NS: Eye Flashcards
Parts of the outer eye and function
- Eyelid (protection)
- Orbital Cavity (support,
protection) - Eyelashes (dust)
- Lacrimal Ducts (tears, antibacterial)
- Extrinsic Muscles (voluntary eye movement
- Conjunctivia (transparent mucous membrane lining inner surface of eyelids, and fold back to cover front surface of eyeball)
Conjunctivitis
- aka pink eye
- inflammation of conjunctivia caused by bacteria or allergies
Sclera
- Dense white connective tissue
- Outermost layer
- Avascular (not a lot of blood)
- Maintains shape
- Cornea is a portion of sclera
Cornea
- Clear portion of sclera
- Covers front of eye
- Focus and protect eye
- aqueous humor (fluid behind cornea) supplies nourishment
Choroid Layer
- Middle layer btwn sclera and retina
- Vascular (nourishes retina)
- Contains melanin to prevent light from scattering
Iris
- Circular muscle (involuntary)
- Controls amount of light entering eye (controls pupils, contracts and dilating)
- Coloured
Pupil
- Opening inside iris
- Size depends on light intensity
- Melanin: black pigment that makes pupil look black (from choroid layer, btwn sclera n retina)
Lens
- Behind Iris
- Transparent, biconcave, elastic, soft, avascular disc
- Held in place by ciliary muscles
- Changes shape to focus image onto back of retina
Retina
- Innermost thin layer on back of eye cavity
- Contains photoreceptors which converts light to nerve impulses
- Lens focuses images on retina
- has 4 layers: pigmented epithelium (prevents light from scattering), light sensitive cells, bipolar cells, cells of optic nerve
Eye cavities and functions
- Anterior eye cavity: “aqueous humor”, maintenance of shape, nourishment and focus
- Posterior eye cavity: “Virtreous humor”, Maintains shape of eyeball and permits light transmission to retina
Photoreceptors
-Two types of photoreceptors
- Rod: for light
- Cones:for colour
Rods
-Light sensitive cells on the periphery of the retina
-many rods per neuron
-18 million times as many rods as cones in the retina
-Detect low intensity light ( black and white and shades if grey) -> most effective at dusk and dawn (limited light)
contains a light sensitive pigment called rhodopsin
-For the rods to continue to work,rhodopsin levels must be maintained.
-vitamin A deficiency can permanently damage the rods
Rhodopsin
- Retinal (derivative of vitamin A)
2. Opsin protein
Cones
Cones are responsible for seeing colour
3 types of opsin proteins: sensitive to blue/green/red wavelengths of light (low light)
each type determines frequency of light able to be absorbed
high concentration of cones in the fovea centralis
fewer # than rods
1:1 ratio with neurons
100 cones : 1 ganglion
Fovea Centralis
Region with highest concentration of cones (detailed colour vision)
rods are around the fovea
depression in middle of retina
Order of Light Transmission
- light enter
- strikes retina (pigmented epithelium)
- rods, cones (sensory receptors on retina) > release neurotransmitters
- Bipolar cells
- Ganglion Cells > form optic nerve
- optic nerve > thalamus
- Occipital Lobe
Ganglion cells
emphasize differences btwn images
Horizontal cell
connect photoreceptors to bipolar cells
Amacrine cells
Light adaptation and moving objects
Pathway of focusing an image
- when light enters the eye
- light bent into pupil by cornea (light slows down when it enters the more dense media like cornea)
- Cornea directs light inward towards the lens (further bending), ciliary muscles control the shape of the lens, suspensory ligaments (on lens) maintain tension
- Inverted image is projected onto retina (light is directed at a focal point)
Neural Pathway of light
- Optic Nerve
- Optic Chiasm
- Primary visual cortex: Occipital lobe of cerebrum
l - Visual association area
What happens at Optic Nerve (Neural Pathway of Light)
- All ganglion cells come together to form one optic nerve
- Carries impulses to brain
- Is the blind spot on retina (where optic nerves and vessels exist, there r no photoreceptors)
Role of Optic Chiasm (neural pathway of light)
- Nerves from both eyes come together and some cross to opposite sides of brain
- Outside stays but inside crosses
- Allows eyes to work as pair
Primary visua cortex: Occipital lobe (neural pathway of light)
- Receive info from optic nerves
- Does not interpret info
Visual association area (neural pathway of light)
- Interpretation of visual info
- turns image right side up n gives it meaning
Accommodations for eyes
- Adjustment made by lens and pupil for near and distant things
- Increased age= decreased accommodation
- Tendency of ppl needing glasses when older
- Protein covering lens increase throughout whole life, make lens harder and less flexible
Accommodation (for clarity of vision)
- ciliary muscle and suspensory ligaments accommodate lens to focus light on retina
- Near objects: ciliary muscles contract, lens thick and round, bends light for more clearer vision
- Far objects: ciliary muscles relax, lens thinner and flatter
Accommodations (light intensity)
- changes diameter of pupil
- near objects: pupil constricts to bring image into shape focus
- far objets: pupils dilates to capture as much light possible into sharp focus
Myopia
- Nearsightedness
- can see close but not far
- eye too long, lens cannot flatten enough
- image focused in front of retina
- treatment: concave lens
Hyperopia
- Farsightedness
- see far, not close
- eye too short
- lens too weak
- image focused behind retina
- treatment: convex lens
Astigmatism
- abnormal curvature of cornea/lens
- treatment: glasses
Cataracts
- cloudiness of cornea/lens due to lots of protein in lens
- treatment: corneal/lens transplant or strong contacts
Glaucoma
- high pressure in anterior cavity (aqueous humour) due to inability to drain regularly
- damages cells in retina
- leads to blindness
- treatment: eyedrops or laser eye surgery
Color blind
- 1 or more cones defective
- most common is red/green blindness
- genetic and most common in males
