Special Senses- Eye Flashcards
Extrinsic components
Lid, brow,lash, extrinsic eye muscle, exocrine gland, lacrimal glad, conjunctiva, rectus muscle
Eyelid
- neuromuscular reflex control
- maintain integrity of corneal surface and tear film
- maintain proper position of globe within orbit
- sensory function of lid
- spontaneous and reflex blinks
- regulates light
- cosmeis ( cosmetics)
- obicularis occuli- moves eyelid
- protection from outside environment ( squint)
Conjuctiva
- over sclera
- spreads tear film
- mucus membrane ( open to outside world) barrier, keeps anterior moist
- thin, translucent
- epithelium continuous with cornea and. Lacrimal drainage
- it is- pink eye
Cornea
Responsible for 70% of focus capabilities
Lacrimal apparatus
Produces tears, float to anterior surface of eye
Lacrimal gland
Natures eye drop , produces film, secretes fluid,lid movement, moves fluid over anterior eye
Tear film
Primarily tears Helps cornea focus light Maintains health of underlying structure Maintains optical stability Antibacterial Corneal nutrition Mechanical- flushes cellular debris
Extrinsic eye muscle
6 attach to outer surface of eye
Produce movement
Controlled by cranial nerve 3,4 and 6
3 tunics
Fiberous- outer
Middle- vascular
Inner- nervous tunic
Fiberous-
Dense CT, outer covering of eye
Sclera
Rigid makes up majority of fiberous
Protects internal structures
Maintains eye shape
Covers anterior, except cornea
Allows for muscle attachment
Focus capabilities composed of elastic and collagen
Extrinsic muscles attach to fiber tunic
Sclera is similar to muscle fibers firm attachment
Fiberous- Cornea
A vascular 5 layers Common transplant Light bends ( refracts) on to lens Filters out UV light
Fiberous- scleral venous sinus- vein- where cornea and sclera intersect
Absorbs excess aqueous humor
Drains AQueous humor to maintain eye pressure
Intraocular pressure in front of lens, built up pressure helps keep retina attached.
Detached retina- too little pressure
Back pressure- blindness/glaucoma
Middle tunic
Vascular
Middle- vascular parts (3)
- Choroid- primary blood supply to retina- nourishes, posterior between sclera and retina (layer), highly pigmented- dark in color, melanocytes, vascular loose CT, blocks light from sides. Thickness decreases from posterior to anterior. Protects retina from invading blood vessels
- Ciliary body- anterior extension of choroid, 2 functions- accommodates- change shape of lens/focus power- extends fibers towards lens. Contraction results in thickening of lens which focuses on close objects. Change shape/ focus power of lens .-also so Ulta fibers secure lens in place. Process- holds lens, makes aqueous humor muscle- shapes lens by contracting and relaxing- refraction power
- Iris- positioned in front of lens, thin, pigmented- epithelial and smooth muscle. Controls size of pupil- regulating light entry. Bright- parasympathetic- constricts— sympathetic-dim- displayed. Surrounded by aqueous humor. Gives color
Lens- not part of vascular works with it. Maintains clarity- refraction (bending) light focused- provides accomodation- focusing @ different distances, absorbs UV — where cataracts form, refraction
Nervous tunic
Inner most layer of eye
Nervous tunic- retina
Thin, transparent, where photoreceptors detect change in light are found
Only rods and cones respond directly to light
2 types of photoreceptors
Rods and cones
Rods
Elongated, contain pigment rhodopsin which can absorb dim light and can detect shades of grey in dim light.
Achromatic- without color
Inner segment contains nucleus- metabolic machinery
Outer segment is transduction sites
Chemicals interact with light waves to create impulse— action potential
Consist of high density stack of disk membrane - flat organelles
Cones- photoreceptors
Contain photopsin- absorb bright light- allows us to see colors in bright light
Chromatic(color)
3 types of photo pigments s cone ( blue), m cones (green) and L (red) cones
Missing cones means color blind, can’t convert light wave to color
We cannot see below infrared or above UV
Recover more rapidly than rhodopsin (50%) in 1.5 min
Landmarks of Retina
Central fovea and macula ( area around fovea) . Free of blood vessels contains only cone cells - 99% in retina- sensitive
Optic disc- blind spot, where optic nerve and retina attach- no rods or cones- no images, no transduction
Anterior cavity- in front of lens
Posterior cavity behind lens
Virtuous humor- maintains retina placement and distributes pressure and fluid over retina
Processes of retinal image formation
All happen at the same time
Process of retinal image formation
Refraction
Bending light rays . Refracted light can be focused. End point- central fovea
Disorders- myopia- near sighted- in front of retina
Astigmatism- distorted
Hyper metro pia- far sight, behind retina
Emotropic normal eye
Refractive structure- 1 cornea 70% 2. Aqueous humor(focus) 3. Lens- only one that can be adjusted- moment to moment(accommodation)- suspended by zonules of zinn 4. Virtuous humor- shock absorb
Presbyopia- difficult accommodating — different glasses for driving, reading etc
Process of retinal image formation
Accommodation
Eye changes refractive power. - curve and thickness increase/decrease lens size- accounts for distance- far lens is flat, close lens is thick and round
Process of retinal image formation
Pupil constrict and dialate
Parasympathetic- constrict- bright
Dilate- sympathetic -ANS- dim dark light- regulates amour of light entering
Process of retinal image formation
Convergence
Convergence- intersect- disgujate (rotation in opposite direction) focus on 1object- rotate eyes toward nose
Movement of eye move inward so line of sight intersect in front of eye aka- synchronous adduction of each eye
Helps maintain bifoveal single vision. Focus of eyes on same object at same time
Visual transduction
Ability to convert stimulus (light)into nerve impulse (action potentials) rods and cones are the only reason this is carried out
Binocular vision
Both eyes focusing on the same object— giving us convergence
Increased field of vision, enhanced visual acuity, contrast sensitivity, visual motor skills
Optical defects in one eye Mae less obvious by other eye safety net from vision loss- depth perception, cross eye, lazy eye would be negative effects here
Bison happens in occipital lobe via visual pathway
PathwY- photoreceptors of retina— cranial nerve 2(optic)- where nerve crosses optic chiasma-optic tracts-optic radiation (thalamus)—visual cortex of occipital lobe
