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Ophthalmology > Module 1 - Optics and Refraction > Flashcards

Module 1 - Optics and Refraction Flashcards

1
Q

What is refraction in medicine?

A

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

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2
Q 
Analogy of the camera to the eye
Lens filter
Adjustable diaphragm
Adjustable aperture
Lens
Film
Camera body
A 
Lens filter - cornea
Adjustable diaphragm - iris
Adjustable aperture - pupil
Lens - crystalline lens
Film - retina
Camera body - sclera
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3
Q

What are the 2 refracting elements of the eye?

A

Cornea

Crystalline lens

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4
Q

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

A

Cornea

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5
Q

How many diopters is the cornea?

A

40 diopters

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6
Q

Describe the focal length of the cornea

A

Constant/fixed

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7
Q

What is the shape of the cornea?

A

Corneal curvature

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8
Q

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

A

Crystalline lens

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9
Q

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

A

Crystalline lens

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10
Q

How many diopters do the crystalline lens have?

A

20 diopters

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11
Q

Describe the focal length of the crystalline lens

A

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

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12
Q

What is the shape produced by the crystalline lens?

A

Real, inverted image on the retina

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13
Q

What is the central opening of the iris?

A

Pupil

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14
Q

What is the diameter of the pupil in the dark?

A

Bigger pupil diameter

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15
Q

What is the diameter of the pupil in bright light?

A

Smaller pupil diameter

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16
Q

What is the effect smaller pupil?

A

Reduces spherical aberration (causes image blur)

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17
Q

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

A

Accommodation

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18
Q

What are the near reflex triad?

A

Accommodation
Convergence
Pupillary miosis

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19
Q

What are the events during accommodation?

A

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

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20
Q

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

A

Ciliary body is relaxed
Lens zonules are taut
Lens is flat

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21
Q

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

A

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

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22
Q

Describe distance vision

A

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

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23
Q

Describe close vision

A

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

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24
Q

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

A

Emmetropia

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25
Q

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

A

Ametropia

26
Q

What are the 4 types of refractive errors?

A

Hyperopia
Myopia
Astigmatism
Presbyopia

27
Q

Discuss the incidence of refractive errors

A

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)

28
Q

What are the determinants of refractive errors?

A

Corneal curvature
Axial length
Loss of accommodation

29
Q

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

A

Axial length

30
Q

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

A

Hyperopia

31
Q

What are the 2 causes of hyperopia?

A

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

32
Q

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

A

Posterior to the retina

33
Q

Who are those people present hyperopia?

A

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

34
Q

What kind of lens corrects hyperopia?

A

Plus (convergent) spherical lens

35
Q

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

A

Myopia

36
Q

What are the 2 causes of myopia?

A

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

37
Q

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

A

Anterior to the retina

38
Q

Is myopia genetically-inherited?

A

Genetically-inherited

39
Q

Who are those people present myopia?

A

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

40
Q

What kind of lens corrects myopia?

A

Minus (divergent) spherical lens

41
Q

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

A

Astigmatism

42
Q

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

A

Astigmatism

43
Q

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

A

Astigmatism

44
Q

What kind of lens corrects astigmatism?

A

Cylindrical lens

45
Q

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)?

A

Presbyopia

46
Q

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

A

Presbyopia

47
Q

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

A

Presbyopia

48
Q

Presbyopia occurs in the presence of what 3 refractive errors?

A

Myopia
Hyperopia
Astigmatism

49
Q

What kind of lens corrects presbyopia?

A

Remedied optically with plus spherical lens

50
Q

What 3 means to correct refractive errors?

A

Spectacle correction
Contact lenses
Refractive surgeries

51
Q

Spectacle correction is composed of:

A

Monofocal
Bifocal
Trifocal/multifocal

52
Q

Contact lenses are composed of:

A

Spherical

Toric

53
Q

Refractive surgeries consist of what 2 surgeries?

A

Corrective corneal surgeries

Lens surgeries

54
Q

Corrective corneal surgeries consist of:

A

Corneal incision

Corneal ablative surgeries

55
Q

What 3 types of surgeries are under corneal incision?

A

Radial keratotomy
Limbal relaxing incisions
Partial thickness peripheral incisions

56
Q

What 3 types of surgeries are under corneal ablative surgeries?

A 
Photorefractive keratotomy (PRK)
Laser-in-situ-keratomileusis (LASIK)
Femtosecond LASIK (Intralase)
57
Q

What are the 3 types of lens surgeries?

A

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

58
Q

What intraocular lenses used in lens surgeries?

A 
Monofocal
Toric
Multifocal
Multifocal + toric
Phalic IOL
59
Q

Is contact lens left in place when examining the eye?

A

Contact lens may be left

60
Q

What are the methods of direct fundoscopy?

A
  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
61
Q

What is the definition of refraction in physics?

A

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

Ophthalmology (3 decks)

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