L2: Opthamology 1: Visual pathways Flashcards
What is the outer layer of the eye made of and why
Cornea and Sclera;
White of the eye- to improve communication/expression. Made of collagen - cornea has very regular fibres to allow light to pass through.
What is the second Vascular layer: UVEA made of
3 structures 1.Iris 2. Ciliary body 3. Choroid Involved in giving blood supply.
What is the most inner layer of the eye
Retina =
Transparent layer that turns visual information into nerve signals
What are the similarities between the eye and a camera anatomy wise
Pupil and iris work to restrict light to the retina like an aperture + diaphragm.
Light goes through the lens which means that images are received upside down (inverted)
Eye is surrounded by choroid which provides nutrients to outer retina but also blocks other light getting into the retina which is the film.
What are the different types of vision
- Visual acuity: clarity/sharpness of vision
- Colour vision: helpful for seeing past camoflague
- Peripheral vision
What is the visual field
Portion of external environment of observer wherein the steadily fixating eye can detect visual stimuli. In one eye Nasal field>nose: 60 Temporal: 100 Superior->brow: 60 Inferior 75
In the center both eyes have 120 overlap which gives depth perception. 30 extra on either side
Is visual acuity the same across the field of vision- what cells involved and why
(Rods v Cones)
what about blind spot
The sensitivity of the eye varies across the visual field with centrally as the most sensitive affecting most of the visual acuity (fovea of macula).
Due to high Cone cell density which work best in high light (but no rod peaks, no blood vessels, ganglion pushed out of the way)
Surrounding areas worse, less cones but have Rod peaks nearby the fovea (peripheral, motion, night/low light vision)
There will a blind spot (no receptors) due to optic nerve (info exiting eye).
Visual sys uses Info from cells around it fill it in
How to find the temporal and nasal retina (each responsible for picking up the opposite visual field)
Which visual field is the blind spot in
- Draw a vertical straight line through the fovea: Vertical meridian.
- Side which has the optic disc is the nasal side, other side is temporal
Blind spot is in the temporal visual field bc optic nerve is on the nasal retina
What visual field does superior and inferior retina subserve (pick up)
Sup gets the inferior visual field and vice versa
Same as the nasal and temporal.
On a visual field diagram how do you tell which eye it is
Read diagram like looking through your eyes, The blind spot (dark) will be on the outside of the correct eye (temporal side)
The Macula will be the point of fixation in the centre
What are the visual pathway again
- Optic nerve
Info from temporal retina of each eye continue down the same side.
- The Nasal retina switch at the optic chiasm continue as the optic tract.
- Then to lateral geniculate nucleus to optic radiations
- To the striate (visual) cortex.
- So left visual field goes to right occipital cortex
What/where causes
1. Right Central scotoma
- Bitemporal hemianopia: Temporal visual field lost in both eyes
- Right Inferior altitudinal defect: loss of vision bottom horizontal half
- Homonymous hemianopia: same visual field lost for both eyes
- Junctional scotoma: only see the nasal visual field of eg. right eye
- Tumour in right optic nerve sheath before chiasm
- pituitary (prolactin or growth hormone) chiasmal, tumour that puts pressure on the nasal fibres in chiasm. early lesion affects the sup temporal visual field
- Swelling of top of nerve optic nerve
- Anything downstream the chiasm ie lesion in occipital lobe
- Lesion (eg. pituitary) in the left optic nerve at the junction where the temporal visual field nerve from the right eyes is going to the left side.
