Eyes Flashcards
What makes the Cornea transparent ?
Regularly arranged collagen fibres
No blood vessels
AH pumped out via endothelial layer pumps
What is the first layer of the retina (outside) ?
Pigmented layer
What is the second layer of the retina (outside) and what is found there ?
Neural layer - rods and cones
What supplies the retina with blood ?
From the outside via the choroid and from the inside via the central retinal artery
What is lens opacification called ?
Cataracts
What predisposes the lens to becoming opacified ?
Avascular and exposure to UV rays
What can be used to visualise tear film ?
Fluroscein
Function of aqueous humor ?
Maintain IOP
Function of vitreous humor ?
Cushion and support the retina
What structures form from the side of the forebrain to make the eyes ?
Optic vesicles
What happens to the optic vesicles next ?
The grow towards the surface ectoderm and cause it to thicken forming the lens placode
What does the lens placode do ?
It invaginates and forms a pit. it eventually pinches off with the optic vesicle. The Optic cup is formed which houses the lens vesicle.
What is the choroidal fissure ?
Hole where blood vessels gain access to the optic cup and lens vesicle. It is found in the optic stalk.
What happens when the choroidal fissure closes ?
The vessels are enclosed in the optic stalk, they form the central retinal artery.
Corneal dystrophies
- Central vision is lost
- Run in families
- Material builds up in the cornea
- Bilateral
How do we treat corneal dystrophies ?
- Corneal transplants
- Laser treatment (PTK)
Corneal degenerations
- Peripheral vision lost
- Unilateral
- Usually seen with systemic diseases
Retinal detachment - what happens ?
VH goes between the pigmented layer and the neural layer causing detachment.
Retinal detachment symptoms
- Flashing lights
- Floaters
- Vision loss/dark curtain
Coloboma
Hole in one of the structures of the eye. Affects vision differently depending on location
Glaucoma - What causes it ?
Raised IOP
Two types of Glaucoma
Primary Open Angle Glaucoma
Closed Angle Glaucoma
Symptoms of Primary Open Angle Glaucoma
- Asymptomatic
- Peripheral vision is usually affected first.
Symptoms of Closed Angle Glaucoma
- Painful
- Loss of vision/blurred vision is immediate
- Nausea and vomiting
- Sore red eye
- Eye is hard
Symptoms of Cataracts
- Blurred vision
- Difficulty seeing in dark
- Sensitivity to bright lights
- Fading of colours
What is the blood-occular barrier created by ?
Barrier between the endothelium of the capillaries in the iris, retina and ciliary body and the retinal pigment epithelium.
why is the blood ocular barrier important ?
Prevents substances from passing through into the eye from blood vessels.
What are the two parts of the barrier ?
1) Blood aqueous barrier - Ciliary epithelium and capillaries of the iris
2) Blood retinal barrier - Capillaries of the retina and the epithelium of the pigment layer
Retinal detachment - How is it treated ?
Surgery known as Pneumatic Retinopexy. A gas bubble is inserted which presses on the detached section pushing it back into place. A laser is they used to attach it firmly in place.
Hordeolum/Stye
Infection of the mebomian (internal) or sebaceous glands (external) of the eyelid.
Definition of refractive error
Problem focusing light accurately onto the retina due to the shape of the eye.
What is Retinitis Pigmentosa ?
Group of genetic disorders that involve the breakdown and loss of cells in the retina. Result in loss of peripheral vision and difficulty seeing at night.
What is Optic Neuritis ?
Inflammation of the optic nerve. Pain and temporary vision loss are common symptoms.
Electroretinography (ERG)
Electrodes are placed on the cornea and this allows you to record signals given off from photoreceptive cells in the retina to the brain in response to light.
Gene therapy - What and when ?
Used to replace missing or defected genes in the eye in order to correct genetic disorders. Used in Wet AMD and diabetic retinopathy currently.
Why do muscles of the eye have more than one function ?
They are attached in the orbital axis where as the eye is in the optical axis.
Definition of Phototransduction
Phototransduction is the process by which the absorbed light triggers an electrical response in rods and cones.
What are the steps of Phototransduction ?
When light falls on 11-cis retinol it isomerise to all-trans retinol. All-trans cannot fit in opsin/rhodopsin and so they split. Activated opsin/rhodopsin cause Na+ channels to close and this hyperpolarises the cell. Hyperpolarisation is transmitted via calcium ions. This ultimately stimulates the retina cell. AP triggered in optic nerve.
What role does vitamin A play in the visual pigment ?
Visual pigment regeneration
What happens if you are deficient in Vit A ?
- Night-blindness
- Unhealthy conjunctiva and corneal epithelium
What are the first signs of Vit A deficiency ?
Bitot’s spots and Corneal Ulceration. Corneal melting occurs later on if deficiency isn’t rectified.
What causes colour blindness ?
Some cone cells are deficient or abscent and this means some people are unable to distinguish certain colours.