The eye and vision Flashcards
What are the 3 layer of the eye?
Outer (Sclera and Cornea)
Middle (Uvea)
Inner (Retina)
What is the sclera?
Tough fibrous outer coat, made up of collagen
What is the cornea made up of?
Collagen
What feature of the outer layer of the eye allows light transmission?
Transparent
What is the outer layer responsible for?
2/3 refractive power of the eye
What are the 5 layered structure of the outer layer of the eye?
Epithelium
Bowman’s Layer
Stroma
Descemet’s Layer
Endothelium
What is the middle layer of the eye made up of?
Iris
Ciliary body
Choroid
What is the iris?
Coloured part at the front of the eye
What does the iris contain?
Dilator and sphincter pupillae muscles
What type of reflexes does the iris have?
Pupillary reflexes
What is the ciliary body?
Glandular epithelium produces aqueous humour
What does the ciliary muscle do?
Controls accommodation
What type of muscle is the ciliary muscle?
Smooth muscle
What is the choroid?
A thin layer of tissue that is part of the middle layer of the wall of the eye, between the sclera and the retina
What is the function of the choroid?
Filled with blood vessels that bring oxygen and nutrients to the eye, supplies blood to the outer third of the retina
What does the inner layer of the eye contain?
Retina
What process takes part in the inner layer of the eye?
Phototransduction
What structures are found in the retina?
Macula lutea
Fovea centralis
Cones
Rods
What is the macula lutea?
The part of the retina that is responsible for sharp, detailed central vision
What is found in abundance in the macula lutea?
Cones
What is the fovea centralis?
A small depression within the neurosensory retina where visual acuity is the highest
What are cones?
Photoreceptor cells that give us our colour vision
What are rods?
Photoreceptor cells in the retina that are sensitive to light levels and help give us good vision in low light
What types of cells make up the retina?
Retinal photorecptors
Bipolar cells
Amacrine & horizontal cells
Mullers glial cells
Retinal ganglion cells
What are retinal photoreceptors?
Rods and cones
Primary neurosensory cells that convert light into an electrochemical message that can be interpreted by the CNS
What are bipolar cells?
One of the main retinal interneurons and provide the main pathways from photoreceptors to ganglion cells
What are amacrine cells?
Intrinsic interneurons of the inner retina representing the most diverse class of neurons in the retina
What are horizontal cells?
Modulate the output of photoreceptors and play many roles in early visual processing contributing to:
Contrast enhancement
Colour opponency
Generation of centre–surround receptive fields in cones and bipolar cells
What are the mullers glial cells?
The principal glial cell of the retina.
They form architectural support structures stretching radially across the thickness of the retina and are the limits of the retina at the outer and inner limiting membrane, respectively
What are the retinal ganglion cells?
Bridging neurones that connect the retinal input to the visual processing centres within the central nervous system
What is phototransduction?
The conversion of light into a change in the electrical potential across the cell membrane
What is the anterior segment of the eye?
Refers to the front-most region of the eye, and includes the cornea, iris, and lens
What does the anterior segment contain?
Aqueous humour
What is aqueous humour?
Fluid produced in the eye
What are the functions of the aqueous humour?
Nutrition to lens and cornea
Maintains intraocular pressure
What shape do the lens have?
Bioconvex
What are the functions of the lens?
1/3 refractive power of the eye
Accommodation
What is emmetropia?
Clinical term used by eye doctors to describe a person with perfect vision, also known as ‘20/20 sight’.
This ideal condition describes an eye that has no refractive error or visual defect
What is hypermetropia?
When people cannot see clearly close up without glasses or contact lenses
What may hypermetropia be due to?
- Corneal curvature too shallow
- Lens not flexible enough
- Axial length of eyeball too short
What is myopia?
Common vision condition in which near objects appear clear, but objects farther away look blurry
What may myopia be due to?
- Corneal curvature too steep
- Axial length of eyeball too long
What is the posterior segment of the eye?
The back two-thirds of the eye, including the vitreous humor, the retina, the choroid and the optic nerve
What is vitreous humour?
Transparent, colorless, gel-like substance located in the posterior chamber of the eye
What are the functions of vitreous humour?
Providing metabolic nutrient requirements of the lens Coordinating eye growth
Providing support to the retina
What is hyaluronic acid?
A natural substance found in the fluids in the eyes and joints.
It acts as a cushion and lubricant in the joints and other tissues
What are the adnexa?
Refers to the parts of the body adjoining the organ, so the subsection on the eye and ocular adnexa includes procedures on the eye itself in addition to the ocular muscles and eyelids
What is included as part of the ocular adnexa?
Eyelids *
Conjunctiva*
Tear film*
Lacrimal drainage system
Lacrimal gland
Orbital contents except for the eye and optic nerve
What parts form the eye lids?
Lids – protect the globe
Anterior skin
Eye lashes
Meibomian glands
Orbicularis oculi
Tarsal plate
Tarsal conjunctiva
Levator palpebrae superioris & sympathetic muscle
What is the conjuctiva?
A thin, clear membrane that protects your eye.
It covers the inside of your eyelid and the white of your eye (the sclera)
What does palpebral conjunctiva line?
Eyelids
Where is bulbar conjunctiva found?
Eyeball over the anterior sclera
What is the conjunctival fornix?
Forms the junction between the bulbar and palpebral conjunctivas.
It is loose and flexible, allowing the free movement of the lids and eyeball
What are limbal stem cells?
Adult stem cells located in the basal epithelial layer of the corneal limbus that aid in the renewal of the corneal epithelium
What adaptations do the ocular adnexa have?
Mucous membrane (Goblet cells)
Lymphoid cells (protective)
What is the tear film?
Thin fluid layer covering the ocular surface
What are the functions of the tear film?
Protects the cornea
Promotes wound healing after injury
Maintains eye comfort and high-quality vision
What are the 3 layers of the tear film?
Anterior lipid
Middle aqueous
Posterior mucous
Which artery is the primary blood supply of the eye?
Ophthalmic artery
What is the ophthalmic artery derived from?
Internal carotid artery?
What are the ocular group branches of the ophthalmic artery?
Central retinal a.
Posterior ciliary a. → long and short
Posterior ciliary a.
Muscular a. → anterior ciliary a
What are the orbital group branches of the ophthalmic artery?
Lacrimal a.several other branches supply face and lids
What arteries are derived from the external carotid which supply the eye?
External carotid a. → facial a. → angular a.
What artery supplies the inner 2/3 retina?
Central retinal artery
What does the central retinal artery branch into?
Superior/inferior/temporal/nasal branches
What veins drain the inner retina?
→ central retinal v. → ophthalmic v. → cavernous sinus→ internal jugular v.
What artery supplies the outer 1/3 of the retina?
Choroid artery
What is the function of the blood retinal barrier?
Regulates movement of nutrition and solutes from choroid into subretinal space
What veins drain the choroid?
Vortex veins
Usually one for each quadrant
Superior drain to SOV, inferior drain to IOV
Where do the superior ophthalmic veins drain into?
Cavernous sinus
Where do the inferior ophthalmic veins drain into?
Pterygoid venous plexus
What would happen if the venous drainage in the eye was valveless?
Orbital cellulitis/facial infection can precipitate cavernous sinus thrombosis
What parts of the eye have lymphatic drainage?
Conjunctiva and lids to submandibular and pre-auricular nodes
What is the ora serrata?
Serrated junction between the retina and the ciliary body
What is the function of the ora serrata?
Marks the transition from the simple non-photosensitive area of the retina to the complex, multi-layered photosensitive region
