Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/850

Rh 786 Diseases of the eyelids. Diseases of the lacrynml appara tus. mous diplopia). The diplopia is always most distressing, and may cause giddiness when the strabismus is slight. The treatment consists in the use of iodide of potassium in the syphilitic, and in nervine tonics in the neurasthenic cases. The muscle may be fara- dized to keep up its tone. In bad cases tenotomy of the internal rectus may be necessary. The squinting eye may be covered to pre vent the diplopia. (2) Convergent strabismus from over-development of the internal rccti (&quot;concomitant&quot; strabismus) is almost always due to hypermetropia. Its production depends on the intimate relation between accommodation and convergence, every degree of the one evoking a constant quantity of the other, so that nor mally the two eyes are converged upon the object accommodated for. In hypermetropia clear vision needs an excess of accommoda tion which in its turn produces an excess of convergence, so that the two eyes meet in a point nearer than that looked at ; they squint, in short. The eyes may squint only during accommodation for a near object (periodic squint), but generally the internal recti be come so developed as to produce a constant convergence. If either eye is used indifferently for vision the squint is &quot;alternating.&quot; Generally one eye is habitually used, the sight in the other eye becoming defective. The amount of squint bears no ratio to the amount of hypermetropia, being frequently absent in the higher degrees where accommodation fails to give clear sight and is not exercised. Double vision does not occur, because the image of the squinting eye is unconsciously suppressed. In periodic squint glasses to correct the hypermetropia ought to be given. For permanent squint division of the tendons of one or both internal recti muscles is necessary. The operation diminishes the power of these muscles by allowing them to become attached to the globe farther back. Care must be taken not to produce too great an effect, it being preferable rather to leave a little convergence. In rare cases myopia is associated with convergent squint. Divergent Strabismus arises from weakness of the internal rectus, as in myopia. In the condition known as muscular asthenopia it is present only after a prolonged effort of convergence. It arises also where the sight is defective, as with corneal opacities, or from unskilful operation for convergent squint. It can generally be improved by tenotomy of the external and &quot;advancement&quot; of the internal rectus muscle. In paralysis of the superior oblique muscle the deviation is slight. Owing to interference with the movement downward and outward, double vision is present when the eyes are directed below the hori zontal line. Paralysis of the Third Nerve causes ptosis, loss of accommodation, and dilatation of the pupil, and the eye can be moved only slightly downwards and outwards. All the branches are seldom affected alike. Ophthalmia Tarsi (blepharitis) is a chronic inflammation of the follicles of the eyelashes and their glands, attacking strumous children, especially after measles. The edges of the lids are covered with small scabs, which gum the lashes into pencils ; when the scabs are removed small freely -bleeding ulcers are exposed. The conjunctiva is also reddened. Eventually the lashes either fall out or become misdirected, the border of the lids looks thickened and bald, and the eyes continually water from eversion of the orifice of the tear-duct. The scabs must be removed daily by means of an alkaline lotion, and a weak mercurial ointment applied to the lids. In bad cases the lashes must be pulled out, and the ulcers touched with nitrate of silver. A Stye is an abscess in a Meibomian gland, or in the cellular tissue of the lid. Styes are apt to occur in crops, and generally point to some derangement of health. They should be poulticed till the_ matter points, then opened with a lancet. Tonics are needed internally. Chalazion is a cyst in a Meibomian gland. It forms a small pea- sized painless swelling under the skin of the lid. It should be opened from the conjunctival surface and its contents expressed. Ejnthelioma (rodent ulcer) occurs in old people, grows slowly, forming a hard irregular mass, with an ulcerated surface covered by scabs ; it may extend in all directions, destroying the tissues it reaches. The treatment consists in complete removal by the knife or chloride of zinc paste. The lacrymal gland sometimes suppurates, and must be treated like any other abscess. Most of the diseases of this system arise in the punctum, canaliculi, lacrymal sac, or nasal duct, and all cause overflow of tears on the cheek. The punctum may be everted, from disease of the conjunctiva, paralysis of the facial nerve, or the dragging of a scar in the cheek. The canaliculus may be constricted or obliterated. The nasal duct may be obstructed from chronic disease of its mucous membrane or bony wall. The result of this is the retention of tears in the lacrymal sac, then the formation by distension of this sac of a small tumour at the inner angle of the eye, from which first clear mucus, and possibly, at a later period, also pus may be pressed back into the eye. * Finally, if the case is neglected an abscess may form which may burst externally and cause a troublesome fistula. The treatment in the first place must be the dilatation of the stricture. The canaliculus is first slit on its conjunctival surface along its whole length, then successively larger probes are passed through the stricture. Abscesses when formed must be opened, and when inflammation has subsided the stricture dilated. The sac may be washed with astringent solutions. When the stricture is due to bone-disease its cure is not hopeful. Blows may rupture the coats of the eye, the sclerotic and Injuria underlying coats being generally injured. Haemorrhage takes place of tlie between the coats and into the chambers of the eye. The eye may eyeball be removed at once ; if any perception of light remain, the excision should be delayed to see if there be any chance of the eye being saved. Usually the eye shrinks and becomes quite iiseless. Blows may cause damage to the interior of the eye without injuring the outer coats. There may be haemorrhage into the anterior or the posterior chamber, the latter a most serious con dition, seldom completely recovered from. The choroid may be raptured, the lens dislocated, or the iris torn from part of its ciliary attachment ; and the retina is not seldom detached from the choroid. Wounds. Small foreign bodies bits of steel, &c. are often impacted in the cornea. They should be removed as soon as possible, as they give rise to great pain, and may seriously injure, the cornea. If there is much after-irritation atropine should be used freely to the eye. Burns with caustic alkalis and acids or molten lead are common. When seen the whole conjunctiva should be carefully freed from all of the irritant. If lime has been the cause, a weak acid lotion should be used. Then oil should be dropped into the conjunctival sac, and any inflammatory symptoms treated as they arise. If the epithelial layer of the cornea only has been destroyed, it often clears to a wonderful extent ; but deeper injuries may cause severe ulcerative inflammation of the cornea, and the conjunctiva may slough in part, with ultimate formation of a scar binding the lid to the eye (symblepharon). Penetrating Wounds. Such wounds of the cornea and sclerotic, if only the foreign body be not in the eye, generally do well. Usually some of the deeper structures are involved, and these cases are always very serious. The eye may be rapidly lost from general inflammation, or if not it may become completely blind. In almost any case, especially where the wound is in the ciliary region, the other eye is apt to be sympathetically involved. If the injured eye therefore is blind, and if there is inflammation in the ciliary region, it must be at once excised. If the eye be not blind, the ciliary region quiet, and no foreign body in the lens or vitreous humour, the eye may be preserved, the danger of involvement of the other eye being put before the patient. In such cases it is impossible to lay down any general rules. Each case must be judged on its own merits by the ophthalmic surgeon. USE OF THE OPHTHALMOSCOPE. The ophthalmoscope consists of a small mirror with a small Use of aperture in the centre. Most instruments have now in addition a the opi series of concave and convex lenses arranged on a disk so that they thalmo- can be brought successively behind the central perforation. A large scope, lens of about 3-inch focus is also required. Kays of light entering the eye in any given direction are reflected by the choroid along the same direction. Ordinarily, therefore, the fundus cannot be seen, because an eye so placed as to see the emerging rays intercepts the entrant ones. The ophthalmoscope, by placing the source of light in front of the observer s eye, enables it to see and examine the interior of the other eye. There are two methods of examination, the indirect and the direct. (1) The indirect method, which forms a real, inverted, and slightly magnified image in front of the observed eye, may be illustrated thus. Place a convex lens of 2-inch focus in front of this page, and let these represent crystalline lens and retina respect ively. Place now a second similar lens in front of the first, and the print will be seen inverted and slightly magnified. (2) The direct method forms a virtual, erect, much magnified image. Place one of the above lenses within 2 inches of the page and your own eye close to it. The letters will appear erect and enlarged. To use the ophthalmoscope, place the patient in a dark room, with a lamp to one side of and a little behind the head. If the indirect method is to be employed, sit in front of the patient, with the mirror in your right hand before your right eye, the large lens in your left. Reflect the light from a distance of about 2 feet into one of the eyes, and when you see a red reflexion place the lens in front of it, and you will obtain the inverted image of the fundus. (A) Begin your examination with the optic disk by telling the patient to direct the observed eye a little inwards. Note the follow ing points : (a] the colour of the disk, normally a yellowish pink, but varying considerably owing to tint of surrounding choroid, &c. ; (b) a paler spot in its centre, which may be due to the funnel-shaped expansion of the nerve, the physiological cup ; (c) the distinctness of the edge (spots of black pigment here are of no importance) ; (d] when the lens is removed from the eye the image of the disk remains of the same size if the eye is emmetropic, becomes smaller if the eye is hypermetropic, and larger if it is myopic, and alters in shape if there is astigmatism. (B) The retinal vessels appear as