Anatomy + Conditions Of The Eye II - How We See Flashcards
What is refraction?
Change in direction of light on passing through boundary of two different mediums
Where does the greatest amount of refraction occur?
Cornea
How does the shape of the eyeball affect your sight?
- too long: myopic (short sighted)
- too short: hypermetropic (long sighted)
What happens in the accomodation reflex?
- object moved closer to eye
- greater refraction required to focus light onto retina
- pupil contracts
- convergence of eyes
- lens fattens
What is presbyopia?
Age related inability to focus on near objects due to lens stiffening with age
What happens to the eye in the accommodation reflex
Pupils constrict
Convergence of eyes
Lens fattens
What is phototransduction?
Conversion of light in into action potential
What are cones responsible for?
- colour vision
- high definition
- active at high light levels
- in macula + fovea
What are rods responsible for?
- non colour vision
- low acuity
- active at low light levels
- in peripheral retina
What are the photoreceptors?
What are their locations
- Cones: macula + fovea
- Rods: peripheral retina
How is light converted into action potentials
- AP propagate via retina ganglion cells
- RGC axons collect in area of optic disc
- optic nerve formed
- APs via optic nerve along visual pathway to occipital lobe
What is normal visual acuity?
6/6
Measuring visual acuity
Distance from snellen chart (constant) 6
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Number person can read to
What distance should a patient be from a snellen chart?
6 metres
Causes of decreased visual acuity
- changes in transparency of structures anterior to retina e.g. cataracts, retinoblastoma
- refractive ability of structures anterior to retina e.g. eyeball shape, presbyopia, abnormal corneal surface
- retina or optic nerve damage e.g. glaucoma, macular degeneration
