How We See

Question 1

What is refraction?

Answer 1

Bending of light when it passes from one optical medium to another

Question 2

What is accommodation?

Answer 2

Changes occurring in both eyes as it changes focus from a distant to a close object

Question 3

What is refractive errors?

Answer 3

When there is a mismatch between how much we bend light rays

Question 4

How does a sharp image form on the retina?

Answer 4

Light waves from an object bend at the cornea

Then bend more at the lens to form a clear image on the retina = refraction

Question 5

What happens when an object moves closer?

Answer 5

Eye needs more bending power to focus = lens becomes thicker = more powerful = clear image

Question 6

What 3 things happen simultaneously and make up accommodation?

Answer 6

1. Lens changes shape (thicker + more spherical)
2. Pupil constricts
3. Eyes converge

Question 7

What is the process of the lens thickening in accommodation?

Answer 7

Ciliary muscle contracts = makes ciliary body bulge
Space in middle decreases
Suspensory ligaments become lax
Lens is no longer under stretch
Lens = thicker

Question 8

What is the pupillary constrictor?

Answer 8

(sphincter pupillae)
Concentric muscle around border of pupil
Parasympathetic innervation (CN III)

Question 9

What muscles are used in convergence of the eyes?

Answer 9

Medial rectus muscles of both eyes

Question 10

What is myopia?

Answer 10

Short-sightedness

Question 11

What is hyperopia?

Answer 11

Long-sightedness

Question 12

What is astigmatism?

Answer 12

Non-spherical curvature of cornea (or lens)

Question 13

What is presbyopia?

Answer 13

Long-sightedness of old age

Question 14

What does it mean if someone is an emmetrope?

Answer 14

They have perfect vision

Question 15

What causes myopia?

Answer 15

Eyeball too long

When cornea + lens bend light rays they form the image in front on the retina

Question 16

What are symptoms of myopia?

Answer 16

Headaches
Not being able to see distant objects
Infants/preverbal children - divergent squint
Toddlers - loss of interest in sports/people and more interest in books/pictures

Question 17

How is myopia corrected?

Answer 17

Bending power needs to be decreased
Biconcave lenses (glasses, contact lenses or laser eye surgery)

Question 18

What causes hyperopia?

Answer 18

Eyeball too short or cornea + lens too flat
Image is formed behind retina
Using all power to see things far away

Question 19

What are the symptoms of hyperopia?

Answer 19

Eyestrain after reading/working on a computer
Convergent squint (children/toddlers)
Squint must be corrected quickly to prevent lazy eye

Question 20

How is hyperopia corrected?

Answer 20

Biconvex glasses (able to rest accommodative power)
Contact lenses
Laser eye surgery

Question 21

What causes astigmatism?

Answer 21

Surface has different curvatures in different meridians
Bending of light different on opposite axis
Image formed is hazy

Question 22

How is astigmatism corrected?

Answer 22

Special glasses = cylindrical glasses
Curved only in 1 axis
Laser eye surgery
Special contact lenses (toric lenses)

Question 23

What causes presbyopia?

Answer 23

Lens get less mobile/elastic with age
When ciliary muscle contracts, it isn’t as capable as before to change shape
Usually in 5th decade of life

Question 24

How is presbyopia corrected?

Answer 24

Biconvex “reading” glasses