Glaucoma.
by Various.
Etiology and Cla.s.sification of Glaucoma
BY
EDWARD JACKSON, M.D.,
Denver.
It is convenient to start with the conception that glaucoma is increased tension of the eyeball, plus the causes and effects of such increase; although a broad survey of the facts may reveal a clinical ent.i.ty to be called glaucoma, without increased tension constantly or necessarily present, and cases of increased intra-ocular tension not to be cla.s.sed as glaucoma.
The physiologic tension of the eyeball is essential to ocular refraction, and closely related to ocular nutrition. Fully to understand the mechanism for its regulation would carry us far toward an understanding of the causes of glaucoma. Normal tension is maintained with a continuous flow of fluid into the eye and a corresponding outflow. Complete interruption of the nutritional stream would be speedy death; partial interruption may be held responsible for most of the visual impairment and pain of glaucoma.
The balance of intra-ocular pressure is not maintained by the slight distensibility of the sclero-corneal coat. Increased pressure does not open new channels for the escape of intra-ocular fluid; if, indeed, it does not tend to close the normal channels.
The affinity of the tissues for water, or, as Fischer explains it, the affinity of the tissue colloids for water, seems too little related to the requirements of ocular function to furnish the needed regulation of tension. The lymph s.p.a.ces and blood-channels of the eye are large, as compared with the ma.s.s of its tissue colloids. In these s.p.a.ces and channels must be sought a means for rapid response to the need for regulation of intra-ocular tension. Fischer has shown, that when the enucleated eyeball is placed in a weak solution of hydrochloric acid, the swelling of the tissue colloids is sufficient in a few hours, to burst the sclero-corneal coat. But this is an eye in which all nutritional changes have ceased. He brings together many facts to support the view that in the living tissues impaired circulation, and especially diminished oxidation, are the chief causes of increased affinity of the colloids for water. Such affinity increased by the impairment of the intra-ocular circulation, may well const.i.tute a factor making for malignancy in glaucoma. But it can hardly explain the original departure from a normal pressure balance.
We must a.s.sume that intra-ocular pressure is kept down to the normal limit, by the prompt response of a regulative mechanism, which diminishes the flow of fluid into the eye, or permits its more rapid escape, whenever fluid tends to acc.u.mulate in the eye and increase its tension.
Little has been done to show that increase of fluid entering into the eye is the cause of glaucoma. A normal, or even a low arterial blood pressure is sufficiently above the normal intra-ocular pressure to furnish a source of increased fluid in the eye. Increased arterial pressure has been found in a large proportion of cases of glaucoma; and may be necessary to the production of the highest intra-ocular tension.
A sudden relaxation of the arterial walls, that would permit the arterial blood pressure to make itself felt in the eye, might cause an important rise of intra-ocular tension and may be a factor in the etiology of acute attacks. It affords a possible mechanism through which may be produced the recognized glaucomatous effects of certain nerve disturbances. But such attacks are not commonly a.s.sociated with noticeable flushing of the head and face generally; and paralysis of the cervical sympathetic is known to lower the intra-ocular tension.
Capillary blood pressure must lie between the arterial blood pressure and the venous blood pressure. It must be closely a.s.sociated with the nutritional processes like secretion or inflammation; beyond this we know little about it. The a.s.sociation of increased blood pressure with glaucoma seems to be generally an indirect one through vascular lesions and disturbances of nutrition.
_Obstructed Outflow_
A reservoir with a free outlet can only fill during a flood; and then quickly empties itself again. The outflow channels in the normal eye provide for carrying away of the waste products of such an active nutrition, that it is hard to think they will become inadequate in glaucoma until there has been a marked decrease from their normal capacity. Priestley Smith has pointed out that the glaucomatous eye softens more slowly than the normal eye after enucleation, in spite of the fact that a greater force is operating to drive fluid out of the eye. In his recent tonometric studies Schoenberg noted that under manipulation the glaucomatous eye softened more slowly than the normal eye; and suggests this diminished drainage as an important evidence of glaucoma.
Obstructed outflow might begin in an abnormal tendency of the tissues to retain fluid, a tendency that Fischer might locate in the colloids. The increase of intra-ocular pressure noted in cases of uveal inflammation, to be presently referred to, may be due to some such tendency. But it is rational to ascribe to obstruction of the filtration angle of the anterior chamber, the important part it has been supposed to play in the pathology of glaucoma. However this obstruction may be brought about, whether by thickening of the iris root during dilatation of the pupil, pushing forward of the iris root by the larger ciliary processes of age, or the enlarged crystalline lens pressing on the ciliary processes; or by inflammatory adhesion of the iris to the filtration area; ballooning of the iris, or its displacement by traumatic cataract; or adhesion to the cornea after perforating ulcer in the secondary glaucomas; or whether the obstruction is due to the acc.u.mulation of experimental precipitates, as shown by Schreiber and Wengler, or possibly of pigment granules into Fontana"s s.p.a.ce; or a process of sclerosis closing the s.p.a.ces by contraction of new-formed connective tissue, or the covering over with proliferating implanted epithelium following injury opening the anterior chamber; glaucoma follows impairment of this drainage s.p.a.ce, and lessened outflow through it. This blocking of the angle of the anterior chamber must be regarded as an established fact in the etiology of glaucoma. But because it is so definitely established, and because so much work has been done with reference to it, we may attach to it an undue importance.
The escape of the outflow of fluid from the eye is ultimately through the veins. The general venous blood pressure is so low (often negative in the great veins of the neck during inspiration) that no obstacle can come from it to the ocular outflow. The venous blood pressure permits the eyeball to become perfectly soft. We have all seen tension of 5 mm., or even less; and general venous pressure does not rise to the normal intra-ocular tension. Increased intra-ocular pressure requires that there must be some obstacle that keeps the intra-ocular fluid from reaching the general venous system. This may be in the lymph drainage system of the eye; but it may also be in the ocular veins themselves.
Experimentally the eyeball can be made to burst by tying all the venous outlets from it. I have seen very high intra-ocular tension develop in a few hours after general thrombosis of the orbital veins. The absence of the ca.n.a.l of Schlemm is noted in congenital buphthalmos. The enlargement of the anterior perforating veins is an old symptom of chronic glaucoma.
Obstruction to outflow of blood through the vorticose veins, by the increased intra-ocular pressure, has long been a recognized explanation of the malignant tendency of glaucoma--a part of the vicious circle established in this disease. There is reason that we should give careful attention to the views of Heerfordt and Zirm, that obstruction to the venous outflow may be the effective cause of the disease. Zirm believes the venous plexus of the choroid is an essential part of the mechanism for the regulation of intra-ocular tension, the necessary vaso-motor control depending on nerve centers situated in the iris.
_Nerve Control_
The accurate control of normal intra-ocular pressure, by mutual adjustment of inflow and outflow of fluid, is scarcely conceivable without some highly specialized, extremely sensitive nerve mechanism to preside over it. This is suggested by a.n.a.logy with the regulation of secretion in the lacrimal, salivary, or peptic glands, or the maintenance of blood pressure in the heart and arteries. Clinical observations point the same way. Many patients connect their attacks (especially their earlier ones of ocular discomfort, impaired vision, haloes around the light, and dilated pupil) with social excitement, anxiety, worry, anger or fatigue. A patient of mine gave up her card parties, because an exciting game generally ended in blurred vision, a rainbow around the light, and a dilated pupil, and sometimes an aching eye. Another woman watching beside her dying husband and exposed to extreme cold, had her first attack of glaucoma, so severe as to destroy the sight of one eye. The other eye, also affected at the time, recovered good vision, and has remained several years without a second attack and without treatment.
Laqueur"s first attack occurred at the end of a long exhausting morning in the operating room, with luncheon delayed two hours. The connection of his later attacks with anger, worry, embarra.s.sment, even the excitement of watching a play at the theatre, was noted again and again. In Javal"s case, the attack fatal to one eye came at the culmination of an exciting electoral campaign. The other eye was stricken at the termination of the Dreyfus case, in which Javal was intensely interested. There seems to be a special liability to glaucoma among those residing at high alt.i.tudes, best explained by nerve influence. The frequency of glaucoma among Jews may be due to a small cornea, as suggested by Priestley Smith; but it is quite as reasonable to connect it with a racial excitability or nervous instability. More definite knowledge of the nervous mechanism concerned in the regulation of intra-ocular pressure and the production of glaucoma is much needed.
_Alterations of Fluids and Tissues_
The influence of increased affinity of the tissues for fluid has already been referred to. That a similar obstacle to the escape of fluid from the eyeball might be due to a change of character in the fluid, is a conception that has been entertained as a working hypothesis, and much experimental and a.n.a.lytical work has been done to test its correctness.
This work has been so slightly related to practical ophthalmology, and so contradictory in its results that alterations in the fluids can only be regarded as a possible etiologic factor. Glaucoma secondary to intra-ocular hemorrhage, operations on the lens or its capsule, or severe nutritional disturbance may be capable of such explanation.
_Different Kinds of Glaucoma_
A better grasp of the etiology of glaucoma may be attained by considering separately various types of cases; although perfectly typical cases may be rare; and cases of mixed type and etiology much more frequent.
Simple glaucoma has been recognized as closely related to atrophy of the optic nerve with deep excavation. No line of demarcation can be drawn between them, except by reserving the term of glaucoma for cases that depart from the pure type, terminating in glaucoma of some other kind, which is no more significant than the pa.s.sage of a conjunctivitis into a kerat.i.tis, or an iritis into a glaucoma. Cases of simple glaucoma do run their course of many years to complete blindness, or to death, without exacerbations, inflammation, or characteristic pain. In such cases the intra-ocular tension does not rise suddenly; and it may be little or not at all elevated above the usual normal limit.
For nine years I have watched the progress of such a glaucoma in a man now aged 87, with slow development of glaucomatous cupping of the optic disc, now more than 3 D. deep. The tension has never been noted at more than Plus T (?), and when taken with the tonometer varied from 9 to 32 mm. for the worse eye, and 13 to 24 mm. for the other. Similar cases in which the tension lay within the commonly accepted normal limits have been reported recently by Bietti and Stock.
In the eye there is probably a normal equilibrium between blood pressure, tissue activity, and intra-ocular tension. This may be destroyed either by increasing the intra-ocular tension, or lowering the tissue activity, or the blood pressure. Lowered blood pressure has been suggested by Paton as an explanation of symptoms usually ascribed to vascular obstruction. Rising blood pressure may be required in old age to compensate for diminished tissue activity; and it is conceivable, under normal intra-ocular tension, that diminished nutritional activity may result in the same symptoms as are produced in other eyes by increased tension. Glaucoma is probably not so much an increase of tension as a loss of balance between intra-ocular tension and nutritional activity.
In contrast with the above are the cases marked by sudden elevations of ocular tension recurring repeatedly over long periods without permanent visual impairment. Laqueur"s case continued of this character for six years, under the use of miotics, and then was cured by iridectomy, the cure remaining permanent with normal vision until his death after 30 years. Millikin has reported the case of a patient who in five years had "many hundreds" of attacks, in which vision was impaired, haloes appeared about the light, the pupil dilated, the cornea became steamy, and tension rose to plus T. 1 or plus T. 2. After iridectomy the attacks ceased, leaving no pathological cupping of the disc, full vision, and a good field. I have seen cases of this type in women under middle age, and of marked nervous instability.
A third type which will come to be more generally recognized, as the tonometer comes to be more widely used, includes cases in which there is little beside the increase of intra-ocular tension to justify their mention in a discussion on glaucoma. A patient, then aged 21, suffered three years ago from a scotoma almost central; and was first seen six months after that with a macular choroidal atrophy and abnormal pigmentation. She suffered, we afterwards concluded, from choroidal tuberculosis. A recurrence involving adjoining choroid occurred fourteen months ago. There was at the start pain, slight dilatation of the pupil, and slight general hyperemia of the globe. The tension of the eyeball rose to 60 mm., that of the fellow eye being 20 mm. Under miotics the tension fell at first but slightly. It was 55 mm. at the end of a week; but after two weeks came down to normal, 20 mm. A month later the tension rose to 28 mm., but for a year has continued normal; the eye did well under tuberculin treatment, and without any local treatment. In September of this year I had two cases of iritis in which the intra-ocular tension rose to 45 and 52 mm., respectively, and gradually returned to normal, with the cure of the iritis under atropine. In one of these cases, a lady of 70, I used atropine also in the other eye, but the tension of that eye remained normal, 22 to 24 mm., throughout.
After needling the lens in young people I have seen a rise of intra-ocular tension to 50 and 60 mm., maintained for many days, with considerable general deep hyperemia, and soreness of the globe, followed by gradual return to normal tension, and no permanent impairment of vision or the visual field.
One other type may be mentioned. That of an elderly patient with marked vascular disease, often renal involvement, and distinctly impaired nutrition. There may be renal retinitis or retinal hemorrhages. The case may easily become one of hemorrhagic glaucoma. It may run a very chronic course. But it may become suddenly worse, or go on to complete blindness with pain, demanding enucleation, after some temporary perturbation, as the performance of a glaucoma operation. It is pre-eminently the kind of a case you would prefer would go to some one else.
Each of these types ill.u.s.trate a distinct cause or group of causes. The first type brings us near to what may be the essential nature of glaucoma, impairment of ocular nutrition by the intra-ocular tension, which is generally elevated, but may not be above the usual normal. A special weakness in the nutrition of nerve tissue may be a.s.sumed. It would help to explain the cavernous atrophy of the optic nerve a.s.sociated with simple glaucoma. The second type shows impairment of the regulative mechanism permitting rapid rise of the intra-ocular pressure.
In persons of good nerve nutrition and strong recuperative power, it may exist for years without doing permanent damage. But joined to causes of the first type, lowered nutritive activity, it causes rapid and permanent loss of sight. The third group are cases a.s.sociated with glaucoma only as causes. In eyes with low nutritive power, or subject to exacerbations of increased intra-ocular pressure, uveal inflammations may prove disastrous. The fourth type shows the results of the combination of the causes of the other types; with the elements of acute or slow malignancy added--the impaired circulation and lowered oxidation producing some degree of edema of the tissues that insures a fatal result.
This is no complete presentation of my subject, but a selection of facts bearing on the etiology, to serve as a foundation for the discussion of those practical aspects of glaucoma which are to claim your attention through the papers and remarks of subsequent speakers.
Dr. Edward Jackson"s Paper on Etiology and Cla.s.sification of Glaucoma
Discussion,
FRANCIS LANE, M.D.
Chicago.
Not one of the theories thus far propounded to explain the essential cause of increased intra-ocular tension is satisfactory. Our present day knowledge apparently ceases with a more or less incomplete understanding of the mere circ.u.mstance under which increase of tension in general depends.
The question of the source of the normal intra-ocular pressure must first be solved before any discussion of a pathological increase can be engaged in. This question primarily hinges on whether the corneo-sclera is to be regarded as an unelastic capsule with a fixed volume, or as a yielding envelope with an ever changing capacity.
This brings us at once to the consideration of that theory which probably has held our attention for the longest period of time, _i. e._, the volumetric theory. According to it, the normal intra-ocular tension depends on the volume of fluids within the eyeball. Any variation in the quant.i.ty of the contents gives rise to a change in the pressure, therefore, the globe has been regarded as "an elastic capsule, whose capacity, form, and internal pressure depend on the balance struck between a constant inflow, or formation of aqueous, and a proportionate outflow or resorption." (Henderson.)
Hill has satisfactorily demonstrated that, under physiological conditions, the hydrostatic pressure within the eye and the skull is identical; it rises and falls simultaneously; it is the same as the cerebral venous pressure; it is constantly varying, depending directly on the general circulation. Upon these findings Henderson based his opinion that the physiological properties of the tunica fibrosa and the skull are identical, realizing at the same time, that the rigidity of the corneo-sclera, because of its fibrous nature, is not as firm as the cranium. In accepting this belief the inference was that the cubic capacity of both coverings is fixed. Applying these conclusions to the eye, it can be said that the pressure of the fixed intra-ocular volume varies with the venous tension within the bulb, which in turn is influenced by the general circulation. Such a conception, while not strictly in accord with recognized physiological teachings, proves that the normal intra-ocular pressure is not a question of volume content, but that it is purely a question of pressure of a fixed volume within an unyielding capsule. Dr. Jackson virtually puts aside the volumetric theory with his statement, that "the balance of intra-ocular pressure is not maintained by the slight distensibility of the sclero-corneal coat."
Further discussion on the inadequacy of the volumetric theory need not detain us.
It is well to recall a few anatomical features because of their bearing on the theories herein considered.