Special Senses: Vision

Question 1

___ % of the body’s sensory receptors are in the eyes.

Answer 1

70

Question 2

What is the function of eyebrows?

Answer 2

Eyebrows - overlie the supraorbital margins; shade the eye from sunlight and prevent perspiration from reaching the eye

Question 3

Define, know the function of, and be ready to label: palpebrae, palpebral fissure, medial commissure, lateral commissure, lacrimal caruncle, tarsal plate, tarsal gland, and conjunctiva.

Answer 3

Eyelids (Palpebrae): thin, skin-covered folds that protect the eye anteriorly

Palpebral Fissure: separation between eyelids

Medial + Lateral Commissures: corners of the eyes

Lacrimal Caruncle: raised structure in medial commissure; oil + sweat glands

Tarsal Plates: supporting connective tissue for the eyelids; anchor points for orbicularis oculi and levator palpebrae superioris

Tarsal Glands: lubricating glands associated with the tarsal plates – when inflamed, causes a sty!

Conjunctiva: transparent mucus membrane that produces a lubricating mucus secretion

Question 4

Differentiate palpebral and bulbar conjunctiva. What is the conjunctival sac?

Answer 4

Palpebral Conjunctiva: membrane on the interior of the eyelids

Bulbar Conjunctiva: membrane that covers the white of the eyes – contains small blood vessels

Conjunctival Sac: space between the palpebral and bulbar conjunctiva – the area where a contact lens rests

Question 5

Be ready to identify the lacrimal gland in the picture.

Question 6

What is contained within tears?

Answer 6

a dilute, saline solution containing mucus, antibodies, and lysozyme

Question 7

What pathway do tears travel?

Answer 7

Blinking spreads tears toward the medial commissure – they enter the paired lacrimal canaliculi via the lacrimal puncta

Tears drain into the lacrimal sac and the nasolacrimal duct

Duct enters the nasal cavity

Question 8

Know the 6 extrinsic eye muscles. In which direction does each of them move the eye?

Answer 8

table on slide 9

Question 9

What is strabismus?

Question 10

What are the 2 humors of the eye? In which compartment would you find each of them? What causes glaucoma?

Answer 10

Aqueous humor (Anterior)
Vitreous humor (Posterior)

…

Question 11

What are the 2 regions of the fibrous layer of the eye?

Answer 11

sclera + cornea

Question 12

What are the functions of the sclera? How about the cornea?

Answer 12

Sclera: opaque posterior region

• Protects and shapes the eyeball
• Anchors the extrinsic eye muscles
• Posteriorly, where the optic nerve exits, the sclera is continuous with the dura mater of the brain

Cornea: transparent, anterior 1/6 of the fibrous layer

• Forms a clear window – allows light to enter, bends light
• Both sides are covered with epithelium – the outer surface is protected from abrasions, the inner surface helps to maintain clarity
• Contains many pain receptors – responsible for blinking and tearing reflexes

Question 13

The vascular layer of the eye is also called the: ________.

Answer 13

uvea

Question 14

What are the 3 regions of the vascular layer?

Answer 14

choroid, ciliary body, and iris

Question 15

What is the function of the choroid? The ciliary body? The iris?

Answer 15

Choroid: posterior portion of the uvea

• Supplies blood to all layers of the eyeball
• Brown pigment absorbs light to prevent scattering and visual confusion

Ciliary Body: anterior portion

• Thickened ring of tissue surrounding the lens

Iris: most anterior portion of the vascular layer

• colored part of the eye
• lies between the cornea and the lens – continuous with the ciliary body posteriorly

Question 16

Know the location and role of the: ciliary muscles, ciliary processes, ciliary zonule, and pupil.

Answer 16

Consists of smooth muscle bundles – ciliary muscles – that control the shape of the lens

Capillaries of the ciliary processes secrete fluid of the anterior segment of the eyeball

Ciliary Zonule (suspensory ligament): extends from the ciliary processes to the lens – holds the lens in position

Pupil: round, central opening that regulates the amount of light entering the eye

Question 17

What 2 muscles make up the iris? How do they work to control the size of the pupil?

Answer 17

Sphincter pupillae + dilator pupillae

For close vision and in bright light, sphincter pupillae contracts and the pupil constricts

Controlled by parasympathetic fibers!

For distant vision and in dim light, dilator pupillae contracts and the pupil dilates

Controlled by sympathetic fibers!

Question 18

Where does the retina originate from? What are its two layers?

Answer 18

Retina: very delicate 2-layered membrane, originates from an extension of the brain

Contains millions of photoreceptor cells that transduce light energy, neurons, + glial cells

Outer Layer: pigmented layer

Inner Layer: neural layer

Question 19

What is the function of the pigmented layer of the retina?

Answer 19

Pigmented Layer of the Retina: single-cell thick lining; next to the choroid; extends anteriorly to cover the ciliary body + iris

The pigmented layer absorbs light/prevents scattering, phagocytizes photoreceptor cell fragments, and stores vitamin A.

Question 20

What 3 types of neurons make up the neuronal layer of the retina?

Answer 20

photoreceptors, bipolar cells, and ganglion cells

Question 21

How do signals pass between these different types of neurons (in what direction)?

Answer 21

Signals are produced in response to light and spread from the photoreceptors to the bipolar cells to the ganglion cells

Question 22

Which of these 3 types produces action potentials?

Answer 22

ganglion cells

Question 23

Axons of the ganglion cells become the _____________________.

Answer 23

optic nerve

Question 24

What is the optic disc? Why it is our blind spot?

Answer 24

Optic Disc: the site where the optic nerve leaves the eye; this site lacks photoreceptors so it is referred to as the “blind spot”

Question 25

About how many photoreceptors are in each retina?

Answer 25

The retina has a quarter-billion photoreceptors

Question 26

What are the two varieties of photoreceptors? What does each variety specialize in?

Answer 26

Rods and cones Rods: dim-light and peripheral vision receptors - More sensitive to light than cones - No color vision or sharp images - Mostly located in the periphery of the retina Cones: bright-light receptors - Provide high-resolution, color vision

Question 27

What is the macula lutea? The fovea centralis? What kind of photoreceptors can you find there?

Answer 27

Macula Lutea: oval region located lateral to the blind spot of each eye – contains mostly cones Fovea Centralis: tiny pit in the center of the macula lutea – contains all cones The goal of eye movement is to provide the fovea centralis with images of different parts of the visual field

Question 28

What is the lens? Where can you find it? What is its function?

Answer 28

Lens: a biconvex, transparent, flexible, and avascular structure Located just posterior to the iris and held in place by the ciliary zonule The lens changes its shape to precisely focus light on the retina

Question 29

What protein can you find in lens fibers? Why does the lens become less elastic with age?

Answer 29

Lens Fibers: form the bulk of the lens; filled with a transparent protein called crystallin – no organelles, no nuclei Lens fibers are continually added – the lens becomes more dense, more convex, and less elastic with age

Question 30

What is a cataract?

Answer 30

clouding of the lens that causes visual distortion; can be genetic or a result of diabetes mellitus or a result of various exposures

Question 31

What is refraction? What causes it?

Answer 31

Refraction: bending of light rays When light travels in a given medium, its speed is constant When light passes from 1 transparent medium to another medium with a different density, the speed of light changes and refraction occurs

Question 32

What is the pathway of light entering the eye? Where is light refracted along this pathway?

Answer 32

Because lenses are curved, light hits them at an angle, and they can refract light Convex lenses bend light so that its rays converge at a focal point In general, the more convex a lens is, the more the light bends, and the shorter the distance will be between the lens and the focal point

Question 33

What structure of the eye has the most refractory power? What structure of the eye can accommodate?

Answer 33

The majority of refractory power is in the cornea, but the cornea cannot change its shape and therefore cannot change focus The lens CAN adjust its curvature to allow for fine focusing – distant and close vision!

Question 34

What’s the average far point for vision? The average near point?

Answer 34

Far Point of Vision: distance beyond which no change in lens shape (accommodation) is needed for focusing ~20 feet for the healthy eye

Question 35

What shape does the lens take for distance vision? For close vision? Know how this is caused by the ciliary muscle!

Answer 35

Ciliary muscles are completely relaxed in distant vision – this causes pull on the ciliary zonule, and the lens is stretched flat

Question 36

What 3 steps are required for effective close vision?

Answer 36

1. Accommodation of the Lens: changing the shape of the lens to increase refraction Near Point: closest point on which the eye can focus – about 4 inches in a healthy eye 2. Constriction of the Pupils: prevents most divergent light rays from entering the eye – mediated by the parasympathetic system 3. Convergence of the Eyeballs: medial rotation of the eyeballs causes convergence of the eyes towards the object being viewed

Question 37

What is presbyopia? Myopia? Hyperopia? Astigmatism?

Answer 37

Presbyopia: loss of accommodation < age 50 Myopia (Nearsightedness) Eyeball is too long – the focal point is in front of the retina A concave lens moves the focal point back – distance glasses Hyperopia (Farsightedness) - Eyeball is too short – the focal point is behind the retina - A convex lens moves the focal point forward – reading glasses Astigmatism: unequal curvatures in different parts of the cornea or lens - Special glasses or laser surgery can correct