Sensory nerve endings may be conveniently studied in the cornea of a recently killed frog or rabbit, or in a freshly extirpated human eye.
Take the cornea of a newly killed frog or cat and stain with chloride of gold (p.
The subdivision of thecornea into two layers of slightly different texture suggests an achromatic correction, and it is quite possible, though unproved, that the two sets of prisms have different dispersive powers.
When thecornea is flattened out for microscopic examination, the images (e.
Beneath the cornea we find a layer of crystalline cones, each of which rests by its base upon the inner surface of a facet, while its apex is directed inwards towards the brain.
Reasons have been given for supposing that images are formed by the cornea and crystalline cones together.
In the simple eye the non-faceted cornea and the retinula are readily made out, but the crystalline cones are not developed as such.
The cornea of the living animal is, however, convex, and the images formed by different facets cannot be precisely identical.
No image is visible when the tip of the cone is in focus, but as the cornea approaches the focus, a bristle, moved about between the mirror and the stage, becomes visible.
The cornea in which I had incited a foreign-body-keratitis, became as insensible as a healthy one.
I have cauterized the cornea with the nitrate of silver stick until it became milky white; during all of this the animal did not move.
In this way I have scratched and transfixed the cornea of the animals used for experiment with needles, and have excited them with electric currents so strong as to cause pain in my fingers, and to become quite intolerable to the tongue.
The last experiment convinced me that the anesthesia involved the whole thickness of the cornea and did not affect the surface only.
Complete anesthesia of the cornea from the use of a two per cent.
The eye is always a closed vesicle, and the internal cornea is extensive.
The "collagen," obtained from tendons and connective tissues, also occurs in the cornea and sclerotic coat of the eye, and in fish scales.
The corneaand aqueous humors are convexo-concave, the vitreous humor is concavo-convex, while the crystalline humor is a convexo-convex medium.
The office of these humors and the cornea is to refract the rays of light in such proportion as to direct the image in the most favorable manner upon the retina.
The cornea is composed of several different layers; its blood-vessels are so small that they exclude the red particles altogether, and admit nothing but serum.
These circumstances modify the direction of the refraction of the rays of light, in their passage from the cornea to the retina.
The cornea (This connects with the sclerotic coat by a bevelled edge.
Have the cornea and the humors of the eye different degrees of density?
The bevelled junction of the corneaand sclerotic coats.
Anteriorly, the sclerotic coat presents a bevelled edge, which receives the cornea in the same way that a watch-glass is received by the groove in its case.
Students disputed whether the conjunctiva extended over the cornea or not, and worried themselves over Gaultier de Claubry's stratified layers of the skin, or Breschet's blennogenous and chromatogenous organs.
In two genera of fishes, Anableps, Dialommus, the cornea is divided by a horizontal partition into two parts.
The cornea is little convex, leaving small space for aqueous humor.
As the disease progresses, the conjunctiva becomes more vascular, the photophobia intolerable, the cornea itself becomes opaque, and sometimes exhibits a vascular appearance.
The conjunctiva remained inflamed, the cornea in due course became ulcerous, and the eye was ultimately destroyed by the discharge of its contents.
In the early stage of this malady there is an unnatural and often terrific brightness of the eye; but the cornea in distemper is from the first rather clouded.
If the disease progresses in its course, unchecked by any remediate means, the cornea may lose its vitality, ulceration commence, and the sight be for ever destroyed by the bursting and discharge of the contents of the eye.
This may be done by puncturing the corneaor the sclerotic coat with a needle.
The larynx and cornea were sensitive, and the plantar reflexes were absent.
The cornea and the conjunctiva are anesthetic, and sometimes the eyelids also,--the so-called anesthesia en lunettes.
The larynx and cornea did not respond to stimulation.
Defn: A white opacity in the cornea of the eye; -- called also albugo.
Defn: The operation of removing a cataract by thrusting a needle through the cornea of the eye, and breaking up the opaque mass.
Defn: An instrument devised by Helmholtz for measuring the size of a reflected image on the convex surface of the cornea and lens of the eye, by which their curvature can be ascertained.
Defn: An instrument for dividing thecornea in operations for cataract.
Defn: A superficial growth of vascular tissue radiating in a fanlike manner from the cornea over the surface of the eye.
Defn: A disease of the eye, in which the iris adheres to the cornea or to the capsule of the crystalline lens.
The mode of formation of the cornea already described appears to be characteristic of most Vertebrata except the Ammocoete.
The derivation of the original structureless layer of the corneais still uncertain.
After it has become completely established, the mesoblast around the edge of the cornea becomes divided into two strata; an inner one (fig.
The ciliary muscle and the ligamentum pectinatum are both derived from the mesoblast between the cornea and the iris.
The outer stratum gives rise to the corneal corpuscles, which are the only constituents of the cornea not yet developed.
The front portion, accompanied by the mesoblast which immediately overlies it, is behind the lens thrown into folds, the ciliary ridges; while further forward it bends in between the lens and the cornea to form the iris.
The edge of the fold constitutes the cornea while the remainder of it gives rise to the sclerotic.
Behind the cornea is a chamber known as the anterior optic chamber.
Their inner face is lined by a prolongation of conjunctiva, which is the modified epiblast covering the cornea and part of the sclerotic.
This layer, which forms the commencement of the cornea proper, at first only forms a ring at the border of the lens, thickest at its outer edge, and gradually thinning off to nothing towards the centre.
The cornea continues to increase in thickness by the addition of laminae on the side adjoining the epiblast.
There is no cavity for the aqueous humour in front of the lens; and there is no cornea as distinct from the epidermis and subepidermic tissues.
Sperino chooses the horizontal meridian of the cornea at the temporal side, at the junction of the cornea and sclerotic.
This entirely hides the corneafor a time, but eventually shrivels and contracts, and the remnants are to be cut off with scissors three weeks after the operation.
The point of a small knife, of which the edge is directed upwards, is inserted at a point fully half a line from the margin of the cornea near its upper part, so as to enter the anterior chamber as peripherally as possible.
There are certain cases in which the whole or greater part of the cornea bulges forward in a great blue projecting tumour.
To make a flap ofcornea large enough to permit of the removal of the entire lens without pressure or bruising.
This point is generally at the opposite margin of the irregular pupil, so that the needle may pass through the cornea in front of the one side of the iris, then through the orifice of the pupil, so as to reach the back of the other side.
These two flaps are united over the vertical meridian of the cornea by sutures, three generally being sufficient.
To make it of cornea only, to prevent the escape of the vitreous, and to avoid injury of the iris.
The point of the knife must then be introduced about a line from the outer sclerotic margin of the transverse diameter of the cornea (Fig.
So also in the vertebrate eye the lens is formed by an extra layer of the epidermal cells between the cornea and the retina.
We see, in fact, that in the compound crustacean eye an extra layer of hypodermal cells has become inserted between the corneaand the retina to form a lens.
Darier has reported that a single subconjunctival injection of a milligram of iodate of sodium has cleared the cornea and lessened the intra-ocular pain in glaucoma.
The haziness of the cornea and slight turbidity of the aqueous contribute greatly to the apparent change in the color of the iris.
In advanced cases of glaucoma after the congestive period has subsided the cornea becomes somewhat condensed, the lymph spaces contracted; a condition of sclerosis obtains.
In infancy and early youth (buphthalmia) the cornea may become uniformly enlarged and globular.
The process causes a roughening of the surface of the cornea and produces a faint haziness.
Alteration in the shape of the cornea occurs only rarely in adult life.
Often, however, the enlargement of the corneais irregular.
As has been shown by Priestley Smith, the cornea in glaucomatous eyes is, as a rule, smaller than in non-glaucomatous eyes, the mean of a series of measurements being 11.
These occur more frequently in the cornea that have suffered a change in shape, as in buphthalmos.
The conjunctival flap thus formed is turned back over the cornea, and the fragment of sclera that is left attached to the cornea is removed by means of a fine pair of delicate curved scissors.
The cornea being unduly exposed is liable to become inflamed, or even ulcerated.
In either case the eyeball is protruded, and the cornea is exposed to irritation and may become inflamed and ulcerated.
The pupil is usually dilated, the cornea becomes opaque and may ulcerate, and there is photophobia and sometimes diplopia.
The lens and the cornea have no cells that are able to become macrophags.
In most organs such fatty degeneration is followed by phagocytosis, but the cornea and the crystalline lens are exempt from this consequence for anatomical reasons.
Cataract and the senile arc which appears as a milky ring at the edge of the cornea are frequent in old age.
They show a flattened cornea extending along the median line of the snout, with a large retina composed of peculiar rods which form a complicated apparatus destined undoubtedly to produce an image and to receive especial luminous rays.
The cornea is thickened, forming two additional lens-like structures.
Attempts have been made to transplant a button of clear cornea of a dog, rabbit, or cat to the cornea of a human being, opaque as the result of ophthalmia, and von Hippel has devised a special method of doing this.
The sight of the right eye was entirely lost, and the anterior surface of the globe was so uniformly red that the cornea could hardly be distinguished from the surrounding conjunctiva.
The ball rested on the cheek, held by the taut optic nerve; the cornea was opaque.
Barkar speaks of a piece of steel which penetrated through the cornea and lens, and which, five months later, was successfully removed by the extraction of the cataractous lens.
The barbed formation of the point explains how, under the stroking with the finger, it was forced through the dense tarsal cartilage and against the cornea of the eye.
The eye was not lost, and opacity of the lower part of the cornea alone resulted.
The cornea was completely anesthetic, and the right cheek, an inch and a half external to the angle of the nose, presented a small patch of anesthesia.
When the eyelid rolled inward the fold rolled with the globe, but never reached so far as the circumference of the corneaand did not interfere with vision.
An instrument devised by Helmholtz for measuring the size of a reflected image on the convex surface of the corneaand lens of the eye, by which their curvature can be ascertained.
A disease of the eye, in which the iris adheres to the cornea or to the capsule of the crystalline lens.
A superficial growth of vascular tissue radiating in a fanlike manner from the cornea over the surface of the eye.
The operation of removing a cataract by thrusting a needle through the cornea of the eye, and breaking up the opaque mass.
An instrument for dividing thecornea in operations for cataract.
In the Aptera the larva differs from the adult only in the number of facets in the cornea and joints in the antennae.
The fold itself gives rise to thecornea in front and to the sclerotic at the sides.
When the centre of the cornea is injured, this tissue having no vessels, all the vascular phenomena take place in the white part of the eye immediately around the cornea, this becoming red and congested.
The cornea or transparent part of the eye contains no blood vessels, the cells which it contains being nourished by the tissue fluid which comes from the outside and circulates in small communicating spaces.
Magitot of Paris, in 1911, took a piece of the cornea from an extirpated human eye, and with it replaced a part of an opaque cornea on another man, and this second man could see through the new cornea.
With insects it is now known that the numerous facets on the cornea of their great compound eyes form true lenses, and that the cones include curiously modified nervous filaments.
To be sure the cornea by itself will not focus on the retina, but a glass lens can be placed in front of it which will add itself to the cornea and the combined lenses will.
It is the condition in which the cornea is not curved equally in all directions; the vertical curvature may be greater or less than the horizontal.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "cornea" in a variety of sentences. We hope that you will now be able to make sentences using this word. Other words: eye; eyeball; lens; lid; optic; orb; peepers; pupil; retina