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
Emmetropia
6 6 Vision
Hypermetropia
Underpowered to focus near objects on retina
May be due to:- corneal curvature too shallow- lens not flexible enough- axial length of eyeball too short
Myopia
Overpowered so can’t focus far objects on retina
May be due to:- corneal curvature too steep- axial length of eyeball too long
Posterior segment
Vitreous humour- jelly like substance made of
Avascular viscoestalic gel
Hyaluronic acid (GAG)
Collagen
Adnexea (near by structures of the eye)
Lids- protection, tear film distribution, maintains ocular surface
Conjunctiva- covering on front of sclera
Tear film
Adnexae- eye lids
Lids – protect the globe and consist of
Anterior skin
Eye lashes
Meibomian glands- contribute to tear film by producing anterior lipid oils
Orbicularis oculi- allow you to close eye
Tarsal plate- separates eyes to 2 layers and muscles attach to it
Tarsal conjunctiva
Levator palpebrae superioris & sympathetic muscle
Adnexea- conjunctiva
Conjunctiva palpebral (tarsal- innerevated beneath eye lid) vs. bulbar (ocular and covers the eyes)
Conjunctival fornix
Limbal stem cells
Mucous membrane (Goblet cells)
Lymphoid cells (protective)
Adnexea- tear film
Tear film
3 layers
-anterior lipid- prevent evaporation- Meibomian glands produce anterior lipid oils -middle aqueous- provides fluidity and nutrition -posterior mucous- maintains rest of tear film and allows for even distribution of tear film
Protective
Nutrition for cornea
Arterial supply
Internal carotid a. → ophthalmic a.
Internal carotid artery does nit give a single branch until it reaches the cranium
Branches of ophthalmic a. (ocular group)central retinal a.posterior ciliary a. → long and short posterior ciliary a.muscular a. → anterior ciliary a.
Branches of ophthalmic artery (orbital group)lacrimal a.several other branches supply face and lids
External carotid a. → facial a. → angular a.
Blood supply- inner retina
Inner 2/3 retina supplied by central retinal a
Branches into superior/inferior/temporal/nasal branches
Drained by branch retinal veins→ central retinal v. → ophthalmic v. → cavernous sinus→ internal jugular v.
Blood supply- outer retina
Outer 1/3 supplied by choroid
Posterior ciliary a. → choroidal a. → choriocapillaris
Blood-retinal barrier at RPE regulates movement of nutrition and solutes from choroid into subretinal space
Venous drainage
Vortex veins drain the choroid
Usually one for each quadrant
Superior drain to SOV, inferior drain to IOV
Superior ophthalmic veins drain directly into the cavernous sinus
Inferior ophthalmic veins drain into pterygoid
venous plexus
Valveless system – orbital cellulitis/facial infection can precipitate cavernous sinus thrombosis
Infection can travel backwards
Lymphatics
No lymphatic drainage from the globe
Conjunctiva and lids do have lymphatic drainage to submandibular and pre-auricular nodes
