Investigative ophthalmology最新文献

Abnormal tear calcium concentrations, which might be expected in ocular and systemic disorders,may be obscured if tear calcium concentration varies with flow rate. The results of the present study indicated that tear calcium concentration is independent of flow rate with rates faster than those which occur with stimulated overflow tearing (i.e., 2 mu1 per minute), but with slower flow rates such as would be encountered with basal, nonstimulated tear flow, tear calcium concentration increases as flow rate decreases. In addition, at given flow rates, tear calcium concentration is the same as that in at least two components of tears, i.e., lacrimal gland fluid, uncontaminated by fluid from the other orbital glands, and fluid from the other orbital glands, uncontaminated by lcarimal gland fluid. It is apparent that only if calcium concentration is correlated with fluid flow rate will determination of calcium in tears and in the components of tears produce valid information not only about tear calcium levels in the presence of ocular and systemic diseases but also about the mechanism of secretion of calcium by the orbital glands.

The electrical potential difference and electrical resistance of the nonswelling cornea of the dogfish, Squalus acanthias, were examined. It was found that routine procedures used in the procurement of fish invariably produce damage to the corneal epithelium which affects electrical measurements and possibly composition of the aqueous humor. We found no electrical evidence of ionic pumps in the corneal epithelium of this elasmobranch. The electrical resistance of corneas with apparently well-preserved epithelium was 300omega-cm.2 (compared to 30omega-cm.2 in corneas with damaged epithelium).

A new technique for the staining of the corneal endothelium combines the actions of the vital stain trypan blue and the intercellular stain alizarin red S. The technique is an improvement over former staining methods, because it defines both viable and nonviable cells and thereby permits an investigator to accurately quantify endothelial cell damage.

The trabecular meshwork of eyes with open-angle glaucoma has been demonstrated to have an increase in gamma globulin and plasma cells, raising the question of an immunogenic mechanism in this disorder. In the present study, however, immunofluorescence assays on the trabecular meshwork of eyes with open-angle glaucoma were negative for specific immunoglobulins and for complement components that would result specifically from an antigen-antibody reaction. The study fails to provide any evidence in support of an immunogenic mechanism in open-angle glaucoma.

A study has been made of the time courses of the pupillary and intraocular pressure responses of conscious rabbits to clonidine administered either topically or intravenously. Topical unilateral application of clonidine caused transient pupil dilatation and a biphasic intraocular pressure response; an initial hypertensive response preceded a hypotensive phase lasting several hours. Pupillary and hypertensive responses were absent in the untreated eye, but there was a rapid decrease of intraocular pressure. Intravenous administration of clonidine caused an immediate and large decrease of intraocular pressure in both eyes. Phenoxybenzamine given intravenously inhibited the pupillary dilatation and the hypertensive responses to clonidine. The role of efferent adrenergic neuronal activity in mediating the local biphasic pressure response was studied in rabbits with unilateral precervical and postcervical sympathotomy. The results showed the hypotensive response to be dependent on an intact adrenergic innervation of the ocular tissues.

The variation of choline acetyltransferase activity in ocular tissues of four mammalian species, rabbits, cats, cattle, and man, was determined. Enzyme activity of irides and ciliary bodies, i.e., parasympathetically innervated structures, tended to be similar in all four species. Two exceptions were bovine irides and human ciliary bodies; these two tissues had higher enzyme activities. Choline acetyltransferase activity was present in the corneal epithelium of rabbit, bovine, and human eyes, but little or none could be detected in that of cats. Feline retina and pigment epithelium-choroid also contained far less choline acetyltransferase activity than the same tissues in the other three species.

Corneal touch thresholds were determined for both eyes of 15 people with different colored irides (a condition known as heterochromia) and of 25 people with similar colored irides. It was found that corneal sensitivity is not significantly different in both eyes of either group. Therefore it is suggested that the fact previously demonstrated that corneal sensitivity is related to iris color is not of corneal origin.

The effects of paracentesis on the blood-aqueous barrier of cynomolgus monekeys were studied by light and electron microscopy. The following regions of the eye were examined: ciliary body, iris, Schlemm's canal, juxtacanalicular connective tissue, and trabecular meshwork. Prominent structural alterations were seen in the ciliary epithelium at the anterior portion of the pars plicata, but the epithelium at the posterior portion of the pars plicata and at the pars plana appeared less disrupted. Plasma proteins which crossed the capillary endothelium accumulated in the stroma, and appeared in the posterior chamber through the enlarged extracellular spaces of the ciliary epithelium. The plasma proteins in the ciliary stroma of the anterior portion of the pars plicata moved to the stroma of the iris root; whereas in the iris the capillary endothelium provide an impermeable barrier to proteins. Following paracentesis, the lumen of Schlemm's canal was invaded by blood, and through newly formed gaps in the endothelial lining of the inner wall of the canal, the plasma proteins and red blood cells rapidly diffused into the juxtacanalicular connective tissue, trabecular meshwork, and anterior chamber. On the basis of the present experiments, the protein of the aqueous humor can be considered as originating from both the anterior portion of the pars plicata and the inner wall of Schlemm's canal.