Visual Pathway

Front 1

Rod Function

Back 1

-High Sensitivity,
-Slow temporal respnse.
-Poor spacial acuity
- Colour-blind

Front 2

Cone Function

Back 2

-Low Sensitivity
-Fast response
-high spacial acuity (one to one contact)
-Red, green and blue

Front 3

The Refractive Media of the Eye

Back 3

1. Cornea - site of most refraction
2. Aqueous Humour
3. Lens (converging)
4. Vitreous Humour

Front 4

Image formation on the retina

Back 4

-Focal point of refracted waves must fall on the retina.
-Fovea Centralis - most cones.
-Lens changes its shape and adjusts focal length in order to focus images of objets on the retina.

Front 5

Accommodation

Back 5

-Reflex
Near Vision
-Ciliary muscle contracts
-parasympathetic fibres from CN III
-pulls ciliary process forward.
-Zonular fibres relax
-Lens Fattens

Front 6

Pupillary Light Reflex

Back 6

- Bright light causes pupillary constriction
- Mediated by afferents in optic nerve which respond to light hitting retina.
-Evokes bilateral response in Edinger-Westphal preganglionic parasympathetic fibres.
-These fibres synapse in ciliary ganglion.
-Postganglionic fibres terminate on the pupillary constrictor muscles of the iris.
-These contract bilaterally and symmertically.

Front 7

Convergence

Back 7

The movement of the eyeballs medially to focus on an object close-up (medial rectii muscles CN III)

Front 8

layers of the retina

Back 8

Pigment Layer - Melanin-containing epithelial cells adjacent to choroid - absorbs stray light.

Neural Layer
-3 layers of retinal neurones
-Photoreceptors
-Bipolar cell layer
-ganglion cell layer

Front 9

Pathway of Retinal Signal

Back 9

1. Receptors
mediated by Horizontal cells.
2. Bipolar cells
mediated by Amacrine cells
3. Ganglion cells
projecting to forebrain.

Front 10

Colour Vision anomalies

Back 10

-X-linked
-Due to absence/deficiency of 1 of the cone opsins.
-Vision is dichromatic.
-Often red and green hues.

Front 11

Phototransduction: Function of cell types

Back 11

1. Photoreceptors
-absorption of light by visual pigments
-Initiates chemical changes in photoreceptor
-Changes membrane potential of photoreceptor
-Subsequent changes in neurotransmitter release in photoreceptor.

2. Bipolar cells
-NT mediated change in membrane potential of bipolar cell.
3. Ganglion cells
-This electrical signal transmited to bipolar and ganglion cells and eventually to the brain via optic nerve.

Front 12

Image formation on the retina.
As it what part of the image goes where?

Back 12

Left image = nasal half of left retina and temporal half of right retina.
Right image= right retina nasal half, left retina temporal half.

Front 13

Visual Pathway

Back 13

1. Retina
2. Optic Nerve
3. Optic Chiasm
4. Optic Tract
5. laternal Geniculate body
6. Geniculo-calcarine tract
7. Primary visual area (striate cortex)

Front 14

Lesions affecting visual field.

Back 14

1. Optic nerve -eg MS, optic nerve tumour leads to monocular blindness.
2. Optic Chiasm - eg pituitary tumour leads to bitemporal hemianopia (loss of temporal fields from decusating temporal tracts)
3. Optic tract - eg CVA leads to homonymous hemianopia (loss of visual field from left or right side.
4. Occipial cortex lesions - leads to macula sparing

Front 15

Post-striate cortex damage

Back 15

1. Where is it? - Optic Ataxia - DORSAL STREAM

2. What is it? eg Early Alzheimer's, prsopagnosia - inability to recognise faces - VENTRAL STREAM