Eye Anatomy

Question 1

sclera

Answer 1

• the white part of the eye that surrounds the cornea
• the dense connective tissue of the eyeball
• forms more than 80% of the surface area of the eyeball
• extending from the cornea all the way to the optic nerve
• only a small portion of the anterior sclera is visible
• some blood vessels pass through the sclera to other tissues, but the sclera itself is considered avascular

Question 2

what accounts for the strength and flexibility of the eyeball?

Answer 2

The sclera is composed of fibrils (small fibers) of collagen that are arranged in irregular and interlacing bundles.

(The random arrangement and interweaving of these connective tissue fibers are what account for the strength and flexibility of the eyeball)

Question 3

limbus

Answer 3

the junction between the white sclera and the clear cornea

the sclera is continuous with the stroma layer of the cornea

Question 4

episclera

Answer 4

• a thin, loose connective tissue layer
• that lies on top of the sclera
• and under the transparent conjunctiva that covers the sclera and episclera

Question 5

choroid

Answer 5

• the vascular layer of the eyeball that is sandwiched between the sclera and the retina
• contains many tiny blood vessels and has the vital role of nourishing the retina

Question 6

3 functions of the sclera

Answer 6

1) maintains the shape of the eyeball (along with the intraocular pressure (IOP) of the eye)
2) the tough, fibrous nature of the sclera also protects the eye from serious damage — such as laceration or rupture — from external trauma
3) provides a sturdy attachment for the extraocular muscles that control the movement of the eyes

Question 7

iris

Answer 7

-the thin, circular structure made of connective tissue and muscle that surrounds the pupil

Question 8

pupil

Answer 8

circular opening (aperture) in the center of the iris which is the opening that allows light into the eye

Question 9

what determines the color of our eyes

Answer 9

the amount of pigment in the iris

Question 10

ciliary body function (3)

Answer 10

-holds the lens of the eye in place
(connected to the lens with a network of many tiny ligaments, called ciliary zonules or zonules of Zinn, that suspend the lens in place behind the pupil)

• secretes the clear aqueous fluid that fills the space in the anterior segment of the eye between the cornea and the iris and lens
• and it contains the muscle that controls accommodation of the eye

Question 11

ciliary body

Answer 11

It surrounds the iris and cannot be seen because it’s located behind the opaque sclera (white of the eye)

Question 12

iris function (2)

Answer 12

• in addition to giving the eye its color, the iris acts like the diaphragm of a camera and controls the size of the pupil
• the colored nerve tissue which works in conjunction with a muscle (sphincter) which regulates how much light comes in

Question 13

uvea

Answer 13

• the pigmented middle layer of the eyeball

- 3 segments: the iris, the ciliary body and the choroid

Question 14

pupil function

Answer 14

-allows light to enter the eye so it can be focused on the retina to begin the process of sight

Question 15

why are pupils black

Answer 15

because light that passes through the pupil is absorbed by the retina and is not reflected back (in normal lighting)

Question 16

what could explain a cloudy pupil

Answer 16

the lens of the eye (which is located directly behind the pupil) becoming opaque due to the formation of a cataract

Question 17

the size of the pupil is controlled by

Answer 17

• muscles within the iris
• one muscle constricts the pupil opening (makes it smaller)
• another iris muscle dilates the pupil (makes it larger)

Question 18

In low-light conditions, the pupil..

Answer 18

dilates so more light can reach the retina to improve night vision

Question 19

In bright conditions, the pupil..

Answer 19

constricts to limit how much light enters the eye

Question 20

If the pupil lets in too much light..

Answer 20

it can cause glare and discomfort, and it may even damage the lens and retina

Question 21

pupil size

Answer 21

• varies from person to person

- also changes with age — children and young adults tend to have large pupils, and seniors usually have small pupils

Question 22

accommodative pupillary response

Answer 22

both pupils normally constrict when you focus on a near object

Question 23

pupil testing

Marcus Gunn pupil testing

Answer 23

While you are looking at a distant object, the examiner will briefly direct the beam of a small flashlight at one of your eyes a few times

“swinging flashlight test” alternately direct the light at each eye and again observe the pupil responses of both eyes

Question 24

direct response

Answer 24

reaction of the pupil of the eye receiving direct illumination

Question 25

consensual response

Answer 25

response of a pupil to light that enters the contralateral (opposite) eye

Question 26

PERRLA

Answer 26

pupils are equal, round and reactive to light and accommodation

Question 27

retina

Answer 27

the sensory membrane that lines the inner surface of the back of the eyeball. It’s composed of several layers, including one that contains specialized cells called photoreceptors

Question 28

macula

Answer 28

tiny, highly sensitive area of the retina that controls central vision and color vision

Question 29

two types of photoreceptor cells (in the human eye)

Answer 29

Rod photoreceptors

 - detect motion
 - provide black-and-white vision
 - function well in low light
 - located throughout the retina 

Cones

 - responsible for central vision and color vision
 - perform best in medium and bright light
 - concentrated in small central area of retina (macula)

Question 30

fovea

Answer 30

-small depression in the center of the macula

• contains only cone photoreceptors
• is the point in the retina responsible for maximum visual acuity and color vision

Question 31

retina function

Answer 31

Photoreceptor cells take light focused by the cornea and lens and convert it into chemical and nervous signals which are transported to visual centers in the brain by way of the optic nerve.

In the visual cortex of the brain (which, ironically, is located in the back of the brain), these signals are converted into images and visual perceptions.

Question 32

conjunctiva

Answer 32

the clear, thin membrane that covers part of the front surface of the eye and the inner surface of the eyelids

Question 33

2 segments of the conjunctiva

Answer 33

• Bulbar conjunctiva* covers the anterior part of the sclera and stops at the junction between the sclera and cornea; it does not cover the cornea.
• Palpebral conjunctiva* covers the inner surface of both the upper and lower eyelids. (also called the tarsal conjunctiva)

Question 34

This feature makes it impossible for a contact lens (or anything else) to get lost behind your eye

Answer 34

The bulbar and palpebral conjunctiva are continuous

Question 35

conjunctiva function (5)

Answer 35

• keep the front surface of the eye moist and lubricated
• keep the inner surface of the eyelids moist and lubricated so they open and close easily without friction or irritation
• protect the eye from dust, debris, and infection-causing microorganisms
• has many small blood vessels that provide nutrients to eye and lids
• also contains special cells that secrete a component of the tear film to help prevent dry eye syndrome

Question 36

cornea

Answer 36

• the clear front surface of the eye

- lies directly in front of the iris/ pupil, and allows light to enter the eye

Question 37

Viewed from the front of the eye, the cornea appears

Answer 37

slightly wider than it is tall

Question 38

cornea function

Answer 38

-provides approximately 65 -75% of the focusing power of the eye

Question 39

Most refractive errors — nearsightedness, farsightedness and astigmatism — are due to

Answer 39

less-than-optimal curvature or symmetry of the cornea

Question 40

Presbyopia, on the other hand, is due to

Answer 40

an aging change in the crystalline lens

Question 41

The eye’s crystalline lens

Answer 41

located directly behind the pupil and further focuses light

Through a process called accommodation, this lens helps the eye automatically focus on near and approaching objects, like an autofocus camera lens