Chapter 49

Question 1

What do convex lenses do to light passing through? How about concave lenses?

Answer 1

• Convex lenses converge light rays onto a single point (the focal point)
• Concave lenses diverge light rays

Question 2

What is the definition of a focal point?

Answer 2

the distance beyond a convex lense at which parallel ray converge to a common point

Question 3

What is the formula for determining focal point?

Answer 3

1/f = 1/a + 1/b

f= focal length

a= distance of the light point source

b= distance of the focal point on the other side of the lens

Question 4

What is a diopter a measue of?

Answer 4

-refractory power

Question 5

What is the equation to calculate diopters?

Answer 5

Diopter= 1meter / focal length

-e.g. focal length of .5m has a diopter of +2 and 0.1 has a diopter of +10

Question 6

When is a diopter a negative value?

Answer 6

• When the focal point is in front of the lens (concave lenses).
• e.g. is concave cylindrical leses

Question 7

In a relaxed state, what is the shape of the lense?

Answer 7

Flattened

Question 8

What is the role of suspensory ligaments in the control of lens shape?

Answer 8

• Attach to the anterior border of the choroid and retina
• pull the lens edges towards the outer circle of the eyeball

Question 9

What are the two sets of ciliary muscles?

Answer 9

• meridional
• circular fibers

Question 10

What do the meridional muscles cause when they contract?

Answer 10

-They pull the insertion of the suspensory ligament closer to the origin and release tension on the lens

Question 11

What is the role and action of the circular portion of the ciliary muscles?

Answer 11

• act like a sphincter decreasing the diameter of the circle of ligaments
• again releasing tension on the ligaments and lens

Question 12

How is the ciliary muscle controlled?

Answer 12

-almost entirely by parasympathetics riding on CNIII

Question 13

What is presbyopia? What causes it?

Answer 13

• a progressive inability to focus on near objects
• caused by a progressive thickening and inelasticity of the lens which, in old age, eventually leads to the inability of the lens to change shape at all (0 diopters)

Question 14

What are the two roles of the pupil?

Answer 14

• control the amount of light entering the eye
• increase depth of focus by constricting

Question 15

What is the name for ‘normal’ vision?

Answer 15

-emmetropia

(from greek emmetro meaning ‘well-fiting’)

Question 16

What does it mean to have emmetropic vision?

Answer 16

Means that distant parallel light rays are focused sharply on the retina when the ciliary muscle is completely relaxed

Question 17

What condition is known as far-sightedness? What are some characteristics?

Answer 17

• hyperopia
• caused by an eyeball that is too short for the lens system or a lens that is too weak
• parallel light rays are focused behind the retina

Question 18

Can a person correct for hyperopia?

Answer 18

• yes
• the lens can relax (accomodate) to bring the focal point onto the retina

Question 19

What is near-sightedness? What are some characteristics?

Answer 19

• Myopia
• eyeball that is too long or a lens that has too much refractive power when relaxed

Question 20

Can a person with myopia compensate for their deficit?

Answer 20

• no
• a person with myiopia has a definite ‘far point’ beyond which they are unable to focus

Question 21

How does one correct for myopia?

Answer 21

By placing a concave lens infront of the eye to diverge the incoming rays before they enter the eye.

Question 22

What is a stigmatism? How is it corrected?

Answer 22

• When light rays passing through an eye have different focal points at perpendicular planes.
• with AWESOME physics: First the focal point of one plane is determined using a set of black bars to focus on (looks like a clock), then that is held constant while the other plane is determined and corrected for.

Question 23

What is a cataract?

Answer 23

-denatured proteins which form a cloudy or opaque area in the lens

Question 24

Hoe are cataracts corrected?

Answer 24

-surgical removal and replacement with either a plastic implant lens or very powerful convex lenses

Question 25

How is visual acuity interpreted?

Answer 25

comparison to the distance that a normal person can see what you can see at 20

• 20/20
• 20/200 (you can see at 20 feet what a normal person can see at 200 feet)

Question 26

How does a person have depth perception from sizes of retinal images of known objects?

Answer 26

-Brain learns how big an object is, therefore a person can estimate the distance of an objuect based on the size of the image projected on the retina

Question 27

What does moving paralax have to do with depth perception?

Answer 27

-when a person moves their head, images that are closer move by quickly while distant objects remain almost stationary

Question 28

What is the name for binocular vision?

Answer 28

Steropsis

Question 29

How does steropsis contribute to depth perception?

Answer 29

-at close range, the image reaching each eye is slightly different the brain uses this to calculate an objects distance and therefore 3D

Question 30

What is the sole method for depth perception at close range? Does it work at long range?

Answer 30

• Stereopsis (binocular vision)
• useless beyond 50-200 feet depending on the person

Question 31

What is the location of the aqueous humor? What about the vitreous humor? Which one is receycled and regulates IOP?

Answer 31

• The aqeuous humor lies infront of the lens and is constantly formed and resorbed (therefore regulates IOP)
• The vitreous humor lies between the back of the lens and the retina and is not made or resorbed

Question 32

Trace the path of aqueous humor through the eye:

Answer 32

-Ciliary processes–> in front of lens–> around pupil into anterior chamber–> corneal angle–> canal of schlemm–> extraocular veins

Question 33

What happens if a patient has a hemorrhage or some other event that relases proteins and other solid substances into the eye?

Answer 33

-Glaucoma

Question 34

How does Glaucoma cause blindness?

Answer 34

-Compression of the optic nerve or compression of the retinal artery