440 



ANATOMY FOR NURSES 



[Chap. XX 



Iris 



Retina 



Refractive 

 Apparatus 



A circular curtain. Central perforation — pupil. 



Pupil contracted by circular muscle-fibres. 



Pupil dilated by radial muscle-fibres. 



Contains pigment — amount gf which determines color of 



the eyes. 

 Hangs free except for attachment at circumference to the 



ciliar}' processes and choroid. 

 Function — Regulates amount of light entering eye. 



Visual layer — transparent membrane of nervous and con- 

 nective tissue situated between the choroid and vitreous 

 humor. Formed by the spreading out of optic nerv'c. 



Has eight layers and two membranes. Counting from the 

 choroid inward as follows : — 



Pigment layer, usually described as a membrane. 



1. Layer of rods and cones (perceptive layer) — external 



layer. 



2. Limitans externa, 



3. External granules. 



4. External molecular. 



5. Internal granules. 



6. Internal molecular. 



7. GangUon or nerve-cells. 



8. Optic nerve-fibres — innermost layer. 

 Membrana Umitans interna. 



( Entrance of optic nerve. 



< There are no rods and cones. 



[ Totally insensitive to light. 



1^ in. outside the blind spot. 



Central pit — fovea centralis — is the centre of 

 direct vision. 



Blind 

 spot 



Macula 

 lutea 



Aqueous 



Vitreous 



Crystal- 

 line 

 lens 



Aqueous chamber is between cornea in front and 

 lens, suspensorj' ligament, and ciliarj' body 

 behind. Aqueous humor is a colorless, trans- 

 parent, watery fluid. 

 ■ Semi-fluid, gelatinous substance. 



Fills the posterior four-fifths of the globe of the 

 eyeball, and is enclosed in the hyaloid mem- 

 brane. Distends the sclera and supports the 

 retina. 



Situated behind the pupil. Double convex in 

 shape. 



Fibrous body enclosed in an elastic capsule. 



Held in position by counterbalancing of the 

 aqueous and vitreous humor and the sus- 

 pensory ligament. 



