What does vision require? (general)
- requires special visual receptors (photoreceptors) located at the back of the eye
What does the lacrimal gland do?
- produces tears
- keeps the cornea (outside) of the eye moist and clean
- lacrimal apparatus (seen in the anterior view of the eye) is also very important in tear drainage
What muscles does the eyelid contain?
- The upper eyelid contains the levator palpebrae superioris muscle and orbicularis oculi muscle
- these control the opening and closing of the eyelid
What are the extraocular eye muscles and where are they located?
- located outside of the eyeball itself
- names are based on their location
- medial rectus, inferior rectus, inferior oblique, superior oblique, superior rectus, lateral rectus
What are the cavities of the eye?
- They are fluid filled
- There are two (posterior and anterior)
- They are delineated by the lens (seperated?)
Describe the anterior cavity.
- composed of the anterior and posterior chambers
- both are filled with aqueous humour (watery type fluid)
What is the posterior cavity filled with?
- filled with vitreous humour (gelatinous fluid)
What does the lens of the eye seperate?
- separates the anterior cavity of the eye from the posterior cavity
What are the three layers (tunics) of the internal portion of the eye?
- Outer layer: Fibrous
- Middle layer: Vascular
- Deep layer: Sensory (Retina)
Describe the fibrous layer of the eye.
- It is fibrous tunic
- The most outermost layer of the eye
- Has two portions located internally and externally to the lens: (sclera and cornea). These portions are continuous with one another
What is the sclera of the fibrous tunic?
- The internal aspect of the fibrous tunic
- Located posterior to the lens
- Form the white portion of the eye
- A layer of dense connective tissue that acts as a point of attachment for the extrinsic eye muscles
What is the cornea of the fibrous tunic?
- The external aspect of the fibrous tunic
- Located anterior to the lens
- Transparent enabling light transmission
What is the vascular tunic, and what is it composed of?
- (AKA the uveal tract)
- the middle layer of the eye
- made up of the choroid, the ciliary body and the iris
What is the choroid of the vascular tunic?
- contains the blood vessels that supply the eye with oxygen and nourishment
What is the ciliary body of the vascular tunic?
- produces aqueous humor
- contains ciliary muscles (intrinsic eye muscles) which control the shape of the lens
What is the iris of the vascular tunic?
- contains the sphincter and dilator muscles (intrinsic eye muscles) which control the narrowing and widening of the pupil
- also contains pigments, which give the eye its colour
What is the sensory tunic and what does it contain?
- the most innermost layer of the eye
- consists of the neural layer, optic disc, macule, and CN II (optic nerve)
- AKA the retina!!
What is the neural layer of the sensory tunic (retina)?
- the outermost region of the neural layer has photoreceptors (rods and cones) which are light sensitive cells.
- these receptors send signals through smaller nerves to the axons of the ganglion cells (innermost layer of the retina) exit the posterior aspect of the globe to the brain to form CN II
What is the optic disc of the retina?
- the area where smaller nerve cell axons converge
- it is the location we can see when we look into the eye
What is the macula of the retina?
- the central area of the retina, lateral to the optic disc
- central depression of the macula (AKA the fovea) is where fine detailed vision occurs
Describe the flow of aqueous humour.
- aqueous humour is produced by ciliary processes in the posterior chamber
- flows through the pupil into anterior chamber and exits at anterior chamber angle (junction of iris, ciliary body and cornea) through trabecular meshwork into Schlemm’s canal and ultimately into episcleral venous channels which drain into the systemic circulation
- probably watch a video on this or something to help
Describe glaucoma, and the effects of it.
- Normally, the aqueous humour is able to flow naturally from the eye
- in glaucoma, the flow is blocked, causing excess fluid to accumulate in the chambers of the eye
- this puts increased pressure on the structures in the eye, which can lead to damage of the neural tunic (or retina) and nerves in this layer
What symptoms would likely occur in a patient with glaucoma if their lens became disrupted and blood flow to the neural tunic or retina stopped?
Some potential symptoms include damage to the retina or neural tunic, inability to see, distortion of the optic nerve, and reduced vision.
