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Biomedical subjects

D M Maurice

Publications and source records attributed to D M Maurice.

85 records · Page 5Linked to original sources
PubMed1967

The active transport of fluorescein by the retinal vessels and the retina.

1. The movement of fluorescein across the retinal surface of the rabbit's eye was estimated by measuring the concentration gradient of the dye in the vitreous body. These measurements were made in vivo by means of a slit-lamp fluorophotometer, or were taken from frozen sections of enucleated eyes.2. In the normal eye, fluorescein does not pass from the blood to the vitreous body across any part of the retina. When injected into the vitreous body it passes rapidly out across the entire retinal surface, even against a very large concentration gradient.3. A variety of metabolic and competitive inhibitors, effective in blocking organic anion transport in the kidney and liver, tend to abolish this unidirectional movement of fluorescein across the retina.4. The region occupied by the retinal vessels is more sensitive to inhibition than other areas of the retina. Occlusion of the vessels by diathermy prevents the exchange of fluorescein in this region.5. It appears, then, that there is an active transport of organic anions out of the vitreous body, both by the retinal capillaries and by the retina itself. The latter system is probably located in the pigment epithelium and seems to be carried forward to the rear surface of the iris.6. Since the walls of the retinal vessels of the rabbit are freely in contact with the vitreous body, the active transport must take place across the capillary endothelial cells themselves. These vessels have structural and permeability characteristics found only in the central nervous system and it is to be presumed that the anion transport system is shared by the capillaries of the brain.7. The function of the transport in the retina may be to protect the nervous tissue from toxic materials by preventing their entry from the blood or by removing products of metabolism conjugated as organic anions. Alternatively, the mechanism may be concerned in maintaining the normal adhesion of the retina to the choroid, since retinal detachment was observed to follow its total inhibition.

Animals↗
PubMedDate not supplied

Inflammatory cells, refractive regression, and haze after excimer laser PRK.

OBJECTIVE: To examine the role of inflammatory cell invasion and aspects of tissue reaction on refractive regression and corneal haze after myopic PRK in rabbits. METHODS: Measurements were made for 12 weeks postoperatively of haze intensity, corneal topography, tear cytology, inflammatory cell invasion, subepithelial fibroblast density, and the thickness of the newly laid down connective tissue and of the regrown epithelium. RESULTS: Inflammatory cell invasion could be prevented by fitting a soft contact lens, but this had no effect on the haze or the regression. Haze intensity correlated with subepithelial fibroblast proliferation but not with new connective tissue formation or epithelial hyperplasia. Neither connective tissue nor epithelium regrew in the form of a lens and thus they could not account for regression. Intensive treatment with corticosteroids resulted in a marked reduction in postoperative haze and a slight lessening of long-term regression. Correspondingly, it reduced fibroblast proliferation. CONCLUSIONS: Haze appears, at least in part, to be a result of fibroblast proliferation. Regression is possibly caused by slow distortion of existing tissue rather than the growth of new.

Adrenal Cortex Hormones↗
PubMedDate not supplied

Quantitative measurement of corneal haze after myopic PRK.

OBJECTIVE: To design and evaluate an instrument for the objective measurement of haze in rabbits after myopic PRK. METHODS: A circular fluorescent lamp bulb projected light onto the cornea through a circular collimating aperture covered with an orange filter. The image was collected on a centrally mounted CCD camera and the profile of the haze circle along its horizontal diameter determined. RESULTS: Haze circles were observed and quantitated. In the first weeks, they were donut-shaped, frequently with a central bright area, but later they became square-topped. The instrument reproduced measurements with an error of a few percentage points and showed good long-term stability.

Animals↗
PubMedDate not supplied

Some puzzles in the microscopic structure of the stroma.

The mammalian corneal stroma has some intriguing features related to its lamellar structure. OPTICAL LAMINATION: Stromal sections under the polarizing microscope show birefringent bands that are about 5 times less numerous than the collagenous lamellae seen in transmission electron microscopy (TEM). Scattered light reveals similar laminae in the intact fresh tissue. COHESION: Very thin sections of stroma do not fall apart under water, indicating the presence of a structural framework that holds the collagen fibrils together. SHEAR DISTORTION: The stroma shears very readily in its plane; the shear amplitude increases and then decreases as the tissue hydrates. This suggests that the structural framework is coiled at physiological hydration and can expand about 10 times. FOLDING: When the stroma swells, the lamellae are thrown into waves that lie both in the plane of and perpendicular to its surface. It is difficult to understand how the latter are packed.

Animals↗