Complete Text (Part 12)

form opacities are first observed at the equator of the lens : they extend in wedge-shaped processes toward the centre, the base of the wedge being toward the equator. The opacities gradually advance until the lens becomes opaque throughout. What is zonular or lamellar cataract? This is a form, usually occurring about the time of birth, which com- prises opacification of a few lamellae of lens-fibres located at the periph- Fig. 15. 2 5 Lamellar Cataract. ery of the nucleus, the centre of the nucleus and the cortex remaining clear. This form of cataract usually changes but little throughout life. What is mixed cataract? This term is applied to the innumerable forms of cataract in which the plan of opacification follows no definite rule. Opaque spots and striae appear throughout the lens-substance. To this form belong many of the congenital cataracts which have little tendency to increase. What is Morgagnian cataract? When senile nuclei or cortical cataract has existed for a long time, the cortical portion sometimes becomes liquefied, only a small solid nucleus remaining. The term Morgagnian is given to this form. What is anterior polar or pyramidal cataract? It is a form of capsular cataract usually caused by adhesion of the anterior capsule of the lens to the cornea, following a perforating ulcer of the cornea and escape of the aqueous humor. When healing of the ulcer occurs and the lens is drawn back into position by reaccumulation of the aqueous, the anterior capsule is slightly detached from the lens- substance, and the small conical protrusion so formed is filled by fibres apparently developed from the epithelioma of the anterior layer of the lens capsule. These new-formed fibres are opaque and remain un- changed. What is posterior polar cataract? Any opacity at the posterior pole of the lens is termed posterior polar 90 THE EYE. cataract. It is usually caused by remnants of foetal blood-vessels. It not infrequently accompanies retinitis pigmentosa. "What are the causes of cataract ? Cataract is undoubtedly due in the vast majority of cases to inter- ference with the nutrition of the lens. In commencing senile cataract careful examination of the periphery of the fundus frequently discloses vascular changes, evident in the presence of peripheral choroiditis. Cataract not infrequently accompanies diabetes mellitus. Convulsions are said to occasion zonular cataract. Injury is a fertile source for the production of cataract, and exposure and privation also act as causes. What is the method employed for the examination of cataract ? The oblique illumination (previously described) is very valuable in the examination of the crystalline lens. If the pupil is dilated, the reflection of light into the eye obliquely will serve to disclose any con- siderable opacity that may exist in the lens. Opacities occurring in the lens usually have a whitish appearance when examined by oblique illu- mination. Certain forms of nuclear cataract give an amber tint, and in the exceptional cases of black cataract the color is a deep brown. The plane mirror of the ophthalmoscope is also used for the examination of opacities in the lens, the opaque portions appearing as dark spots against the red field of the fundus. What are the symptoms of cataract ? The patient frequently first experiences an interference with the vision in the form of dark lines or branching opacities which are projected into space. In some cases a general dimness of vision is first noticed. In the case of nuclear cataract the patient will say that he sees better when the day is dark or just at twilight, when the illumination is so weak that the pupils become somewhat dilated. No pain is experienced. If the cataract is well advanced, the pupil is occupied by an opaque mass which may be white or of a pearly color or brown or almost black. In lamellar cataract examination discloses a circular line of opacity which is most dense at its periphery. It can be seen that the centre of the lens between the layers of opacity is clear, and if the pupil is widely dilated a transparent zone is seen at the periphery of the lens. What is the treatment of cataract ? In lamellar cataract it is sometimes advisable to make an artificial pupil, which will enable the patient to utilize the transparent cortex for visual purposes. If by dilating the pupil, maximum vision is greatly improved in this form of cataract, it is warrantable to make an iridecto- my, as the operation is attended with little danger. Cataracts that occur before the age of twenty-five or thirty years are said to be soft cataracts, because the substance of the lens is not so firm as it becomes in later years. In this form of cataract the operation known as "needling" is employed. THE LENS. 91 How is the needle operation performed ? The eye is cocainized or the patient is given ether. Since the opera- tion under cocaine is painless, this local anaesthetic may be employed. A stop speculum is used to separate the lids. The eye is then fixed with the fixation forceps. A sharp needle known as a cataract needle is made to enter the anterior chamber at a point midway between the centre and periphery of the cornea, usually in the horizontal meridian. The an- terior capsule of the lens is divided and a portion of the lens cortex broken up. This is done through the pupil. The needle is withdrawn, atropine is instilled, the eye bandaged, and the patient put to bed. The Fig. 16. The Needle Operation. operation of needling affords opportunity for the absorption of the lens- substance. It must be repeated three or four times, one operation fol- lowing the other at intervals of three to eight weeks, to promote perfect absorption of the lens. What is the flap extraction? This is the method employed for the complete extraction of the lens, usually without its capsule. It consisted orjginally in making a flap of the lower half of the cornea, The flap was then tilted outward, the lens-capsule wounded, and the lens compelled to escape through the pupil, after which the iris was returned to its former position and a bandage applied. Instead of making a flap of the lower half of the cornea, Jacobson modified the operation by making a flap below, with the incision passing through the sclerotic about 1 mm. back of the sclero-corneal junction. Fig. 17. Fig. 18. oo 92 THE EYE. Fig. 20. <3 Fig. 19. — Fixation Forceps. F;g. 20.— Von Graefe's Linear Cat- aract Knife. What are the instruments required for the extraction of cataract? A stop speculum, Graefe or Beers cat- aract knife, fixation forceps, cystitome, iris scissors, spatula, and small scoop or spoon. What is the linear extraction of Graefe ? It consists in making a linear incision in the globe above the cornea. The in- cision is commenced on a tangent with the horizontal meridian of the cornea, beginning about 2 mm. below the tan- gent with the perpendicular meridian. The point of the knife, after making the puncture, is directed toward the centre of the pupil ; it is then carried upward, and emerges at a point corresponding to the puncture on the opposite side where the counter -puncture is made. By a gentle sweep- Fig. 21. ing motion the blade is made to cut its way out, B 'y ^^A the centre of the incision reaching to the clear mar- gin of the cornea. An iridectomy is then made. The capsule of the lens is then divided with the cystitome. Pres- sure on the lower portipn of the cornea, directed toward the centre of curvature of the globe, made with a small spoon, is sufficient to cause the lens to tilt forward and to escape from the wound. The iris is then disengaged from the wound by means of the spatula, the margins of the wound adjusted, and the eye bandaged. What is the simple operation for cat- aract ? At the present time this operation is much in vogue. The incision made is usually in the nature of a flap. It con- sists in opening the anterior chamber to the extent of about a third of the circum- ference of the cornea, the incision being carried through the sclero -corneal June- u THE LENS. 93 tion just within the clear margin of the cornea or just external to the clear margin in the sclerotic, finishing in the corneal tissue at the sclero- corneal junction or just within the opaque border, according to the idea of the individual operator. The lens-capsule is lacerated either in its centre or near the periphery, pressure is made on the lower part of the cornea, and the lens is expelled through the pupil. No iridectomy is made. The subsequent treatment is as in the Graefe operation. What accidents are apt to occur at the time of operation ? It sometimes happens that the lens, instead of escaping, is pressed backward into the vitreous chamber. When this occurs the wire loop Fig. 22. Operation for Cataract : the incision. may be passed into the vitreous chamber, the lens engaged, and with- drawn. The manoeuvre is not easy, and considerable damage may be done to the eye before the lens is extracted. Escape of vitreous may occur. If this is not large in amount, it is of little importance. The protruding vitreous should be excised, the wound rendered as free as possible from the protruding tissues, and the eye bandaged. In making the incision the iris may fall before the knife and a portion of it be ex- cised. This usually is of little importance. It, however, almost always 94 THE EYE. necessitates the making of an iridectomy. The iris may be engaged by the point of the knife as it enters the anterior chamber. If the knife cannot be readily withdrawn sufficiently to disengage the iris, it should be passed through boldly and the incision completed. Fig. 23. Operation for Cataract : the removal of the lens. What accidents may occur during the healing process ? From engagement of the capsule in the wound a filtration opening may remain, which may cause a permanent fistula of the anterior chamber. Usually, however, when this complication arises the anterior chamber remains empty for some days, when the wound closes firmly and the anterior chamber is re-estabiished. If fistula occurs, it may usually be closed by means of the cautery. The wound may reopen at any time in from twenty-four hours to ten days after the operation by reason of force applied to the eye. This usually simply entails the emptying of the anterior chamber and some hemorrhage into it, except after simple extraction, when prolapse of the iris is sure to follow. Pro- lapse of the iris, if observed soon after its occurrence, should be rem- edied by replacement or excision. What is the treatment of traumatic cataract ? It may be treated as the ordinary form of senile cataract. If, how- THE LENS. 95 ever, laceration of the lens-capsule has taken place, it sometimes hap- pens that the lens-substance swells to such an extent that injury to vision is threatened from the production of a glaucomatous condition. A cor- neal incision must then be made and the lens-substance permitted to escape. In many cases where laceration of the capsule occurs the lens may be permitted to become absorbed, as in the operation for soft cat- aract. What is secondary cataract? Secondary cataract is opacification of the remnants of lens-matter and of the capsule of the lens, which sometimes occurs after the extraction of cataract. What is the treatment for secondary cataract ? An endeavor shouM be made to effect a clear opening through the opaque structure. This may often readily be done by the use of the knife-needle, the operation being conducted as is the operation for the division of soft cataract. In certain cases it will be found necessary to operate by the use of double needles. When this is done the needles are made to enter the anterior chamber at opposite points. They are then made to pierce the opaque structure at the same point (at the centre of the pupil), and an opening is made by separating the points of the nee- dles from each other. When the opening is made sufficiently large the needles are withdrawn, atropine is instilled, and the eye bandaged. What is dislocation of the crystalline lens ? It is a condition in which the lens is freed from the suspensory liga- ment partially or completely. It may be a congenital condition, and is then known as ectopia lentis ; however, it is most frequently traumatic in origin. What are the symptoms of dislocation of the lens ? The patient's vision is markedly impaired. _ On examination the lens is found to have dropped from its normal position : it sometimes hangs by shreds of the suspensory ligament, but is often found lying at the bottom of the vitreous chamber on the ciliary processes. The iris is tremulous and the anterior chamber deep. It sometimes happens that the dislocation takes place into the anterior chamber. When this occurs marked symptoms of irritation are produced. The dislocated lens usually becomes opaque, and when this is the case and partial displacement only has occurred, diminution in vision is very great. What is the treatment of dislocation of the lens ? If the lens falls into the vitreous chamber, or if it is still retained nearly in its former position and is not opaque, no treatment is necessary. If the lens, however, becomes opaque and occludes the pupil, or if it is dislocated into the anterior chamber and is producing inflammatory symptoms, an attempt should be made to remove it. The same plan of 96 THE EYE. operation is employed in most cases as that used for the extraction of cataract. THE VITREOUS HUMOR. What is the vitreous humor? It is a transparent, jelly-like mass that occupies the large posterior chamber of the globe known as the vitreous chamber. It is composed of very fine fibrillae which enclose a gelatinous fluid in their meshes. What pathological changes take place in the vitreous humor? Small molecular opacities occur (usually accompanying a debilitated condition of the system) which are likened to flies by the patient, who projects their images into space. These are of little significance. They are known as muscse volitantes. Large floating opacities, the remnants of exudation and of hemorrhages into the vitreous, also occur. What is synchisis scintillans? It is a condition in which the interior of the eye is filled with small glistening particles, principally in the vitreous. On movements of the eye they become kaleidoscopic. They consist of crystals of tyrosin and cholesterin, and occur in degenerated conditions of the globe. This condition calls for no special treatment. What is the treatment when foreign bodies enter the vitreous? These may consist of substances of all kinds, but particles of iron and steel are most frequently met with. If the foreign body is not of a nature to produce inflammatory reaction, it is probably best to permit it to remain. If it is large or is apt to produce inflammatory changes, an attempt at its removal is advisable. If the substance is of a metallic nature, such as may be attracted by the magnet, an opening through the sclerotic may be made, the magnet point introduced into the vitreous, and an attempt made to find and remove the foreign body. Failing in this, the eye should be enucleated. What parasites are sometimes found in the eye ? The parasite most frequently found is the aysticercus cellulosse. This parasite is seen most frequently in the vitreous. It may appear sub- retinal, and is also found at times in the anterior chamber. The treatment consists in removal. Failing in this, the eye should be enucleated. OPTICAL PRINCIPLES. What is meant by the term "refraction"? This term is used to indicate that change in direction which a ray of light undergoes when it passes from one transparent medium into another of greater or less density. OPTICAL PRINCIPLES. 97 What is a ray of light ? A single line or beam of light emanating from a luminous point. What is the normal of a surface ? This term is used in physics to indicate an imaginary line drawn at right angles to the surface. What is the law of refraction relative to the passage of a ray of light from one transparent medium into another of differ- ent density? The ray of light is refracted toward the normal of the denser medium when it enters in a direction other than the normal to its surface. The Fig. 24. Law of Refraction : AB, incident ray ; B C, refracted ray ; M', rare medium ; M", dense medium ; S S, surface separating media. reverse is true when a ray of light passes from a denser into a lighter medium under the same conditions regarding direction (Fig. 24). What is an incident ray of light? A ray of light that impinges on the surface of a refracting medium. What is implied by the term "index of refraction " ? This term is applied to the number indicating the ratio between the sine of the angle of refraction and the sine of the angle of incidence. What is the unit from which the index of refraction is com- puted ? The conduct or course of a ray of light through air is taken as the unit for the computation of the index of refraction of all other media. Computed in this manner, the index of refraction of crown glass is 1.53 ; of rock-crystal pebble, 1.56; of flint glass, 1.70; of the crystalline lens of the eye, 1.42. 7— Eye. 98 THE EYE. What is the effect produced on a ray of light as it passes through a prism? It is refracted toward