456 



Messrs. L. Hill and M. Flack. 



[May 29, 



promoting the healing process. The effect is just the same as that obtained 

 on laying open a boil. The increased tension is not the cause of the trouble ; 

 that lies in the pathological condition which produces the tension. If the 

 tissues of the eyeball become swollen by imbibition, the volume occupied by 

 the blood in the veins is diminished, and the circulatory pressure and flow 

 of blood is increased. If the imbibition proceed far enough and the arterial 

 pressure be not increased by the compensatory action of the heart and vaso- 

 motor system, the circulation may become strangulated. Hence the utility 

 of the hot fomentation which softens and of the surgeon's knife which cuts 

 the confining structures and promotes the flow of blood and the outflow of 

 plasma with its immunising power. 



Arthur Thomson* has brought forward anatomical evidence for the view 

 that the ciliary muscle opens the channels in the pectinate ligament. " They are 

 kinked and compressed when drawn forward, opened and straightened when 

 the scleral process is pulled back, thus imparting to them a valvular action." 

 " In this way a negative pressure is established within Schlemm's canal into 

 which fluids will pass along the line of least resistance. When the ciliary 

 muscle, meridional and circular fibres, and sphincter of iris, cease to contract, 

 the pectinate ligament by its inherent elasticity pulls the scleral spur 

 forwards and outwards again, thus mechanically effecting the collapse of the 

 inner wall of the canal of Schlemm against its outer wall, and so restoring 

 it to the ordinary influences of the intraocular pressure." He supposes that 

 filtration (outflow) of aqueous is maintained by this negative pressure and 

 pumping action of the ciliary muscle, and that glaucoma may be caused by 

 impairment of this action, e.g. by over-prolonged contraction of the hyper- 

 trophied circular fibres in the hypermetropic eye. We conclude that 

 Arthur Thomson accepts the received explanation of glaucoma, viz., that it 

 is due to obstructed absorption of the aqueous, and defines a mechanism 

 which he believes acts as a valved pump and furthers the exit of the 

 aqueous. 



Holding as we do that the inflow of the aqueous is governed by secretion, 

 that is, by the vital action of the cells lining the ciliary processes, and 

 that it is not a filtration fluid dependent on the blood pressure, we do not 

 recognise the need for any such mechanical pump controlling the outflow. 

 We believe that absorption is no less controlled by the endothelial cells 

 which separate the fluid from the veins. Both secretion and absorption we 

 maintain are functions dependent on the living energy of the cells. We 

 agree, however, with Thomson Henderson when he says that " the ciliary 

 muscle by its contraction opens up the channels which allow aqueous to pass 

 * 'The Ophthalmoscope,' London, July, 1911. 



