Lecture 36 DA Flashcards
What forms the optic nerve?
Formed by the output of the axons of ganglion cells of the retina.
How does the optic nerve pass through the sclera?
Outer 2/3rds of the sclera run down the side of the optic nerve. The remaining inner 1/3rd continues across through the optic nerve.
What is the intersection of the inner 1/3rd scelera with the optic nerve called?
Lamina cribosa.
What is the structure of the lamina cribosa?
A band of dense connective tissue, forms a sieve-like mesh of collagen fibres.
How many sheets make up the lamina cribosa, and what is its purpose?
3-10 sheets of collagen, anchors the optic nerve and gives it structure.
Makes sure the axons are in the right spot. Can be bent & impact vision.
What happens to the lamina cribosa in glaucoma?
Gets distended, affecting vision.
Where does the ophthalmic artery originate?
From the internal carotid artery.
What are the four main arteries of the eye?
Central retinal artery
Long posterior clilliary artery
Short posterior cilliary artery
Anterior cilliary artery
Where does the short posterior cilliary artery pierce the eye?
Posteriorly, just around the optic nerve.
Where does the long posterior cilliary artery pierce the eye?
Similar to the short posterior, but further up, and away from the optic nerve, and is longer as a result, hence its name.
Does the anterior cilliary artery pierce the globe?
No, it doesn’t.
Where does the anterior cilliary artery run?
It runs anterior to the globe without piercing, and supplies the anterior eye.
Which artery do all arteries within the choroid originate from?
One of the posterior arteries, including central retinal.
What is the blood supply to the retina?
It has a dual supply.
The central retinal artery supples the inner retina, while the outer retina is supplied by the posterior cilliary arteries
What is the optic nerve supplied by?
Short posterior cilliary artery.
What supplies the iris?
Long posterior cilliary artery.
What supplies the cilliary bodies?
Long posterior cilliary artery.
What are photoreceptors aside from the inner and outer retina supplied by?
Long posterior cilliary artery.
Where do the long posterior and anterior cilliary arteries anastamose?
At the junction between the sclera and corna, via a major perforating artery.
What does inflammation within the eye cause?
Localised redness.
What are 4 factors affecting visual acuity?
Pupil size
Clarity of optic media (cornea, lens)
Refrective errors
Diseases (myopia, astigmatism)
What bends light as it enters the eye?
60% of whats required bent by the cornea.
40% by the lens
What is myopia? Where is the focus?
Eyeball too long, focus is in front of the retina. Minus lenses needed.
What is hypermetropia? Where is the focus?
Eyeball is too short, focus is behind the retina. Positive lenses needed.
Is the fovea avascular? Why?
Yes, so give visual acuity.
What is astigmatism? Where is the focus?
The eyeball is football shaped rather than circular. Focus is steeper in one meridian/axis than the other, light hits one side better than the other.
Cylindrical lenses needed.
What is keratoconus?
Non inflammatory condition of the cornea, cone shaped cornea. Thinning of the central cornea.
Irregular astigmatism.
What is the incidence rate of keratoconus?
1/2000, 70% female.
What is keratoconus associated with and how is it treated?
Associated with allergic conditions.
Treated by hard contact lenses.
10% need corneal transplant.
What is wet form macular degeneration?
Blood vessels grow into the fovea and destroy it.
What is dry form macular degeneration?
Cellular debris (drusen) accumulates between the choroid and retina.
What are the causes of macular degeneration?
Age, smoking, diet.
Many genetic, relating to lipid transport and immune function.
Can macular degeneration be treated?
Yes, but requires a monthly injection into the eye. Only works for wet form.
Which form of macular degeneration is more serious?
Wet form (10% of cases).
What is a theory on the cause of macular degeneration?
Fovea metabolic demands aren’t being met, stimulating blood vessel growth.
What is Bruch’s membrane? How is it believed to be involved in macular degeneration?
Boundary between vessels and fovea. Believed to thicken in macular degeneration and impinges on nutrient transfer.
What age does macular degeneration usually start and what does it look like?
50 years and over. Begins as a white blob on the retina.
How can Bruch’s membrane be thinned?
Use of a nanosecond laser.
