The Eye Flashcards
Sclera
White of the eye tough white skin that protects and covers all of the eye except cornea supports eyeball provides attachments for muscles
Cornea
Is the clear portion of the sclera allows light into the eye acts as fixed lens two thirds of light refraction takes place in cornea
Pupil
Size determines amount of light entering eye bright light pupil constricts dim light pupil dilates
Iris
Parasympathetic stimulation causes circular muscles to contract,sympathetic stimulation causes radical muscles to contract 1. Coloured part of eye
2. Circular muscle
3.controls opening of pupil
Lens
- Made of transparent fibres in clear membrane
- Allows precise focusing of light onto retina
3.suspended by ligament
4.finefocussing mechanism
5.non uniform index of refraction
Aqueous humour and vitreous humour
- Transparent gel like liquid filling the eye
2.provides nutrient too cornea and eye lens
3.helps maintain eye ball shape with its pressure
Retina
1.internal membrane
2.contains light receptive cells cones and rods
3. Converts light to electric signals
4.signals leave eye via optic nerve
Optic nerve
1.transmits electrical impulses from retina to brain
Blind spot
Focussing light onto retina
Light is focussed at cornea entering lens exiting lens lens curvature and shape allow for fine focussing of an image
Focussing for distance and near viewing
The lens has a small depth of field
Cannot see something close and far with both objects in focus at the same time
Accommodation distance and near
Distance light rays almost parallel do not need as much refraction ciliary muscles relaxed fibres taut flat lens
Near light rays diverge need more refraction ciliary. Muscles contract fibres slack rounded lens greater strength for near vision
Presbyopia
Lens harden with age
Cannot accommodate for near
Bifocal lenses
Retina
Receives light focussed by lens convert light via network of nerve cells
Choroid
Vascular layer providing oxygen and nutrients to outer retina especially fovea
Absorbs any light not absorbed by photoreceptors
Retinal pigment epithelium
Pigment layer for light absorption. Sand reducing oxidative stress tight junctions and blood brain retina barrier supports photoreceptors
Cones
Concentrated in fovea high acuity day vision and colour vision
Rods
Dark vision Not present in central retina
Horizontal cells
Interneurons connecting photoreceptors laterally help integrate and regulate from multiple photoreceptors cells
Bipolar cells
Connect photoreceptors to retinal gangalion cells
Facilitate sensory processing through horizontal amacrine cells
Amacrine cells
Interneurons connecting bipolar laterally
Inhibitory
Interact with retinal gangalion cells
Retinal ganglion cells
Out
It cells from retina relay info from retina to brain via optic nerve
4 types in humans parvocellular magnocellular Kongo cellular photosentive ganglion cells
Rod cells
120 million throughout retina
Absent from fovea
Rod shaped
Sensitive to dim light not sensitive to colour
Many rods feed into one ganglion cell poorly resolved images
Light sensitive pigments rhodopsin low visual acuity but good indark
cones
6-7 million condensed at fovea cone shaped require bright light 3 types for colour vision 1 cone feeds into 1 ganglion cell at fovea well resolved images light sensitive pigments iodopsin high visual acuity and colour vision
Phototransduction
Recess through which light is converted into electrical signals occurs in the retina through photoreceptors to encodes a light stimulus as chemical output deception to encodes a light carried out on membrane disks contain 1000s of molecules or rhodopsin
Phototransduction
Rhodopsin contains ops in protein and retinal
Dark=cis form
Absorbs light=trans form
Changed shape of ops in protein bleaching
Reverse action trans to cis requires enzyme reaction and is very. Slow
Path of Phototransduction
Light changes rhodopsin structure then alters permeability to na+ in photoreceptors then sensory neurone in optic nerve then to brain
Lateral geniculate nucleus
Structure in thalamus part of midbrain receives input from retinal ganglion cells input and output connections to visual cortex one in each to sphere one in each hemisphere leave LGN and goes to visual cortex
Primary visual cortex
Located in occipital lobe input from LGN via optic radiation send information to 2 pathways
1) ventral stream from recognition a object presentation
3) Dorsal stream motion object location eye and arm control
Depth perception.
Retinal disparity allows judgment of distance
The closer an object the great and disparity
Requires binocular vision
Visual Disease sclera
Scleritis inflammation of sclera usually associated with u derlying disease can progress to other parts of the eye immediate treatment to reduce long term vision loss
Visual disease cornea
Open sore of the cornea many causes infection physical chemical trauma corneal drying over contact lenses very serious may result in blindness
Disease in pupil and iris
Colombo a hole in iris underdeveloped tissue during pregnancy can be syndromes or caused by foetal alcohol syndrome variable impact on vision treatment coloured contact lens
Visual disease lens
Cataracts age related congenital or trauma clouding of lens decrease vision surgery removal of old lens via suction and insertion of plastic lens
Disease in retina macular degeneration
Age related degeneration affects retina build up of was5e occurs in 50 to 60 year olds. Progressive without treatment injections mild vision lost
Retinal detachment
Tear allows fluid under retina risk
Risk trauma family history
Surgery
Strabismus
Misalignment of the eyes common on children alblymopia suppression of image
Loss of depth perception treat amblyopia with patching surgical correction
