Visual Systems Flashcards
What three layers form the eyeball
Fibrous
Vascular
Inner layer- Retina
Fibrous Layer
Outermost layer
Consists of Sclera and cornea
What is the Sclera of the fibrous layer
Makes up most of the fibrous layer, visible as the white part of the eye, provides attachment to the extraoccular muscles (responsible for movement of eye)
Cornea (fibrous layer)
transparent and positioned centrally in the front of the eye.
Light entering the eye is refracted by the cornea
Vascular Layer
Underneath the fibrous layer, consists of the choroid, ciliary body and iris
Choroid (Vascular layer)
layer of connective tissue and blood vessels, which provides nourishment to outer layer of retina
Ciliary Body ( Vascular Layer)
comprised of ciliary muscle and processes.
Ciliary muscle consists of smooth muscle fibres which are attached to the eye by ciliary processes
Controls the shape of the lens and contributes to the formation of aqueous humor
Iris ( Vascular Layer)
Circular structure with an aperture in the centre (pupil)
The diameter of the pupil is altered by smooth muscle fibers within the iris, which are innervated by the ANS
Situated between the lens and the cornea.
Inner layer= Retina
Light detecting component, consisting of two layers
What are the two layers of the Retina
Pigmented Outer layer
Neural Inner layer
Pigmented Outer Layer of Retina
Formed by single layer cells
Attached to choroid , supports choroid in absorbing light, prevents scaterring of light
Neural Inner Layer
Consists of photoreceptors = light detecting cells
Macula
Area in the centre of the retina
Yellowish in colour, highly pigmented
Contains a depression called the fovea centralis
Fovea Centralis
High concentration of light detecting cells
Responsible for high acuity of vision
Optic Disc
Blind Spot
Area where the optic nerve enters the retina
Contains no light detecting cells
Macula Lutea, Fovea Centralis
Small yellowish area lateral to the optic disc, highest visual sensitivity
Fewer rods (functions in dim light)
More Cones (bright light)
Vitreous Body/Humor
Two fluid filled areas of the eye
- Anterior Chamber (located between the cornea and iris)
-Posterior Chamber (located between iris and ciliary processes)
Filled with aqueos humor
Function of Vitreous Body/ Humor
Clear like plasma fluid nourishes and protects the eye
Clinical relevence of Vitreous Body/ Humor
glaucoma is when the drainage of aqueous humor is obstructed
Blood Supply of Eyeball
Receives arterial blood via the opthalamic artery (branch of the internal carotid)
Venous drainage is carried out by the superior and inferior opthalamic veins
Lens
Located between the vitreous humor and pupil
Shape of the lens is altered by ciliary body
Clinical Relevence of the lens
old age, the lens can become opaque which is a Cataract
Accomodation
Ability of eye to change the focal length of lens by changing the curvature of the eye lens
Change in Refractive Power
Unaccomodated lens
when viewing distant objects the lens is made relatively thin and flat and has the least refractive power
Accomodated Lens
for near vision the lens becomes thicker and rounder and has the most refractive power
this involves a change in the ciliary muscles surroudning the lens
Ametropia
a group of visual disorders caused by errors in the refractive power of the eye
Emmetropia
normal refractice condition of the eye
Myopia
Nearsightedness
Close up objects look clear but distant objects are blurry
Cause: corneal surface too curved
Correction: concave (-) lens
Hyperopia
Farsightedness
Distant objects are usually seen more clearly than close ones
Cause: eyeball being too short or refracting system too weak
Correction: convex (+) lens
How many layers in the retina
8
Name 5 types of neurons in the retina
Photoreceptors
Bipolar Cells
Ganglion Cells
Horizontal Cells
Amacrine Cells
Three neuron chain of the retina
photoreceptors- bipolar cells- ganglion cells
Major route of info flow from photoreceptors to optic nerve
Photoreceptors of optic nerve
rods and cones
What do rods and cones both have
Outer segment - composed of membranous disks that contain light sensitive photopigment
Inner Segment- contains the cell nucleus and gives rise to synaptic terminals that contact bipolar or horizontal cells
How can photoreceptors be distinguished
Shape
Type of photopigment
Distribution across retina
Pattern of synaptic connections
Rod
Low spatial resolution
Extremely sensitive to light
Specialised for sensitivity at the expense of resolution
Photopigment: contain single (RHODOPSIN)
Function: peripheral vision and in vision under low light conditions
Cone
High spatial resolution
Insensitive to light
Colour vision
Specialised for acuity at the expense of sensitivity
Photopigment : photopsin
Three types of cones that differ in the photopigment they contain
Function: function under bright light and are responsible for the central discriminative vision and for colour detection
Cone Cells and Colour Blindness
Three types of cones differ in photopigment
Each of these pigments has a different sensitivity to light of different wavelengths, referred to blue, green and red or short, medium and long wavelength cones
What is color blindness
the inherited failure to make cone pigments
Alteration on absorption spectre of cone pigments
Retinis Pigmentosa
genetic disorder characterised by progressive vision loss due to a gradual degeneration of photoreceptors
Progressive loss of vision»_space; dark clumps of pigment visible in eye
Symptoms of retinis pigmentosa
Initially night blindness
Reduced peripheral vision
Pigment migration of disrupted retinal pigment epithelium into the retina, over years cones also degenerate
Macular degeneration
Loss of cone function
Most commone in people over 55
Risk Factors» cvs disease, smoking, light, nutrition
WET AMD
10% of all cases
progress rapidly
Abnormal blood vessel growth occurs under the macula
»leak fluid into retina, damaging the photoreceptors
Therapy = laser therapy
DRY AMD
90% of all cases
Gradual disappearance of retinal pigment epithelium
What is the visual pathway
Structure that are responsible for the perceiving, relaying and processing of visual info
Discuss Visual Pathway
look at page
Primary Visual Cortex (Brodmann area 17)
Also known as calcarine cortex, striate cortex or V1
Main site of input of signals coming from the retina
Located on the medial aspect of the occipital lobe, in the gyrus superior and inferior to the calcarine sulcus.
What information does the primary visual cortex extract
edges
depth
orientation
motion
color of objects
What two pathways transfer info from primary visual cortex to association areas
Ventral Stream
Dorsal Stream
Ventral Stream
passes through the secondary visual cortex and extends downward into the inferior temporal gyrus. The processing
done by neurons in this pathway allows us to recognize faces and objects based on their size, shape, and color (what objects are?)
Dorsal Stream
passes through the secondary visual cortex and extends upward to the posterior parietal cortex. Neurons in this pathway provide information about the motion of objects (where object are?)
Pathway and Visual Field Defects
look at last three pages of notes to study this
