VISUAL SYSTEM: STATE OF THE ART 



37 



Uj 



(/) 



5 

 O 



Uj 



0. 



WAVELENGH OF LIGHT Inm) 



Figure 7 Pupillary dilation in Scyliorhinus canicula. Kuchnow's 

 (1970) data were corrected for quantal absorption and replotted. 

 The resultant curve resembles the absorption spectrum of the visual 

 pigment of this species. 



Ciliary Body— The remaining studies on the ciliary zone of elasmo- 

 branchs are concerned with production, composition, and drainage of 

 aqueous humor. In many vertebrates aqueous humor is produced by an 

 active process in the epithelium of the ciliary body and secreted into the 

 posterior chamber of the eye. From there it flows to the anterior chamber 

 via the pupil, to be drained away at the iridocorneal angle. The aqueous has 

 important optical, nutritive, and excretory functions in the largely avascular 

 anterior segment of the eye, but perhaps most important are its hydro- 

 mechanical properties and their relation to the optics of image formation. 



Rate of aqueous production and resistance to drainage are the principal 

 factors determining intraocular pressure (IOP). Changes in these factors lead- 

 ing to increased IOP produce the condition know as glaucoma, one of the 

 leading causes of blindness in man. Thus intensive study has aimed at under- 

 standing factors affecting IOP in the vertebrate eye. As already mentioned, 

 similarities between the mammalian and elasmobranch ciliary body make the 

 shark an ideal model for the study of basic mechanisms of aqueous produc- 

 tion and drainage. 



Duke-Elder (1932) claimed that aqueous humor was merely a dialysate of 

 the plasma, presumably derived from the ciliary vascular system. However, 



