The Eye And Vision Flashcards
Why do we have 2 eyes?
Widens our visual field
Allows us to see in 3D
3 layers of the eye
Outer layer: Sclera and cornea
Middle layer: Uvea- choroid, ciliary body and iris
Inner layer: Retina
The outer layer- sclera
Tough fibrous outer coat, made up of collagen
Provides protection and maintenance of shape
Collagen results in the sclera to have a white colour
Outer layer- cornea
Made up of collagen
1/6th of the sclera
The point at which the sclera and the cornea meet is the limbus- the place where the stem cells of the cornea are made
Must be tough to act as a barrier to trauma and infection
Extension of sclera
Transparent to allow light to pass through
Fibres of cornea lie parallel to allow transparency
Responsible for approx 2/3rd of refractive (focusing) power of the eye
Other 1/3rd of refracting power comes from the intro ocular lens
The lens continuously grows throughout a persons lifestyle leading to cataract
How many layers does the outer layer contain?
5
Epithelium- which can be regenerated
Bowman’s layer
Stroma- the fibres of the stroma are parallel which allows the cornea to be transparent
Descemets layer
Endothelium- can’t be regenerated, one layer of cells thick. Responsible for keeping the cornea dehydrated and transparent. Actively pumps water out of the stroma and keeps cornea transparent
The Middle layer contains
Iris
Ciliary body continues anteriorly to become the iris
Ciliary process produces aqueous humour
Choroid
3 layers provide: nuitrition, vision and protection
This system maintains the homeostasis of the eye
Slide 11
Middle layer- iris
Extension of choroid
Coloured part at front of eye
Contains dilator and sphincter papillae muscles
Pupillary reflexes
Changes diameter of aperture
Middle layer- ciliary body
Glandular epithelium of ciliary process produces aqueous humour
-Aqueous humour travels from ciliary body to pupil to
-Aqueous humour provides nutrition to eye and maintains pressure
Reponsible for holding the lens in place by the suspensory ligaments
Ciliary (smooth) muscle controls accommodation (changing focus from distant to near)
Middle layer- choroid
Blood supply to outer third of retina
Provides nutrition to the retina
Coloured (contains melanocytes) to absorb light and prevent scatter
Uveal tract will be composed of the choroid posteriorly and as it approaches anteriorly it becomes a layer off muscles called the ciliary body
The inner layer
Retina
Specialised organ of phototransduction- cells convert light energy into a electrochemical gradient so that it turns light into an impulse to be sent to the back of the brain to be perceived as an image
Many layers
Retina
Macula lutea- sharp detailed central vision (slide 14)
Clarity, colour vision
Fovea centralis- where visual acuity is the highest
Cones- higher resolution and colour
Rods- lower resolution and black & white
The ora serrata is the junction between the retina and the ciliary body- after this point there are no more photoreceptors so you can’t receive light upon that area
Inner layer- Retina
Light signals
—> photo receptors
—> tear film (transmission)
—> cornea (transmission and refraction)
—> Aqueous humour (transmission)
—> lens (transmission and refraction)
—> vitreous humour (transmission)
—> ganglion cell (transmission)
—> Amacrine cell (transmission) for support
—> Bipolar cell (transmission)
—> horizontal cell (transmission) for support
—> cone (transduction)
—> rods (transduction)
—> pigmented epithelium (absorption of excess photons)
All of axons of ganglion merge to become optic nerve leaving the back of the eye
Phototransduction
11 cis-retinal, which is a derivative of vitamin A.
When the photons come in they will cause 11 cis-retinal to become an 11-transretinal
This is then recycled back through an enzyme
Anterior segment
Aqueous humour
Nutrition to lens and cornea
Maintains intraocular pressure
Lens
Biconvex
Responsible ~1/3 refractive power of the eye (~20D)
Accommodation
