CHAPTER X Tue Iris (Part 1)

CHAPTER X Tue Iris We need to be familiar with the appearance of the normal iris, and with its muscular movements, if we are to detect with certainty any abnormal deviations. Its surface is lustrous, but uneven; its color varies physiologically from blue to a brownish-black, and it presents near its center a round opening called the pupil, and we have to observe any lack of luster, any pathological unevenness or color, and any fault in the contour, position, or reactions of the pupil. The pupillary margin has a black edge, which is the termination of the retinal layer, and the only part of the central nervous system that can be seen without artificial aid. It appears to be broader when the pupil is contracted, and to become narrower as the latter dilates; it is finely serrated, and sometimes presents a circumscribed black mass that may look like a little tumor, or may overhang the tinted part of the iris so as to counterfeit the appearance of a notch in the margin. When such a mass is congenital and does not increase in size, it is called an ectropion of the uvea, and is of no pathological importance. Next to this black edge comes the region of the sphincter, a narrow circular band with minute radi- ating folds on its surface that become deeper as the pupil contracts. Next to this is a circular elevation, the minor circle or corona, which divides the iris into two unequal parts, the pupillary zone, that includes the black edge and the region of the sphincter, and the ciliary zone, that occupies the greater part of the visible iris. In the latter we see folds which radiate out from the minor circle, and other lines that run deviously, but in a generally radiating direction, with depressions known as crypts between them, which give the iris a mottled appearance through the shadows formed in them, or through an irregular distribution of pigment. In addition to these there are circular furrows that run concentrically to the circumfer- ence and grow deeper as the pupil dilates; these are the contraction furrows or folds. The outermost part of the iris which is hidden 202 THE IRIS 203 from view by the opaque margin of the cornea is called the periph- eral zone, and an arterial plexus in its outer edge is known as the major circle. The elevations and depressions are symmetrical and form the details of the design of the iris, and any elevation of the surface that is not symmetrical and does not form one of the details of this design is abnormal. PERSISTENT PUPILLARY MEMBRANE Occasionally we see an eye in which cords or tags of tissue extend from the anterior surface of the iris partly or wholly across the pupil. When they arise from the corona, or from the ciliary zone, they are remnants of the fetal pupillary membrane, but when they arise from the pupillary zone they are to be looked upon as indica- tive of some pathological condition. Remnants of the pupillary membrane sometimes extend across the pupil from one point to another on the surface of the iris, always outside of the pupillary zone, and occasionally one can be seen to be attached to the anterior capsule of the lens. COLOR OF THE IRIS The color of the normal iris depends not only on the pigment in the retinal layer, but also on the amount of pigment in the chromatophores which lie in the connective tissue of the stroma, and may be blue, gray, hazel, or some shade of brown. When the pigment in the chromatophores is scanty the color of the iris is blue. The iris of an albino appears to be pink when seen by light re- flected from the fundus, and blue at other times, because pigment is wanting in both the chromatophores and the retinal layer. The greater the amount of pigment in the chromatophores the darker is the iris, which may be almost black, and the more does its sur- face have a dusty or granular appearance. The color of the two irides is usually, but not always, the same, yet often we have to rely on a comparison of the two in order to detect a pathological change of color, which may be simply a darkening and readily escape notice. When the iris of a diseased eye is greenish and that of its mate is blue, we infer that the stroma is infiltrated. A muddy, greenish, or brownish color with loss of luster indicates the pres- ence of exudates either on the surface of the iris itself, or on the 204 DIAGNOSIS FROM OCULAR SYMPTOMS posterior surface of the cornea, or else a turbid aqueous, very often any two or all three of these. A yellow-brown, rusty color sug- gests siderosis, or old, recurrent hemorrhages within the eye. A brassy, or dirty straw color leads us to think of a purulent iritis. The distribution of pigment is not always even. In many irides there are little dark or light colored spots, aside from the crypts, where the pigment is more or less dense than elsewhere. These pigmented nevi are physiological in the great majority of cases, but when a little dark spot in his iris has recently caught the atten- tion of an adult patient we should look to see if it is elevated above the surrounding surface, and try to keep it under observation until we can ascertain whether it is stationary, or is increasing in size, for a melanosarcoma has been known to start in this manner in very rare cases, and to grow for quite a while without causing irri- tation. In other cases the distribution of the pigment is so irregular that one part of the iris may be blue or gray, while another part is brown, but as long as the normal luster is present we need not think of an atrophy confined to a certain sector. Such a hetero- chromia may exist in one or both eyes. The color of the two irides is altogether different in some cases, and the same name, hetero- chromia, is applied to this condition. The luster of a light-colored iris is brighter than that of a dark one, but no matter what the color, it is never dull under normal conditions. THE NORMAL PUPIL We speak of the pupil as central, though when we wish to de- scribe its location accurately we have to say that it is slightly below and to the inner side of the center of the iris. It is round, has a regular contour, and varies greatly in size under physiological con- ditions, so much so that figures which purport to give its average diameter are of little practical service. It is smallest, and its mar- gins are quiet, during deep sleep, but if we watch it through a strong magnifying glass during consciousness we shall see that it is never quiet, but makes incessant minute movements to regulate the quantity of light which enters the eye, to shut off diffusion circles that tend to blur the retinal images, and perhaps in response to mental processes. Any change in the light causes a perceptible change in its diameter, and when the light is steady its diameter may vary as much as 2 mm., according to the amount of THE IRIS 205 accommodation called into action, and is increased greatly by the play of certain emotions. The pupil of a myope is apt to be larger than that of a hypermetrope, but its size varies in both with the age of the patient. It is small in infancy, increases in size till about the age of five, remains at its maximum until about twenty-five, then begins to grow smaller, and is quite small again in old age. This wide physiological variation renders it impossible for us to detect minute abnormal deviations, but we can tell when a pupil is dilated to an unusual extent, or strongly contracted. Abnormal dilatation of the pupil is called mydriasis, abnormal contraction myosis. In the great majority of people the pupils of the two eyes are practically equal, and a marked difference in size commonly is a pathological symptom, but occasionally we meet with a case in which this anisocoria is physiological. REACTIONS OF THE PUPIL The contractions and relaxations of the muscles of the iris in re- sponse to stimuli make themselves manifest in certain reactions of the pupils, modifications of which are of great diagnostic importance. Reaction of the Pupil to Light The pupil contracts when the illumination is increased, and dilates when it is decreased; this is the direct reflex reaction to light. Ordinarily we test this reflex by covering both eyes for a short time and suddenly removing the screen from before one of them, or by flashing a stronger light than that of the room into one pupil, which is then seen to contract. The pupil of the other eye contracts at the same time by what is called the consensual or indirect reaction; this contraction is very slightly less, but practically equal to that produced by the direct reaction. It is believed at the present time that the light stimulus is re- ceived by the rods and cones of the retina, possibly only by those of a rather small area in the region of the macula, transmitted through the coarser fibers of the optic nerve to the chiasm, where part of them decussate, thence along the dorsolateral parts of the optic tracts to the corpora quadrigemina, and then, by a course as yet uncertain, from this point to the nucleus of the sphincter, which forms a part of the oculomotor nucleus. This nervous tract for conveying the stimulus from the rods and cones to the nucleus is 206 DIAGNOSIS FROM OCULAR SYMPTOMS called the centripetal neuron. The stimulus for the contraction of the sphincter starts in its nucleus and follows the centrifugal neuron in the inner part of the motoroculi into the orbit, through a branch of this nerve to the ciliary ganglion, and in the short ciliary nerves to the iris and the sphincter. The centripetal and centrifugal neurons together form the light reflex arc. Probably association fibers exist between the light reflex arcs of the two sides which, together with the centripetal neurons that decussate at the chiasm, account for the consensual reaction, for the pupil of a blind eye may not respond to light directly, and yet light thrown into the other eye may excite a consensual reaction. Rather less than half a second elapses between the entrance of light into the eye and the beginning of the visible contraction of the pupil, which occupies from three fourths to one second, but the reaction may be rendered slow or slight by a pathological condition, and then it may be of considerable diagnostic importance to deter- mine whether it has been completely abolished or not. When we feel uncertain as to the results of the above test we take the patient into a dark room, let him remain a few minutes until his retine have become adapted to darkness, then flash a bright light directly into his eye and watch closely for any movement of the pupil. If there is no movement the reflex is abolished, if there is a slight or slow one it has been impaired. Reaction of the Pupil to Convergence If we place an object a few inches in front of a patient’s eyes, in the midplane between them, his two internal recti, ciliary mus- cles, and pupils will contract as he fixes upon it, if they are all in a normal condition. Thus we have an associated convergence, accom- modation, and contraction of the pupils when we look at near ob- jects. Whether the accommodation or the convergence is responsible for the condition of the pupil has been the subject of much discus- sion, but at present its contraction is referred by most students to the convergence. Although it is automatic this reaction is dependent to a certain degree on the will and therefore is not a pure reflex. The centripetal neuron runs from the cortex of the brain to the oculomotor nucleus, the centrifugal through the motoroculi, the ciliary ganglion, and the short ciliary nerves to the sphincter and Mueller’s muscle, both of which contract. THE IRIS 207 Myotonic Convergence Reaction Once in a great while we meet with a patient in whom the re- action to convergence is slow in one or both eyes, the pupil remains contracted for some time after the convergence has ceased, and then proceeds to dilate slowly. The phenomenon is more noticeable when one eye only is affected. In a case reported by Oloff the left pupil contracted slowly while the eyes were fixed on a near object, but finally became smaller than the right; then when the patient gazed into the distance the right pupil dilated promptly, while the left remained contracted for about thirty seconds and finally dilated slowly. The nature of this trouble is uncertain; some observers have thought it to be an incomplete absolute immobility of the pupil, but this opinion has not been accepted. In most cases it is asso- ciated with a faulty light reflex, and sometimes the accommodation is paretic, but these conditions are not present in every case. It has been met with after traumatism, and in such diverse diseases as alcoholism, measles, tabes, migraine with attacks of fainting, general ‘paresis, diabetes, multiple sclerosis, exophthalmic goiter, and neuras- thenia. Probably it has a central origin, but it is of little or no diag- nostic value at present. Reaction of the Pupils to Closure of the Lids If we hold the lids apart and the patient tries hard to close the eye, we see the pupil contract, probably because the impulse sent to the muscles through the facial branch of the motoroculi is com- municated to the sphincter. This reflex is both direct and indirect, and is to be seen most plainly in cases of reflex immobility of the pupils. It was discovered by von Graefe, and has been studied con- siderably by Gifford, but it is of little diagnostic value, except that when we have to deal with a lesion at the oculomotor nucleus, it enables us to learn whether the sphincter is paralyzed or not. Cortical or Attention Reflex of the Pupils Haab discovered that when a person’s attention is called to a light placed at his side as he looks forward at a dark wall, his pupils will contract and remain small until his attention has been called to something else, although his eyes have not moved and the illumi- 208 DIAGNOSIS FROM OCULAR SYMPTOMS nation has been constant. Other observers have found that the same _ reflex was obtained when the presence of a light was suggested even though it were absent. The only information gained from this test is that the nucleus of the sphincter and the centrifugal neuron are unimpaired. It has been obtained in eyes that were totally blind from optic atrophy, and in some cases of reflex and total immo- bility of the pupil. Reflex Dilatation of the Pupil It goes without saying that dilatation of the pupil follows all of these reactions as soon as the cause of the contraction ceases to act, but the pupils dilate also in reflex response to sensory and psychic stimuli, as well as to irritation of the sympathetic nerve. Such a reflex dilatation is caused by pain, whether internal, like the various forms of colic, or external through irritation of the sensory nerves of the skin, conjunctiva, or cornea. The pupil can be made to dilate slowly and widely by pricking the skin of the malar region for half a minute, and then it contracts suddenly. Strong emotions, like fear and anger, likewise cause the pupils to dilate widely. The dilatation induced by these sensory and psychic stimuli is able to overcome the most powerful contraction that is produced by light. Another dilatation which is considered to be psychic occurs when a person awakes from a sound sleep. During sleep the pupils are very small, but they dilate widely the moment the person wakens, so that he is dazzled if he is in a bright light; if he is not dazzled we are likely to find the pupil in a state of spastic or paralytic myosis, induced perhaps by toxemia, opium, or morphine. MALFORMATIONS OF THE PUPIL In addition to abnormal dilatation and contraction we often see pupils which may be central and oval or irregular, or displaced from the center and more or less distorted, while occasionally we find more than one aperture in the iris, or that a part or the whole of the iris is wanting. Most of these malformations are the results of pathological conditions, but some are congenital, and we need to be able to distinguish these at once. THE IRIS 209 Posterior Synechiz When a central pupil has an irregular contour, or assumes one when it has been dilated, we know that one or more parts of its margin are bound down to the anterior capsule by adhesions which are called posterior synechia, and are infallible indications of a present or past iritis. These posterior synechie usually form pro- jections of the iris tissue that jut out into the pupil and distort the latter into a great variety of shapes, but occasionally they glue the edge alone along a part of its length to the anterior capsule. The synechiz may be few or many, and sometimes the entire margin is bound down, when we say that the pupil is excluded, or secluded; in such a condition the aqueous is apt to accumulate in the posterior chamber and bulge forward the ciliary zone of the iris so as to form what is called a crater pupil. In other cases the entire contiguous surfaces of the iris and lens