1912.] Relation between Capillary Pressure and Secretion. 455 



the eyeball. Just as the tissues surrounding a bee stin^, or a boil, swell and 

 become tense, so does the eye become tense in an attack of acute glaucoma. 

 The conditions are the same as in the salivary gland when the secretion is 

 obstructed. The tissues confined by a capsule swell and the capillary- venous 

 pressure is raised pari passu with the pressure of the imbibed or secreted 

 tissue fluid. Thomson Henderson regards sclerosis of the cribriform ligament 

 as the prime cause of glaucoma. The pathways of absorption of the aqueous 

 are obstructed. This, he says, converts the circulatory system of the eye 

 from an elastic to a rigid system. 



"The free contact between aqueous and veins causes the intraocular 

 pressure to be maintained at the normal intravenous level, as this is the 

 lowest circulatory pressure. In glaucoma the contact is diminished, and the 

 intraocular fluids, being contained in an unyielding capsule, act as a rigid 

 volume which, operating through the tissues, compels the intraocular circula- 

 tion to run in rigid lines. In a rigid system the outflow pressure is always 

 higher than in a similar system of elastic tubes."* 



We are not in complete agreement with this view, for the living tissues 

 are not fixed mechanical structures. Moreover, supposing the cribriform 

 ligament is sclerosed, the venous outflow no less remains patent, and for the 

 aqueous there is the pathway of absorption through the iris veins. Obstruc- 

 tion of the absorption of aqueous per se can have no effect on intraocular- 

 pressure so long as the secretory pressure remains unchanged. Alterations 

 in tissue metabolism undoubtedly are the primary cause. The obstruction of 

 the natural circulation of the aqueous may possibly contribute to the 

 alteration of tissue metabolism. However produced, it is increased 

 imbibition which diminishes the venous content and raises intraocular 

 tension. 



Thomson Henderson has demonstrated, and we can confirm his demonstra- 

 tion, that " so long as the anterior chamber remains a closed space, the 

 balance of fluid pressure between it and the vitreous chamber is perfect, so 

 that if the vitreous pressure is raised, the aqueous pressure mounts to exactly 

 the same height." We admit that fluid injected into the excised eye 

 quickly flows out from the cut ends of the episcleral veins, but ceases to do 

 so when the lens is pushed forward and the filtration angle blocked. We 

 have pointed out, however, that the conditions in the living eye are entirely 

 different, that the aqueous and venous pressure stand at the same level, and 

 we have no proof that the angle acts as a filtration mechanism in it. 



In our opinion surgical operations, e.g. iridectomy, relieve glaucoma by 

 increasing the flow of tissue lymph through the inflamed part, thus 

 * Thomson Henderson, loc, cit., p. 135. 



