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Biomedical subjects

D H Dickson

Publications and source records attributed to D H Dickson.

35 records · Page 2Linked to original sources
PubMed1982

Corneal splitting in the developing lamprey Petromyzon marinus L. eye.

The cornea of the adult lamprey has both dermal (spectacle) and scleral components. These are separated by a thin mucoid layer that allows free movement of the globe. This study has shown that during the larval (ammocoete) stage, the lamprey cornea develops in a manner similar to that of other lower vertebrates. Just prior to the period of transformation to the adult parasite, the outer dermal portion of the ammocoete cornea (spectacle) consists of an anterior stratified columnar epithelium with goblet cells at the surface. The stroma of the dermal cornea consists of a thick outer layer of orthogonally oriented collagen with branching fibroblasts and a thin, loosely organized inner layer with slender elongated fibroblasts. The scleral cornea is lined internally by a flattened monolayer of mesodermal cells, the corneal endothelium. Its narrow stroma is composed entirely of thin, orthogonally arranged, collagen-fiber lamellae, and is bounded externally by a thin continuous mesothelial layer of cells that abuts directly onto the loose stromal component of the dermal cornea. During the early stages of transformation, the anterior epithelium of the dermal cornea becomes stratified squamous in type. Later, the inner loose stroma of the dermal cornea (spectacle) begins to separate from the scleral cornea components, and a third complete mesothelial layer forms a distinct inner border for the dermal cornea. A mucoid layer is formed between the dermal (spectacle) and scleral corneas and remains throughout the adult life.

Animals↗
PubMed1981

An alternative to the flat substrate method of preparing electron microscope autoradiographs.

Difficulty with flat substrate methods of preparing electron microscope autoradiographs has prompted reconsideration and refinement of a technique in which an electron microscope grid is placed beneath the specimen prior to dipping. This technique avoids the problems commonly associated with the direct application of emulsions to specimen grids, and should be considered as an alternative to flat substrate techniques when difficulty with these methods is encountered.

Animals↗
PubMed1979

Retinal development in the lamprey (Petromyzon marinus L.): premetamorphic ammocoete eye.

Development of the retina of the ammocoete begins early in embryogenesis, with the formation of the optic vesicle, but development of the rudimentary eye is suspended and remains arrested during larval life. Prior to the onset of metamorphosis, the retina of the ammocoete is completely undifferentiated, with the exception of a small area (Zone II) surrounding the optic nerve head, where all of the adult retinal layers are found. The photoreceptors in this area have developed to include synaptic contacts as well as inner and outer segments. The pigment epithelium in this area, too, has differentiated to include well-formed melanin granules, myeloid bodies and endoplasmic reticulum and is closely associated with the receptor cell outer segments. With the approach of metamorphosis, differentiation of the remainder of the retina (Zone I) begins, taking place in a radial fashion from the optic nerve head. Differentiating pigment epithelial cells adjacent to the differentiated retinal zone begin to accumulate melanin granules. In the neural retina, junctional complexes are established in the form of an external limiting membrane, and connecting cilia project into the optic ventricle. Photoreceptor differentiation begins with the formation of a mitochondria-filled ellipsoid within the inner segment. Development and differentiation of the ammocoete retina is unique to vertebrates in that only a small area of differentiated retina is present during the larval stage. The remainder of the retina differentiates and becomes functional during metamorphosis.

Animals↗
PubMed1979

Symposium on pseudocapsular exfoliation and glaucoma. Fibrillopathia epitheliocapsularis: review of the nature and origin of pseudoexfoliative deposits.

Although opinions vary to some extent, the general consensus is that the pseudoexfoliative component is an abnormal basement membrane material with amyloid-like characteristics; this is synthesized at a variety of ocular and extraocular sites. The resultant material is found to accumulate within, and in some instances to replace, the normal basement membranes of the producing cells. Also, some of the material detaches and, through aqueous humour dispersal, becomes deposited on a variety of surfaces throughout the anterior segment of the eye.

Amyloid↗
PubMed1976

Synapse formation in retinoblastoma tumours.

Developing photoreceptor-like cells in retinoblastoma tumour fleurettes were found to contain apical tight junctions, mitochondrial-filled inner segment regions with cilia, and basally located synaptic ribbons and vesicles. Synaptic contract appeared to be established with adjacent neuronal-like elements. We suggest that photoreceptor differentiation in retinoblastoma tumours follows a sequence similar to normal human photoreceptor embryogenesis.

Humans↗
PubMed1975

Lens fringe in homocystinuria.

The lens from a patient with homocystinuria was examined by scanning and transmission electron microscopy. A fringe of zonular remnants was found attached to the anterior lens capsule, and was observed to be composed of masses of short filaments in disarray, together with occasional bundles of normal-appearing zonular filaments. Although a pericapsular membrane (zonular lamella) was not observed, the remainder of the lens capsule and epithelium appeared unremarkable. The lens fringe of white zonular remnants may be characteristic, if not pathognomic, for homocystinuria.

Adolescent↗
PubMed1975

Fibrillopathia epitheliocapsularis (pseudoexfoliation): a clinical and electron microscope study.

The light microscopic and transmission and scanning electron microscopic findings from two cases of fibrillopathia epitheliocapsularis (pseudoexfoliation) are presented. The ciliary processes, posterior iris and preequatiorial lens capsule were found to be covered with a fine, white, flocculent material. Light microscopic examination revealed feathery, eosinophilic deposits on all three tissues; electron microscope studies showed the exfoilative deposits to be composed of a fine meshwork of fibrils ranging in size from 200-300 A. Fibrils were found on the apical surfaces of the epithelial cells, as well as on and throughout the epithelial cell basement membranes. The general distribution and possible sources of the pseudoexfoilative material are discussed with respect to other recent investigations. The value of the scanning electron microscope as a tool in pathological studies is presented.

Age Factors↗
PubMed1975

Fine structure and mechanics of the anterior border of the primate iris: a scanning and transmission electron microscope study.

The morphology of the anterior border of the primate iris has been examined by transmission and scanning electron microscopy. The results confirm that the anterior iris is composed of heavily pigmented melanocytes, fibroblasts, and a loosely arranged network of collagen fibres. The melanocytes are slender, elongate structures, which show some branching in the peripheral iris. They run parallel to the surface and are filled with spindle-shaped pigment granules which are oriented in the long axis of the cell. In the miotic state, the peripheral iris melanocytes form a dense, interlacing network. As the pupillary margin is approached, the angles between intersecting melanocytes diminish; the melanocytes appear to be parallel and in close contact with one another.During mydriasis, the peripheral iris melanocytes are compressed and pupillary components are found to intersect at angles greater than 90%. The superficial fibroblasts are flattened cells, closely applied to the underlying melanocyte processes and in the mydriatic iris form a resonably continous monolayer over the anterior iris surface. Iris pores are present, exposing the underlying melanocytes and stromal collagen. During miosis, the surface fibroblasts become attenuated and the pores increase in size and number. This paper demonstrates the value of the scanning electron microscope in presenting an accurate three dimensional model of the iris.

Animals↗