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Biomedical subjects

D J Keegan

Publications and source records attributed to D J Keegan.

12 recordsLinked to original sources
PubMed2005

High resolution imaging of fluorescein patterns in RCS rat retinae and their direct correlation with histology.

To assess the progressive changes in the retinal vascular bed of dystrophic and non-dystrophic Royal College of Surgeons (RCS) rats, retinae, were visualised correlating in vivo fundus fluorescein angiography (FA) with histology. FA was performed in rats aged 5 weeks to 2 years, using a Zeiss confocal scanning laser ophthalmoscope (cSLO). After the final imaging session, a subset of retinae were prepared for flat-mount histology and the vascular bed was visualised using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) staining. While non-dystrophic rat retinae showed no substantive changes in vascular patterns with age and no demonstrable fluorescein leakage up to at least 1 year, dystrophic rat retinae showed abnormal vascular formations, demonstrable on FA and NADPH-d staining, which could be correlated in single retinae. Hyperfluorescent spots and late angiographic leakage were evident beginning at 10 weeks and progressed in severity with time: they were coincident in distribution with abnormal histological vascular complexes. The ability to monitor the same retina serially makes this approach a valuable tool for studying the dynamics of vascular change in the diseased retina, not only during the course of degeneration but also when assessing efficacy of potential therapeutic approaches.

Animals↗
PubMed2005

Primary cutaneous mucinous carcinoma of the eyelid in a young male.

Primary cutaneous mucinous carcinoma of the eyelid is an adenocarcinoma of the eccrine glands. It is rare and locally aggressive but the prognosis following local excision, confirmed with tumour-free margins, is good. This tumour is usually described in the elderly. We present the occurrence, clinical and histological features, and management of this tumour in a young male.A 36-year-old male presented with a small cystic right lower lid lesion, which had increased in size and pigmentation over two years. He underwent excision biopsy for diagnostic purposes followed by Moh's micrographic surgical removal. The defect was repaired with an upper eyelid skin graft. A full oncological screen including whole-body computed tomography scan excluded the presence of primary mucinous carcinoma elsewhere and any metastatic spread. There has been no recurrence of tumour 18 months following excision. Ophthalmologists should be aware of the occurrence of this tumour in a younger age group than previously described. Moh's micrographic surgery is the most suitable method of treatment following exclusion of both distant primaries and metastases.

Adenocarcinoma, Mucinous↗
PubMed2003

Retinal transplantation: progress and problems in clinical application.

There is currently no real treatment for blinding disorders that stem from the degeneration of cells in the retina and affect at least 50 million individuals worldwide. The excitement that accompanied the first studies showing the potential of retinal cell transplantation to alleviate the progress of blindness in such diseases as retinitis pigmentosa and age-related macular degeneration has lost some of its momentum, as attempts to apply research to the clinic have failed so far to provide effective treatments. What these studies have shown, however, is not that the approach is flawed but rather that the steps that need to be taken to achieve a viable, clinical treatment are many. This review summarizes the course of retinal transplant studies and points to obstacles that still need to be overcome to improve graft survival and efficacy and to develop a protocol that is effective in a clinical setting. Emphasis is given particularly to the consequences of introducing transplants to sites that have been considered immunologically privileged and to the role of the major histocompatibility complex classes I and II molecules in graft survival and rejection.

Animals↗
PubMed2002

Preservation of visual responsiveness in the superior colliculus of RCS rats after retinal pigment epithelium cell transplantation.

The dystrophic RCS rat undergoes progressive photoreceptor degeneration due to a primary defect in retinal pigment epithelial (RPE) cells. This has a major impact on central visual responsiveness. Here we have examined how functional deterioration is contained by subretinal transplantation of immortalized human RPE cells. Transplantation was done at three to four weeks of age prior to significant photoreceptor loss and recipients were kept on cyclosporin. At six months of age, sensitivity maps and multi-unit response properties were obtained across the visual field by recording at 76 equidistant sites encompassing the whole superior colliculus.A significant degree of functional protection, both in terms of area of responsive retina and response characteristics was observed following RPE transplantation. At best, the sensitivity, latency of onset, and response rise time were all maintained within normal ranges and this was achieved with no more than half of the normal complement of photoreceptors. Although partial, the degree of anatomical preservation (both in terms of outer nuclear layer thickness and area of rescue) correlated well with the level of preserved visual sensitivities. Sham injections also resulted in rescue, though the area of preservation was strictly confined to the needle injury site and the response properties were significantly worse than with RPE injections. This study shows that central physiological responsiveness and correlated retinal morphology can be preserved in an animal model of retinal disease by implantation of an immortalized cell line. The use of retinal sensitivity measurements provides a background for assessing higher visual functions in these animals and a direct comparison for human perimetry measures.

Action Potentials↗
PubMed2002

Long-term preservation of cortically dependent visual function in RCS rats by transplantation.

Cell transplantation is one way of limiting the progress of retinal degeneration in animal models of blinding diseases such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Here we transplanted a human retinal pigment epithelial (RPE) cell line into the subretinal space of one such model, the Royal College of Surgeons (RCS) rat, and showed, using head tracking to moving stripes and pattern discrimination in conjunction with single-unit cortical physiology, that cortically mediated vision can be preserved with this treatment.

Animals↗
PubMed2001

Subretinal transplantation of genetically modified human cell lines attenuates loss of visual function in dystrophic rats.

Royal College of Surgeons rats are genetically predisposed to undergo significant visual loss caused by a primary dysfunction of retinal pigment epithelial (RPE) cells. By using this model, we have examined the efficacy of subretinal transplantation of two independent human RPE cell lines each exhibiting genetic modifications that confer long-term stability in vitro. The two cell lines, a spontaneously derived cell line (ARPE19) and an extensively characterized genetically engineered human RPE cell line (h1RPE7), which expresses SV40 large T (tumor) antigen, were evaluated separately. Both lines result in a significant preservation of visual function as assessed by either behavioral or physiological techniques. This attenuation of visual loss correlates with photoreceptor survival and the presence of donor cells in the areas of rescued photoreceptors at 5 months postgrafting (6 months of age). These results demonstrate the potential of genetically modified human RPE cells for ultimate application in therapeutic transplantation strategies for retinal degenerative diseases caused by RPE dysfunction.

Animals↗
PubMed2001

Cell transplantation as a treatment for retinal disease.

It has been shown that photoreceptor degeneration can be limited in experimental animals by transplantation of fresh RPE to the subretinal space. There is also evidence that retinal cell transplants can be used to reconstruct retinal circuitry in dystrophic animals. Here we describe and review recent developments that highlight the necessary steps that should be taken prior to embarking on clinical trials in humans.

Animals↗
PubMed2000

Schwann cell grafting into the retina of the dystrophic RCS rat limits functional deterioration. Royal College of Surgeons.

PURPOSE: To examine whether congenic Schwann cells grafted into the subretinal space of dystrophic Royal College of Surgeons (RCS) rats can prevent photoreceptor loss and maintain visual function. METHODS: Purified neonatal Schwann cells derived from congenic rats were grafted into the subretinal space of 3- to 4-week-old dystrophic RCS rats. Graft placement was confirmed using Schwann cells labeled in vitro with the fluorescent dye Hoechst 33342 or in grafted eyes processed for electron microscopy (48-hour to 1-month survival). At longer intervals, up to 9 months after surgery, animals were examined for photoreceptor survival; preservation of a visual reflex, head-tracking to moving stripes; and preservation of visual receptive fields associated with the region of graft placement. RESULTS: One week after the graft was performed, Schwann cells had integrated into the subretinal space with little evidence of a reactive response. When screened for head-tracking to moving stripes, Schwann cell-grafted animals performed better than sham-treated or control dystrophic animals. Threshold sensitivity measurements and visual field assessment made by recording from the superior colliculus also showed a significant level of preserved function compared with control animals. Functional rescue was correlated with photoreceptor survival and could be observed for at least 9 months after grafting. CONCLUSIONS: Schwann cells injected into the subretinal space limit functional deterioration and prolong photoreceptor survival. It is suggested that they act by local release of growth factors that either support photoreceptors directly and/or stimulate phagocytosis in RPE cells.

Animals↗
PubMed1998

Immunocytochemical identification of endocrine cells in the pancreas of the fruit bat, Rousettus aegyptiacus.

The fruit bat, Rousettus aegyptiacus, is able to absorb large amounts of glucose in very short periods of time. This ability is partly reflected by the structure of the gastrointestinal tract and pancreas. The aim of this study was to confirm preliminary histochemical studies of the bat pancreas and to identify and quantitate endocrine cells by immunocytochemical techniques in order to understand the ability of the bat to absorb these large amounts of glucose. Endocrine cells were distributed in islets throughout the gland and also occurred as discrete cells in the exocrine ducts. Three-dimensional reconstruction and quantitation showed that the endocrine component of the pancreas occupied 9.1% of the total volume. This is far more than that reported in any other species. Four endocrine cell types were demonstrated. Insulin (beta) cells (51.4%) were located throughout the islet and extended between the glucagon (alpha) cells (30.6%). Somatotostatin (delta) cells (8.8%) and pancreatic polypeptide (PP) cells (17.1%) were irregularly scattered throughout the islets. While the percentage of alpha, beta, and delta cells was similar to that in other species, the percentage of PP cells was higher. The high percentage of endocrine tissue found in the pancreas of the fruit bat may reflect metabolic adaptations involved in the absorption of the high carbohydrate diet of this animal.

Animals↗
PubMed1993

Thoracic outlet syndrome: a useful exercise treatment option.

The current study is a prospective evaluation of a supervised physiotherapy program of graduated resisted shoulder elevation exercises in eight patients with thoracic outlet syndrome. All had severe neurovascular symptoms and limited neck movements before treatment. After 3 weeks of intervention, symptoms had significantly improved in all patients, and all achieved a full range of cervical neck and shoulder movement. This study confirms the efficacy of a simple treatment program for patients with thoracic outlet syndrome.

Adult↗