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Biomedical subjects

F M Barker

Publications and source records attributed to F M Barker.

At least 19 recordsLinked to original sources
PubMed2001

Influence of near-ultraviolet radiation on reproductive and immunological development in juvenile male Siberian hamsters.

The aim of this study was to characterize the lenticular ultraviolet transmission of the Siberian hamster (Phodopus sungorus) and to probe the range of near-ultraviolet (UV-A, 315-400 nm) and visible wavelengths (400-760 nm) for modulating the photoperiodic regulation of its reproductive and immune systems. Ocular lenses from adult hamsters were found to transmit UV-A wavelengths at similar levels to visible wavelengths, with a short-wavelength cut-off of 300 nm. Five separate studies compared the responses of juvenile male hamsters to long photoperiods (16 h:8 h L:D), short photoperiods (10 h:14 h L:D) and short photoperiods interrupted by an equal photon pulse of monochromatic light of 320, 340, 360, 500 or 725 nm during the night. The results show that UV-A wavelengths at 320, 340 and 360 nm can regulate both reproductive and immune short-photoperiod responses as effectively as visible monochromatic light at 500 nm. In contrast, long-wavelength visible light at 725 nm did not block the short-photoperiod responses. These results suggest that both wavelengths in the visible spectrum, together with UV-A wavelengths, contribute to hamster photoperiodism in natural habitats.

Animals↗
PubMed2000

Dose dependency of canthaxanthin crystals in monkey retina and spatial distribution of its metabolites.

PURPOSE: To establish the threshold level of canthaxanthin crystals in the retina of cynomolgus monkeys. To correlate the spatial distribution of all-trans canthaxanthin and its metabolites with the grade of crystals. METHODS: Monkeys were orally administered 0, 0.2, 0.6, 1.8, 5.4, 16.2, and 48.6 mg/kg body wt canthaxanthin daily for 2.5 to 3 years. A second group of monkeys were administered 200 and 500 mg/kg body wt/d for 5 years. Ophthalmoscopy, electroretinography (ERG), retina and carotenoid analysis were performed as previously reported. RESULTS: Crystals in the retina periphery were observed by ophthalmoscopy preterminally only in the extreme high doses of 200 to 500 mg/kg body wt/d. There were no adverse effects on visual functions as measured by ERG. Crystals in the peripheral retina, and/or in the macula, were detected microscopically in all canthaxanthin treated groups except at the lowest dose of 0.2 mg/kg body wt/d. The grade of crystals increased up to a dose of 16.2 mg/kg body wt/d. Dose-dependent increases in canthaxanthin content also were noted in the retina, the liver, and in plasma. All-trans canthaxanthin was the major compound in the peripheral and paracentral retina of very highly dosed animals, where its concentration correlated largely with the grade of inclusions. In the macula, 4'-OH-echinenone was the dominant canthaxanthin metabolite. CONCLUSIONS: The grade of crystals in monkey retinas was dose dependent with a threshold level at 0.6 mg canthaxanthin/kg body wt/d. It correlated in the retinal periphery with the concentrations of all-trans-canthaxanthin and in the macula with its metabolites.

Administration, Oral↗
PubMed1997

Occurrence of birefringent retinal inclusions in cynomolgus monkeys after high doses of canthaxanthin.

PURPOSE: To reproduce and investigate in a primate animal model the phenomenon of the red carotenoid canthaxanthin (beta, beta-carotene-4'4'-dione) to induce crystal-like retinal deposits as they have been observed in the ocular fundus of humans after high canthaxanthin intake (i.e., more than 30 mg/day). METHODS: Groups of four cynomolgus monkeys (Macaca fascicularis) per gender and dose were administered 5.4, 16.2, or 48.6 mg canthaxanthin/kg body weight daily by oral gavage for 2.5 years. Eight control animals received placebo. In vivo ophthalmoscopy was performed at intervals of 3 months along with electroretinography after 12 and 24 months and retinal biomicroscopy just before the monkeys were killed. Retinal wholemounts or frozen sections were investigated postmortem by polarization, bright field, and differential interference contrast microscopy. Retinal and preterminal plasma canthaxanthin concentrations were determined by high-performance liquid chromatography (HPLC). RESULTS: By ophthalmoscopy and retinal biomicroscopy in vivo, no crystals or other light-reflecting particles were observed in the central paramacular retina. However, postmortem polarization microscopy of all 24 canthaxanthin-treated animals showed a circular zone in the peripheral retina containing birefringent, polymorphous red, orange, or white inclusions. The density of these inclusions was diminished within 1 to 8 mm posterior to the ora serrata. These inclusions were located mainly in the inner retinal layers, that is the nerve fiber layer and ganglion cell layer, inner plexiform layer, and inner nuclear layer. Twelve of the 24 canthaxanthin-treated animals showed yellow, golden birefringent inclusions in the macula. Retinas of placebo-treated monkeys were free of birefringent, crystal-like inclusions. The HPLC confirmed the presence of all-trans canthaxanthin, and 4-OH-echinenone and isozeaxanthin as well, in the retinas of all canthaxanthin-treated animals. Neither electroretinography nor histopathology indicated any adverse effects of the canthaxanthin-induced retinal inclusions seen in this study. CONCLUSIONS: A high intake of canthaxanthin for 2.5 years led to the deposition of crystal-like birefringent inclusions in the inner layers of the peripheral retina and, to some extent, the central retina of cynomolgus monkeys. The presence of these deposits did not interfere with morphology nor with retinal function.

Animals↗
PubMed1995

Laser hazards and safety.

Lasers are a key component of the vision practitioner's arsenal of care, and provide a wonderful new frontier of diagnostic and therapeutic options. In light of their expanded utilization, it is crucial that eye care practitioners have a thorough understanding of potential laser hazards and the regulations that establish guidelines for their safe application. This review describes the American National Standards Institute (ANSI) standards applicable to the safe use of lasers (Z 136.1) and the safe use of lasers in health care facilities (Z 136.3). Laser hazard classification, the organization of a laser safety program, and administrative and procedural controls are included.

Equipment Safety↗
PubMed1994

Ultraviolet regulation of neuroendocrine and circadian physiology in rodents.

UV wavelengths can regulate neuroendocrine and circadian responses in some rodent species. Appropriately timed UV exposures can block the short photoperiod-induced collapse of the reproductive system, cause a rapid suppression of nocturnal melatonin synthesis, regulate melatonin rhythms and phase shift wheel running rhythms. These biological effects of UV are not dependent on the Harderian gland or melanin in the eye, but appear to be related to the degree of transmission through the ocular lens. Such results are consistent with the hypothesis that elements in the retina can transduce UV stimuli for circadian and neuroendocrine regulation.

Albinism↗
PubMed1994

Effect of depth upon the smoothness of excimer laser corneal ablation.

The Argon Fluoride (ArF) Excimer laser is currently used for experimental reshaping of the front surface of the cornea for the correction of myopic refractive error (photorefractive keratectomy, PRK) and for smoothing corneal irregularities (phototherapeutic keratectomy, PTK). Both PRK and PTK are in FDA clinical trials, but are more readily available outside the U.S.A. These techniques have achieved reasonable success in spite of early reports that deeper ablation procedures can cause reduced corneal clarity (haze) or a result which is less accurate or tends to regress. We studied how different depths of excimer tissue removal affect the smoothness of the ablation zone of the rabbit cornea. Dutch belted rabbits were immediately sacrificed by pentobarbital overdose. Their corneas were de-epithelialized with a knife or by the excimer laser and then were photoablated. A 4.5-mm circular ablation beam was delivered to each denuded area, but the beam was masked by positioning a steel blade to partially block the laser beam, thus creating variable ablation depths corresponding to 0.0, 12.5, 37.5, and 62.5 microns. The eyes were fixed in situ by topical and anterior chamber application of glutaraldehyde and the corneas were excised after 5 min and placed in glutaraldehyde for tissue processing. The corneas were whole-mounted and examined by scanning electron microscopy (SEM). The resultant micrographs show increasing irregularity of the ablated surface as a function of depth. The irregularity appeared to be due largely to the inhomogeneities of the anterior stroma, which is known to be layered by alternately directed collagen fibrils.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Effect of corneal edema upon the smoothness of excimer laser ablation.

We studied the effect of corneal hydration upon ablation rate in excimer laser photorefractive keratectomy (PRK). This variable may alter the subepithelial smoothness and the resulting clarity of the result. The eyes of freshly slaughtered pigs (N = 5) and the eyes of Dutch-belted rabbits (N = 4) (in vivo) were de-epithelialized and central ablation zones 3.0 to 4.5 mm in diameter were produced in the subepithelial corneal layers using a 193 nm argon fluoride (ArF) ophthalmic excimer laser. Ablation was performed immediately or after a 15-min incubation period in distilled water as a means of inducing corneal edema. Smoothness was evaluated using specular reflection microscopy and showed the water-treated surface to be increasingly less regular than the nonwater-treated samples. Water treatment may affect the final outcome of the PRK procedure and indicates the need to monitor the preoperative cornea for the development of any edema, especially after the epithelium is removed.

Animals↗
PubMed1992

Review of Horner's syndrome and a case report.

Sympathetic denervation of the eye [Horner's Syndrome (HS)] usually presents as ptosis, miosis, and facial anhydrosis. HS presents a challenge to the clinician because the causative lesion may involve a first, second, or third-order neuron. This paper reviews the literature regarding HS, the anatomy of the sympathetic pathway to the eye, the diagnosis, and the localization of the lesion. Our patient developed reversible HS after a migrainous episode which presumably caused "bruising" of the sympathetic plexus within the carotid canal.

Female↗
PubMed1990

Does the ANSI Z80.3 nonprescription sunglass and fashion eyewear standard go far enough?

The recent public concern regarding sunglass protection from UV energy has sparked a significant debate among those in the research community and industry. This debate grows out of concern for the known effects of UV energy in producing or contributing to eye effects such as keratitis, cataract formation, and retinal damage. The ANSI Z80.3 Standard addresses itself to this issue by setting levels of UV energy that are permitted to be transmitted in various labeling categories for over-the-counter sunlenses. One important issue is that the ANSI Standard does not provide for an absolute block of UV energy in any category of these lenses. Because the technology to provide this sort of total UV block is currently available, it is argued that there should be at least one category of lens that is fully protective in the UV range.

Animals↗
PubMed1990

Auxiliary lenses in fundus biomicroscopy--a comparison of fields of view.

The use of the biomicroscope in fundus examination requires an auxiliary lens to overcome the high focal convergence of the eye. This study presents the results of subjective field of view determinations with a variety of auxiliary biomicroscopy lenses. Direct/mirror view Goldmann type contact lenses demonstrated the smallest field in the range of 25-30 degrees. Indirect view pre-corneal condensing lenses were about twice this amount in their field. Wide field indirect view lenses with contact lens elements (Rodenstock Panfunduscope, Mainster retinal lens, Volk Quadraspheric) range between 85 and 125 degrees d of field. The use of each type of lens in routine and specialized examination of the fundus as well as in photocoagulation are discussed.

Fundus Oculi↗
PubMed1990

Ultra wide field fundus biomicroscopy with the Volk Quadraspheric lens.

Fundus biomicroscopy as a clinical technique has been enhanced significantly by the addition of indirect view condensing lenses. The combination of this type of lens with a corneal contact element allows higher power and better stability so that a wider field can be obtained. The Panfunduscope of Schlegel and the Mainster retinal lens are examples of this design that have been successfully applied to both examination and to pan-retinal photocoagulation. Volk has recently introduced a new aspheric design indirect contact lens system which is higher in power and provides a wider field of view (125 degrees) than previously obtainable. This article describes the optical properties and use of the Quadraspheric lens.

Evaluation Studies as Topic↗
PubMed1989

Monitoring of patients taking canthaxanthin and carotene: an electroretinographic and ophthalmological survey.

1. Patients who have taken canthaxanthin and beta-carotene to avert phototoxicity have been monitored by electroretinographic testing. 2. Patients took the compounds only during the summer months, but were monitored for more than 1 year to determine if seasonal changes in the ERG were visible. 3. The characteristic refractile retinal crystals reduced during the winter. 4. The scotopic b-wave amplitude increased during the winter, whether evoked by red or blue flashes. 5. No other ERG parameter altered. 6. Changes noted in 3 and 4 above are reversible. 7. A dose/ERG-amplitude response relationship was established, but no correlation between blood level or total cumulative dose and b-wave amplitude could be found. 8. It is suggested that the Müller cells concentrate canthaxanthin and this is the mechanism which affects the ERG.

Aged↗
PubMed1988

The Volk steady mount holder for the +90D lens.

Since its introduction in early 1985, the Volk +90D lens has become a very popular auxiliary lens for biomicroscopic fundus evaluation. The Volk +90D lens provides a wide field of view which is accessible by simple scanning of the biomicroscope. The necessity to hand hold the lens, however, has not always provided enough stability, particularly for the novice user. This article describes a newly introduced holder for the Volk +90D lens which mounts on the base of the biomicroscope headrest providing rapid and stable lens placement. Use of this holder improves the technique of retinal examination and photography by stabilizing the image and by freeing both hands to operate the slit lamp biomicroscope. The enhanced stability afforded by this holder also gives the examiner the practical capability of viewing the posterior pole without mydriasis.

Equipment Design↗
PubMed1987

Vitreoretinal biomicroscopy: a comparison of techniques.

A description is made of the uses of the Hruby lens, the Goldmann 3-mirror lens, and the recently introduced Volk +90D lens for biomicroscopic examination of the fundus. The optical principles and clinical techniques of each lens are discussed along with their advantages and disadvantages. The Hruby lens is shown as a convenient technique that is easy to learn. Hruby lens benefits are qualified due to its relatively low field of view and due to the need for excellent patient cooperation to achieve the exact retinal view desired. The Goldmann 3-mirror contact lens is supported as an important clinical technique because of its reliability in providing clear views of the central and peripheral retina. The Volk lens is cited as providing the widest retinal field of view possible with the biomicroscope without the need for corneal contact.

Humans↗
PubMed1986

Ocular effects of treatment with various psoralen derivatives and ultraviolet-A (UVA) radiation in HRA/Skh hairless mice.

Hairless (HRA/Skh) mice were administered one of four dietary concentrations (50, 100, 625 or 1250 ppm) of 8-methoxypsoralen (8-MOP) or 5-methoxypsoralen (5-MOP), or molar equivalent concentrations of 5-methylisopsoralen (5-MIP) or 3-carbethoxypsoralen (3-CPS) by 'pulse feeding' technique, 3 days per week for 13 weeks. For the final 11 weeks psoralen derivative administration was followed by exposure to 0.2 or 48 J/cm2 of unfiltered ultraviolet-A (UVA) radiant energy from FR74T12PUVA lamps. At 0 and 13 weeks eyes were dilated with 0.2% atropine solution and were examined using a binocular indirect ophthalmoscope with a +20.0 D condensing lens. The lids, cornea, anterior chamber and the lens were evaluated for pathological changes. Ocular damage consisting of dense central corneal opacification was seen at significant levels in animals given 8-MOP or 5-MOP and exposed to UVA. In addition, opacities in the area of the posterior lens were seen in all experimental groups and appeared to be related to drug treatment, independent of light exposure, and therefore appeared not to be related to drug-light interaction. Some corneal and lenticular opacification was seen at non-significant levels in all experimental and control groups.

5-Methoxypsoralen↗