Treatise on the diseases of the eye : including the anatomy of the organ / by Carl Stellwag (von Carion) ; translated from the fourth German edition and edited by D.B. St. John Roosa, Charles S. Bull, and Charles E. Hackley.

Karl Stellwag von Carion

Date:: 1873

Credit: Treatise on the diseases of the eye : including the anatomy of the organ / by Carl Stellwag (von Carion) ; translated from the fourth German edition and edited by D.B. St. John Roosa, Charles S. Bull, and Charles E. Hackley. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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$tire]y useless as measurers of the intra-ocular pressure. They can only measure the resistance which the surface of the globe offers to a substance pressing upon it (Dm; Monnik), that is to say. they measure a power which depends upon the intra- ocular pressure and the elasticdistensibility of the selenitic, or capsule of the globe, but which may be modified verymuch by the contraction of the external muscles of the eye, the circulation in the orbit, and so on. Besides all this, on account of the diffi- culty of applying the instruments twice in exactly the same maimer, a proper com- parison of the condition of the two eyes in the same individual is not always to be obtained. If the equilibrium between the intra-ocular pressure and the elastic counter-pres- sure of the capsule of the globe be destroyed by an increase of the pressure of the arterial blood, the tension of the sclerotic, and with it its elastic counter-pressure, must evidently lie increased. Since this elastic counter-pressure affects equally the whole intravascular region, which rests upon an incompressible basis, the arterial current will also meet with increased resistance upon its entrance into the interior of the eye. and will he weakened, while the venous Mood is forced out from the interior of the globe at a somewhat accelerated rate. If, on the contrary, a dis- turbance of the equilibrium results from a lessening of the arterial blood-pressure, the tension, and with it the elastic counter-pressure of the capsule, must be lowered. The arterial current will then meet with less resistance upen its entrance into the intra-ocular space, and there press upon the walls of the vessels with a greater amount of force from the heart, while on the other hand the venous current is rendered somewhat slower on account of the weakening of a factor with consider- able impelling force, that is. the pressure of the heart transmitted from the arteries through the capillaries. The intra-ocular pressure, according to what has been said, may not increase or decrease proportionately with the pressure of the arterial blood, but to a much less proportionate degree. The effective power of the heart is. on the whole, a Limited one. and the genera] pressure of the blood throughout the system appears to be capable of increase only within narrow limits. This is especially true of the per- iphery of the vascular system, when the blood has overcome so many resistances. We must therefore believe that the intra-ocular pressure can only be inc Blightly, if at all, by a mere increase of the general pressure of the blood. Experi- ence sustains this view, and at the same time justifies the correlative supposition, that mere diminution of the arterial blood-pressure will produce scarcely a notice- able diminution of the intra-ocular pressure. Indeed, no difference can be detected in the average tension of the globe, when we compare the eyes of persons with decided plethora, who have a strong and full radial pulse with violent action of the heart, with those of very anaemic persons, or with persons Buffering from Asiatic cholera ( Orarfi ). or i ven whi n we compare tie m with the eyes of patient- with a very weakened h art-action, and who are near their last moment, where the radial pulse is scarcely perceptible, thread-like, and very compressible. The ten-ion of the eyeball is not decreased to any marked extent until the moment of death, when the visible internal \( Bsels empty themselves, and the fundus of the eye becomes pale (Bmiehut, Hippel, Qrunhagt The slighl variation of the intra-ocular pulse, and a certain constancy of the amount of blood-circulation in the interior of th ■ eye, are intimately connected with the steadiness of the intra-ocular pressure, and regulate it- effects. This constancy in amount does not prevent irregular distribution, however, but only$