Eye and Orbit

Question 1

what is the Orbit and what are its structure and function

Answer 1

the orbit is a boney cavity of the skeleton, it contains

• Eyeball and muscles
• Nerves
• Blood vessels
• Most lacrimal apparatus

The main function is to protect these structures

Question 2

where is the apex of the orbit?

Answer 2

found at the optic canal, in the lesser wing of the sphenoid, just medial to SOF.

Question 3

How many layers does the eyeball consist of?

Answer 3

The eyeball has three separate layers

• Outer fibrous layer ( sclera and cornea)
• Middle vascular layer ( Choroid, ciliary body and iris )
• Inner layer ( Retina, optic and non-visual parts)

Question 4

Structure and function of the outer fibrous layer

Answer 4

Sclera

• Opaque part of the fibrous coat of the eyeball, often referred to as the “whites of the eyes”.
• Consists 5/6 of the posterior eye

Cornea

-Transparnt part of the fibrous coat
Covers the anterior 1/6 of the eye
- A vascular and sensitive to touch
Supplied by the ophthalmic nerve, trigeminal nerve branch 1
- Nourished by aqueous humor, tears and absorbs oxygen from the air.

Question 5

Structure and function of the middle layer

Answer 5

Choroid

• Dark brown membrane between the sclera and the retina
• Contains blood vessels and pigment which absorbs excess light.

Ciliary body

• Has a muscular and vascular part
• Connect the choroid with the circumference of the iris
• Has folds on its internal surface called the “Ciliary process”
• Secretes aqueous humor which fills the anterior and posterior chambers of the eye

Iris

• Thin contractile muscular diaphragm
• lies anterior to the lens

Pupil

• Central aperture in the iris
• Varies in size so it can regulate the amount of light entering the eye
• controlled by two muscles
• Sphincter muscles (closes the pupil)
• Dilator muscles ( dilates the pupil)

Question 6

what is the Inner layers, structure and function

Answer 6

• 10 delicate layers of nervous tissue membrane
• Continuos with optic nerve
• outer layer is in contact with the choroid
• inner layer is in contact with the vitreous body
• Posteriorly have a circular depressed region called the optic disc

Question 7

What are the two photoreceptors in the eye?

Answer 7

Rod cells

• Over a 100 million per eye
• positioned on the perphireal part of the retina
• Responds to dim light from black and white vision
• responds to form and movement but provides poor visual activity

Cones

• about 7 million per eye
• Provides colour vision and greater visual activity
• Concentrated in the fovea

Question 8

what are the refractive media of the eye?

Answer 8

• Cornea
• Aqueous humor
• Lens
• Vitreous body

Question 9

What is the structure and function of the lens

Answer 9

• Posterior ti the iris
• Transperent biconvex structure, enclosed within a capsule
• The capsule is anchored to the ciliary body by suspensory ligaments
• Convexity of the lens depends on whether or not you want to focus on near or far objects
• this is achieved by the ciliary muscles in the ciliary body
• increased convexity for near vision, flatter for far objects

Question 10

Innervation of the orbit

Answer 10

• Oculomotor nerve (CN 3)
• Trochlear ( CN 4)
• Abducent (CN 6)
• Opthalmic nerve (branch of the trigeminal nerve CN5)

Question 11

Arteries of the orbit

Answer 11

mainly the ophthalmic artery

- a branch of the internal carotoid artery

Question 12

Veins of the orbit

Answer 12

Inferior and Superior Ophthalmic vein ( passes through SOF)

Question 13

What are some red flags regarding the eye

Answer 13

• Severe ocular pain
• Severe orbital pain
• Microbial keratitis ( +/- contact lens use)
• Endophthalmitis (inflammation affecting the vitreous fluid)