L04 - Retina 1 An Overview Flashcards
CASE STUDY: MELISSA
- Wavy vision (objects look wavy - can’t see face)
- Trouble reading (even with strong light)
- Can walk the dog with no problem
What is her problem?
Central vision obscured hence area affected is macula therefore age related macula degeneration where blood vessels growing at back of eye has leaked everywhere, destroyed macula
Optical factors affecting visual acuity
Pupil size (dilated in dark therefore blur), clarity of optical media, refractive errors
a) Phototopic light levels - ?/6
b) Scotopic light levels - ?/60
c) Plexiform aka
d) No. of rod-BP cell
e) No. of cone-BP cell
a) 6/6
b) 6/60
c) Synapse
d) 1
e) 9
Why does our night vision seem so poor if there’s 20:1, rods: cones?
Rods have high convergence. Not about numbers but about connectivity (Bon Jovi example from Phys)
Lateral inhibition is from?
Horizontal cells (outer retina)
- Input and output = photoR
- Releases GABA (hyperpol.)
Amacrine (axonless) cells use what NT?
GABA or Glycine
Cones:
- Low or high convergence?
- Low or high absolute light sensitivity?
Low convergence 1 cone: 2 BC: 2 GC
Low absolute light sensitivity (needs lots of light to work)
Are size and shape of cones thicker or thinner at the fovea?
Thinner
3 adaptations that increase vision at fovea
1) Red + Green cones only
2) Central avascular zone (no blood vessels to occlude vision)
3) Cells pushed to a side
*Blue light makes vision blurry, not as much blue cones
!Treatments for age-related macular degeneration?
2 Forms
- Dry (atrophic form) - no treatment
- Wet (neovascular form) - monthly injection
Where is the blind spot in the eye located?
The blind spot is located about 12–15° from the middle of the eye towards the nose - the raised disc on the retina at the point of entry of the optic nerve, lacking visual receptors and so creating a blind spot.
Centre of macula is called?
Centre of macula is fovea centralis - where it is avascular
*only place where 20/20 vision is attainable
