Complete Text (Part 14)

Paralysis of Accommodation results from (a) cen- tral lesion of the fourth ventrical, as from brain, tu- mor, cerebral sclerosis, toxins (diphtheria), consti- tutional diseases, (b) interruptions of the course of the third or ciliary nerve, as in cerebral tumors, neu- romata, etc., or (c) peripheral paralysis of the ciliary nerves, as in the action of certain drugs, notably atropin. The location of the lesion may be diagnosed by the involvement or otherwise of other muscles. Spasm of Accommodation results from over-use of the ciliary nerves, and is a common accompaniment of errors of refraction. ^i 1. *m Convergence is the faculty of directing the yel- low spots of both eyes toward a point for the recep- tion of divergent rays, i. e., toward a near point, and is accomplished by means of the internal recti. Innervation is mediated by the third cranial nerve. Convergence and accommodation are closely asso- ciated, and in the normal eye are performed in direct 178 FUNCTIONAL DIAGNOSIS ratio, but they are quite independent faculties and may be exercised independently. Anomalies of Convergence have already been dis- cussed under the heading of ocular movements. ■"W fm •k The Iris serves as a cut-off to the light that enters the eye, much the same as the shutter of a camera, so that the image upon the retina may be clear. Its circular muscle (sphincter), contracting, contracts the pupil; its longitudinal muscles, by contracting, dilate the pupil. Sluggish or Immobile Pupil results from adhesion of the iris, to the lens in iritis with exudation. Photophobia and Disordered Vision are seen in iritis because of interference with the regulation of light entering the eye. The Pain of iritis is spasmodic because it increases with contraction of the longitudinal muscles, and worse at night because these muscles are then in steady contraction. •W V V Innervation of the Iris is a reflex phenomenon. The afferent stimulus is furnished by light falling upon the retina, the impulse being carried by fibres which accompany the optic nerve as far as the corpora quadrigemina, where they branch off to the centre in the fourth ventricle. The efferent (motor) im- pulse is conveyed to the sphincter by means of the third cranial nerve through the ciliary ganglion. The longitudinal muscles are innervated by the sym- FUNCTIONAL DIAGNOSIS 179 pathetics. It is an involuntary phenomenon, which may be inhibited, but not consciously, by the brain, as in case of emotions, nervous conditions, etc. Mydriasis (dilation of the pupil) is caused by any condition which (a) paralyzes either the central or peripheral end of the third nerve, (b) inhibits its functionation through the brain, or (c) stimulates the sympathetic. Tumors of the brain, and of the third nerve, and the action of certain drugs, notably atropin, are ex- amples of the first class. Fevers, comatose conditions, hemasthenia, tubercu- losis, and nervous depression are instances of the second class. Pain, sensory irritation, and visceral diseases fur- nish illustrations of the third variety. Myosis (contraction of the pupils) on the other hand, results from influences which (a) irritate the third nerve, or (b) depress the sympathetic. Photophobia, from any cause, brain tumors, men- ingitis and certain drugs, as eserin, are instances of the former; spinal sclerosis, aneurisms (by pressure)' and opium of the latter. Argyll-Robertson Pupil, in which the pupil reflex is wanting, is seen in tabes dorsalis and dementia paralytica, supposed to be due to involvement of Minert's fibres. Wernicke Pupillary Reaction is a test for deter- mining the location of an injury to the optic tract, (usually employed in cases of hemianopsia). If the 180 FUNCTIONAL DIAGNOSIS reflex is present, in the half of the eye that is af- fected, then the lesion is back of the corpora quad- rigemnia; if not, it is in front of these ganglia; be- cause at that point the reflex path leaves the optic tract to go to the ventricle. Hippos, a periodic contraction and dilatation of the pupil, due to alternate excitation and inhibition, is seen in disorders affecting the emotions, as in mania, hysteria, etc. "b ^. «W The Humors of the eye, consisting of the aqueous, the vitreous, and the lens, serve as a refracting me- dium for rays of light, their resultant index of re- fraction, together with that of the surfaces of the cornea, lens, and vitreous, being just sufficient in a normal eye to focus parallel rays on the retina. Inter-Ocular Tension results from a disturbance between the secretion and absorption of the humors. This condition is known as Glaucoma. The steady increase of internal pressure in this dis- ease produces a characteristic train of symptoms, such as steady pain, cupping of the disc, vascular stasis, dimness of vision, and, if not relieved, even- tual blindness due to destruction of the eye. Scotoma (blind spot) is frequently due to opaci- ties in the humor, especially the vitreous, in which case they are seen by the patient as spots before the eyes (muscae volitantes). Cataract, an opacity of the lens, produces, of course, diminished acuteness of vision, most marked FUNCTIONAL DIAGNOSIS 181 when it is central, least marked when it is peripheral in location. Vision is better in dim light, because the pupil is then dilated and more rays (relatively) en- ter the eye. Increase in index of refraction, due to increased density of the lens, occurs in cataract producing my- opia (short sight). 1i •!» % Stimulation of the Retina. — The light, falling on the retina, stimulates the rods and cones, which in turn, transmit the vibrations to the fibrils of the op- tic nerve. Inasmuch as the image on the retina is a crossed one, the halves of the retina receive stimuli from the opposite field of vision, i. e., the nasal half receives light from the temporal field and the tem- poral half from the nasal field. The character of the impulse generated by the light is not clear, some holding it to be thermic, some electric, some chem- ical. Certain it is, however, that the rods and cones transform the light vibrations into another type of impulse, for light falling directly on the optic nerve makes no impression (blind spot). In the ordinary use of the eye, the visional percep- tion is concentrated entirely upon those stimulations which fall upon the central portion of the retinal field; those which fall upon the peripheral areas make no conscious effect upon the brain unless spe- cial conscious effort is made to perceive them. Hemianopsia (blindness of one-half of the retina) must be subjectively diagnosed with a view to the 182 FUNCTIONAL DIAGNOSIS crossed rays — paralysis of the nasal half producing blindness to objects in the temporal field of vision, and vice versa. Flashes of light are seen in retinitis, due to the sensitive condition of the retina to stimulation, but steady over-stimulation is almost unknown, because the inflammation quickly renders the rods and cones impermeable to stimulus. Diminution of Vision is far the commoner symp- tom in all forms of retinitis, also in degeneration of the retina, glioma (tumor of the retina), anemia, due to poor circulation. Sudden Blindness results from embolism of the central retinal artery, cutting off its entire blood supply and gradual blindness from retinal throm- bosis. Scotoma (blind spot) results from a defect in the retina. If the defect is in the peripheral field the spot is not perceived by the patient; but when it is in the central field the patient perceives it as a fixed defect of vision. •m •. •. The Optic Nerve serves to conduct the light im- pulses from the retina to the chiasm, each optic nerve conveying impulses from its respective retina alone. Lesions of the Optic Nerve alone, naturally affect only that eye supplied by the pathologic nerve. In- asmuch, however, as optic neuritis (practically the only known pathologic condition) is usually due either to brain lesions or to infectious diseases, it is FUNCTIONAL DIAGNOSIS 183 usually bilateral. It is, of course, always attended with diminution of vision, and eventually, if not cured, by blindness. Complete Blindness of one eye always indicates injury to the optic nerve for reasons explained under The Optic Tracts. -» > "W The Optic Tract. — At the chiasm the impulses decussate, those from the right half of each ret- ina proceeding to the right occipital lobe, and those from the left half to the left. Impulses from the macula lutea, however, go to both lobes. Hence, re- membering the crossed image on the retina, visual impulses excited by objects in the left visual field are represented in the right occipital hemisphere, and vice versa. Hemianopsia. — This arrangement makes possible that frequent form of visual disturbance known as hemianopsia or hemianopia, paralysis of one lateral half of the retinal field, manifested, of course, by blindness to the opposite visual field. Temporal Hemianopsia, i. e., blindness to both tem- poral fields, must necessarily be due to an interrup- tion involving the inner half of the optic tracts, viz., either one lesion in the center of the chiasm, or two separate lesions, one in each occipital lobe. Nasal Hemianopsia, i. e., blindness to both nasal fields, is due to interruption of the outer halves of the tract, and must be two separate lesions, one each side of the chiasm, or one in each occipital lobe. 184 FUNCTIONAL DIAGNOSIS Homogeneous Hemianopsia, i. e., blindness to the nasal field in one eye, and to the temporal field in the other, is due to an interruption of one whole tract, or destruction of one whole occipital lobe. Scintillating Scotoma, temporary hemianopsia, due to circulatory disturbances in one of the occipital lobes is seen in migraine. Complete Blindness of One Eye, as will readily be seen, must be due in every case to a lesion in front of the chiasm, as only there are both fields of one eye alone represented. 1. •m "W Visual Centre. — From both the occipital lobes the impulses are conveyed to the visual centre in the left frontal convolution of the cerebral cortex, where all the areas of both eyes have central representation. Functional Disturbances of the centre have al- ready been fully discussed under the Nervous Sys- tem, q. v. Congenital Amblyopia, a defect of vision, not rem- ediable by glasses, and usually associated with high degrees of refractional error, is due to the fact that a distinct image never having been thrown upon the retina, the brain has never learned to interpret the stimulus aright. ■fc "W *m Theories of Color Perception. — Two theories pre- vail to account for color perception. The Young-Helmholz Theory holds that there are present in the normal retina three photo-chemical FUNCTIONAL DIAGNOSIS 185 substances, whose decomposition imparts to the optic nerve three distinct sensations. The maximum stim- ulation of these separate substances is produced re- spectively by red, green and violet waves, but every spectrum wave stimulates all three to a greater or less degree, and the relative degrees of stimulation thus produced in the three substances determine the color sensation perceived by the brain. The Hexing Theory also assumes the existence of three photo-chemical substances in the retina, but at- tributes to each a double stimulative faculty, certain spectrum waves causing assimilation of the substance and other waves disassimilation, these two effects in their turn producing correspondingly different color sensations. The double capacity and stimulation ef- fect of these substances may be thus expressed. Assimilation. Disassimilation. Red-Green Red Green Yellow-Blue Yellow Blue White-Black White Black Varying degrees of assimilation and disassimila- tion in the various substances, of course, produce corresponding combined color sensations. Color Blindness. — Frequently a patient is met with who is unable to perceive certain colors, and is therefore said to be color blind to that particular color and its combinations. The commonest colors to which color blindness is found are red and green. This condition may be (a) retinal, i. e., due to a de- 186 FUNCTIONAL DIAGNOSIS ~~'3E feet in the retina, by far the most common variety, or (b) central, i. e., due to a defect in the visual center. Whichever of the two theories above out- lined be accepted, the retinal defect must consist in an absence of the photo-chemical substance whose maximum modification is brought about by the spec- trum wave corresponding to the color to which sen- sation is lacking. Because of its investigation by Dalton, this con- dition is sometimes known as Daltonism. FUNCTIONAL DIAGNOSIS 187 HEARING. The Muscular Movements of the ear are limited to the action of the tensor tympani and stapedius, both of which render the tympanic membrane more re- ceptive to sound, the former by direct tension of the membrane, the latter by traction on the stapes. Innervation of these muscles is mediated by the fifth cranial nerve. In Facial Paralysis (of the fifth nerve) the fac- ulty of rendering the ear drum tense is lost, and the hearing is impaired to that extent. m ^ «U The Tympanic Membrane is set in motion by the air waves, and by virtue of its funnel-like structure, transmits them in diminished amplitude and in- creased intensity to the ossicles. Imperfect Vibration of the tympanic membrane occurs in any condition which (1) interferes with the diaphragmatic adjustment of the membrane, as in myringitis (inflammation of the drum), chalk de- posits on the drum, catarrh, and impaction of ceru- men, all of which thicken the membrane, and in perforation, which destroys its tension and integrity; and (2) bars the meatus leading to the drum, as in catarrh, impacted cerumen, and growths of the meatus. ■k ?W "m The Eustachean Tube admits air to the tympanic chamber, thus maintaining equal atmospheric pres- 188 FUNCTIONAL DIAGNOSIS sure on both sides of the membrane and enhancing its delicacy of vibration. Bulging of the Membrane, and consequent impair- ment of its vibrations, result from blocking of the tube, as in exudative inflammation, catarrh, and ab- scess. •m Tm "1« The Ossicles, comprising the malleus, incus and stapes, receive the vibrations of the tympanic mem- brane and transmit them to the membrane of the fenestra ovalis. By virtue of their arrangement they also diminish the amplitude of the vibrations (Helm- holz estimates by one-third) and increase their in- tensity (according to the same authority, by one- half). Impaired Hearing results from any influence which either changes the relative sizes and relations of the ossicles as hypertrophy due to catarrh, caries, etc., or interferes with their free motion, as anky- losis. k V • The Perilymph, filling the internal ear, receives the vibrations from the fenestra ovalis, and trans- mits them to the rods of Corti in the cochlea. Rhine's Test for determining the location of a lesion causing deafness depends upon the fact that if the course from the external meatus to the fenes- tra ovalis is interrupted while the internal ear and auditory nerve are intact, vibrations will be com- FUNCTIONAL DIAGNOSIS 189 municated to the perilymp more readily by way of the bones of the head than by the meatus (Rhine +), the lesion is located in the external or middle ear; but if the contrary (Rinne — ) the lesion is in the internal ear. Weber's Test shows that in affections of the mid- dle ear and integrity of the nervous mechanism, a tuning fork held up the vertex is heard better in the •deafer ear (Weber +) and vice versa (Weber — ). This depends upon the fact that where the middle ear is blocked the vibrations received through the head bones find no outlet through the meatus and are confined to the perilymph, being thereby intensi- fied. ^i •m • The Rods of Corti, comprising the organ of Corti, perform the essential part of the function of hear- ing. They are from 16,000 to 20,000 in number, and are stimulated by sound waves in much the same way that the rods and cones of Jacob's are stimu- lated by light waves. The Piano Theory of Hearing assumes that each rod of Corti is a resonator, responding to a distinct pitch or wave-length, and that simple and com- pound sensation of sound depend upon the stimula- tion of one or more of these resonators, recording a specific reaction in the brain for each rod. The Telephone Theory holds that the compound sound wave stimulates the organ of Corti as a unit, and that the analysis of the sensation is performed in the brain centre. 190 FUNCTIONAL DIAGNOSIS In Disease of the Labyrinth extending from the middle ear, the hearing for high pitched notes ia greatly impaired, because the few short rods at the commencement of Corti's organ, hear the vestibule resonate to high pitched sound waves. ■b ?W "in Auditory Limits. — The range of perceptible sound waves varies in different individuals, but the aver- age audible gamut is from 30 vibrations per second (low pitch) to 40,000 per second (high pitch). Slower vibrations than the former, if perceived at all, are usually only perceived as stimulations of the sensory nerve of the tympanum — the auditory nerve does not react to them ; or else the auditory nerve re- sponds to their overtones, for particulars of which a work on acoustics must be consulted. Pathological Limitations of Fitch are caused by ankylosis of the ossicles which prevents those bones from vibrating rapidly. ■w "1. «w The Auditory Nerve collects the vibrations from the rods of Corti and transmits them to the auditory centre in the temporal lobe, each ear being separate- ly represented in each corresponding temporal lobe. Sudden Deafness is a prominent symptom of Men- iere's disease, caused by a hemorrhage into the audi- tory nerve or labyrinth. Timitus is a symptom of all ear disorders which increase tension in or shut off egress from the in- ternal ear, because the physiological noises, such as FUNCTIONAL DIAGNOSIS 191 circulation, muscle tonus, etc., which under ordinary conditions are too diffused to be heard, are