESULTS: We used this new endoscope in 6 eyes of 6 patients during anterior segment surgery. Preliminary clinical experience has demonstrated the usefulness and practical application of this new instrument. CONCLUSION: The clear views the instrument provides of the ciliary sulcus and ciliary body behind the iris make it useful in secondary posterior chamber intraocular lens implantation, retroprosthetic membrane behind keratoprosthesis, Molteno valve, and in endolaser photocoagulation.

Aged↗
PubMed1996

Lasers, optical systems and safety in ophthalmology: a review.

This is a review of optical methods related to biomicroscopy and laser treatment of the posterior segment of the eye. Contact lenses can be used to observe optical structures and couple laser radiation into the eye for a vast range of conditions and techniques. A small laser spot size is indispensable for photodisruptive work, though this requires a large beam diameter at the pupil and therefore optical systems and techniques such as scleral indentation which maximize the pupillary beam diameter are preferred. For coagulation work the choice of beam focusing optics is crucial for optimum safety. Vitreous replacement can be used to change the refractive power of the eye and permit new combinations of treatment and optical systems. This review covers many aspects of laser irradiation of the eye. It should be clear that, with the multitude of different procedures and optical systems involved, the laser surgeon is faced with a daunting task in assessing and meeting safety limits.

Contact Lenses↗
PubMed1996

Bright light therapy in focus: lamp emission spectra and ocular safety.

In recent years, bright light treatment of seasonal affective disorder (SAD), recurrent depressions in fall and winter, has been discovered. Newer applications include circadian sleep phase disorder, shift work and jet lag. Apart from creating the visual signal, light can modify retinal structure and physiology. UV and visible light lead to distinct lesions of ocular tissues under certain experimental und naturalistic conditions. In light therapy, a large variety of fixtures is used but the spectral emission of lamps is mostly unknown to the user and clinician leading to the potential hazard of ocular lesions. Therefore, we have analyzed a wide selection of light sources commonly used for treatment. We measured the spectral emission and calculated irradiant doses for several light therapy regimens. Based on these measurements, potential hazards are analyzed, physiological mechanisms of light action are discussed and safety measures for bright light therapy are proposed. They include recommendations for lamps devoid of damaging spectral emissions and standardized therapy fixtures, ophthalmological monitoring of patients with eye diseases and control by optometrists for patients with healthy eyes who are likely to undergo light treatment for extended periods.

Equipment Safety↗
PubMed1996

A new laser scalpel--a brief report.

One may consider the clad silica fibre cutting probe as a cheap alternative of the popular sapphire probe, sharing some of its properties. Made of silica, the scalpels have a fair heat tolerance and may be used without cooling by liquids or gas as is necessary with sapphire blades. The laser scalpel described here is driven (powered) with a 10 W cw Nd:YAG laser energy source (1064 nm) and possesses good cutting and haemostatic properties. It may also be used with lasers emitting other wavelengths. One may assume that a diode laser emitting in the near infrared (800-810 nm) may have very similar, although no analogous cutting properties when used with the described scalpel.

Equipment Design↗
PubMed1995

[Critical thoughts on current laser surgery of the cornea].

OBJECTIVE: To analyze critically refractive surgery of the cornea by excimer laser and to compare laser surgery with other methods of treatment of refractive errors of the eye. MATERIAL AND METHODS: This analysis has to be restricted to a comparison of the treatment of myopia by keratotomy and photoablation with the ArF excimer laser. Correction of hypermetropia and of astigmatismus has to be left out, along with all the other methods to correct myopia, such as glasses, contact lenses, keratomileusis, epikeratoplasty, alloplastic implants, implantation of intraocular lenses with negative power, and replacement of the clear lens by an posterior chamber lens. The essential literature is screened. For intrastromal ablation with the picosecond Nd:YLF laser we relay on own experiences, also with the use of the ArF excimer laser we are not without own experiences. RESULTS AND STATEMENTS: For comparison of refractive surgery of the cornea not only the PERK study and the recommendations of the American Academy of Ophthalmology have to be considered, but also the newest developments in radial keratotomy such as two-step incision and reoperation with reopening of the keratotomy wounds. With these techniques the same precision can be reached as with the excimerlaser, and also higher myopias can be corrected. The dangers of the procedure, such as infection, perforation at surgery or laceration by contusion remain much larger. Intrastromal photoablation did not reach clinical maturity. Superficial photoablation is an almost safe procedure. A reduction of 3 D of myopia can be reached with satisfying precision, although higher myopias are still a problem. Pain following the ablation is considerable. Haze and disturbed vision at night can be present; infectious keratitis is rare, but possible. CONCLUSIONS: The critical fact of both procedures, keratotomy and photoablation with excimer laser, remains that healthy eyes are treated; therefore, even rare complications weigh much heavier than if sick eyes are treated. Because this is cosmetic surgery, the individuum asking for this type of procedure has to pay for on his own. Olson demands: "In determining when new technology is acceptable, we must consider the financial cost and the expected benefit to society. Is it an equitable tradeoff?" If we look at refractive surgery, especially laser photoablation, in the context of the needs for ophthalmic care of the whole world, then this type of surgery is out of proportion. The balance could be restored if, with every laser application, funds were given for third-world projects. Excimer-laser surgery may be justified insofar as the research with these lasers leads to useful therapeutic methods.

Follow-Up Studies↗
PubMed1994

[GRIN-endoscopy for laser treatment in ophthalmology].

Endoscopes for use in ophthalmology can be manufactured with diameters smaller than 0.89 mm. Because gradient-index (GRIN) lenses yield a higher resolution than ordered fiber bundles having the same diameter, GRIN lenses with a diameter of either 0.35 mm or 0.50 mm were utilized to manufacture thin high resolution endoscopes. Whatever the working distance, the resolution obtained with a GRIN lens having a diameter of 0.50 mm was higher than that obtained with a GRIN lens of 0.35 mm. Thanks to the miniaturization, an additional working channel could also be integrated within the endoscope. This allowed new combinations of various surgical instruments. This channel can be used as a guide for an optical fiber for laser therapy or as an irrigation/aspiration channel. The use of such an instrument where the observation path is parallel to the surgical instrument was compared to the application of the endoscope as a separate monitoring system. The advantages and inconveniences of both systems are discussed. Preference is given to a system where the diameter of the observation channel is maximum and the optical fiber for laser delivery is integrated but adjustable along its length within the endoscope.

Endoscopes↗
PubMed1993

[Surgery with the laser scalpel. Physical principles and clinical effectiveness].

BACKGROUND: The conventional surgical method for cutting vascularized tissue with scalpel and scissors may now be improved by use of the laser scalpel. In particular, the frequent interruption necessitated and the poor visibility caused by bleeding may be mitigated owing to the haemostatic properties of laser light. This instrument may be of particular value for tasks involving extrabulbar structures, such as extraocular muscles and lacrimal tissue, as well as for facial surgery. MATERIALS AND METHODS: The mode of action and physical properties of a new laser scalpel are described and its characteristics compared with those of other instruments on the market. The probe consists of a clad, sculptured silica fibre with a core diameter of 0.6 mm and a conical 0.15 mm-diameter cutting tip. Radiation generated by a low cw-Nd:YAG laser module is fed into the probe, at the exit point of which a maximal power density of 57 kW/cm2 is attained. Radiated laser energy penetrates the tissue as an incision is made, thereby inducing an efficient blood flow stasis which is amplified by thermal energy diffusing from the immediate surroundings of the scalpel tip. RESULTS: In this report, the laser scalpel is implemented for the excision of a vascularized, amelanotic, facial naevus. Both the cutting and haemostatic effects were found to be excellent, occurrence of the latter phenomenon being supported by ultrastructural findings. The healing response was comparable to that observed after conventional surgery. CONCLUSION: The new laser scalpel represents an inexpensive and effective cutting and haemostatic tool powered by a standard cw Nd:YAG laser module, with a wide spectrum of potential applications.

Aged↗
PubMed1992

Devices for the control of laser transmission across the sclera during transscleral photocoagulation.

Improving the reproducibility of transscleral photocoagulation necessitates controlling the transmission of the laser beam through the sclera. Two factors make such control problematic: the locally increased transparency of the sclera resulting from the contact procedure and the occurrence of time-related relaxation phenomena. Two instruments have been devised to help control these factors. The first is a mechanical compensation unit comprised of magnets and a spring that allows the force exerted on the sclera to be adjusted to between 0.1 and 0.4 N, the pressure being determined by the outer diameter of the contact tip. The second instrument monitors the portion of the aiming beam reflected by the sclera as a means of determining the exact level of power actually transmitted through it. This information theoretically could be fed back to the treatment laser, allowing the level of power being delivered to be adjusted accordingly.

Ciliary Body↗
PubMed1990

[Multifocal diffraction contact lens as an indicator of subjective tolerance of a multifocal diffraction intraocular lens].

The tolerance of a multifocal diffraction contact lens was tested on the better eye (20/40) in a group of twenty cataract patients. The results were later compared with the postoperative tolerance of a multifocal diffraction intraocular lens. Patients manifesting problems with the multifocal contact lens are more likely to have problems with the multifocal intraocular lens. But since the intraocular lens is tolerated much better than the contact lens, this preoperative test would unnecessarily exclude some patients from the benefits of a multifocal diffraction intraocular lens.

Aged↗