Transcript The Eye - Downey Unified School District

The Eye
VISION
Alyssa Jimenez
&
Cristina Santiago
Components Of the eye
❖ Eyelid (palebra)
❖ Lacrimal apparatus
❖ Extrinsic Muscles
❖ Cranial Nerves
Components cont.
Eyelid
● Also known as the
palebra
● Protective shield for the
eyeball
● Conjunctiva
Lacrimal Apparatus
● Tear secretion and
distribution
● Lacrimal gland
● Nasolacrimal gland
Extrinsic Muscles
● Hold eyeball in orbital cavity
and allow for eye movement
● Superior Rectus Muscle
● Inferior Rectus Muscle
● Lateral Rectus Muscle
● Medial Rectus Muscle
● Superior Oblique Muscle
● Inferior Oblique Muscle
Structure of the eye
● three tunics
■
■
■
fibrous
vascular
interna
The outermost tunica
function: protection
● Consists of:
Cornea: helps focus incoming light rays
 Sclera: protection, attachment of eye muscles
 aqueous humor

The middle tunica
● tunica vascular
o
supplies eye tissue with
oxygen and nutrients
● Consists of:
choroid coat: contains
many blood vessels
 Pupil
 lens
 iris: colored ring around pupil


ciliary body:
o
o
o
o
ciliary muscles: control shape of
lens
ciliary processes: hold lens in
place.
accommodation: lens changes
shape to focus on close objects
Aqueous Humor: thin, watery
fluid that fills the space between
the cornea and the iris
the innermost tunica
● Tunica Interna

the retina
●
●
●
inner lining of
eyeball
site of
photoreceptors
vitreous humor
Cranial Nerves
● Occipital Lobe
● Oculomotor Nerve
*ex: maintaining the opening of an
eyelid/pupil constriction
● Optic Nerve
*ex:
brightness,perception,contrast
Structure cont.
● Blind spot: no photoreceptors present
● posterior cavity: filled with vitreous humor
●
jelly-like fluid,which maintains the spherical shape of the
eyeball
Visual Receptors
● Two types of visual receptors

Cones:
o
o
o
o

color vision
produce sharp images
absorb light
less sensitive in low light levels
Rods:
o
o
o
o
o
night vision
produce silhouettes of images
do not differentiate color
sensitive to low light levels
peripheral areas of retina
Rhodopsin & Iodopsin light
● Rhodopsin light:
o
o
absorbing pigment
embedded in membranous discs
● Iodopsin light:
o
a photosensitive violet pigment that occurs in the
cones of the retina and is transformed by light into
retinal and an opsin protein.
Dark Currents in photoreceptors
*Sodium channels stay open in photoreceptor
when no light is being absorbed
*Constant current of sodium into cell keeps
photoreceptor the most active in darkness
Refraction
●
The refraction process is similar to the way a camera’s lenses tale in light
●
The bending of a wave when a light passes a fast medium to a slow medium bends the light ray
toward the normal to the boundary between the two media, this is how the eye interprets
refraction
●
80% of refraction occurs in the cornea is the most drastic change in the index of refraction which
the light experiences
●
●
●
20% of refraction occurs in the inner crystalline lens
Light is refracted, or bent, when it passes from one medium to a medium with different density
Ex: air to glass to air
Convergent vs. Divergent
●
●
-
Convergent waves are rays of light that converge light that is traveling parallel to their principal
axis
Convex lenses refract light in a towards each other
Divergent waves are rays of light that diverges light that is traveling parallel to their principal
axis; travels through the center of either lens,straight through and is not refracted
Concave lenses refract parallel light rays away from each other
Dark vs. Light Vision
Dark light is dim vision, when an individual’s eye adapts to a loss of illumination
The pigmentation of the eye in dark vision ,is very minimal, consists of rod cells, but since
neither rods or cone can survive in the dark for long, blindness is a definite possibility
The photoreceptors found in dark light are rods
A. Factors that affect Dark Light
- Intensity and duration of the pre- adapting light
●
-
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Size and position of the retinal
-
Wavelength distribution
-
Rhodopsin regeneration (deficiency of vitamin A)
Dark vs. Light Vision Cont
During Light vision, the eye quickly adapts to background illumination and is then able to
distinguish and identify objects
The photoreceptors found in light vision are cones
1.
S- cones, short- wavelength sensitive cones
2. M- cones, middle- wavelength sensitive cones
3.
L- cones, long wavelength sensitive cones
●
Stereoscopic Vision
●
The single perception of a slightly different image from each eye
●
Gives us the ability to see objects with height, width, and depth ( a sort of 3-D experience)