Neuro Block 5: The eyeball

Give the general structure of the eye:

• globe-shaped organ in the orbit

• 3 layers and 3 chambers

• chambers separated by iris, pupil and lens

List the 3 chambers of the eye:

1. Anterior + Posterior chambers

2. Lens

3. Vitreous chamber

Where are the anterior and posterior chambers located and what is their function?

• anterior and posterior chambers are continuous with each other via the pupil

• filled with aqueous humour which nourishes the cornea via supplying nutrients (avascular)

What is the canal of Schlemm?

• venous sinus that aqueous humour from anterior + posterior chambers drains into and is reabsorbed

Where is the lens located and what is its function?

• located posterior to pupil

• transparent, bioconvex disc that changes shape to alter refraction of light

Where is the vitreous chamber located and what is its function?

• located posteriorly to lens

• filled with gel = padding

List the 3 walls of the eyeball:

1. Outer Layer; sclera + cornea

2. Middle Layer; Uvea + ciliary body + iris

3. Inner Layer; retina layer

Which muscle controls the iris and causes constriction of pupil and what type of innervation does it have?

• sphincter pupillae (smooth muscle)

• innervated by parasympathetic nervous system (involuntary and reacts to light)

What muscle dilates the pupil and what innervation does it have?

• myoepithelial cells form the dilator pupillae muscle (smooth)

• innervated by sympathetic fibres

What is the optic retina?

• the light-sensitive layer of tissue at the back of the inner eye that converts light into neural signals

• contains photoreceptors: rods and cones

What neural cells relay night vision?

rods

What neural cells relay colour?

• cones

Describe how light enters the eye:

light converges → focal point → diverges in opposite direction → image is formed on retina which is inverted (vertical and horizontal reversal)

Where do visual fields project to?

• visual fields project to contralateral cortex

What 2 fibre types are present from the eyeball to optic chiasm?

1. temporal fibres

2. nasal fibres

Describe the direction in which temporal fibres travel?

• stay ipsilateral

Describe the direction in which nasal fibres travel?

• decussate at optic chiasm

What does the right part of brain after the optic chiasm process?

• the left visual field

What does the left part of brain after the optic chiasm process?

• right visual field

Describe the blood supply to the eyeball:

ALL BRANCHES OF OPHTHALMIC ARTERY (branch of internal carotid)

• short & long posterior ciliary arteries

• anterior ciliary arteries

• central retinal artery (travels with optic nerve)