The Human Eye

1. Fibrous tunic – outer protection and support.
• non-elastic (it has the same constant refractory index)
• consists of high amounts of collagen fibers
• only organ transplanted from one individual to another without rejection
• for light refraction (light bending),(most important. feature regarding refraction)
• cornea and lens are involved with refraction
o the lens is not part of any tunic, because of the variable elastic change (it is elastic) hence the refractive index can change, the lens is also avascular
• non-elastic (therefore part of the tunic)
• anchors extrinsic eye muscles LR6[SO4]3
• the optic nerve, CN II , pierces the sclera in the back of the eye creating a blind spot (where there is no sight) = optic disc
• perioptic nerve exits out of the eye where the optic disc blind spot is located
• the optic disc lacks photoreceptors: rods and cones
• anterior chamber  H2O secretion (bathes eye)
• posterior chamber  vitreous humor, a gel like substance, gives the eyeball its shape
2. Vascular tunic – also called the uvea, forms the middle tunic
a) choroid – contains melanocytes and serves to absorb light and prevent light from scattering with in the eye ball itself
b) cilliary muscle body – continuation of choroid, made of smooth muscle, attaches to the suspensory ligaments (made of collagen fibers).The suspensory ligaments inturn attach to the lens.It is really composed of two different types of muscle
i. radial muscle – (longitudinal), important in distinguish dim light
ii. circular muscle – cones, color, central vision, close vision
c) iris – is a continuation of the cilliary body/ cilliary muscle.It encircles the lens.

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