Visual Pathway Flashcards
Give the anatomical overview of the visual pathway
- Light information reaches the back of the eyes in the retina.
- The optic nerves (CN II) emerges from back of retina and travels back until it reaches the optic chiasma (where the 2 optic nerves converge).
- The optic tracts then pass towards the back of the midbrain until they hook upwards to connect with the lateral geniculate body of the thalamus (this includes the lateral geniculate nucleus).
- From the LGB, there are the optic radiations; the fibres that bring visual information from the thalamus to the primary visual cortex in the occipital lobe.

Where do the optic nerves emerge from?
The retina
After converging at the optic chiasma, where do the optic tracts then pass?
To the lateral geniculate body of the thalamus (this includes the lateral geniculate nucleus)
What is the lateral geniculate nucleus important for?
This is an important nucleus in the thalamus; important in relaying visual information.
From the lateral geniculate body of the thalamus, how is information brought to the primary visual cortex?
From the LGB there are the optic radiations

Where is the primary visual cortex?
Occipital lobe

There are 3 layers encircling the eye. What are they composed of?
- Outer layer; cornea and sclera (these are continuous)
- Middle (vascular) layer; choroid
- Inner layer; retina

Describe the cornea. Main function?
- Description:
- Transparent part of the eye that covers the front portion of the eye (pupil and iris)
- Thick, transparent, avascular.
- Function: major area of refraction

Describe the sclera. Main function?
- Description:
- Covers most of the ocular surface, “white of the eye”.
- Continuous with the cornea
- Tough, white, fibrous tissue
- Function: Insertion point for muscles that move the eyeball.

Describe the choroid. Function?
- Description:
- Vascular
- Continuous with the lens and ciliary muscle.
- Functinon: Nourishes the cornea and retina

Describe the iris. Function?
- Description: Pigmented, vascular.
- Function:
- Eye color is defined by that of the iris
- Muscles of the iris control the amount of light entering the eye by controlling the diameter of the pupil (the central opening of the iris).

Function of the ciliary body?
Controls the shape of the lens by pulling on the suspensory ligaments.

Describe the lens. Function?
- Description: Biconvex, avascular. Light passes through the lens after passing through the pupil.
- Function: changes shape (due to ciliary body)
- When rounded, can focus on objects which are near.
- When flattened, can focus on distant objects

When rounded, what can the lens focus on?
can focus on objects which are near
When flattened, what can the lens focus on?
distant objects
What is the retina an extension from?
Diencephalon
How many layers is the retina composed of?
2
What are the 2 layers of the retina?
-
Non-neuronal layer:
- Consists of pigmented epithelium.
- Sits against the choroid and is light absorbing
-
Neural layer:
- Nerve tissue; photoreceptors, bipolar cells, ganglion cells
- Ganglion cell axons form the optic nerve –> This allows transmission of light information (photons) into electrochemical information
What is the optic disk?
Where the optic nerve exits –> this is a blind spot

Why is the optic disk a blind spot?
we do not perceive any light information that falls in this region as there are no photoreceptors
What is the macula? Where is it located? Function?
- Region at very back of retina that falls right in middle of visual axis (peripheral vision not as clear)
- Found medial to optic disk
- Any light rays that travel directly in this region and fall upon the macula, this information is interpreted with high visual acuity –> as the macula contains a high density of photoreceptors

Why does the macula have a high visual acuity?
as the macula contains a high density of photoreceptors
Where is the fovea located? Function?
- Found in centre of macula
- Contains some specialised photoreceptors called cones –> highest point of visual acuity

What are ‘cones’? Where are they located?
Cone cells, or cones, are photoreceptor cells in the retinas (in the fovea) of vertebrate eyes






































