Lecture 2 How We See

Question 1

Define refraction

Answer 1

• Change of speed when light passes from different mediums

Question 2

When light passes through the cornea and lens

Answer 2

Light waves from an object ben at the cornea, and ben some more at the lens to form a clear image on the retina

Question 3

Between the Cornea and Lens which one can change their power

Answer 3

The Ciliaris muscle can make the lens more powerful to allow the eye to see objects up close and make the lens biconvex

Question 4

When an object comes closer what does the eye need to do

Answer 4

The eye needs more bending power to focus on the object- the becomes more thicker and rounder

Question 5

Define accommodation

Answer 5

Eyes ability to focus for distant to close objects

Question 6

What 3 things happen silmultaneously during accommodation

Answer 6

o Lens changes shape (becomes thicker & more spherical)
o Pupil constricts
o Eyes converge

Question 7

What causes the lens to become more rounder and fatter when the eye focuses on close objects

Answer 7

Ciliary body contracts

Question 8

What CN brings parasympathetic innervation to the eye muscle

Answer 8

CN III

Question 9

What muscles causes the eyes to converge and move inwards

Answer 9

Medial rectus

Question 10

Between the lateral recti and medial recti what muscle is thicker and why

Answer 10

Medial recti

Humans spend a lot more time ding close work

Question 11

Name the 4 types of refractive errors

Answer 11

Myopia
Hyperopia
Astigmatism
Presbyopia

Question 12

What is Myopia

Answer 12

Can see images up close but not far away (short sightedness )

Question 13

In myopia where does the image seen by the eye form

Answer 13

Forms in front of the retina because the eyeball is too long

Does not need accommodation to see objects up close

Question 14

What are the consequences of myopia

Answer 14

Divergent squint

not using accommodating power that would normally cause your eye to converge, instead it diverges

Question 15

Symptoms of myopia

Answer 15

Headaches
Not being able to see blackboard
Loss of interest in sports/people
More interested in books

Question 16

Myopia correction

Answer 16

o	Bending power needs to be decreased.
o	Biconcave lenses
o	Spectacles
o	Contact lenses
o	Laser eye surgery

Question 17

What is Hyperopia

Answer 17

Cant see objects up close, but can see objects far away

Image forms behind retina as eyeball is too short

Question 18

What is the consequence of hyperopia

Answer 18

The person starts to use accommodation power automatically- using lens power to see far off things
When looking at close objects all their power is used up
Can lead to convergent squint

Question 19

Symptoms of Hyperopia

Answer 19

o Symptoms of eyestrain after reading/ working on the computer in a young individual.
o Convergent squint in children/ toddlers

Question 20

Correction of Hyperopia

Answer 20

o Biconvex glasses alleviates use of glasses for focussing distant objects and ‘rests’ the accomodative power
o Contact lenses
o Laser Eye surgery

Question 21

What is Astigmatism

Answer 21

up close or far away still blurry
• More bending in axis than the other
• 2 images formed and cannot bend to focus on one
• Can be behind or in front of the retina

Question 22

Correction of Astigmatism

Answer 22

• Cylindrical lenses- one axis more bent than the other
• Laser eye surgery can also be used to correct the defect.
• Need special contact lenses called toric lenses

Question 23

What is Presbyopia

Answer 23

• Lens becomes less elastic and more rigid
• Lens is not able to become more spherical when you want to see something up close
• So when the ciliary muscle contracts, it is not as capable as before to change shape
• Usually starts in 5th decade of life.

Question 24

How is Presbyopia corrected

Answer 24

Biconvex reading glasses