Sclera = opaque part of fibrous coat
a. Covers posterior five sixths of eyeball
b. Visible through conjunctiva is the white of the eye
c. Pierced posteriorly by optic nerve
Cornea
a. Transparent part of fibrous coat
b. Transmits light
Middle vascular layer
Choroid
a. Outer pigmented layer
b. Inner vascular layer
c. Lies between sclera and retina
d. Lines most of sclera
e. Terminates anteriorly as ciliary body
Ciliary body
a. Connects choroid with iris
b. Contains smooth muscle that alters the shape of lens
c. Folds on internal surface (ciliary processes) produce aqueous humor and attach to suspensory ligament of lens
Iris
a. Pigmented diaphragm with central aperture: the pupil
b. Contains smooth muscle that alters the size of the pupil to regulate the amount of light entering the eye
c. Radial fibers of the dilator pupillae open the pupil
d. Circular fibers of the sphincter pupillae close the pupil
Inner (retinal) layer
Consists of three parts
Optic part (1)
a. Receives light
b. Composed of two layers: inner neural layer and outer pigmented layer
c. Inner neural layer contains photosensitive cells: rods for black and white and cones for color
Ciliary and iridial parts (2 and 3)
a. Continuation of pigmented layer plus a layer of supportive cells
b. Cover ciliary body and posterior surface of retina
Fundus
a. Is posterior part of eye
b. Contains optic disc = depressed area where optic nerve leaves and central artery of the retina enters
c. Optic disc contains no photoreceptors = "blind spot"
Macula lutea
a. Small oval area of retina
b. Contains concentration of photoreceptive cones for sharpness of vision
c. Depression in center = fovea centralis, area of most acute vision
Neural retina ends anteriorly at ora serrata
Serrated border posterior to ciliary body
Termination of light receptive part of retina
Vasculature of retina
Central artery of retina from ophthalmic artery
Retinal veins drain to central vein of retina
Rods and cones receive nutrients directly from vessels in the choroid
Chambers of the eye
Anterior chamber
a. Between cornea anteriorly and iris/pupil posteriorly
b. Contains aqueous humor
Posterior chamber
a. Between iris pupil anteriorly and lens and ciliary body posteriorly
b. Contains aqueous humor
Vitreous chamber
a. Between lens and ciliary body anteriorly and retina posteriorly
b. Contains vitreous body and vitreous humor
Light refraction
Cornea
Refracts light that enters eye
Transparent and sensitive to touch (ophthalmic nerve = CN V 1 )
Aqueous humor in anterior chamber
Refracts light
Provides nutrients for cornea
Produced by ciliary body
Circulates through Canal of Schlemm in iridocorneal angle
Lens
Transparent, enclosed in capsule
Shape changed by ciliary muscles via suspensory ligaments attached around periphery
Convexity varies to adjust for focus on near or far objects
Parasympathetic stimulation of ciliary muscle reduces tension of suspensory ligaments and lens rounds up for near vision
Absence of parasympathetic stimulation relaxes ciliary muscle, increases tension on suspensory ligaments and flattens
lens for far visionpage 53
page 54Muscles of the Orbit