THE NUTRITION OF THE EYEBALL 667 



metres of fluid per minute suffices to maintain the pressure at this 

 height. 



If the formation of intraocular fluid be increased by rise of blood 

 pressure, the intraocular pressure must also rise until a point is 

 reached at which the increased filtration through the anterior angle 

 is just equal to the increased production resulting from the rise of 

 blood pressure. Within wide limits therefore the intraocular pressure 



mm. Hg. 



IHBBBBBHH^H 



I.O.P. 



mm. Hg. 



10 sec. 



FIG. 307. Curve showing effects on the intraocular pressure (in the dog) of 

 mechanical interference with the circulation. Blood-pressure measured in 

 left carotid, intraocular pressure in right eye. From p to S the descending 

 thoracic aorta was occluded. From Q to R the right vertebral and sub- 

 clavian arteries were also occluded. (HENDERSON and STARLING.) 



varies with the blood pressure. This is shown by the following records 

 of both pressures in different animals (Henderson and Starling) : 



DOG 



Arterial pressure Intraocular pressure 



128 mm. Hg. . . 26 mm. Hg. 



158 mm. Hg. . . 34 mm. Hg. 



180 mm. Hg. . . 40 mm. Hg. 



70 mm. Hg. . . 23 mm. Hg. 



Conversely the intraocular pressure may be altered by increasing 

 or diminishing the ease with which the fluid escapes through the 

 filtration angle. If the anterior angle becomes blocked as the result 

 of inflammatory changes, or other causes, the intraocular pressure 

 rises gradually until it attains a height far above normal. The 

 eyeball to the finger feels stony hard, and the increased pressure 



