Applied Anatomy of the Eye Flashcards
What is the role of the vestibular nuclei in the visual system?
Gaze stabilisation
What is the role of the occipital lobe regarding vision?
Pursuit eye movements
Accomodation
What is the role of the frontal lobe regarding vision?
Voluntary eye movements
Also helps control voluntary body movements
What is the function of the cornea?
Refraction of light
What is the function of the lens?
Focusing light - aim for the macula/fovea - this is refraction
Accommodation reflex
Fine focus of visions
What is the function of the iris?
Controls the amount of light entering the eye.
What makes up the structure of the Cornea?
The outer epithelial layer
Bowmans layer (anterior limiting lamina) - acellular collagen fibres
Stroma - keratocytes (specialised fibroblasts)
Descement membrane (posterior limiting lamina) - basement membrane for corneal endothelium
Endothelium.
What are the key features of the corneal epithelium?
Several layers of cells
Barrier to water and bacteria entering the cornea
Maintains a smooth optical surface for refraction
Is constantly replaced/regenerated.
What are the key features and function of the corneal endothelium?
Single layer of hexagonal cells
Allows transport of nutrients including glucose into the cornea
Pumps water out to maintain clarity of stroma
Never replaced
What does emmetropia mean?
Normal refraction of light by the cornea onto the lens.
What is hypermetropia and how should it be corrected?
Long sighted
Light is refracted from the cornea too far back behind the retina
Fixed with converging/convex contact lenses.
What is myopia and how should it be treated?
Short sightedness
Refraction error - cornea refracts light too far forward, does not hit retina
Fixed with concave/diverging lenses.
What is astigmatism of the eye?
How is this corrected?
When the eye is not spherical in shape, rather is more rugby ball shaped aka curvature is steaper in the vertical compared to the horizontal axis
is corrected using cylindrical lens with different powers.
What are some common pathologies of the cornea?
Corneal ulcer
Corneal dystrophy
Keratoconus
Corneal odema
Corneal graft
What is a corneal ulcer?
An open sore in the outer layer of the cornea.
Can occur due to scratches on eye surface, severely dry eyes, complication of incorrect use/hygiene with contact lenses
Commonly become infected typically by Pseudomonas aeruginosa.
Can perforate
Vision is reduced.
What is the common treatment for a corneal ulcer?
Start treatment as soon as possible
Often requires two days of topical antibiotics (eye drops) every 30 mins.
What is corneal dystrophy?
A group of genetic disorders often progressice in which abnormal material often accumulates in the cornea.
Can lead to visual impairement
What is keratoconus?
The cornea thins and gradually buldges outwards and downwards in a cone shape
Can cause blurry and distorted vision.
What is corneal oedema?
Appears as a cloudy eye
Swelling in cornea after injury or infection
May be associated with degneration of epithelial cells
What is a corneal graft?
Corneal transplantation where damaged tissue is removed and placed with a donated corneal tissue
What initiates the change in the lens during accommodation?
Circumferential ciliary muscles contract and relaxes to alter the tension of the lens capsule allowing lens to change shape.
Contraction - less tension of suspensory ligament of lens - becomes shorter and wider (more convex) - refract light closer - focus on short distance.
What is a common pathology of the lens?
Cataract formation - causes progressive opaque eye lens, reduces light entering the eye hence reducing visual acuity.
Normally affect lens nucleus - associated with aging and denaturation of proteins in the lens.
Can be treated surgically.
What is the anatomy of the lens of the eye?
Epithelial differentiated organ - elastic, transparent and biconvex in shape
Consits of lens capsule, lens epithelium (stable functioning and production of lifelong lens fibres), lens fibres and the zonules.
Fibres cells make up the lens nucleus.
What are some risk factors for cataract formation?
Age
Diabetes
Corticosteroids
Congenital
Trauma to the eye
What are the ten different layers of the retina?
Nerve fibre layer
Ganglion cell layer
Inner plexiform layer
Inner nuclear layer
Outer plexiform layer
Extrenal limiting membrane
Inner segment of photoreceptors
IS/OS junction
Outer segment of photoreceptors
Retinal pigment epithelium
Bruchs membrane
Choroid.
What is the simplification of the different layers in the retina?
Nerve fibre layer
Ganglion cells
Bipolar cells
Photoreceptors
Retinal pigment epithelium
Choroid (blood supply)
What is the structural difference at the fovea?
Highest concentration of cones
Nerve fibre layer, ganglion cells and inner nuclear layer are deviating away from the fovea, allow light to hit directly onto photoreceptors - higher level of visual acuity.
What type of vision are rods responsible for?
Scotopic vision - under low light conditions
What type of vision of cones responsible for?
Phototopic vision - in high light intensities
What is the arrangement of opsin in cones cells?
Iodopsin is found in cones
3 different opsins present in all cones, but one predominates in each - each type of opsin is sensitive to a different wavelength of light, enables to differentiate between different colours
Red, green, blue in order of descending wavelength
What is the different micro structure of rods/cones?
Each consist of an outer segment, inner segment and a synaptic terminal.
The inner segment contains a nucleus, endoplasmic reticulum and mitochondria in both.
The outer segment contains a disks and plasma membrane in rods, cones only have plasma membrane.
The inner and outer segments are connected by a connecting cilium.
What is the distribution of photoreceptors on the retina like?
No photorecepotrs at the optic disk
Cones - highest concentration at the fovea, decrease in concentration as you spread outwards
Rods - none at fovea, highest concentration just outside fovea then decrease at outwards, are widely spread throughout the retina
There are significantly more rod than cones in the retina.
What is the role of the retina pigment epithelium in phototransduction?
Stores vitamin A
Production nd recycling of photo-pigments
Phagocytoses old discs
What is the role of recoverin in phototransduction?
Provides adaptation to high light environments
Recoverin is a calcium dependent inhibitor of rhodopsin kinase, which turns off phosphodiesterase
Hence more light, less Calcium, recoverin is less active, rhosopsin kinase not inhibited, PD is inhibited, regulate on signalling.
What is the role of amacrine cells in phototransduction?
Amacrine cells are inhibitory cells in the retina
They receive signals from bipolar cells and regulate activity of bipolar and ganglion cells.
Provide negative feedback
What is the process of lateral inhibition in phototransduction?
Mediated by horizontal cells
Light in central PR - hyperpolarised - less glutamter - reduced activation of horizontal cells - reduced inhibition on neighbouring PR - more depolarisation of surrounding PR - perceive dark
Same vice versa
Enhanced the central signal by increasing contrast with surroundings.
What are some common pathologies of the retina?
Colour blindness
Retinal vascular occlusion
Diabetes
Macular Degeneration
Retinal Detachment.
What are the different types of colour blindness?
Prot - red cones (L)
Deuter - green cones (M)
Trit - blue cones (S)
Anomaly - malfunctioning
Anopia - absent
Deuteranomaly is the most common (5% of pop), followed by protanomly, protanopia, deutranopia (1% pop each).
How do we test for colour vision?
Use Ishihara plates
What is the process of central retinal artery occlusion?
Loss of blood supply to the retina (not the optic nerve).
Retina thins as cells die.
Opthalmogic emergency, presents with sudden, paniless, monocular vision loss over seconds. Often have a history of atherosclerotic disease.
What pathology is shown on the image?
Central retinal artery occlusion
Pallor of the infected retina
Central cherry red spot - due to odema in the fovea, causes to retain is normal colour
What is central retinal vein occlusion?
Venous thrombosis leading to haemorrhage, oedema, cotton wool spots and neovascularization on the retina.
Blood vessels in the back or the retina may leak or the retina may become ischemic.