Investigative ophthalmology最新文献

In Part I1 of this study, the thermolability of lens hexokinase was implicated in the development of an experimental "hypoglycemic" cataract. After eight hours of glucose deprivation, there is a precipitous loss of lens hexokinase. This occurs approximately nine hours prior to the disorganization of the other enzymatic steps in glycolysis. Epithelial hexokinase, as an immediate response to glucose deficiency, shifts from the soluble to the insoluble phase. There is no such shift in the cortex-nucleus where only soluble hexokinase is found. After eight hours of glucose deprivation, both soluble and insoluble hexokinases throughout the lens undergo rapid deactivations. During the first eight hours of glucose deprivation the loss of lenticular ATP and K+ and the gain in wet weight can be reversed by restoring normal glucose levels; beyond eight hours the changes are irreversible. During the period of reversibility, hexokinase activity levels are normal; during the period of irreversibility hexokinase activity is 10 to 20 per cent of normal. Of the substances tested (mannose, galactose, fructose, glutamine, adenosine) only mannose could sustain the lens in the absnece of glucose. Neither endogenous free glucose nor glycogen could sustain the lens in the face of glucose deprivation. There appear to be no alternative exogenous or endogenous energy yielding substrates. The younger the animal, the more susceptible is its lens to glucose deprivation. This most certainly is a reflection of the increased susceptibility of younger lenses to osmotic stress, since lenses in each age group manifested similar changes in hexokinase activity, ATP, Na+, and K+ level.

An addition to the specular microscope is described which allows it to record the thickness of the excised cornea automatically as a function of time. The focus of the instrument is scanned mechanically through the tissue, and the position of the reflecting surfaces is detected by a photo-electric system and marked on a chart recorder. The system is able to follow thickness changes over periods of many hours and with an accuracy greater than obtainable by manual operation. This system has been helpful in the evaluation of a new medium which considerably extends the useful lifetime of the corneal endothelial fluid pump.

Beef eye anterior chambers were perfused with media containing radiolabeled glycogen precursors. Incorporation of 14C from 1-alanine-U-14C into corneal epithelium glycogen suggested the presence of a gluconeogenic pathway in the eye. Failure to isolate radioactive glucose from 1-alanine-U-14C-containing perfusate after passage through the anterior chamber strongly suggests a corneal site for this pathway.

In addition to its centrally mediated hypotensive action, clonidine causes a decrease in intraocular pressure associated with a long-lasting mydriasis. The present study was conducted to determine to what extent this drug-induced pupillary dilation is of central or peripheral origin. Pupil size was observed in cats anesthetized with pentobarbital. Clonidine (1 to 100 mug per kilogram, intravenously) resulted in a dose-dependent increase in pupillary diameter in intact as well as sympathectomized preparations. These same doses of clonidine produce no effect on the eserinized, parasympathectomized iris. Epinephrine administration (0.1 to 30 mug, intra-arterially) produced an equivalent pupillary dilation in all preparations. In addition, clonidine caused a dramatic decrease in postganglionic ciliary nerve activity and both the decreased nerve activity and pupillary dilation were reversed by intravenous administration of yohimbine hydrochloride. These results suggest that the inhibition of parasympathetic tone by clonidine may involve a central adrenergic inhibitory mechanism.

A highly-ordered array of filaments is found within the apical processes of retinal pigmented epithelial cells in monkeys and humans. These filaments, approximately 100 A in diameter and 250 A apart, line the cytoplasmic face of the plasma membrane, in parallel with the long axis of the apical processes. Since these filaments bind rabbit myosin subfrafment-1 to form arrowhead complexes, we conclude that they contain actin. Such membrane-bound actin filaments could have any of several different functions: they could stabilize the apical projections and by so doing play a cytoskeletal role, and/or they could take part in the phagocytosis of shed outer segment discs.

Outflow facility responses to pilocarpine were determined in ten cynomolgus monkey eyes after disinsertion of the ciliary muscle from the scleral spur. The effect of large intravenous dose given on one occasion was compared to the effect of intense topical treatment for 18 to 24 hours on another occasion. The effect of the two modes of treatment differed from eye to eye, but were similar in the individual eye. In some eyes facility rose while in others it fell. The average effect of both treatments was very small.

The potentially teratogenic effect of antiviral drugs, particularly when given systemically, prompted the evaluation of the teratogenic effect of Ara-A when given systemically in doses significantly higher than those used clinically. Under the conditions of this study, neither teratogenic nor embryocidal effects of Ara-A were observed.

Vascularization of the spectacle or brille of the reptile was demonstrated by biomicroscopy, histology, fluorescein (in vivo), and Microfil silicone rubber (in situ) injections. This unusual vascularity provides new evidence for reassessment of the origin and development of this structure, and a useful tool with which to do so.

A biomicroscopic technique for observation of the ciliary process was developed, and cycloscopy and fluorescein cycloscopy have been done as a routine clinical examination. The observations reported here show that a great, previously unimaginable variety of changes in the ciliary process is the usual sequel of congenital or acquired disorders. Fluorescein was seen to leak mainly from the "summit" of the ciliary process in the normal eye. Little or no leakage from the rudimentary ciliary process was seen in cases of aniridia, while vigorous leakage occurring in inflammation or uveal effusion was of particular clinical importance.