Visual System Flashcards
What are the three layers of the eye?
Corneoscleral coat
Uveal tract
Retina
What is the outermost layer of the eye?
Corneoscleral coat
What in the middle layer of the eye?
Uveal tract
What is the inner layer of the eye?
Retina
What is the cornea?
Transparent anterior extension of sclera
What is the vascular coat of the eye?
Uveal tract
What does the uveal tract consist of?
Iris and ciliary body anteriorly and vascularised choroid coat posteriorly
What does the retina consist of?
Layers of nerve cells, their processes, support cells and a layer of pigmented epithelium
What is the function of a biconcave lens?
Elastic to allow it to change its shape to permit accommodation for near vision
What is in front of the biconcave lens?
Two chambers (anterior and posterior)
What are the anterior and posterior chamber filled with?
Aqueous humor
What is posterior to the lens?
Vitreal cavity
What is the vitreal cavity filled with?
Vitrious humor
What is avascular and gleatinous due to collagen fibres and hyaluronic acid?
Vitrious humor
What covers the optic nerves?
Dura and arachnoid
How many rods does the retina contain?
130,000,000
How many cones does the retina contain?
6,5000,000
What does each rod contain?
Rhodopsin
What does each cone contain?
3 opsin pigments
Are rods and cones in the retina evenly distributed?
No
What colours are the cones sensitive to?
Red, green and blue
What have ‘centre surround’ receptive fields with a central circular region and a ring shaped surround?
Retinal Ganglion Cell Receptive Fields (RGC’s)
RGC’s can be?
On centre or off centre
What are the reasons for high visual activity?
Thinning of retinal layers, Lack of rods, high concentrations of cones and low convergence
Are axons myelinated within the eye?
No
Are axons myelinated after passing the lamina cribrosa?
Yes
What is myelin in the optic nerve formed by?
Oligodendrocytes
Visual fields of the retina are described as?
Nasal or temporal
Nerve fibres from the nasal part of the retina cross at?
Optic chiasma
Where do fibres from the retina project to?
Pretectal area and superior colliculus
Superior colliculus functions in?
Saccadic eye movements
A small number of retinal fibres leave the dorsal surface of the optic chiasma and enter what?
Suprachiasmatic nucleus of the hypothalamus
Fibres from what nucleus of the thalamus reach the primary visual cortex in the geniculocalcarine tracts?
Lateral geniculate nucleus
What fibres form part of the internal capsule?
Fibres from the lateral genicuate nucleus
What surrounds the calcimine sulcus in the occipital cortex?
Primary visual cortex
What is the primary visual cortex referred to as?
Area 17 of Brodmann
What can be called the striate cortex?
Primary visual cortex
What is the line of Gennari?
A stripe of myelinated fibres found in layer IV in the primary cortex
How many layers is the geniculate?
6
What layers of the geniculate receive visual information that has crossed from the opposite eye?
1, 4 and 6
What layers of the geniculate receives uncrossed fibres?
2,3 and 5
Each ocular dominate column contains?
A complete cycle of orientation columns
What is hemianopia?
Blindness for half the field of vision in one or both eyes
What is homonymous?
When vision is lost on the same visual field in both eyes
The opposite of homonymous is?
Heteronymous
Other forms of partial visual field deficit is referred to?
Scotoma
Frontal eye fields are thought to be involved in?
Saccadic movements
Posterior eye fields are thought to be involved in?
Pursuit movements
