Topic 6 - The eye Flashcards
Draw the structure of the eye
*answer on laptop due to inability to put a picture on here :(
What is the lacrimal gland?
- It’s on the outer section of each eye
- Where tears are formed
- Tears function = keep cornea moist & clean
Where do tears go after being formed?
- They diffuse across eye & are drained from lacrimal sac (near inner corner of eye) into nasolacrimal duct
*Note: important not to place eye drops too close to lacrimal sac otherwise could drain too quick & X work
What is the aqueous humor & what’s its function?
- It’s a clear water fluid formed near ciliary muscle, perfuses past iris into anterior (front) of eye & drains out
- Function = provide nutrients to structures w/o blood vessels (i.e cornea) & remove waste
What are the 2 muscles that control amount of light entering in iris + functions?
- Circular muscle = activated by bright light, part of PSNS. When contract, pupil becomes smaller thus less light enters
- Radial muscle = activated by low lvls light, part of SNS. When contract, pupil becomes larger thus more light in
*Note: circular & radial muscles alter size of iris/pupil to provide optimum sight in diff. light lvls
How light entering affects eye
- Light enter eye & focused on by cornea & lens (where light is refracted/bent & shape controlled by ciliary muscle)
- This goes onto the retina which contains photoreceptors
- Photoreceptors (rods & cones) change energy from light into neuronal firing
- Neurons assoc. retina exit it at optic nerve
What does the Ciliary muscle do?
- It’s connected to zonulas (fibres)
- When it relaxes zonulas (by contracting), lens becomes more rounded & enables close vision focus
- When zonulas pulled (by relaxing muscles), lens becomes more stretched & enables far vision focus
What is behind the photoreceptors in the retina?
Dark (pigmented) epithelial layer = absorbs any light rays that escaped the rods & cones (prevents distortion of visual image)
What does the fovea do?
- Fovea is point on retina where vision is most clear b/c no cells in front of rods & cones (w/ also being little convergence b/w cells at fovea)
- Thus fovea point where light is focused & rest of retina is peripheral vision
What are rods & cones (photoreceptors) responsible for?
- Rods = black & white
- Cones = colour vision
What is the structure of rods & cones?
They both have same basic structure:
1. outer segment has discs w/in it facing onto pigmented epithelial layer
2. inner segment with cell nucleus & organelles
3. synaptic terminal region that synapses w/ ganglion cells
What do the parts in the rods/cones structure do?
- Outer segment = contain pigments (rods=1 & cones=3) converting light energy to membrane potential
*Note: cones colours = red, green & blue
What is phototransduction?
- ## Process of converting light to electrical signals
What is Hyperopia?
Far-sightedness - light focus behind retina thus fix with convex lens
What is myopia?
Short-sightedness (near-sightedness) - light focuses front retina thus fix with concave lens
What area in photoreceptors (that contains retinal) react to light entering the eye?
Discs in the outer segment
