Intraocular pressure

“ The general venous blood pressure is so [Pg 16] 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 ”

“ A rise of the general vascular tension alone will not cause glaucoma, because any alteration in intra-ocular pressure resulting would be purely a temporary change, easily taken care of by the extensive access of aqueous to the intra-ocular venous system. ”

“ Fully to understand the mechanism for its regulation would carry us far toward an understanding of the causes of glaucoma. Normal [Pg 10] 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 ”

“ The other fingers rest on the margin of the orbit. All normal eyes have about the same measure of tension and one can use his own eye as a means of comparison. The educated touch is essential. In increased tension, the sense of hardness and resistance, and the indisposition to become indented on pressure is present in the early stages of internal ophthalmias (iritis, choroiditis, retinitis) , phlegmon of the eyeball, glaucoma, hydrophthalmos, and tumors of the bulb. ”

“ Should the blood pressure be very high, paracentesis, for example, would apparently not be the proper procedure, and the resulting difference produced between the blood pressure and the eye tension would cause a rapid reformation of fluid with higher specific gravity and higher osmotic coefficient. ”

“ All are agreed as to the essential feature of the malady, namely, increased tension of the eye ball, but every case of increased tension of the bulb is not recognized as glaucoma, and the true cause of the persistent and progressive increase of pressure in cases recognized as glaucoma is not absolutely settled. ”

“ I believe that in the management of a case of glaucoma, whether it be chronic or chronic with sub-acute exacerbations, the greatest care with the aid of an expert clinician must be exercised to find out exactly what mean pressure of the arterial and venous system best conforms with the patient's general welfare, and I am bitterly opposed, and I think with right, to the sudden reduction of tensions, except in emergencies, without a perfect understanding of the facts I have ventured to indicate. ”

“ Syphilis, rheumatism, gout, auto-intoxication and many other constitutional disorders are well recognized agencies which induce sclerosis in body tissues, so there can be little doubt that these conditions produce pathological sclerosis of the meshwork of the iris angle. Psychic disturbances, congested portal or renal system, hard mental or muscular work, etc., etc., induce increased pressure of the general circulation, and so simultaneously the intra-ocular pressure. ”

“ There is consequently spasm of accommodation, so that clear vision of distant objects becomes impossible. The intra-ocular tension is markedly lowered. This action, at first sight somewhat obscure, is due to the extreme pupillary contraction which removes the mass of the iris from pressing upon the spaces of Fontana, through which the intraocular fluids normally make a very slow escape from the eye into its efferent lymphatics. ”

“ Exactly how the myotics reduce intra-ocular tension is not definitely proven. Usually it is taught that because of the myosis the base of the iris wedged in the angle of the anterior chamber is loosened and withdrawn, precisely as a fold in a coat is straightened by a tug on the fabric beneath it. Experiments, however, for example, by E. E. Henderson, have shown that the rate of filtration in an eye with artificially raised pressure is considerably larger when it is under the influence of eserin than it is when under the influence of atropin ”

“ It is well known that when the eye is struck a cloud of sparks is seen, which is caused by the mechanical concussion of the retina. These luminous images, often perceived involuntarily, take, speaking scientifically, the form of the body producing the pressure; at the same time we observe the relation between the position of the irritation and the position of the sensation of sight. We transpose a point on the left side of the retina to the right, because we imagine that a ray of light has penetrated the eye from the right, which must fall upon the left half of the retina. ”

“ There seems to be a special liability to glaucoma among those residing at high altitudes, 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. ”

“ There is a marked diminution in the secretion of tears, and often a dilatation of the veins of the exposed part of the conjunctiva bulbi, which are turgid with the black blood, this state being at times accompanied by subconjunctival hemorrhages. The pupils are usually contracted. The retinal arteries are much diminished in size, and the veins although not dilated, are filled with blackish blood. Owing to the great feebleness of the circulation, the slightest pressure with the finger on the eyeball produces arterial pulse ”

“ Too fine work, dim light, wrong diet, and want of exercise produce the dull and strained eye, which eventually becomes seriously diseased. Opening the eyes under cold water will help to strengthen them, and massaging the muscles of the eye by passing the finger and thumb round the socket (with scarcely any pressure on the ball itself) will be found of advantage.
Eyes, Inflamed.—For all kinds of burning inflammatory pain in the eyes, the following treatment is most effective. Place a hot bran poultice (see) beneath the back of the head and neck while the patient lies on the back. ”

“ It has long been known that couching is frequently followed by secondary glaucoma. In the present series of 54 globes, 19 of them showed evidence of high intra-ocular pressure. This figure must not, however, be taken as a reliable index of the numerical frequency of glaucoma as a complication of the operation. On the one hand, we must remember that the present series deals with the failures only, and that a large number of eyes are met with clinically in which the lens is floating free in the vitreous chamber without any sign that75 the intra-ocular tension is raised. ”

“ Another method of reducing the intra-ocular tension is by the suction method, which consists in the use of certain cups from which the air is exhausted by means of a suction apparatus. Domec uses an elliptical eye cup, the concave margins of which fit closely about the globe. The air is exhausted with each respiration of the patient and from 50 to 200 tractions are made at each sitting. ”

“ A kind of net-work, darker than the other parts of the wall, appears and vanishes alternately with every pulsation. This change of the colour of the wall he well ascribes to the compression of the retina by the diastole of the artery. The various colours produced in the eye by the pressure of the finger, or by a stroke on it, as mentioned by Sir Isaac Newton, seem likewise to originate from the unequal pressure on various parts of the retina. ”

“ Pressure or electrical currents may act on the eyeball, but in doing so they not only affect the retina, consisting of its various layers and of Jacob's membrane, but also the fibres of the optic nerve. It is possible that the retina, by which is meant all the layers except those on its surface formed by the fibres of the optic nerve, is affected only by its specific kind of stimulus, light. This stimulus so affects the terminal apparatus as to set up actions which in turn stimulate the optic fibres. ”

“ 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 assumed. It would help to explain the cavernous atrophy of the optic nerve associated with simple glaucoma. ”

“ A characteristic of this condition is increase of the intra-ocular tension, which has a deleterious effect on the optic nerve end and its ramifications in the retina. The cause of the rise of tension is partly congestive, partly mechanical. The effect of glaucoma, when untreated, is to cause ever-increasing loss of sight, although the time occupied by the process before it leads to complete blindness varies within such extraordinary wide limits as from a few hours to many years. ”

“ 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 canal of Schlemm is noted in congenital buphthalmos. The enlargement of the anterior perforating veins is an old symptom of chronic glaucoma. ”

“ 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. ”

“ VOLUNTARY PRODUCTION OF EYE TENSION A SAFEGUARD AGAINST GLAUCOMA It is a good thing to know how to increase the tension of the eyeball voluntarily, as this enables one to avoid not only the strain that produces glaucoma, but other kinds of strain also. ”

“ Panas and Duvigneaud have assumed rightfully that “If the nervous mechanism of intra-ocular secretion or, to speak without hypothesis, the action of the nervous system on intra-ocular tension can be known, the pathology of glaucoma will be cleared up, iridectomy will be explained, and perhaps a new and scientific basis for the treatment of glaucoma will be established.” Many observers have sought to solve the problem. Donders attributed the hypertension to a neuro-secretory cause and believed 261the trigeminus to be the agent of excessive secretion. ”

“ When exposed the pupil will be found to be widely dilated, and in the healthy eye it will rapidly contract and dilate alternately until it has reached a condition of adaptation to the intensity of the light when it will remain immovable. With the inflamed iris these contractions and dilatations will be lacking altogether, or they will be sluggish and imperfect in various degrees according to the intensity of the inflammation, the degree of congestion or the tension of the liquid media of the eye. ”

“ All the muscles of both eyes appeared to work normally. Upon pressure on the right globus, especially pressure directed from above and behind on the internal part, the patient would raise his left eyelid, but the paresis reappeared the moment the pressure was released; a fact which the patient himself noted while a tampon was being placed upon his eye. ”

“ Pressure symptoms. The impairment of venous flow in those radicles which drain into the cavernous sinus is evidenced by the marked engorgement of palpebral, conjunctival, episcleral, and retinal veins. Obstruction to lymph flow is shown by a hazy cornea, chemosis, and œdema of the parts surrounding the orbit. The danger thus incurred by the cornea is rendered more serious by the inability on the part of the patient to close the eyelids over the protruded globe. Keratitis and sloughing of the globe are to be feared. From muscular involvement, squints and diplopia are frequently observed. ”

“ When a part is stimulated, the circulation is accelerated, and a greater quantity of blood is transmitted by its vessels: if the excitement is speedily removed, they recover themselves, though perhaps a little dilated, and no inflammation ensues. If, for instance, a foreign body of any kind gets entangled betwixt the upper eyelid and the bulb of the eye, and it is permitted to remain a few moments only, redness of the whole surface of the conjunctiva takes place, but it is transitory, and disappears entirely some short time after the extraction of the foreign body. ”

“ In either case the eyeball is protruded, and the cornea is exposed to irritation and may become inflamed and ulcerated. The optic nerve may be lacerated, and complete and permanent loss of vision result. Sometimes the ocular muscles and nerves are damaged, and deviation of the eye or loss of motion in one or other direction results. The globe itself may be injured. Foreign bodies lodged in the orbit, so long as they are aseptic, may give rise to little or no disturbance, and are liable to be overlooked. The Röntgen rays are useful in determining the presence and position of a foreign body. ”

“ It has already been pointed out that the great danger in intra-ocular operations is sepsis. It is the aim and object of every ophthalmic surgeon to make such wounds into the globe as will become rapidly shut off from the conjunctival sac. Delay in the healing tends to the formation of a fistulous opening into the globe. This aperture in the continuity of the globe may lead either directly on to the surface or beneath the conjunctiva, subsequent inflammation in which may spread to the interior of the eye. ”