Describe the route of nerve impulses through the retrobulbar visual pathway
The optic nerves from each eye merge at the optic chiasm. Axon fibers from the nasal retina of each eye cross to the opposite side of the chiasm, while axons from the temporal retina of each eye continue on the same side. The realigned axons emerge from the chiasm as the left and right optic tracks, ending in the left and right lateral geniculate bodies. There the axons synapse to the optic radiations, which travel to the right and left half of the visual cortex of the brain
How are the functions of these two types of retinal photoreceptor cells different?
Rods are largely responsible for vision in dim light and for peripheral vision
Cones provide sharp central vision and color perception
Briefly describe how the retina works to produce site
The retinal rods and cones receive light rays, and in turn, generate electric (nerve) impulses .
These impulses are transmitted to the brain, where the visual messages they carry are converted to the sensation of sight
What is the main function of the vitreous?
Acts as a shock absorber for the eye and helps maintain the spherical shape of the globe
What is the physiologic process and purpose of accommodation?
The curvature of the lens can change, becoming rounder, to focus images of objects that are closer to the eye
What is the main function of the choroid?
To supply blood (nourishment) to the outer layers of the retina
Describe how the pupil dilates and contracts, naming the muscles involved
Fibers of the dilator muscle that extend from the pupil to the boundary of the iris contract to dilate the pupil; contraction of the sphincter muscle that encircles the pupil makes the pupil smaller
Describe the course of aqueous humor into and out of the eye, naming the principal ocular structures involved
Aqueous humor enters the eye behind the iris, flows across the back of the iris, through the pupil, and into the anterior chamber; it leaves the anterior chamber at the filtration angle and passes through the trabecular meshwork, the canal of Schlemm, and into the blood vessels
Why is a balance between the inflow and outflow of aqueous humor important?
To maintain intraocular pressure
Name the five layers of the corneal tissue with their functions (2 layers perform the same function)
Epithelium-serves as first line of defense against infection and injury
Bowmans Membrane-acts as an anchor for epithelium
Dscemets Membrane-contributes rigidity
Endothelium-maintains proper fluid balance
What is the principal function of the cornea?
To focus light rays reflected to the eye, contributing about two thirds of the focusing power of the eye
Name the three layers of tear film and their functions
Outer oily layer-help prevent evaporation of moisture from the middle, aqueous layer
Middle layer-provides moisture, oxygen, and nutrients to the cornea
Inner layer-mucinous layer, promotes even spread of the tear film
What is the relationship between the lacrimal gland, lacrimal sac, and nasolacrimal duct?
Tears are produced by the lacrimal gland; collected in the lacrimal sac; and drain into nasal cavity by means of the nasolacrimal duct
Give two reasons why tears are important to the functioning of the eye
Name three layers of the eyelid
Outer layer of skin
Middle middle layer of fibrous tissues and muscle
Inner layer of tissue (conjunctiva)
What are three functions of the eyelids?
To protect the eye from injury
To exclude light
To aid in lubricating the ocular surface
Name the six extraocular muscles and their functions
Medial rectus-in (adduction)
Lateral practice-out (abduction)
Superior oblique-down and in
Inferior oblique-up and out
Describe the structure and function of the orbit
The bony cavity in the skull that houses the globe, extraocular muscles, blood vessels, and nerves; protects the globe from major injury by a rim of bone
Name the four primary structures included in the adnexa
Briefly describe how the eye convert light rays to a perceived image, naming the principal structures involved in the process
Light rays reflected from an object are focused by the cornea and the lens to produce an upside-down image of the object on the light sensitive retina. The retina converts the image to electric impulses, which are carried by the optic nerve to the brain's visual cortex, where they produce the sensation of sight.