Module 1 - Optics and Refraction

Question 1

What is refraction in medicine?

Answer 1

Clinical test in which a phoropter/loose lenses may be used to determine the eye’s refractive error and the best corrective lenses to be described

Question 2

Analogy of the camera to the eye
Lens filter
Adjustable diaphragm
Adjustable aperture
Lens
Film
Camera body

Answer 2

Lens filter - cornea
Adjustable diaphragm - iris
Adjustable aperture - pupil
Lens - crystalline lens
Film - retina
Camera body - sclera

Question 3

What are the 2 refracting elements of the eye?

Answer 3

Cornea

Crystalline lens

Question 4

What refracting element acts like a converging lens that accounts for 2/3 refractile power of the eye?

Answer 4

Cornea

Question 5

How many diopters is the cornea?

Answer 5

40 diopters

Question 6

Describe the focal length of the cornea

Answer 6

Constant/fixed

Question 7

What is the shape of the cornea?

Answer 7

Corneal curvature

Question 8

What refracting element acts a converging lens that accounts for 1/3 refractile power?

Answer 8

Crystalline lens

Question 9

What refracting element is thicker at the center than at the edges?

Answer 9

Crystalline lens

Question 10

How many diopters do the crystalline lens have?

Answer 10

20 diopters

Question 11

Describe the focal length of the crystalline lens

Answer 11

Varies by changing the shape of the lens which allows eyes to focus at different distances

Question 12

What is the shape produced by the crystalline lens?

Answer 12

Real, inverted image on the retina

Question 13

What is the central opening of the iris?

Answer 13

Pupil

Question 14

What is the diameter of the pupil in the dark?

Answer 14

Bigger pupil diameter

Question 15

What is the diameter of the pupil in bright light?

Answer 15

Smaller pupil diameter

Question 16

What is the effect smaller pupil?

Answer 16

Reduces spherical aberration (causes image blur)

Question 17

What is the process by which the eye changes in optical power to maintain clear image of an object as its distance varies?

Answer 17

Accommodation

Question 18

What are the near reflex triad?

Answer 18

Accommodation
Convergence
Pupillary miosis

Question 19

What are the events during accommodation?

Answer 19

Ciliary body contracts > slackening of the zonule fibers > lens assumes a spherical shape > lens become more positive > allows eye to have a focused image of near object

Question 20

What happens to the ciliary body, lens zonules and lens when there is distance vision?

Answer 20

Ciliary body is relaxed
Lens zonules are taut
Lens is flat

Question 21

What happens to the ciliary body, lens zonules and lens when there is close vision?

Answer 21

Ciliary body contracts
Lens zonules are relaxed
Lens assumes a spherical shape

Question 22

Describe distance vision

Answer 22

Light rays from distance objects are parallel, so do not need much refraction to focus properly

Question 23

Describe close vision

Answer 23

Light rays from closer objects diverges and need much refraction to focus properly

Question 24

What term is used when parallel light rays are focused sharply on the retina?

Answer 24

Emmetropia

Question 25

What term is used when the eye is unable to bring parallel light rays from a distant object into focus on the retina?

Answer 25

Ametropia

Question 26

What are the 4 types of refractive errors?

Answer 26

Hyperopia Myopia Astigmatism Presbyopia

Question 27

Discuss the incidence of refractive errors

Answer 27

2.3 billion people worldwide suffer from poor vision due to refractive errors 670 million have uncorrected or inadequately corrected refractive errors 90% reside in rural areas and low-income countries One of 5 priority eye diseases of "Vision 2020: Right to Sight" program (WHO)

Question 28

What are the determinants of refractive errors?

Answer 28

Corneal curvature Axial length Loss of accommodation

Question 29

What determinants of refractive errors determines the length of the eyeball?

Answer 29

Axial length

Question 30

What type of refractive errors is known as far-sightedness?

Answer 30

Hyperopia

Question 31

What are the 2 causes of hyperopia?

Answer 31

Insufficient convergence power (lens or cornea) to focus light rays on the retina Short eyeballs

Question 32

To where the rays focus to the retina in hyperopic patients?

Answer 32

Posterior to the retina

Question 33

Who are those people present hyperopia?

Answer 33

Babies Young children *outgrown as they get older and the eyeball gets longer

Question 34

What kind of lens corrects hyperopia?

Answer 34

Plus (convergent) spherical lens

Question 35

What type of refractive errors is known as near-sightedness?

Answer 35

Myopia

Question 36

What are the 2 causes of myopia?

Answer 36

Excessive convergence power (lens or cornea) to focus light rays on the retina Long eyeballs

Question 37

To where the rays focus to the retina in myopic patients?

Answer 37

Anterior to the retina

Question 38

Is myopia genetically-inherited?

Answer 38

Genetically-inherited

Question 39

Who are those people present myopia?

Answer 39

Children between ages 8-12 progresses during teenage years, stabilizes by age 20

Question 40

What kind of lens corrects myopia?

Answer 40

Minus (divergent) spherical lens

Question 41

What type of refractive error occurs when the cornea and crystalline lens may not have same radius of curvature in all meridians?

Answer 41

Astigmatism

Question 42

What type of refractive error has more than 1 focal points?

Answer 42

Astigmatism

Question 43

What type of refractive error results in distortion of vision at all distances?

Answer 43

Astigmatism

Question 44

What kind of lens corrects astigmatism?

Answer 44

Cylindrical lens

Question 45

What type of refractive error has progressive loss of accommodative ability of the crystalline lens caused by the natural process of aging (beginning at age of 40 years old)?

Answer 45

Presbyopia

Question 46

What type of refractive error has progressive hardening of the lens which result to loss of ability to change its shape?

Answer 46

Presbyopia

Question 47

What type of refractive error experiences difficulty with near visual work such as reading, "eye strain"?

Answer 47

Presbyopia

Question 48

Presbyopia occurs in the presence of what 3 refractive errors?

Answer 48

Myopia Hyperopia Astigmatism

Question 49

What kind of lens corrects presbyopia?

Answer 49

Remedied optically with plus spherical lens

Question 50

What 3 means to correct refractive errors?

Answer 50

Spectacle correction Contact lenses Refractive surgeries

Question 51

Spectacle correction is composed of:

Answer 51

Monofocal Bifocal Trifocal/multifocal

Question 52

Contact lenses are composed of:

Answer 52

Spherical | Toric

Question 53

Refractive surgeries consist of what 2 surgeries?

Answer 53

Corrective corneal surgeries | Lens surgeries

Question 54

Corrective corneal surgeries consist of:

Answer 54

Corneal incision | Corneal ablative surgeries

Question 55

What 3 types of surgeries are under corneal incision?

Answer 55

Radial keratotomy Limbal relaxing incisions Partial thickness peripheral incisions

Question 56

What 3 types of surgeries are under corneal ablative surgeries?

Answer 56

``` Photorefractive keratotomy (PRK) Laser-in-situ-keratomileusis (LASIK) Femtosecond LASIK (Intralase) ```

Question 57

What are the 3 types of lens surgeries?

Answer 57

Cataract surgery with implantation of intraocular lens Clear lens surgery + IOL implantation Phakic IOL

Question 58

What intraocular lenses used in lens surgeries?

Answer 58

``` Monofocal Toric Multifocal Multifocal + toric Phalic IOL ```

Question 59

Is contact lens left in place when examining the eye?

Answer 59

Contact lens may be left

Question 60

What are the methods of direct fundoscopy?

Answer 60

1. Patient should be seated comfortably. Instruct the patient to look at a point on the wall straight ahead, trying not to move the eyes 2. Set the aperture wheel to select the large, round, white light 3. Begin to look at the right eye about 1 foot from your patient. Use your right eye with the ophthalmoscope in your right hand. Shine the light to the patient's pupil. Look for red reflex 4. Slowly come close to the patient at an angle of about 15 degrees temporarily to the patient's line of sight 5. When the retinal vessels come into view, follow it as it widens to the optic disc which lies nasal to the center of the retina. If the image is not clear, turn the lens dial up or down until the image is clear 6. Examine the optic disc, retinal blood vessels, retinal background and macula, in that order 7. Repeat for the other eye

Question 61

What is the definition of refraction in physics?

Answer 61

Change in the direction of a wave due to change in its transmission medium - bending of a light wave as it enters a medium where its speed is different