VISION part III Flashcards
innermost layer of the eyeball
NERVOUS TUNIC/RETINA
the inner coat of the eyeball, lines the posterior three-quarters of
the eyeball and is the beginning of the visual pathway
RETINA
is the site where the optic (II) nerve exits the eyeball. Bundled together with the optic nerve are the two blood supply: central retinal artery,
a branch of the ophthalmic artery, and the central retinal vein
OPTIC DISC
2 LAYERS OF RETINA
- PIGMENTED LAYER
- NEURAL LAYER
- non-visual portion of retina
-It is a sheet of melanin-containing epithelial cells located between the choroid
and the neural part of the retina
PIGMENTED LAYER
- multilayered outgrowth of the brain
that processes visual data extensively before sending nerve impulses into axons that form the optic nerve
NEURAL LAYER
3 distinct layers of retinal neurons:
- PHOTORECEPTOR LAYER
- BIPOLAR CELL LAYER (horizontal and amacrine cells)
GANGLION CELL LAYER
are specialized cells in the photoreceptor layer that begin the process by which light rays are ultimately converted to nerve impulses
PHOTORECEPTORS
2 TYPES OF PHOTORECEPTORS
RODS AND CONES
HOW MANY RODS ARE IN THE RETINA
120 MILLION
HOW MANY CONES ARE IN THE RETINA
6 MILLION
- very sensitive to light (have low light threshold)
- dim light (black and white vision)
- PERIPHERAL VISION
RODS
RHODOPSIN IS MADE UP OF CHON
SCOTOPSIN
- responsible for color vision
CONES
CONE ARE MADE UP OF CHON -
PROTOPSIN
derivative of vit. A
RETINAL
3 types of CONES
- Blue cones, which are sensitive to blue light.
- Green cones, which are sensitive to green light.
- Red cones, which are sensitive to red light.
inability to distinguish between certain colors because of the absence or deficiency of 1 or 3 photopigment
COLOR BLINDNESS
inability to see well at dim light
NIGHT BLINDNESS/NYCTALOPIA
Good vision depends on adequate intake of
CAROTENOID
a small yellow spot near the center of the posterior portion of the retina
MACULA LUTEA
A small pit/depression at the center of the
macula lutea. It contains only CONES, thus, the area of highest visual acuity or resolution
CENTRAL FOVEA
ABILITY TO SEE IMAGES MOST CLEARLY
VISUAL ACUITY
SHARPNESS OF VISION
RESOLUTION
BLIND SPOT is a white spot just medial to the macula lutea. Where blood
vessels, optic nerve enter the eyes. It contains no photoreceptors, thus objects
focused on this area cannot be seen.
OPTIC DISC
FUNCTIONS OF THE COMPLETE EYE:
- REFRACTION
- ACCOMMODATION
- is the bending of light as it passes from one medium to another.
REFRACTION
is a process by which the lens of the eye changes in shape/curvature to adjust for vision at various distances; the lens either increase/decrease in its curvature
ACCOMMODATION
4 MEDIA OF REFRACTION
- cornea
- aqueous humor
- lens
- vitreous humor
is the crossing point of light rays
FOCAL POINT
is the process of causing light to converge (bend toward each other
FOCUSING
CHARACTERISTICS OF IMAGES FOCUSED ON THE RETINA:
- INVERTED/UPSIDE-DOWN
- RIGHT TO LEFT REVERSAL
what is the image seen on the retina when there is a convergence of light rays
INVERTED/UPSIDE-DOWN
what is the image seen on the retina when the light from right side strikes the left side of the object and vice versa
UNDERGO RIGHT TO LEFT REVERSAL
The light rays reflected from the object are nearly PARALLEL to one another
VIEWING AN OBJECT @ 20 ft. DISTANCE
Light rays that are reflected from the object are DIVERGENT ( they move away from each other
VIEWING AN OBJECT - NEAR OBJECT (NEAR VISION)/CLOSER THAN 20 ft.
Thus, when viewing at closer objects, light rays must be refracted more
to allow the image to be focused on the retina called
accommodation
What makes the lens increase in its curvature?
The CONTRACTION of the ciliary muscle, allowing the ciliary process & choroid to be pulled forward toward the lens – this action releases tension on the lens & on the suspensory ligaments
Because the lens is elastic, it changes its shape: shortens, thickens, bulges (increase in convexity)
In order to accommodate light rays, the ciliary muscles should RELAX,
causing the suspensory ligaments to exert greater tension on the lens, thus the lens becomes more flat: stretched in all direction by the suspensory ligaments decreased convexity of the lens
DISTANT OBJECT (FAR VISION)
3 REQUIREMENTS FOR ACCOMMODATION (1)
- CHANGE IN THE SHAPE
near vision: increased in curvature
far vision: decreased in curvature
3 REQUIREMENTS FOR ACCOMMODATION (2)
- CONSTRICTION/DILATION OF THE PUPILS
bright light: constriction
dim light: dilation
3 REQUIREMENTS FOR ACCOMMODATION (3)
- CONVERGENCE OF THE EYES
- medial movement of eyeballs
(*The nearer the object, the greater is the degree of convergence needed to maintain binocular vision)
convergence is not complete, it produces double vision
DIPLOPIA
minimum distance for near point vision
4 inches in young adult
Image is focused in front of the retina, thus the person has to move closer
to the object to allow clearer vision
MYOPIA – Nearsightedness
causes of myopia
a. Elongated eyeball
b. Thickened lens
correction for myopia
CONCAVE LENS
FARSIGHTEDNESS
HYPEROPIA/HYPERMETROPIA
CAUSES OF HYPEROPIA
a. Shortened eyeball
b. Thin lens
CORRECTION FOR HYPEROPIA
CONVEX LENS
The cornea’s curvature is asymmetrical, so light rays are focused at 2 points on the retina, rather than at one point resulting to:
o blurred vision, shadows on the letters, squinting
o double vision
ASTIGMATISM
CORRECTION FOR ASTIGMATISM
Eyeglasses wherein its anterior outer surface corrects visual defects & the posterior surface. Matches the curvature of the cornea.
–inflam of the conjunctiva, from bacterial infxn
CONJUNCTIVITIS
*Contagious Conjunctivitis:
pink eye
– a cyst caused by infection of the sebaceous glands along the edge of the eyelids
CHALAZION
infection of an eyelash/hair follicle
STYE
NEARSIGHTEDNESS
MYOPIA
FARSIGHTEDNESS
HYPEROPIA
decrease in the ability of the eye to accommodate for near vision; comes with aging
PRESBYOPIA
a defect in which the cornea or lens is not uniformly curved & the image is not sharply focused
ASTIGMATISM
absence of perception of 1 or more colors; most of which have genetic origin
COLOR BLINDNESS
most common cause of blindness
-clouding of the lens as a result of aging, infection or trauma; also excessive
exposure to UV rays
CATARACT
- excessive pressure build up; results from an interference with normal
circulation of AH or from overproduction - tunnel vision/increase of IOP
- lost of peripheral vision
GLAUCOMA
*increase pressure w/in the eye can interfere with circulation & may lead to
malfunction/destruction of the optic nerve
BLINDNESS
