How We See 1 - refraction/accommodation

Question 1

What is refraction?

Answer 1

Bending of light due to transition from travelling through one medium to another
Different speeds through different mediums

Question 2

Which parts of the eye bend light as it enters?

Answer 2

Cornea and lens

Question 3

Why does the lens need to change shape to see objects that are closer?

Answer 3

Because when an object is closer only the divergent rays hit the cornea (physics stuff)
Light is not hitting the eye at parallel, it is coming at an angle so the lens needs to change shape to focus it

Question 4

What bends light more, the cornea or the lens?

Answer 4

The cornea - but it can’t change its shape

Question 5

What is accommodation? 3 things that occur to accomplish it?

Answer 5

The capacity to change focus from distant objects to close objects

• Lens changes shape
• Pupil constricts
• Eyes converge

Question 6

When the ciliary muscle contracts what happens?

Answer 6

The ciliary body bulges and and the two halves become closer together
This releases tension of the zonules on the lens and so it becomes thicker

Question 7

Nerve that innervates the ciliary muscle?

Answer 7

Oculomotor (CN III)

Question 8

How does the constriction of the pupil contribute to accommodation? Muscle responsible?

Answer 8

When objects are closer the pupil constricts to allow only a few light rays in - increases sharpness of focus

Sphincter pupillae (CN III)

Question 9

When focusing on something close, what extrinsic muscle of the eye contracts? What does this do to the position of the eye?

Answer 9

• Medial rectus muscle (CN III)

- Causes the corneas of the eyes to converge, rotates the eyeball medially

Question 10

What are the refractive errors of the eye?

Answer 10

1. Myopia - short sightedness
2. Hyperopia - long sightedness
3. Astigmatism - non-spherical curvature of cornea
4. Presbyopia - long sightedness of old age

Question 11

What is someone with perfect vision called?

Answer 11

An Emmetrope (they have emmetropia)

Question 12

What is short sightedness? Long sightedness?

Answer 12

Short - can see up close but objects far away are blurry

Long - Can see things far away but up close is blurry

Question 13

Most common reason for myopia?

Answer 13

The eyeball is too long

Object focuses before it hits the retina

Question 14

Signs of myopia?

Answer 14

• Divergent squint (eyes don’t converge on close objects)
• Headaches
• Complain of blurry vision far away

Question 15

What type of glasses correct myopia? How do they do so?

Answer 15

Biconcave glasses

They diverge the light so that it focuses further back in the eye (on the lens)

Question 16

Possible treatments for myopia/hyperopia?

Answer 16

• Glasses
• Contacts
• LASIK surgery to reshape cornea

Question 17

Most common reason for hyperopia?

Answer 17

Eyeball is too short

Object focuses behind retina

Question 18

Signs of hyperopia?

Answer 18

• Eyestrain (discomfort after reading/computer work)

- Convergent squint (can become lazy eye if untreated)

Question 19

How do biconvex lenses correct hyperopia?

Answer 19

Converge the light rays so they’ll focus sooner

Question 20

What is astigmatism?

Answer 20

Unequal curvature of the lens or cornea in the horizontal and vertical planes - improperly curved lens/cornea

Question 21

Type of lenses that correct astigmatism and how?

Answer 21

Cylindrical lenses

Curved more on one side than the other to correct for incorrect curvature in the eye

Question 22

Type of contacts needed for an astigmatic?

Answer 22

Toric lenses

different because they need to be weighted more on one side so that they rotate to the right orientation when placed in the eye - because improper curvature requires specific lens orientation to correct

Question 23

What causes presbyopia?

Effect?

Answer 23

Lens becomes less elastic and so can’t change its shape (contract) as much anymore

Nearby objects become hard to see

Question 24

When does presbyopia usually start? What type of lens corrects it?

Answer 24

Usually begins in 5th decade of life

Corrected by use of biconvex lenses

Question 25

On a lens prescription what does a negative number indicate? A positive number?

Answer 25

• Negative - myopia

Positive - hyperopia