Structure and Function of the Eye (A) Flashcards
What is the average anterior-posterior diameter of the orbit?
24 mm
What are the three layers of the eye? Describe their propertiesand function.
Sclera Hard and opaque Maintains the shape of the eye Choroid Pigmented and vascular Provides circulation to the eye Shields out unwanted scattered light Retina Neurosensory Converts light into neurological impulses
What are the two segments of the eye separated by?
Lens separates anterior and posterior segments
Which humours are found in the two segments of the eye?
Anterior = aqueous humour Posterior = vitreous humour
What name is given to the fibrous strands that suspend the lens from the ciliary bodies?
Zonules
Describe the production and drainage of aqueous humour.
Aqueous humour is produced by the ciliary body behind the iris. The fluid moves anteriorly around the iris and is drained in front of the iris via 2 pathways:
Either the trabecular meshwork into the canals of Schlemm (80-90%, active process)
Or uveal scleral outflow (20%, passive)
What is the role of aqueous humour?
Provides nutrients to the cornea and other tissues in the anterior chamber
Describe the composition of vitreous humour.
99% of vitreous humour is water, trapped in a jelly like matrix
What is the function of vitreous humour?
Mechanical support for the eye
Describe how the vitreous humour changes with age.
It loses its jelly consistency, liquefies and can become detached from the retina (can shrink basically).
Vitreous detachment in seen as floaters in the eyes and is a common problem as people age
What are the potentially disastrous consequences of vitreous humour detachment?
Detaching from the retina could cause a small tear in the peripheral retina
If there is a small tear, liquid vitreous could seep into the sub-retinal space and lead to retinal detachment
If untreated, it can lead to blindness
What is the uvea
collective term for the choroid, iris and ciliary body
What is the normal range for intraocular pressure?
12-21 mm Hg
What is glaucoma?
Optic neuropathy with characteristic structural damage to the optic nerve, associated with progressive RETINAL GANGLION CELL DEATH, loss of nerve fibres and visual field loss
What changes can be seen in the retina in glaucoma?
Retinal ganglion cell death
Enlarged optic disc cupping
(optic cup is the yellowy part of the optic disc)
What are the consequences of untreated glaucoma?
Progressive loss of peripheral vision
Blindness