Special Senses 2 Flashcards
What are the 3 layers of the eye?
Corneoscleral coat - outermost
Uveal tract - middle
Retina - inner
Structure of the uveal tract
Consists of iris and ciliary body anteriorly
Vascularised choroid coat posteriorly
Structure of the retina
Layers of nerve cells, their processes, support cells and on the outside a layer of pigmented epithelium
Properties of the lens
Biconvex
Elastic to allow change in shape permitting near vision
What is in front of the lens?
Two chambers (anterior and posterior) filled with aqueous humor
What is posterior to the lens?
Much larger vitreal cavity filled with vitrous humor which is avascular and gelatinous
What is the conjunctiva?
A thin transparent mucous membrane
What lines the conjunctiva?
Stratified columnar epithelium with goblet cells and has a lamina propria of loose connective tissue
Where is the conjunctiva?
From the corneoscleral margin and reflects over the inner surface of the eyelids
What is the cornea?
Outer layer of thin non keratinised stratified squamous epithelium sitting on Bowmans membrane
What is the Bowman’s membrane?
A thin layer of collagen composed of randomly oriented, condensed thin collagen fibrils
What is the corneal stroma?
Many layers of precisely oriented, hydrated collagen with each layer at roughly right angles to eachother
There are corneal fibroblasts between layers
What is the Duscemet’s membrane?
A layer of endothelium sitting on a layer of meshwork collagen
What is a kaiser-fleischer ring?
An accumulation of copper in duscemet’s membrane at the corneo-scleral junction
Most often seen in Wilson’s disease
What is the sclera?
Tough coat of collagen and elastic fibres defining the globe
Where the tendons of the extraocular muscles attach
What is the ciliary body?
Contains smooth muscle that releases tension on zonular fibres during near vision allowing lens to round up due to its natural elasticity
What is the canal of Schlemm?
Where excess fluid from the anterior chamber is drained
When drainage is not adequate = glaucoma
What is the iris?
Mostly loose connective tissue with a layer of pigmented epithelium on its posterior surface
Contains melanocytes and smooth muscle which changes its diameter
How do you produce blue and brown eyes?
Abundant melanocytes = brown eyes
Few melanocytes = blue eyes
What do sphincter pupillae fibres do?
Located near tip of iris and circumferentially oriented
Constrict pupil under parasympathetic stimulation
What do dilator pupillae muscles do?
Radially oriented
Open pupil under sympathetic stimulation
What is the flow of aqueous humor?
Secreted by ciliary processes into posterior chamber
Flows between iris and lens to reach anterior chamber
Structure of the lens
Made of lens fibres - cellls that lose nuclei and organelles as they mature and are packed with crystallins
Anteriorly covered by connective tissue capsule and layer of simple cuboidal epithelium
During development where are new lens cells produced?
At the lateral margin of the lens - the germinal zone
Structure of lens fibres
Long
Run in an arc anterior to posterior
Roughly hexagonal in cross section
Densely packed together
How many rods and cones does the retina contain?
130,000,000 rods
6,500,000 cones
What do rods contain?
Rhodopsin - a light sensitive pigment
Usually for low light vision
What do cones contain?
One of 3 opsin pigments sensitive to either red green or blue light
Red - long wavelength
Green - medium wavelength
Blue - short wavelength
What are the layers of the retina?
Inner limiting membrane Layer of optic nerve fibres Ganglion cell layer Inner plexiform layer Inner nuclear layer Outer plexiform layer Outer nuclear layer Outer limiting membrane Rods and cones Retinal pigment epithelium Lamina vitrea Choroid
Where is the fovea?
At the centre of the optical axis on the retina
Where is the foveola?
At the centre of the fovea
What is the foveola?
Where the retina thins and is avascular
Only cones found here covered only by outer plexiform layer
Very high acuity vision
What is the optic disc?
The site where the axons of the retinal ganglion cells exit the eye to form the optic nerve
Why is the optic disc known as the blind spot?
Lacks photoreceptors
What are the lamina cribosa?
A series of openings in the sclera that fibres which will form the optic nerve exit through the eyeball
What is the red eye effect?
Mainly due to blood supply in choroid
More intense in pale people with blue eyes as they have less melanin in pigmented epithelium
