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Biomedical subjects

S D Klyce

Publications and source records attributed to S D Klyce.

At least 73 records · Page 4Linked to original sources
PubMed1989

Mechanism of chloride uptake in rabbit corneal epithelium.

The mechanism of chloride uptake at the basal membrane (stromal side) of rabbit corneal epithelium was examined by observing the effects of ion transport inhibitors and ion concentrations on the stimulated epithelial short-circuit current (Isc). Loop diuretics inhibited the theophylline-stimulated peak and sustained Isc. Treatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 0.2 mM) and/or 5-(N,N-dimethyl)amiloride (0.1 mM) as well as the potent anion exchange inhibitor, 5c(+)[(2,3,9,9a-tetrahydro-1H-fluoren-7-yl)oxy]acetic acid (0.01 mM), had no significant effect on Isc. These results are consistent with Cl- uptake by a Na+-Cl- or Na+-K+-2Cl- cotransport mechanism rather than Cl(-)-HCO3(-)-OH- exchange coupled to Na+-H+ exchange. Incubation in low [Na+] or [Cl-] before stimulation with forskolin (0.1 mM) reduced both peak and sustained Isc, and saturation kinetics were exhibited. Hill coefficients for [Na+] and [Cl-] were 0.99 and 1.04, respectively, for peak Isc and 0.66 and 1.18, respectively, for sustained Isc. Apparent ion affinities for Na+ and Cl- were 13.5 and 18 mM, respectively, for peak Isc and 15 and 22 mM, respectively, for sustained Isc. These results favor Cl- uptake by a 1 Na+:1 Cl- cotransport mechanism for the rabbit corneal epithelium, but involvement of K+ in this process has not been eliminated.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

Imaging of the cornea.

The aim of the LSU Eye Center Corneal Topography Project was to apply computer analysis to keratoscopy and develop graphic presentation methods to provide accurate and easily assimilated information regarding the status of patient corneal topography. The analysis contains four diagrams: a plot of the raw keratoscope data for quality control, a three-dimensional wire model of corneal surface power distribution, a plot of dioptric point surface powers, and a color-coded contour map of corneal surface powers. While the analysis uses a current generation 11 ring keratoscope for producing keratoscope photographs, it can be adapted to newer keratoscopes, which promise to give broader coverage of the corneal surface. Examples of normals and several surgical patients will be shown, including cases in which the method has pointed to potential refinements in the theory and application of refractive surgical techniques.

Adult↗
PubMed1987

Corneal topography in myopic patients undergoing epikeratophakia.

We analyzed the corneal topography of eight eyes in seven patients who had undergone myopic epikeratophakia, using a 1.5-mm graft/host disparity. Topographic maps of corneal power generated by computer analysis of keratoscope photographs disclosed a central spherical optical zone smaller in diameter than was predicted by the preoperative lathing measurements. Outside this optical zone, the dioptric power of the graft surface increased steadily, indicating a progressive steepening of the corneal slope as the graft/host interface is approached. This pattern occurred in patients with accurate and inaccurate refractive results. The center of the graft was noted in some cases to be decentered from the patient's visual axis. The corneal topography analysis system has made clear the need to maximize the diameter of the effective optical zone.

Cornea↗
PubMed1987

Graphic presentation of computer-analyzed keratoscope photographs.

We describe a corneal topography analysis system that creates accurate high-resolution graphics of corneal surface power from computer analysis of keratoscope photographs, and we present several examples of corneal shape analyses. The major improvement in the updated version presented here is the development of a contour map of corneal surface power. Improvements in computer algorithms used to analyze the raw data obtained from the keratoscope photographs have also been made, resulting in increased accuracy. This system allows the ophthalmologist to see the patterns of power distribution on the corneal surface more easily than is possible by visual inspection of keratoscope photographs. Improved corneal topography analysis should find wide clinical application in the study of refractive corneal surgery techniques and in the study of corneal disorders that cause irregular astigmatism.

Adult↗
PubMed1987

Corneal topography of pellucid marginal degeneration.

Our computer-based corneal topography analysis system was used to study the keratoscope photographs (keratograms) from two patients with classic pellucid marginal degeneration and a third patient with no inferior corneal thinning, whose keratoscope mire pattern was suggestive of the condition. All three patients showed marked flattening of the central cornea along a vertical axis and marked steepening of the inferior corneal periphery, which also extended into mid-peripheral inferior oblique corneal meridians. The mid-peripheral cornea gradually decreased in power above the inferior oblique meridians.

Astigmatism↗
PubMed1987

Visual distortion after myopic keratomileusis: computer analysis of keratoscope photographs.

A patient experienced marked visual distortion following myopic keratomileusis, despite the presence of a clear graft and an apparently smooth corneal surface. A color coded topographic map of corneal surface power generated by computer analysis of a keratoscope photograph of the operated eye identified a degree of irregular astigmatism and asphericity not readily apparent from simple visual inspection of the keratoscope photograph. Contour map graphics display of corneal surface power is a useful clinical tool in the evaluation of visual distortion complications following myopic keratomileusis.

Adult↗
PubMed1986

The effect of phorbol esters on the chloride secreting epithelium of the rabbit cornea.

Tumor-promoting phorbol esters have been shown to modulate a number of physiological events in various cell types, and these events are associated with the activation of protein kinase C. The purpose of this study was to examine the effects of phorbol ester stimulation on protein kinase C activity and epithelial ion transport in the Cl- secreting rabbit corneal epithelium. We report here that nanomolar concentrations of tumor-promoting phorbol ester, 12-0-tetradecanoyl-phorbol-13 acetate (TPA), stimulate active ion transport via a putative receptor located in the corneal epithelium. This stimulation is a Cl- -dependent process, but is independent of beta-adrenergic receptor activation and prostaglandin formation. Biochemical data support the idea that TPA activates Ca++/phospholipid-dependent protein kinase C in the corneal epithelium. Therefore, we suggest that protein kinase C may have a role in the regulation of membrane Cl- transport in the mammalian corneal epithelium.

Animals↗
PubMed1986

Epithelial wound closure in the rabbit cornea. A biphasic process.

The rapid and complete repair of the corneal epithelium following ocular surgery or trauma is essential for the maintenance of normal visual acuity. In this study the authors examined epithelial wound healing in the rabbit after cells were mechanically removed leaving the basal lamina intact. The decrease in wound area (mm2/hr) was neither linear nor amenable to simple kinetic analysis. However, analysis of the data in terms of the decrease in wound radius (mm/hr) revealed a biphasic process consisting of an initial latent phase with no epithelial movement (5.5 +/- .3 hr), followed by a linear healing phase. The rate of epithelial movement in the linear healing phase was 64 +/- 2 microns/hr. Neither the latent phase nor the rate of epithelial migration during the healing phase was affected by variations in initial wound size. Ultrastructural studies demonstrated that during the latent phase there was an increased desquamation of surface cells as well as cellular and subcellular reorganization of the basal cells. At the end of the latent phase, the leading edge of the wound was composed of a single cell layer. The onset of epithelial migration coincided with the first ultrastructural observation of typical ruffled membranes and filopodia. This work demonstrates that the analysis of the decrease in wound radius provides a straightforward and accurate means to assess the kinetics and therapeutic modulation of epithelial wound healing.

Animals↗
PubMed1985

Epikeratophakia for myopia correction.

Epikeratophakia is based on the principles of the Barraquer refractive procedures, with modifications that simplify the surgical technique and eliminate the use of the microkeratome by placing the donor corneal tissue lens on the anterior surface of the cornea. Procedures developed to permit freeze-drying the preshaped lens for storage enable these lenses to be obtained from a central source, freeing the surgeon from the complexities of the computer and the cryolathe. The correction of theoretically unlimited amounts of myopia is possible with these lenses. In 12 eyes that underwent the final epikeratophakia procedure, the average desired correction achieved was 98%.

Cornea↗
PubMed1985

Transport processes across the rabbit corneal epithelium: a review.

The corneal epithelium of the rabbit is functionally characterized as a "tight" ion transporting cell layer. Its barrier properties arise from the high electrical resistance of both the outermost cell membranes and the paracellular zonulae occludens. The specific ion transport process and secondary fluid transport by this tissue are modulated via cyclic AMP. There is evidence for the autonomic control of C1- secretion by the corneal epithelium.

Animals↗
PubMed1985

Alteration of corneal epithelial ion transport by sympathectomy.

The cornea is dually innervated, receiving afferent nerves from the trigeminal ganglion and efferent nerves from the superior cervical ganglion. This study examines the specific effects of superior cervical ganglionectomy (SCGX) on the in vitro ion transport characteristics of the rabbit corneal epithelium. Two weeks after SCGX, epithelial Cl--dependent transport and total ionic conductance were increased in comparison to values obtained in paired control eyes. This increased transport level appeared to be independent of membrane receptor activity as demonstrated by lack of responsiveness to alpha-adrenergic, beta-adrenergic, serotonergic, dopaminergic, nicotinic cholinergic, or muscarinic cholinergic blockade. Nevertheless, SCGX produced a supersensitivity to epinephrine-stimulated transport as measured by the responsiveness of the ion transport current. Furthermore, SCGX abolished the responsiveness of the epithelium to serotonin. On the basis of these and earlier findings, the authors conclude that corneal sympathetic innervation influences membrane and receptor properties. Autonomic neurotrophic effects in the corneal epithelium include suppression of apical membrane Cl- permeability and of beta-adrenoreceptor sensitivity to biogenic amines. It is proposed that the corneal serotonergic receptors that activate Cl- transport lie on the sympathetic nerve terminals and stimulate this transport process by causing the neural release of a catecholamine.

Animals↗
PubMed1984

Cellular mode of serotonin action on Cl- transport in the rabbit corneal epithelium.

The present work examines serotonin-induced changes in cell potential difference and barrier resistances in the corneal epithelium in vitro using voltage-measuring microelectrodes and related techniques. Component resistances were determined using voltage and resistance profiles of the epithelium before and during the serotonin response. Serotonin, added to the stromal side of the cornea in the presence of nialamide, markedly reduced transcorneal and apical membrane resistances, while basal barrier resistance increased slightly and shunt resistance was unchanged. The marked drop in apical membrane resistance after serotonin treatment reflects an increase in apical membrane chloride permeability, inasmuch as the serotonin-stimulated short-circuit current is indistinguishable from the increase in net chloride flux. Prolonged (more than 1 h) exposure of corneas to serotonin markedly depolarized the epithelial cells and reduced the voltage divider ratio from 12.3 +/- 2.1 to 1.5 +/- 0.5, while not significantly affecting the stimulated short-circuit current. These later effects suggest changes in epithelial ion distribution during long periods of stimulation by serotonin.

Animals↗
PubMed1984

Dopamine modulation of active ion transport in rabbit corneal epithelium.

The addition of micromolar quantities of dopamine stimulated ion transport in the isolated rabbit corneal epithelium. This response was blocked by pretreatment with the dopamine antagonist, haloperidol, and by the elimination of Cl- from the bathing solutions. The beta-adrenergic antagonist, timolol, was also a potent inhibitor of the epithelial response to dopamine. The presence of the serotonin antagonist, methysergide, or the dopamine beta-hydroxylase inhibitor, FLA-63, did not significantly alter the corneal response to dopamine. Following superior cervical ganglionectomy, the epithelial response to dopamine was abolished. These findings are consistent with the idea that Cl- secretion in the rabbit corneal epithelium can be modulated by preterminal dopamine receptors located on the sympathetic nerve fibers; therefore, dopamine stimulation appears to be a serial process mediated by the release of norepinephrine from sympathetic nerve terminals in the epithelium.

Animals↗
PubMed1984

Aqueous hyposecretion after penetrating keratoplasty.

Following penetrating keratoplasty, aqueous hyposecretion results in marked thickening of the cornea identical to that seen when the donor endothelium is unsatisfactory. The lack of secretion is accompanied by hypotony, and the persistence of fluorescein in the anterior chamber can be measured by fluorophotometry or observed clinically 24 hours after the instillation of topical fluorescein. An eye with aqueous hyposecretion will usually recover in seven to ten days, and additional surgery is not only unnecessary, but harmful to an already damaged eye. However, poor donor tissue can often be replaced promptly and successfully with repeated penetrating keratoplasty. Therefore, clinical differentiation of these conditions is important in management decisions.

Aqueous Humor↗
PubMed1984

Computer-assisted corneal topography. High-resolution graphic presentation and analysis of keratoscopy.

Keratoscopy is a useful clinical tool for the evaluation of topographic abnormalities of the corneal surface. However, not all the detailed information presented by keratoscope photographs is assessed easily by visual inspection. A computer-based analysis system therefore was developed to assist in the clinical interpretation of keratoscope images. With this system, deviations from sphericity are displayed in graphic form to aid in the recognition of abnormalities, and surface powers are presented in tabular form. Human eyes that are emmetropic, and eyes with keratoconus and severe astigmatism were analyzed. This process provides a useful quantitative method with which to determine corneal shape, as well as a useful adjunct to the clinical evaluation and teaching of keratoscopy. In addition, such a quantitative analysis may provide the basis for the development of new techniques for the correction of visual distortion caused by corneal surface irregularities.

Astigmatism↗
PubMed1983

Cellular and paracellular pathway resistances in the "tight" Cl- -secreting epithelium of rabbit cornea.

The high transverse resistance of the isolated rabbit cornea (6-12 l omega . cm2) is associated with the corneal epithelium, a Cl- -secreting tissue which is modulated by beta-adrenergic and serotonergic receptors. Three methods were employed to determine the resistances for the apical membrane, basolateral membrane, and paracellular conductive pathways in the epithelium. In the first method, the specific resistance of the apical membrane was selectively and reversibly changed. Epinephrine was used to increase apical cation permeability. The second method utilized a direct measure of the spontaneous cellular ionic current. The third method obtained estimates of shunt resistance using transepithelial electrophysiological responses to changes in apical membrane resistance. The results of the first method were largely independent of the agent used. In addition, the three methods were in general agreement, and the ranges of mean values for apical membrane, basolateral membrane, and shunt resistances were 23-33, 3-4, and 12-16 k omega . cm2, respectively, for the normal cornea. The apical membrane was the major, physiologically-modulated barrier to ion permeation. The shunt resistance of the corneal epithelium was comparable to that found previously for other "tight" epithelia. Experiments using Ag+ in tissues that were bathed in Cl- and HCO3-free solutions indicated that under resting conditions the apical membrane is anion-selective.

Animals↗
PubMed1983

RIPS: a UNIX-based reference information program for scientists.

A set of programs is described which implement a personal reference management and information retrieval system on a UNIX-based minicomputer. The system operates in a multiuser configuration with a host of user-friendly utilities that assist entry of reference material, its retrieval, and formatted printing for associated tasks. A search command language was developed without restriction in keyword vocabulary, number of keywords, or level of parenthetical expression nesting. The system is readily transported, and by design is applicable to any academic specialty.

Books↗