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PRECLIN OD1 > Emmetropia & Ametropia > Flashcards

Emmetropia & Ametropia Flashcards

1
Q

What is emmetropia?

A
  • Conjugate focus of the retina is at infinity, with accommodation relaxed.
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2
Q

Emmetropia @ distance?

A
  • Distance objects are focused sharply on

the photoreceptor plane of the retina

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3
Q

Emmetropic eye @ near?

A

When a near object is viewed
– image is in focus behind the photoreceptors
– image can be brought forward into focus on
the photoreceptors by the process of
accommodation

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4
Q

What is Emmetropia Rx?

A

Generally -0.25 to +0.75 DS

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5
Q

What is Ammetropia?

A

Eyes inability to correctly focus the image of objects on the retina.

  • includes: myopia, hyperopia and astigmatism
  • failure of emmetropisation.
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6
Q

What is myopia?

A

– Generally, eye has grown too long for the remaining refractive components
– Image cannot be brought into focus by
accommodation, lens is too strong
– Distant objects are focused in front of the retina.

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7
Q

Myopia @ near objects?

A

– closer objects can be brought into focus by accommodation

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8
Q

How to correct for Myopia?

A

– concave (diverging) spectacle, contact or intraocular lenses
– move the image onto the retina
– OR refractive surgery to reduce corneal power

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9
Q

What is Myopia Rx?

A
  • Generally ≤ -0.50 DS
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10
Q

What is Hypermetropia/ Hyperopia?

A
  • Generally, eye is too short
  • Distant objects are focused behind the photoreceptors when accommodation is relaxed
  • -> focusing power of the lens is ‘too weak’
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11
Q

Myopia @ distance?

A

Distant objects:
– are focused in front of the retina.
– blurred & near vision is clearer
(= shortsighted)

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12
Q

How do hyperopes focus distant objects?

A

– brought into focus by accommodation
ie. distance vision can be clear if degree of hyperopia is less than accommodative
amplitude
–> latent hyperopes

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13
Q

What can Myopes see?

A

i) Near vision is clear

ii) Distance vision is uniformly blurred

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14
Q

Vision in Px with astigmatism ?

A

Blurry

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15
Q

How to correct Hyperopia?

A
  • positive/ convex lenses

may not be full correction

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16
Q

What is Hyperopia Rx?

A

Generally ≥ +0.75

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17
Q

Define latent hyperopia?

A
  • accommodative amplitude > degree of hyperopia
  • farsightedness that is ‘masked’ when the accommodative muscle are used to increase eye’s focusing power
  • therefore appear to have distant vision
  • don’t require a corrective lens
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18
Q

Complaints made by latent hyperopes?

A
  • tired eyes

- headaches

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19
Q

How to uncover a latent hyperope?

A
  • if Px VA < 6/4.8, assume they are either plano or latent.

- start with +1 blur. allow time for accommodation to relax

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20
Q

How do hyperopes focus near objects?

A
  • At near, diverging light is entering the eyes
  • more + power required to focus light on the retina
  • prescribe reading glasses
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21
Q

What is Astigmatism?

A
  • curvature of the cornea or lens are NOT the same in all merdians
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22
Q

What happens with astigmatism?

A
  • light will bend in all different directions

- different amounts of light will pass through falling on the retina

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23
Q

Consequences of Astigmatism?

A
  • some direction of image more focussed or out of focus than others
  • image is double/ distorted
  • letters difficult to distinguish
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24
Q

What might a Px with astigmatism do?

A

squint eyes

- allows temporary distortion of the cornea for focus

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25
Q

Chart used for astigmatism?

A

Fan and block

- clarity of the lines

26
Q

How is astigmatism classified ?

A

Mixed Astig
Myopic Astig: simple or compound
Hyperopic Astig: simple or compound

27
Q

What are the 2 requirements for astigmatism?

A
  1. > 1 toroidal refracting surfaces of the eye
  2. image of a point object is not a single point but 2 perpendicular lines at different distances from the optical system
28
Q

What are the types of astigmatism?

A

Against the rule
With the rule
Oblique

29
Q

What is ‘against the rule’ astigmatism?

A

blurry in the vertical direction
–> vertical lines are blurry
axis= ~90

30
Q

What is ‘with the rule’ astigmatism?

A

horizontal lines blurry
–> horizontal lines are blurry
axis= ~180

31
Q

What is ‘oblique’ astigmatism?

A

Oblique lines blurry

axis= ~45-135

32
Q

Identify the components of Rx.

A

OD: +1.00/-2.00 x 180

+/- sphere power (DS)/ - cyl (DC) x axis ( 1-180, R to L)

33
Q

What is the cylindrical notation in Australia ?

A

NEGATIVE

*opthalmologist use positive cyl

34
Q

Steps for Rx with cyl?

A

1: pick the most positive as the Sphere power
2: calculate the difference between the two meridians as the cyl power
3: Pick the axis of the most negative as the cyl axis

35
Q

What is the script in negative cyl?
Cyl 1= -0.50DC x 90
Cyl 2= -2.50DC x 180

A

-0.50/-2.00x180

36
Q

What is the script in negative cyl?

Sphere 1= +1.25DC x 45, Sphere 2= -2.50DC x 135

A

+1.25/-3.75x135

37
Q

What is Presbyopia?

A

Difficulty with near work due to lens inflexibility with age, resulting in decreased ability to accommodate.

  • seperate mechanism to ametropia, ‘ADD’ Rx
  • meveryone gets presbyopia
38
Q

What is the onset of Presbyopia?

A

~40-45 years old

39
Q

What are some of the symptoms of presbyopia onset?

A
  • Eye strain/tiredness
  • Emmetropes/ Hyperopes: increased working distance
  • Myopes: removal of SVD
40
Q

How to optically correct for presbyopia?

A

Three ways to correct…
1. positive/ concave lens for near
2. ADDITIONAL Rx (up to +2.50DS) ONTOP of distance (SVD) Rx
(require bifocals, trifocals, multifocal lens)
3. Reading glasses (SVN)

41
Q

What are the type of lenses?

A

Single vision
Bifocal
Multifocal (progressive)
Extended focus (occupational)

42
Q

What are single vision lens?

A

near OR distance vision

43
Q

What are bifocal lens?

A

distance with near section

- use if ADD

44
Q

What are multifocal lens?

A

distance - intermediate - near

  • good for driving
  • intermediate allows for computer work
  • ADD for reading
45
Q

What are extended focus lens?

A

intermediate - near

- computer work

46
Q

What if SVN RX if distance= -4.00DS, ADD= +2.50DS?

A

SVN: -1.50DS

*reading glasses not always positive

47
Q

Rx: plano

A

Emmetropia

48
Q

Rx: -5.50DS

A

Simple Myopia

49
Q

Rx: +2.25/-0.75 x55

A

Compound Hyperopia

*positive DS, has cyl

50
Q

What is compound astigmatism?

A

2 points for on different spots on the retina

- evident when script has cyl and axis

51
Q

Rx: +0.50/-1.00 x 90?

A

Mixed Astigmatism

52
Q

Rx: +1.00DS?

A

Simple Hyperopia

53
Q

Rx: -1.25/1.25 x 180?

A

Compound Myopia

54
Q

Describe what happens to the conjugate focus when looking at an object at a distance, when focus is shifted to a nearer object.

A

At rest on a distant object, the conjugate focus on the retina is at infinity. When focus shifts to a nearer object, the focus is behind the retina, and accommodation must occur to bring it back to the retina.

55
Q

Define far point.

A

Furthest distance at which a relaxed eye can focus on the retina without correction.
- zero accommodation

56
Q

Define the conjugate focal point.

A

object point at infinity and its corresponding image points on the retina

57
Q

What are the factors to consider when refracting Px ametropia?

A
  • corneal curvature
  • axial length
  • lens thickness
58
Q

What are the tools for corrective ametropia?

A
  • minus lens (myope)
  • positive lens (hyperope)
  • cylindrical lenses (astig)
59
Q

What are the steps for correcting a Px with presbyopia?

A
  1. Correct Px ametropia in the distance (including astig).

2. Add a positive spherical lens to the distance Rx

60
Q

Describe the light rays & physiology in presbyopia.

A

Incoming light rays from near objects are divergent. In presbyopia, the lens loses its flexibility accommodate hence unable to correct for the diverging rays, so the light is unfocused and behind the retina.

61
Q

Do ophthalmologists specific cylindrical lenses + or - DC? And why?

A

Ophthalmologist specify cylindrical power as + DC instead of - DC.
This is because lenses used for surgical implantation are front toric and back spherical.

PRECLIN OD1 (1 decks)

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