Anatomy & Physiology of the eye

Label

The External eye: How many muscles make up the extraocular muscles (EOM)? What are they for?

EOM = 7 muscles that enable movement

• Superior rectus = Up

• Inferior rectus = Down

• Lateral rectus = Left

• Medial rectus = Right

• Superior oblique + Inferior Oblique = Counteract head movement

• Levator palpebrae = eyelid

The External eye: What is the bony orbit and fat surrounding it for?

• Bony orbit = Cavity of the skull in which the eye sits and is protected from mechanical injury

• Fat = Surrounds eye in bony orbit to provide smooth movement via lubrication

The external eye: Label

Describe the function of the conjunctiva, conjunctival sac and lacrimal gland

• Conjunctiva = Thin mucus membrane covering the sclera (Whites of the eyes)

• Conjunctiva FOLDS & JOINS the inner lining of the upper & lower eyelid to form a bag-like structure called the conjunctiva sac (prevents contacts from going to the back of the brain)

• Lacrimal gland = Important in tear film & mucus production - keep eye clean & moist

What is the sclera and what is its function?

• The ‘white of the eye’

• It serves a protective function

• Made up of non-uniform collagen & elastic fibres

• Fuse w/ extraocular muscles for attachment

What is the cornea and what is its function?

• Transparent, no blood supply, continuous with the sclera

• It’s the eye’s major REFRACTIVE structure and is responsible for 2/3 of the eye’s refractive power

• Cannot change shape

IRIS: What is the iris and what is its function?

• Determines eye colour depending on melanin content. Colour & pattern is as unique as a fingerprint

• Controls light levels in the eye - similar to a camera aperture. The opening is known as the PUPIL

IRIS: The iris is embedded with tiny muscles that dilate (widen) or constrict (narrow) the pupil size. What are the 2 muscles that do this

• SPHINCTER MUSCLES : Bright light causes the sphincter muscles to contract causing pupil to constrict

• DILATOR MUSCLES : Dim light causes the dilator muscle to contract & widen/dilate the pupils

LENS: What is the lens and what is its function?

• Transparent & biconvex structure (Consists of 2 convex structures)

• In addition to the cornea it also reflects light + accounts 1/3 of the eye’s refractive power

• Lens CHANGE SHAPE to focus on images at various distances - declines w/ age

LENS: Explain this image

• When focusing on an object FAR AWAY —> lens does not have to refract light as much —> therefore lens become THINNER

• When focusing on an object CLOSE BY, the lens has to refract that light more —> therefore lens becomes THICKER

How does the lens change shape?

• The CILIARY MUSCLES & FIBRES play a role in stretching the lens

• Under normal conditions the lens is naturally thicker for near vision. But is pulled thinner for long distance vision