Stroma-endothelium preparations from rabbit corneas were mounted between two chambers and incubated with identical media on either side which contained different bicarbonate levels and, in some experiments, organic (Good's) buffers. Active fluid flow across the preparations was measured by means of a capillary tube attached to the stroma-side chamber. With media containing 2 to 50 mM bicarbonate (pH 6.2 to 7.8 in equilibrium with 5% CO2-air at 37 degrees C), the fluid pump was constant for at least 3 hr at a rate of 5 microliter/hr cm2 and was not significantly affected by the bicarbonate level. Over the same range of pH and bicarbonate but supplemented with 50 mM organic buffer, fluid pump was 8 microliter/hr cm2 for all bicarbonate concentrations used. Using Ringer solutions supplemented with 50 mM buffer (pH 6.3 to 8.4) but without added bicarbonate and in equilibrium with air, fluid pump was observed at approximately 4 microliter/hr cm2 at pH 6.3 and increased to 8 microliter/hr cm2 at pH 7.8. In all cases, fluid pump persisted for at least 5 hr.

Animals↗

PubMed1987

The rate of diffusion of fluorophores through the corneal epithelium and stroma.

The time taken to cross the rabbit corneal epithelium and stroma was estimated for fluorescein (F), carboxyfluorescein (CF), rhodamine B (RB), and sulforhodamine B (SRB). Paired corneas were mounted in vitro; one was intact and the dye solution was kept in continuous contact with its epithelial surface; the epithelium was scraped from the other and the dye was applied as a pulse to the bare stroma. The time course of the dye appearing in a solution rapidly passing over the endothelial surface was determined by fluorometry. This rate of appearance was compared in the two cases and used to estimate the diffusional lag time introduced by the epithelium. For the very hydrophilic CF and SRB, the delay was too short to measure; this is compatible with the passage of these dyes taking place through the paracellular spaces. For the very lipophilic RB, the delay was about 2 min; this was rather too slow for it to be explained as being controlled entirely by diffusion in the cytosol. For the intermediate F, the delay was 5 min; it is suggested that this is a result of it partitioning between the spaces and the cytosol during its passage. The experiments also led to determinations of the permeability of the epithelial and endothelial layers to the dyes. In both cases lipophilicity was a strong determinant of penetration, but not the only one. The permeability of the endothelium to F was unchanged from its in vivo value in these experiments, but that of the epithelium was increased four-fold. The diffusion rate of the dyes across the stroma could also be determined. There was no clear relationship with molecular size or partition coefficient. The rate of diffusion of F across the tissue was about half that in its plane, as determined in previous experiments. This is possibly a result of the anisotropic structure of the tissue.

Animals↗

PubMed1986

A permeability test for acute corneal toxicity.

The penetration of sulforhodamine B (SRB) into the two corneas of a freshly killed mouse was measured after one eye was briefly exposed to a solution of a possibly toxic substance. The ratio of the penetrations provides a numerical index of acute toxicity to the corneal epithelium. With a group of 6 animals, a 50% rise in the index can be distinguished at the 95% confidence level; the maximum rise achievable in practice seems to be about 30. NaOH and benzalkonium chloride (BAK) gave graded increases in the value as their concentrations rose; the rise in index corresponded roughly to the injury caused to the living eye.

Animals↗

PubMed1984

A simple method of measuring aqueous humor flow with intravitreal fluoresceinated dextrans.

Fluoresceinated dextran was injected into the vitreous cavity of rabbits and its concentration was followed in the vitreous and aqueous humors for a period of weeks by slip-lamp fluorometry. The concentrations in both fluids fell in parallel and in an exponential manner where the time constant was determined by the molecular weight of the dextran. The rate of movement of the dextran from the vitreous into the anterior chamber is controlled by passive diffusion and may be assumed to be relatively steady; accordingly, the faster the rate of flow in the aqueous humor the lower will be the concentration of dextran in it. Circadian variations in the aqueous flow were observed, a drop at night time being noted. These were small enough for changes due to systemic influences to be determined; in particular, it was found that general anesthesia with ketamine had no significant effect. The ratio of the concentration in the anterior chambers of the two eyes of one animal normally remains constant with time. Changes in the ratio can be used to determine the influence of unilateral interventions. This was illustrated by the use of adrenergic drops which led to a brief rise in flow rate and then a longer-lasting fall, and by X-ray irradiation with 1000 rads, which caused an immediate fall in flow rate interrupted for a time by a phase of increased flow. An absolute estimate of the aqueous flow can be derived from measurements of the total amount of dextran in the eye and its concentration in the anterior chamber. A definite value has not yet been established owing to ambiguities in determining the former quantity.

Anesthesia, General↗

PubMed1979

The dynamics of IgG in the cornea.

Fluoresceinated IgG was injected centrally into the rabbit's cornea and both its rate of loss from the tissue and its rate of spread in the stroma were estimated by objective fluorometry. A new technique for determining the rate of loss was established which required only the measurement of the maximum fluorescence in the tissue. The rate at which freshly formed IgG in the blood would arrive at the central regions of the cornea was estimated for the human eye. As penetration continues from the limbus and the protein is lost to the aqueous humor, a standing concentration gradient is set up with a minimum at the corneal center. Calculation suggests that this gradient should be small for IgG in the human eye.

Animals↗

PubMed1977

Striations of light scattering in the corneal stroma.

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Animals↗

PubMed1977

Permanent destruction of the corneal endothelium in rabbits.

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Animals↗

PubMed1977

Sensory recording from the isolated cornea.

A technique of recording from single units of the isolated rat cornea is described. The corneal surface is stimulated by a jet of fluid, which allows continuously graded pressure and thermal or chemical stimuli to be applied at the same point. Some units respond to stimulation anywhere in a field of about one-third the corneal area, and others only to point stimulation.

Action Potentials↗