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Biomedical subjects

P Dayhaw-Barker

Publications and source records attributed to P Dayhaw-Barker.

9 recordsLinked to original sources
PubMed2001

The role of the retinal pigment epithelium: topographical variation and ageing changes.

The retinal pigment epithelium (RPE) is a single layer of post-mitotic cells, which functions both as a selective barrier to and a vegetative regulator of the overlying photoreceptor layer, thereby playing a key role in its maintenance. Through the expression and activity of specific proteins, it regulates the transport of nutrients and waste products to and from the retina, it contributes to outer segment renewal by ingesting and degrading the spent tips of photoreceptor outer segments, it protects the outer retina from excessive high-energy light and light-generated oxygen reactive species and maintains retinal homeostasis through the release of diffusible factors. The ageing characteristics of the RPE suggest that in addition to cell loss, pleomorphic changes and loss of intact melanin granules, significant metabolic changes occur resulting, at least in part, from the intracellular accumulation of lipofuscin. This pigment has been shown to be highly phototoxic and has been linked to several oxidative changes, some leading to cell death. While the aetiology of age-related macular degeneration is complex and is as yet unresolved, it is likely that accelerated ageing-like changes in the RPE play a fundamental role in the development of this condition.

Aging↗
PubMed1995

Mechanisms of pathogenesis in diabetes mellitus.

Diabetes mellitus is a syndrome of complex etiology and pathogenesis involving abnormal insulin synthesis, release, binding, and target cell activation. These are manifested differently in the two most common forms of this disease: insulin-dependent diabetes mellitus (IDDM) and noninsulin-dependent diabetes mellitus (NIDDM). Although there still remains much to be discovered to complete our understanding, significant contributions have been made in the last few years by molecular genetics and immunology. This paper reviews many of these facets in contrast to others, which deal primarily with issues of management.

Aldehyde Reductase↗
PubMed1995

The effect of sodium fluorescein on argon green photocoagulation.

BACKGROUND: The absorptive and photosensitizing properties of sodium fluorescein (NaFl) injected prior to laser photocoagulation may affect the retinal laser burn threshold. METHODS: Photocoagulation was performed using an argon green laser with a Volk QuadrAspheric fundus lens in three anesthetized rabbits. Using a 500um spot size and a 100msec duration, varying laser powers were delivered before and at various intervals after intravenous (i.v.) injection of NaFl. RESULTS: Photocoagulation effects were enhanced in all subjects after fluorescein injection with threshold reduced for up to 48 hours following injection. CONCLUSIONS: The effectiveness of photocoagulation following fluorescein angiography may be underestimated, although this may be clinically insignificant since most photocoagulation procedures are performed well above threshold. Nevertheless, these data should be considered in those situations where carefully controlled threshold burns are desired. In such circumstances, it is advisable to take additional care in selecting treatment powers if fluorescein has been injected or to delay photocoagulation for a minimum of 48 hours.

Absorption↗
PubMed1992

Hematological testing.

Hematological testing is a routine aspect of health care. It is invaluable for determining the physiological status of a patient, screening for indicators of systemic disease, determining a differential diagnosis, monitoring the effectiveness of therapeutic drugs, and justifying the management plans of both ocular and systemic conditions. Since doctors of optometry continue to provide a greater spectrum of medical care to patients, it is imperative that appropriate use be made of this important clinical adjunct to the practice of primary care. This paper reviews the use of hematological testing within optometry by discussing the various elements of the complete blood count and by describing selected diseases of the eye and visual system that are associated with hematological disorders.

Blood Cell Count↗
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↗
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↗
PubMed1983

Spectral irradiances of and maximal permissible exposures to two indirect ophthalmoscopes.

Recent reports in the literature have indicated that exposure to certain high intensity sources used in clinical procedures may be damaging to the retina. To investigate this problem, the spectral irradiance of two indirect ophthalmoscopes [American Optical (AO) and Keeler] was measured. The instruments do show operational differences, the most striking of which was the difference in the total irradiance produced at the maximum voltage setting, the Keeler instrument providing nearly 3.6 times greater irradiance than the AO indirect ophthalmoscope. The sources are evaluated as blue light hazards, and maximal permissible exposures (MPE) are calculated and compared to the MPE established by ANSI Z-136 guidelines.

Humans↗