Structure and Function of the Eye 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
It is drained via the trabecular meshwork into the canals of Schlemm
What is the role of aqueous humour?
Provides nutrients to the cornea and other tissues in the anterior chamber
Describe vitreous humour.
It is 99% water trapped inside a jelly 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
Vitreous detachment in seen as floaters
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 are the two layers of the iris?
Anterior – stromal layer containing muscle fibres
Posterior – epithelium
Describe how the retina and choroid contribute to the different parts of the iris and ciliary body.
Retina gives rise anteriorly to the ciliary body epithelium and the posterior (epithelial) layer of the iris
Choroid gives rise anteriorly to the ciliary body stroma and the anterior layer of the iris (stromal layer)
What is the collective term for the choroid, iris and ciliary body?
Uvea
What is the normal range for intraocular pressure?
11-12 mm Hg
What is glaucoma?
Condition of sustained raised intraocular pressure
What changes can be seen in the retina in glaucoma?
Retinal ganglion cell death
Enlarged optic disc cupping
What are the consequences of untreated glaucoma?
Progressive loss of peripheral vision
Blindness
What is the most common type of glaucoma and what is it causedby?
Primary open angle glaucoma
It is caused by a functional blockage of the trabecular meshwork
State another relatively common type of glaucoma. What is it caused by?
Closed angle glaucoma
This can be acute or chronic
It is caused by the forward displacement of the iris-lens complex –narrowing the trabecular meshwork
In what type of patients does closed angle glaucoma tend to occur and what is the treatment?
Small eyes (hypermetropic) Treatment: peripheral laser iridotomy
Describe the structure of the lens.
It has an outer acellular capsule
There are regular inner elongated fibres, which give the lens its transparency
NOTE: may lose transparency with age
Which two structures provide the majority of the refractive power of the eye?
Cornea = 2/3 Lens = 1/3
What layer of the eye is the cornea continuous with?
Sclera
Other than its role in refracting light, what else is the corneanecessary for?
Physical barrier – protects the eye from opportunistic infection
What are the consequences of prolonged contact lens wear?
Reduce the oxygen supply to the cornea
What are the three layers of the cornea?
Epithelium
Stroma
Endothelium