Special senses - vision

Question 1

What are the accessory structures of the eye? Briefly describe them

Answer 1

Eyebrows: short hairs that overlie the supraorbital margins to shade the eye and protect from perspiration

Eyelids (palpebrae): separated by the palpebrae fissure, lacrimal caruncle contains sebaceous and sweat glands

• eyelash follicles are richly innervated (triggers reflex blinking)
• tarsal glands lubricate the eyelid and eye with oily secretion

Conjunctiva: transparent mucuous membrane that lines the eyelids and folds back over the eye as the bulba conjunctiva

• covers only the white of the white
• produces a mucus that prevents drying of the eyes (they need to stay moist because they are constantly exposed to the environment)

Question 2

What are the 3 layers of the eyeball? Briefly describe them

Answer 2

1. Fibrous (dense CT that is avascular)

• Consists of the sclera and the cornea
• Sclera forms majority of the fibrous layer while the cornea forms the anterior 1/6 of the fibrous layer)
• The sclera protects and shapes the eyeball and is an anchoring site for extrinsic eye muscles
• The sclera can be seen anteriorly as the white of the eye
• the cornea is transparent due to collagen and glycosaminoglycans and allows light entry and is important in light refraction

2. Vascular (pigmented)

• contains the choroid = deep the the sclera and nourishes all layers of the eye, also contains melanin to absorb any light
• ciliary bodies form the anterior 1/6 and encircles the lens, is primarily composed of ciliary muscles (smooth muscle that influences lens shape)
• Iris gives eye colour and is continuous with ciliary body posteriorly
• The central opening is the pupil
• its 2 layers of smooth muscle allows for constriction and dilation

3. Inner (retina)

• millions of photoreceptors that transduce light energy, other neurons and supporting glial cells
• 2 layers; outer pigmented layer and inner neural layer, only the neural layer is involved in vision
• contains optic disc

Question 3

Within the vascular layer what is the difference between the two sublayers?

Answer 3

Outer pigments layer absorbs light; cells can be phagocytic and store vitamin A

Inner neural layer composed of photoreceptors, bipolar cells and ganglion cells

Question 4

What are photoreceptors?

Answer 4

Rods and cones

Rods process dim light and peripheral vision

• There are more rods than cones
• Dont giev sharp images

Cones process bright light and high resolution

• Allows for colour vision

Question 5

What is the optic disc?

Answer 5

AKA our blind spot

• Has no photoreceptors
• Found in the inner (retina) layer of the eyeball

Question 6

What is the macula lutea?

Answer 6

An area of high concentration of cones for visual acuity (seeing finer details)

• Mostly cones found in the macula lutea and a gradual transition from cones to rods as you move further out of the macula

Question 7

What is the fovea?

Answer 7

A central pit within the macula lutea, other cells are displaced to the side so light has direct access to photoreceptors

NOTE there are only cones in the fovea

Question 8

What are the 2 humors within the eye? What are each of their functions? and what differs between them?

Answer 8

Aqueous humor; small fluid chamber that supplied nutrients and oxygen to the lens and cornea and carries any metabolic waste

Vitreous humor; forms in embryo and lasts our lifetime unlike the aqueous humor, found inthe posterior and transmits light

• Holds hte 2 retinal layers firmly together through intraocular pressure