Lacrimal gland

“ Thus when any extraneous material on the eye-ball, or the dryness of the external covering of it, or the coldness of the air, or the acrimony of some vapours, as of onions, stimulates the excretory duct of the lacrymal gland, it discharges its contents upon the ball; a quicker secretion takes place in the gland, and abundant tears succeed, to moisten, clean, and lubricate the eye. ”

“ Another good specimen may be made by removing all of the inner tissues, and leaving only the sclerotic and cornea. This specimen will show that the first coat is almost entirely a coat which affords strength and protection to the parts that lie within.
[92]
THE PAPILLA, PUNCTA LACRIMALIA, AND NASAL DUCT
The only way to dissect the lacrimal apparatus, other ocular accessories, and the extrinsic muscles, is to procure the head of some animal, preferably a calf’s head, because of its size. Any butcher will supply one for from forty to sixty cents. Have the lower jaw removed. ”

“ The gland lies directly over the eye and near the outer angle of the orbit. In the enucleated eye, it will be found to lie near the outer canthus and over the eye. The gland may be easily dissected out of its position and then examined more closely. A hand lens will show the racemose construction of the gland. If the gland is cut in two, the racemose construction may be seen even better. ”

“ The lachrymal gland is constantly secreting tears, which are carried by narrow ducts to the upper surface of the eyeball, whence they flow down over the eye, finally being collected at the inner corner of the eye and passing into the nose through the lachrymal punctures described above. Under certain circumstances, as from emotion, a blow, or the irritation of a cold wind, the tear fluid is secreted faster than it can escape through the punctures, and so flows over the lids and down the cheeks. ”

“ Its cavity eventually forms the inner optic chamber. The anterior wall of the sack is lined by a much less columnar layer than the posterior, the former giving rise to the epithelium on the inner side of the ciliary processes, the latter to the retina.
Fig. 279. Transverse section through the head of an advanced embryo of Loligo. (After Bobretzky.)
gls. salivary gland; g.vs. visceral ganglion; gc. cerebral ganglion; g.op. optic ganglion; adk. optic cartilage; ak. and y. lateral cartilage or (?) white body; rt. retina; gm. limiting membrane of retina; vk. ciliary region of eye ”

“ The eyelids are developed as ectodermal folds, which blend with one another about the third month and separate again before birth in Man (fig. 7, κ) . The lachrymal sac and duct are formed from solid ectodermal thickenings which later become canalized.
It will thus be seen that the optic nerve and retina are formed from the brain ectoderm; the lens, anterior epithelium of the cornea, skin of the eyelids, conjunctiva and lachrymal apparatus from the superficial ectoderm; while the sclerotic, choroid, vitreous and aqueous humours as well as the iris and cornea are derived from the mesoderm. ”

“ The eyes on the dorsal surface are formed of a cornea, a lens composed of 1-7 cells, and a retina surrounded by pigment; which is perforated in the centre by an optic nerve, the retinal elements being in the inverted position above mentioned.
The development of these eyes has been somewhat imperfectly studied in the adult, in which they continue to be formed anew. They arise by a [Pg 479] differentiation of the epidermis at the end of a papilla. At first a few glandular cells appear in the epidermis in the situation where an eye is about to be formed. ”

“ Anaesthesia of the cornea develops, due to pressure on the nerve fibers that are distributed to the epithelium, the compression probably occurring along the course of the long ciliary nerves, from which the corneal nerves are derived, as they pass between the choroid and the unyielding sclera (Collins & Mayou) .
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. Alteration in the shape of the cornea occurs only rarely in adult life. ”

“ The lacrimal sac, into which the lacrimal ducts open, may fail to discharge its contents by reason of constriction or closure of the duct leading to the nose, and it then forms a rounded swelling beneath the inner angle of the eye. The duct leading from the sac to the nose may be compressed or obliterated by fractures of the bones of the face, and in disease of these bones (osteosarcoma, so-called osteoporosis, diseased teeth, glanders of the nasal sinuses, abscess of the same cavities) . ”

“ This curious circumstance cannot be owing to the action of light on the inflamed vessels of the cornea; it therefore shews, that the extremity of the optic nerve or retina is also rendered more exquisitely sensible to light, by partaking of the inflammation; and I have been told, that red colours are in these cases sometimes painfully perceived even in perfect darkness. This shews that the retina is excited into motion by the stimulus of light; and that, when it is inflamed, these motions give great pain, like those of other inflamed parts, as the muscles, or membranes. ”

“ Now, you must think of the eye as a lens, but one made up of cells, of tissues. It can know inflammation. As a result of many inflammations there is what we call an exudation—a liquid passes from the tissues. This may be thin or serum-like, or it may be heavier, something like granulations. The tissues are weak—they exude something in their distress, in their attempt to correct this condition when they have been inflamed.
"The pupil of your eye is the aperture, the stop of the lens. That is the hole through which the light passes. Around it lie the tissues of the iris. ”

“ Eye of Ammocœtes. The optic vesicle arises as an outgrowth of the fore-brain, but the secondary optic cup is remarkable in the young larva for its small size (fig. 291, opv) . The thicker outer wall gives rise to the retina, and the thinner inner wall to the choroid pigment. The lens is formed as an invagination of the single-layered epidermis (fig. 291, l) . As development proceeds the parts of the eye gradually enlarge, and the mesoblast around the hinder and dorsal part of the optic cup becomes pigmented. ”

“ The proper coats of the eye are reckoned five in number; viz. the sclerotica, cornea, choroides, iris or uvea, and the retina.
After the tunica conjunctiva, or adnata, (a membrane, which, having lined the eyelids in the manner of a cuticle, surrounds the anterior part of the globe) is removed, we perceive a white, firm, membrane, called the sclerotica, which takes its rise from that part of the globe where the optic nerve enters, and surrounds the whole eye, except a little in the fore part; which fore part has a membrane, immediately to be described, called the cornea. ”

“ In inflammation of the external parts of the eye, the redness begins from the margins of the organ, and gradually diffuses itself towards the cornea. Such is not the case in inflammation more deeply seated. There is intolerance of light in a slight degree, and the patient is inclined to keep the eyelids shut. At first the discharge from the conjunctiva and meibomian glands is increased and changed, and flows occasionally over the cheek, producing a scalding sensation. When the eyelids are at rest, as during the night, they become glued together by the viscid fluid from the meibomian follicles ”

“ There is a little gland snugly placed away in the socket of the eye just above the eyeball, which makes tears in the same way that the salivary glands make saliva. It is called the tear gland. The gland usually makes just enough tears to keep the eye moist. There are times when it makes more than enough, as when something gets into the eye, or when we suffer pain or feel unhappy. Then the tears are carried off by means of a little tube which runs down into the nose from the inner corner of the eye. ”

“ This inflammation begins either on or near the edges of the eyelids, or in the loose skin of them, and is sometimes very slow either in coming to suppuration or in dispersing. The skin beneath the lower eyelid is the most frequent seat of this tumor, which sometimes never suppurates at all, but becomes an incysted tumor: for as this skin is very loose for the purpose of admitting great motion to the eyelid, the absorbent power of the veins seems particularly weak in this part; whence when any person is weakened by fatigue or otherwise, a darker shade of colour is seen beneath the eyes ”

“ The emotions exert a remarkable influence upon the action of the perspiratory glands. Intense fear causes great drops of perspiration to accumulate on the skin, while the salivary glands remain inactive.
Tears. The lachrymal glands are small lobular organs, situated at the outer and upper orbit of the eye, and have from six to eight ducts, which open upon the conjunctiva, between the eyelid and its inner fold. This secretion is an alkaline, watery fluid. According to Dr. Dalton, its composition is as follows:
The function of this secretion is to preserve the brilliancy of the eye. ”

“ One particular layer of the cornea may be first attacked, but the whole structure soon becomes involved. The inflammation generally commences in the conjunctival covering. Vision is necessarily much obscured from even slight inflammatory affection of the cornea. Part only of the organ may be affected, but frequently the whole is involved. Sometimes only one or two vessels remain dilated; but still they, passing over the centre of the cornea, render vision indistinct. Opacity of the cornea, to a greater or less degree, always attends dilatation of its vessels. ”

“ The greater or less degree of separation of the retina met with in the different globes is doubtless in part a question of time, but it is also, and probably to a much larger extent, one of the character and grade of the inflammatory process excited in the eyeball. The more plastic the type of inflammation and the more intense the process is, the greater will be the measure of ultimate cicatrisation, always provided that the inflammation is not intense enough to result in suppuration. ”

“ There was a pricking feeling on winking, and the patient could not bear to have the upper lid touched in its outer half. She could only obtain ease by keeping the eyes closed and perfectly still, or wide open with the lids motionless. On examination no foreign body could be seen, and the lids were normal. In the lower outer quadrant of the cornea careful observation showed that the epithelium was ruffled and freely movable over a small area, and in part of the same area was a tiny circular, slightly opaque, raised patch of the corneal tissue. Nothing more could be made out. ”

“ The probable ætiology in this case was an overgrowth of granulation tissue closing the perforation in the cornea, which, owing to an unhealthy condition of the wound and eye, which was anæsthetic and atrophic, had become exuberant, simulating exactly the condition known as “proud flesh” elsewhere. By a process of accumulation and heaping up, the granulations gradually formed a cap over the cornea, whilst the external layers gradually became stratified and horny from the pressure of fresh growth from the central core and by the action of the air. ”

“ The vessels of the anterior quarter enter the lymphatic gland at its most anterior point; those of the posterior quarter join it a little below.
567The retro-mammary lymphatic glands are two in number, and are situated very high and towards the back, above the posterior quarters and close to the perineum, outside the fibrous envelope of the gland. They are sheltered in a recess excavated within the depths of the gland itself. The main collecting lymphatics from the anterior and posterior quarters enter it separately. ”

“ In chronic inflammation the redness is more dull, reddish-blue or grayish; the secretion, sometimes more scanty and sometimes more abundant, is puriform and usually spread out over larger portions of the surface; and the glands are enlarged and prominent, with their ducts so dilated that their mouths are readily visible, sometimes, to the naked eye, and always with a low-power lens, and the rest of the tissue is hypertrophied, especially at the back wall of the trachea. ”

“ The term Lippitudo in this legend, and which we will find recurring in the sequel, was, according to Galen, anciently applied to that form of ophthalmy which consists of inflammation of the conjunctival covering of the cornea (lippitudo inflammatio est membranæ, quæ corneæ adnata est.) 513 But the term was also used to designate other forms or varieties of ophthalmic inflammation. ”

“ The increased tension is supposed to be due to an excess of fluid in the eyeball, and this is commonly attributed to an impeded outflow. The aqueous humor, which is secreted very rapidly, is supposed to escape at the angle formed by the junction of the iris with the cornea, and in glaucoma it is believed that the iris adheres to the cornea so that the angle is obstructed. ”

“ The inner side is lined with a mucous membrane that is exceedingly sensitive, and thus aids in protecting the eye from any irritating substance. The looseness of the skin favors swelling from inflammation or the effusion of blood, as in a "black eye." The eyelashes serve as a kind of sieve to exclude the dust, and, with the lids, to shield against a blinding light. Just within the lashes are oil glands, which lubricate the edges of the lids, and prevent them from adhering to each other. ”