Optics of the Visual System

Question 1

Describe the phenomenon of refraction

Answer 1

When light travels through one medium to another it changes velocity causing the ray to refract, this makes it bend

Question 2

What is the equation for calculating index of refraction?

Answer 2

Speed of light in a vacuum/speed of light in the medium (n= c/Vn)

Question 3

What should the index of refraction always be?

Answer 3

Greater or equal to 1 because the denominator is always smaller than the numerator

Question 4

When the light goes from less dense to more dense where does it bend?

Answer 4

Towards the normal

Question 5

How many types of lens are there? What are they called?

Answer 5

2 types:
Concave
Convex

Question 6

Describe the properties of a convex lens

Answer 6

Converging lens that causes light rays to come together at a point

Question 7

Describe the properties of a concave lens

Answer 7

A diverging lens that causes light rays to spread away from each other

Question 8

What is ametropia?

Answer 8

Refractive error, there is a mismatch between axial length and refractive power
This means parallel rays don’t fall on the retina and there’s no accomodation

Question 9

What is the medical name for near sightedness?

Answer 9

Myopia

Question 10

What is the medical name for far sightedness?

Answer 10

Hyperopia

Question 11

What are the types of ametropia?

Answer 11

Myopia (nearsightedness)
Hyperopia (farsightedness)
Astigmatism
Presbyopia

Question 12

What happens to light rays in those with myopia?

Answer 12

Light rays converge at a point anterior to the retina

Question 13

What are the types of myopia? Describe them

Answer 13

Axial myopia= excessively long globe

Refractive myopia= excessive refractive power

Question 14

What type of myopia is more common?

Answer 14

Axial myopia

Question 15

What are symptoms of myopia?

Answer 15

Blurred distance vision
Squinting to help overcome this
Headache as a result

Question 16

How is myopia corrected?

Answer 16

A) Diverging lens (negative power)
B) Contact lens
C) Removal of lens to reduce refractive power

Question 17

What happens to light rays in those with hyperopia?

Answer 17

Light rays converge at a focal point posterior to the retina

Question 18

What are the types of hyperopia? Describe them

Answer 18

Axial hyperopia= excessively short globe

Refractive hyperopia= insufficient refractive power

Question 19

What type of hyperopia is more common?

Answer 19

Axial

Question 20

Do those with near sightedness struggle to see near or far objects?

Answer 20

Far

Question 21

Do those with far sightedness struggle to see near or far objects?

Answer 21

Near

Question 22

Do those with myopia struggle to see near or far objects?

Answer 22

Far

Question 23

Do those with hyperopia struggle to see near or far objects?

Answer 23

Near

Question 24

What are symptoms of hyperopia?

Answer 24

Blurred vision when looking at things up close eg reading,
- worse if there is reduced light, print is weak or if person is tired
Asthenopic symptoms: eye pain, headache in frontal region, burning in eyes, blepharoconjunctivitis

Question 25

What do we call uncorrected hyperopia? And what refraction do they have?

Answer 25

Amblyopia | Refraction above 5D

Question 26

How is hyperopia corrected?

Answer 26

A) converging lens (positive power) B) contact lens C) correction with intraocular lens D) correction with positive lens and cataract extraction

Question 27

What happens to light rays in astigmatism?

Answer 27

Parallel rays focus in 2 focal lines instead of at a singular focal point because the refractive media is not spherical

Question 28

What are symptoms of astigmatism?

Answer 28

Asthenopic symptoms: Headache, eye pain blurred vision distorted vision head tilting/turning

Question 29

How is astigmatism treated?

Answer 29

Regular astigmatism: Cylinder lens with or without spherical lens (convex/concave) Irregular astigmatism: rigid cylinder lens, surgery

Question 30

What is the near response triad? Describe it

Answer 30

Its how the eye adapts to look at close objects 1) pupillary miosis (by sphincter pupillae) to increase depth of field 2) convergence (by medial recti of both eyes) to align both eyes towards a near object 3) accomodation (by circular ciliary muscle) to increase the refractive power of the lens

Question 31

What is presbyopia?

Answer 31

Naturally occuring loss of accommodation | Distant vision intact

Question 32

What is accomodation?

Answer 32

Focus on near objects

Question 33

At what age is there usually onset of presbyopia?

Answer 33

40 years

Question 34

How is presbyopia corrected?

Answer 34

``` Convect lenses: -Reading glasses -Bifocal glasses -Trifocal glasses -Progressive power glasses Contact lenses: Given for cosmetic, athletes, occupational, irregular corneal astigmatism, high anisometropia, corneal disease ```

Question 35

What are the 3 main types of optical correction?

Answer 35

Contact lens Intraocular lens Surgical correction

Question 36

What are some advantages of contact lens?

Answer 36

Higher quality of optical image, influences the size of the image less than spectacles

Question 37

What are some disadvantages of contact lens?

Answer 37

They need careful daily cleaning and disinfection, they're expensive

Question 38

What is the best use of intraocular lens?

Answer 38

The replace the cataract crystalline lens Optical correction of aphakia (no crystalline lens) as they avoid significant magnification and distortion via spectacles

Question 39

What happens when the lens is cleared surgically?

Answer 39

Patients loose the ability to accomodate and require reading glasses

Question 40

What happens to the zonules and lens in accomodation?

Answer 40

Zonules relax | Lens thickens and increases in their refractive power

Question 41

What is emmetropia?

Answer 41

Adequate correlation between axial length and refractive power Parallel light rays fall on the retina

Question 42

What are complications of contact lenses?

Answer 42

Infectious keratitis, giant papillary conjunctivitis, corneal vascularisation, severe chronic conjunctivitis

Question 43

What are types of surgical corrections?

Answer 43

Keratorefractive surgery: RK,AK, PRK, LASIK, ICR, thermokeratoplasty Intraocular surgery: clear lens extraction (with or without IOL). phakic IOL

Question 44

What kind of lens is inserted for the correction of myopia or astigmatism?

Answer 44

Intra-collamer lens (ICL)

Question 45

What is IOL?

Answer 45

Intra ocular lens | Its the implantation of an artificial lens