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Biomedical subjects

S D Klyce

Publications and source records attributed to S D Klyce.

At least 91 records · Page 5Linked to original sources
PubMed1983

The cornea press: restoring donor corneas to normal dimensions and hydration before cryolathing.

The shaping of swollen, abnormally hydrated donor corneal tissue on the cryolathe for use in keratorefractive surgery yields lenticules of insufficiently predictable dioptric powers. The irregular nature of this abnormal hydration precludes the use of mathematical compensating factors. To improve control over the shape of the lenticule, we have developed a cornea press which restores normal hydration and dimensions to the donor tissue by mechanical dehydration.

Cornea↗
PubMed1982

Effects of Ag+ on ion transport by the corneal epithelium of the rabbit.

Exposure of the in vitro rabbit corneal epithelium to Ag+ by the addition of AgNO3 (10(-7)-10(-5) M) to the apical surface or by the use of imperfectly chlorided Ag/AgCl half-cells in Ussing-style membrane chambers, greatly increases short-circuit current and transepithelial potential. The early phase (the first 30 min) of the short-circuit current stimulation by Ag+ is linearly dependent on tear-side sodium concentration, is largely a result of a tenfold increase in net Na+ uptake and is incompletely inhibited by ouabain, suggesting that Ag+ increases cation (primarily Na+) conductance of the apical membrane. This mechanism for the Ag+ effect is supported by microelectrode experiments, wherein Ag+ depolarizes specifically the apical barrier potential and increases apical barrier conductance. A later phase in the effect (0.5-3 hr) is characterized by a gradual increase in 36Cl- and 14C-mannitol unidirectional fluxes, by a decline in epithelial resting potential and short-circuit current, by complete ouabain inhibition and by fit to saturation kinetics with respect to Na+ concentration in the bathing media. This phase of the effect apparently reflects a nonselective opening of the paracellular pathway in the epithelium and is rate-limited by Na+ pump activity at the basolateral membrane. Both phases are associated with swelling of the corneal stroma and may be rapidly reversed using thiol agents (reduced glutathione and dithiothreitol). The results suggest that Ag+ may be useful in the study of cation transport by epithelia and the work provides basic physiological information that is pertinent to the prophylactic use of AgNO3 in clinical ophthalmology.

Animals↗
PubMed1982

Neural serotonin stimulates chloride transport in the rabbit corneal epithelium.

Evidence is presented that serotonin acts as a neurotransmitter in the cornea of the adult rabbit. Serotonin was localized to granules in a sparse population of subepithelial corneal nerves by an electron microscopic histochemical procedure. Significant endogenous levels of serotonin and its principal metabolite, 5-hydroxyindoleacetic acid, were detected in the central cornea by a fluorometric assay. Exogenous serotonin stimulated ion transport by corneal epithelium. This effect was potentiated by monoamine oxidase inhibition and was unaffected by an alpha-adrenergic receptor antagonist. Serotonin-stimulated ion transport was inhibited by the specific antagonist, methysergide, and by the replacement of Cl- with an impermeable anion. In tracer experiments, the serotonin-stimulated ion transport was shown to be caused by increased epithelial Cl- secretion. The serotonin response was partially inhibited by the beta-adrenergic antagonist, timolol. In a companion article, assay of corneal cyclic AMP showed stimulation of cyclic AMP synthesis by serotonin, inhibition by the specific antagonist, lysergic acid diethylamide, and potentiation by monoamine oxidase inhibition. We postulate that specific serotonergic receptors are present in the corneal epithelium and that activation of these receptors by serotonin released from serotonergic neurons increases the level of cyclic AMP, which stimulates active Cl- secretion by the corneal epithelium.

Animals↗
PubMed1982

Serotonin-stimulated cyclic AMP synthesis in the rabbit corneal epithelium.

Serotonin increases the level of cyclic AMP in incubated rabbit corneas; the concentration of agonist producing half-maximal stimulation is approximately 1.5 microM. Nialamide, an inhibitor of monoamine oxidase, potentiates the response to serotonin but not to epinephrine. Amitriptyline, an inhibitor of neuronal uptake of serotonin, does not potentiate the stimulation of cyclic AMP synthesis. Lysergic acid diethylamide, but not timolol, antagonizes the response to serotonin; the half-maximal inhibitory concentration is approximately 6 nM lysergic acid diethylamide. A comparison of the time course of the increase in cyclic AMP synthesis after addition of serotonin or epinephrine to the incubation media indicates that serotonin, but not epinephrine, must penetrate a barrier to its free diffusion. We conclude that the corneal epithelium contains specific serotonergic receptors that, upon activation, cause the synthesis of cyclic AMP, which mediates the stimulation of chloride transport (c.f. companion article, Klyce et al.). The serotonergic receptors must be at a location posterior to the beta-adrenergic receptors, which are on the anterior-surface of the apical cells.

1-Methyl-3-isobutylxanthine↗
PubMed1981

The origins of Sattler's veil.

The symptoms of Sattler's veil accompany prolonged wear of thick contact lenses and are thought to be the result of epithelial hypoxia. We studied light scattering in the isolated rabbit cornea after hypoxia with optical techniques. We found that hypoxia produced a polygonal mesh of light scattering, outlining cells in the intermediate and basal epithelium. An optical transform of this mesh produced a halo of the same dimensions observed in Sattler's veil. Additionally, prolonged hypoxia produced an increase in stromal light scattering that may add to increased glare sensitivity. Consistent changes in epithelial thickness were not observed, raising the probability of radial swelling or compensatory epithelial volume regulation.

Animals↗
PubMed1981

Stromal lactate accumulation can account for corneal oedema osmotically following epithelial hypoxia in the rabbit.

1. The mechanism underlying stromal oedema subsequent to epithelial hypoxia was investigated in isolated rabbit corneas. 2. Stromas swelled about 20 micrometer following a 1 hr period of tear side hypoxia in both whole corneal isolates and in preparations in which fluid movement across the endothelium was blocked with silicone oil. In the experiments using whole corneas, stromal thickness was independent of tear side oxygen tension as long as aqueous humour PO2 was greater than 40 mmHg. 3. Neither epithelial thickness nor epithelial electrical resistance, a measure of total ion permeability, was significantly affected by blocking respiration. 4. A 10 degrees C reduction in corneal temperature markedly reduced the rate of hypoxic swelling, suggesting the involvement of a metabolism-dependent hydrating process and implicating the stromal accumulation of a catabolyte. 5. When CN- was used to mimic the hypoxic effect in isolated whole corneas, the passive 36Cl unidirectional flux was unaffected, but lactate production rate and stromal [lactate] more than doubled. 6. These measurements were used with a mathematical model for corneal hydration dynamics to examine the causes of hypoxic oedema. The principal conclusions were: epithelial hypoxia enhances epithelial lactate production and release to the stroma; this process causes an increase in stromal lactate concentration and a decrease in stromal NaCl concentration (primarily through dilution); stromal lactate accumulation exceeds in osmotic load and dilutional effect on [NaCl], producing stromal oedema. Whereas hypoxia produces corneal metabolic acidosis, effects on endothelial permeability of HCO3- transport need not be postulated to explain the stromal oedema that results from hypoxia.

Animals↗
PubMed1981

Epikeratophakia: the surgical correction of aphakia. I. Lathing of corneal tissue.

Epikeratophakia is a newly developed form of refractive corneal surgery for the correction of hyperopia. In this procedure, a piece of donor corneal tissue is lathed to a specific dioptric power. The epithelial cells are removed from the recipient cornea, and the donor tissue is sutured to the front of the eye. The resulting change in corneal curvature provides the visual correction, as, for instance, in the correction of aphakia. We describe here the computational analysis used to lathe human donor corneal tissue for use as epikeratophakia grafts. With these equations, the precision of the observed thickness of the lathed lenticule was +/- 0.05 mm and the precision of the observed diameter was +/- 0.25 mm. We found that, in a graft of a given diameter, the smaller the optical zone, the greater the maximal dioptric power of the graft, limited only by the central thickness of the donor cornea and the mechanical limitations of the cryolathe. In our case, the highest theoretical correction obtainable was 37 diopters.

Aphakia, Postcataract↗
PubMed1979

Numerical solution of coupled transport equations applied to corneal hydration dynamics.

1. A quantitative basis for the currently accepted theory on the regulation of corneal hydration was derived using the technique of finite element analysis to integrate a set of coupled flow equations. The model was based on non-equilibrium thermodynamics and incorporated the transport and permeability properties of the corneal epithelium and endothelium as well as the gel properties of the central connective tissue layer. 2. Considerable errors were introduced in the prediction of corneal hydration dynamics (unsteady-state behaviour) unless allowance was made for the development of trans-stromal gradients in pressure and solute concentration. 3. Thickness of in vitro rabbit corneal epithelium and stroma were measured with an automatic specular microscope during responses to changes in the osmolarity of the tear-side bathing medium. The time course of these experiments was fitted with the mathematical model to obtain a set of membrane phenomenological coefficients and transport rates. 4. The model with the redetermined membrane parameters was tested by predicting the influence of other variations in boundary conditions with excellent match to several well-documented experimental observations, including an explanation for the slight stromal swelling observed in hibernating mammals. 5. The regulation of corneal stromal hydration can be explained accurately by balance between the dissipative flows across the serial array of corneal layers and the active HCO3 transport by the endothelium, supporting the earlier 'pump-leak' hypothesis. 6. It was found that stromal retardation of fluid flow, as well as gradients in solute concentration, significantly influences the dynamics of corneal stroma hydration. Tissue gel properties may be a more important factor in coupled transport across cell layers than generally appreciated.

Animals↗
PubMed1977

Site and mode of adrenaline action on chloride transport across the rabbit corneal epithelium.

1. Membrane events accompanying adrenaline-stimulated Cl secretion by the isolated rabbit corneal epithelium were investigated with micro-electrodes. 2. Pulses of adrenaline (5 X 10(-10) M final concentration) delivered to either side of the epithelium produced a transient decrease in epithelial resistance occuring at the outer membrane of the squamous cell. This response was reversible and could be blocked completely by total Cl substitution with SO4. 3. Adrenaline generally produced a small transient increase in epithelial potential occuring also at the squamous cell outer membrane. Reversal potentials obtained for the adrenaline response were 45-1 mV for corneal potential and 22-8 mV for outer membrane. 4. Adrenaline always hyperpolarized epithelial potential when the tear side was bathed in Cl-free solution. Reversing the gradient (Cl-free on the stromal side) slowly and consistently changed the response to a depolarization which reached a steady level after 2 hr. 5. The reversal potential of the outer membrane for the adrenaline response was found to be a semilogarithmic function of the tear side Cl concentration over a broad range with a slope of 56 mV/decade. The reversal potential was zero at a tear side Cl concentration of 41-5 mM, which value may be taken to be representative of cell Cl concentration. 6. After abolishing the adrenaline response by perfusing both sides of the tissue with Cl-free solution, reintroduction of Cl to the stromal side led to a recovery of the epithelial potential response in the hyperpolarizing direction. The recovery of the response was inhibited by ouabain (10(-5) M). 7. The results supported the following model for the influence of adrenaline on anion transport in the epithelium: Cl is transported against an electrochemical potential gradient into the cells from the stromal side by an active process linked to Na-k activated ATPase. Normally a slight gradient exists from cells to tears favouring the passive outward diffusion of Cl. This latter process is enhanged by adrenaline, which increases cell cyclic AMP, in turn increasing the passive Cl permeability of the outer cellular membrane.

Animals↗
PubMed1977

Electrophysiologic and morphologic effects of ophthalmic preparations on rabbit cornea epithelium.

The effects of several components of ophthalmic preparations on isolated rabbit cornea were studied by continuous electrophysiologic monitoring followed by fixation for scanning electron microscopy (SEM). Benzalkonium chloride (0.001 percent), thimerosal (0.0004 percent), and amphotericin B (0.0025 percent) all briefly increased ion transport, then greatly decreased epithelial resistance. Severe disruption of surface cell layers occurred simultaneously with resistance decrease. Silver nitrate (0.00017 percent) stimulated transport with less accompanying morphologic damage. Tetracaine (0.05 percent) disrupted epithelial function and caused exfoliation of several cell layers. Chlorobutanol (0.1 percent) produced a nearly complete loss of the squamous cell layer. Chloramphenicol, epinephrine, and pilocarpine produced minor changes in structure and electrophysiology at full clinical concentration. It was concluded that low concentrations of preservatives in ophthalmic preparations disrupt the barrier and transport properties of the corneal epithelium.

Amphotericin B↗
PubMed1977

Enhancing fluid secretion by the corneal epithelium.

Swollen rabbit corneas incubated in vitro with their posterior surfaces blocked with silicone oil maintained fairly constant thickness over an 11 hr. period. Increasing the simulated intraocular pressure from 10 to 30 mm. Hg did not produce stromal thinning. When theophylline was added to stimulate epithelial Cl secretion by increasing the Cl permeability of the tear-facing epithelial membrane, corneas thinned at the average of 1.3 micrometer/hr. over a 6 1/2 hr. period. When the epithelial perfusion solution was made Cl-free by SO4 substitution to favor the passive flow of Cl from the cells to the tear solution, thinning of 3.91 micrometer/hr. over a 7 hr. period was observed. When corneas were perfused with Cl-free medium plus theophylline, thinning at the average rate of 6.20 micrometer/hr. over an 8 hr. period was achieved. Therefore the corneal epithelium is capable of thinning a swollen stroma by transport of fluid coupled to its Cl secretion, which can be enhanced by simple substitutions in the tear-side bathing solution.

Animals↗
PubMed1976

Automatic recording of corneal thickness in vitro.

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.

Animals↗
PubMed1975

Transport of Na, Cl, and water by the rabbit corneal epithelium at resting potential.

Theophylline (1 mM) produced a net transport of Na and Cl from aqueous humor to tears (.02-.04 mumol/cm2 h) in the isolated rabbit cornea denuded of endothlium and in the presence of normal resting potential (25-35 mV). The active transport of Na (tears to aqueous) and of Cl (aqueous to tears), estimated with the Goldman constant-field equations, was confirmed. A 10 degrees C rise in temperature produced changes close to those predicted for passive processes in both unidirectional fluxes of Na and in the tears-to-aqueous flux of Cl, but not for the aqueous-to-tears flux of Cl. Theophylline treatment doubled Cl permeability but did not significantly affect Na or urea permeability, suggestingspecificity of affect. In separate experiments it was shown that stromal thinning occurred in previously swollen corneas when the endothelium was blocked by silicone oil and the epithelium was treated with theophylline. These findings provide further support for the argument that the mammalian epithelium could have an active role in the regulation of corneal thickness in situ.

Animals↗