vision Flashcards
What is the function of the cornea?
Refracts light
What is the function of the optic nerve (II)?
Sensory, vision; pierces sclera at posterior of eye
What is the lens?
The transparent structure behind the pupil that changes shape to help focus images on the retina
What are suspensory ligaments?
A fibrous membrane that holds the lens of the eye in place
What do ciliary muscles do?
Contract to thicken the lens (for closer things), relax to thin the lens (for further things)
What is the anterior cavity of the eye?
Between cornea and lens; filled with aqueous humor
What do the muscles of the iris control?
Size of the pupil
What is the pupillary reflex?
The automatic process by which the iris contracts and relaxes to control the size of the pupil, in response to the relative brightness of light entering the eye
What are cataracts?
Clouding of the lens; artificial lens can replace it
What is the Retinal Pigment Epithelium (RPE)?
Layers of cells at the back of the eye; how photoreceptors get nutrients
What is the fovea centralis?
Pinpoint depression in the center of the macula lutea that is the site of sharpest vision; contains cones
What is a concave lens?
A lens that is thinner in the center than at the edges
What is presbyopia?
Farsightedness caused by loss of elasticity of the lens of the eye, occurring typically in middle and old age
What is myopia?
Nearsightedness; due to elongated eyeball or thickened lens; focal point is in front of the retina; corrected with concave lenses
Which provides a less precise image, rods or cones?
Rods
Which synapses with one nerve fiber, rods or cones?
Cones
What is stereoscopic vision?
Combination of two retinal images to give a 3-D perceptual experience and allows depth-perception; requires binocular vision
What is age-related macular degeneration?
Progressive and irreversible destruction of receptors from any of a number of causes
What is nystagmus?
Involuntary, darting movements of the eyes
What is cataract surgery?
Surgical removal of a clouded lens of the eye
What does the orbicularis oculi do?
Closes eyelids
What does the levator palpebrae do?
Elevates (opens) eyelid
What are the extrinsic eye muscles?
Superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, inferior oblique; attached to the sclera; move the eyeball
What is strabismus?
Abnormal deviation of the eye
What are the three tunics of the eyeball?
Fibrous outer, vascular middle, nervous inner
What is the cornea?
The transparent layer forming the front of the eye
What is the sclera?
White of the eye; protects the delicate inner layers of tissue; extrinsic eye muscles attach here
What is the middle tunic of the eye?
Choroid coat, ciliary body, iris
What is the choroid coat?
Nourishes the retina and absorbs scattered light to keep inside of eye dark
What is the ciliary body?
Structure surrounding the lens that connects the choroid and iris; contains ciliary muscles, which control the shape of the lens, and it secretes the aqueous humor
What is accommodation?
The process by which the eye’s lens changes shape to focus near objects on the retina
To focus on a more distant object, the lens is…
Flatter
To focus on a closer object, the lens is…
Rounder
What is the iris?
A ring of smooth muscle tissue that forms the pigmented portion of the eye around the pupil and controls the size of the pupil opening
What is the function of aqueous humor?
Maintains the pressure needed to inflate the eye and provides nutrition for the central cornea and lens
What is the scleral venous sinus (canal of Schlemm)?
A circular channel in the eye that collects aqueous humor from the anterior chamber and delivers it into the bloodstream
What is glaucoma?
Increased intraocular pressure results in damage to the retina and optic nerve with loss of vision; scleral venous sinus does not drain aqueous humor from eye
What is the retina?
Light sensitive layer of the eye; contains rods and cones
How many rods and cones are there in the eye?
100 million rods; 3 million cones
What is the macula lutea?
Yellowish spot on the back of the retina; contains the fovea centralis; area of sharpest vision
What is the optic disc (blind spot)?
Site where optic nerve leaves the eye; lacks photoreceptors
What is the pathway of light through the eye?
Light enters eye -> cornea -> aqueous humor -> lens -> vitreous humor -> neural layer of retina (where photoreceptors are)
What is refraction?
The bending of a wave as it passes from one medium to another
What parts of the eye refract light?
Cornea (most), aqueous humor, lens (fine-tunes), vitreous humor
What is a convex lens?
A lens that is thicker in the middle than at the edges
What does a convex lens cause light to do?
Converge
What is the near point of vision?
The closest an object can be and still come into focus
What is emmetropia?
Normal refractive condition of the eye
What is hyperopia (farsightedness)?
Farsightedness; due to shorter eyeball or thinner lens; focal point is behind the retina; corrected with convex lenses
What is astigmatism?
Defective curvature of the cornea or lens of the eye; vision is blurry
Which are more sensitive to light, rods or cones?
Rods
Which produce color images, rods or cones?
Cones
Which are concentrated in the fovea centralis of the macula lutea, rods or cones?
Cones
Which are more common in the periphery of the retina, rods or cones?
Rods
What are visual pigments?
Light sensitive chemicals that react to light and trigger electrical signals
What is rhodopsin?
A light-sensitive pigment found in the rod cells that is formed by retinal (derived from vitamin A) and opsin
How many kinds of cones are there?
3 types that detect blue, green, and red
What is the visual pathway to the brain?
Light stimulus causes impulses to travel from the: Light > retina > Optic nerves > optic chiasma (medial fibers cross to opposite side) > optic tracts > thalamus > optic radiations > occipital lobe (visual cortex)
What is retinal detachment?
Separation of the retina from the underlying epithelium, disrupting vision and resulting in blindness if not repaired surgically
What are photoreceptors?
Respond to light; rods and cones
What are the accessory structures of the eye?
Eyebrows, eyelids, conjunctiva, lacrimal apparatus, extrinsic eye muscles
What is the orbit of the skull?
Bony socket in the skull containing eyes
What is the conjunctiva?
Mucous membrane lining the eyelids and covering the anterior portion of the sclera (not cornea)
What is conjunctivitis (pink eye)?
Inflammation caused by infection of the conjunctiva, characterized by redness and often discharge
What are tarsal glands (Meibomian glands)?
Modified sebaceous glands along inner margin of the eyelids; lipid-rich secretions keep eyelids from sticking together
What is the lacrimal apparatus?
The structures that produce, store, and remove tears
What do the lacrimal glands produce?
Tears
What is lysozyme?
An enzyme found in tears that destroys the cell walls of certain bacteria
What cranial nerves innervate extrinsic eye muscles?
Oculomotor (III), abducens (VI), trochlear (IV)
What is diplopia?
Double vision
What is abduction in terms of body movement?
Movement away from the midline of the body
What is adduction in terms of body movement?
Movement toward the midline of the body
What is elevation in terms of body movement?
Raising a body part
What is depression in terms of body movement?
Lowering a body part
What is the outer tunic of the eye?
Cornea, sclera; (optic nerve II pierces sclera)
Does the cornea have pain receptors?
Yes
Can the cornea be transplanted?
Yes
What are floaters?
Particles of cellular debris that float in the vitreous fluid and cast shadows on the retina; see ‘moving specks’
