Lecture 2: The eye Flashcards
Describe innervation of the orbital muscles:
LR 6
SO 4
Rest is CN 3
Describe the innervation of the eyelids:
Obicularis oculi closes the eye and is innervated by CN7
Levator palpebrae opens the eye and is innervated by CN3 (occulomotor)
Describe the tear film:
The tear film is comprised of 3 layers;
- > Oil (Tarsal gland, stops evap)
- > Aquous (lacrimal gland, tears)
- > Mucus (Goblet cells of conjunctiva)
What is the lacrimal system?
Lacrimal gland produces tears, this and blinking washes debris down to the puncta where they can drain into the lacrimal duct.
Describe the optical component of the eyes:
Light is refracted slightly by the cornea (2/3 focusing) and then again by the lens (1/3 focusing) to be focused on the retina.
The pupil dilates etc to control the amount of light entering the eye.
What is an astigmatism?
When there is two focal points on the retina
What is myopia?
Short sightedness
What is hyperopia?
Long sightedness
Describe the physiology of the eye and its relation to maintaining shape:
Hyaluronin in the eye is hydrophilic and drags in water
Epithelium of the cornea pump ions to keep the cornea relatively dehydrated ensuring good shape is maintained.
Intra-occular pressure also aids maintaining shape.
Lamellar of collagen fibres are arranged orthogonally. (strength)
How is the lens suspended?
By the zonules of zen to the ciliary bodies
Loosely describe the lens structure?
Centre = nucleus
Layers of cells are deposited over life
What are cataracts and their classification?
Cataracts are opacities
- Cortical or nucelar
- Senile or juvenile
- Diabetic or traumatic
Describe the cilliary body:
Circular layer (seen inner circle and outer) (constricts) Longitudinal layer (dilates)
What is accomodation?
Contraction of the ciliary muscles to increase the curve of the lens and increase refraction allowing near sightedness.
Presbyacusis is loss of accomodation with age.
What is the aquous humor? where is it? what does it do? what produces it?
- Fills space between lens and iris. (ant. chamber)
- Epithelium on ciliary body produce aq. humor
- Nourishes lens and cornea which are avascular.
- Maintains shape and pressure of ant. chamber
- Flows out through the trabecular mesh network and when this is damaged, it impedes flow.
What is the fovea of the reina?
Centre of visual acuity
Describe the fovea:
- Has no ganglion cells infront of it or blood vessels
- Contains only cones
- Light hits the cones directly.
- Offset from the optic disc (which is just where the optic nerve connects)
Why is the retina back to front so to speak?
So that the rods and cones are closest to the nutrient source as they are the largest consumers and waste producers relatively in the body.
Describe the function of the bipolar cells of the retina:
Bipolar cells; Like multiplug board
How does the central and peripheral retina compare?
Central retina has a much higher density of photoreceptors
What is the macula lutea?
Area surrounding the fovea and contains many Xanthophyll caratenoids - Zeaxanthin and lutein which are protective in function.
What is found at the optic disc / nerve?
No photoreceptors.
Just ganglion cells for inputs
Describe the relative rods and cones density of the retina:
Cones are highest density in the fovea and relatively low everywhere else.
Rods are not present in the fovea but increase in density from the peripheral towards the fovea.
What do rods and cones do?
Cones = visual acuity Rods = movement detection / low light
