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Optics Block 8 > Axial Length > Flashcards

Axial Length Flashcards

1
Q

What is the normal axial length

A

22-24mm

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2
Q

In combination with the corneal curvature, it determined the refractive state of the eye

A

Axial length

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3
Q

What is axial length important for

A

Calculating the power for the IOL along with keratometry

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4
Q

With an axial length of 20mm, we may suspect

A

HYPEROPE

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5
Q

With an axial length of 26mm, we may suspect

A

Myopia

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6
Q

Long eye

A

Myopic

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7
Q

Short eye

A

Hyperopic

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8
Q

What is the axial length in myopes

A

Longer than 24mm

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9
Q

What is the axial length in hyperopes

A

Shorter than 24mm

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10
Q

What does each mm of axial mismatch correspond to

A

2.3D to 3.4D of a refractive deviation

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11
Q

Separation between the posteiror corners and the anterior lens

A

Anteiror chamber depth

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12
Q

Normal AC depth

A

3.0-3.4 mm

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13
Q

What happens to the AC depth with age

A

Decreases to 2.0mm

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14
Q

What happens to axial length with age

A

Nothing

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15
Q

AC depth and cataract

A

Cataracts decrease AC depth

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16
Q

How soon should you treat a closed angle

A

ASAP, within 2 days

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17
Q

Anterior chamber volume

A

220 and 171 +- 36 microliters

About 0.007 fluid ounces

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18
Q

Anterior angle chamber (iridocorneal angle) normal range

A

30 degrees

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19
Q

Anterior chamber angle less than 30

A

Narrow

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20
Q

Anterior chamber angle more than 30

A

Wide open

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21
Q

The angle formed by the posteiror cornea at the root of the iris

A

Anteiror chamber angle

22
Q

What is associated with small anteiror chamber depth

A

Cataracts and glaucoma

23
Q

The measurement of pupil diameter

A

Pupilometry

24
Q

Clinical importance for pupilometry

A

Selection of optical zone in laser refractive surgery

25
Q

Clinical importance of centroid shift

A

IOL andLaser ablation centration

26
Q

Best way to measure pupils

A

Infrared

27
Q

What size pupil should you look at when picking optical zone size

A

Scotopic

28
Q

Centroid shift

A

When the pupil dilates, it doesn’t necessarily stay in the center

29
Q

Cyclotorsion

A

When pt lay done, there eyes rotate about 10 degrees. You don’t want to be off by more than 3 degrees

30
Q

Measuring the thickness of the cornea

A

Corneal pachymetry

31
Q

Why is it not easy measuring the corneal thickness

A

It is not the same thickness throughout

32
Q

What is the most reliable pachymetry

A

Cornea pachymetry map

33
Q

The thickness of the cornea at the pupil center

A

CCT

34
Q

Where is the cornea thickest

A

Superonasal

35
Q

Is corneal thickness symmetric

A

No

36
Q

What are the two numbers we report for corneal pachymetry

A

CCT and MinCT

37
Q

Corneal enantiomorphic symmetry

A

Inferotemporal cornea should be the thinnest

38
Q

Corneal thickness in the morning

A

Thicker

39
Q

Measuring corneal pachymetry between two different eyes

A

Will not give you the same numbers

40
Q

Where is the corneal thinnest

A

Apex (minCT), slightly inferotemporal

41
Q

What is CCT defined at

A

The pupil center

42
Q

Average CCT

A

520-580

43
Q

CCT and age

A

No change

44
Q

When is CCT thicker

A

Upon waking

45
Q

Between two different devices, what kind of difference will you see in measuring CCT

A

20 microns difference

46
Q

Why is corneal thickness important

A

It can mask an accurate reading of eye pressure

47
Q

When is IOP underestimated

A

Thinner CCT

48
Q

When is IOP overestimated

A

Thicker CCT

49
Q

What kind of cornea will you see in corneal dystrophy

A

Thick

50
Q

Ocular health indicators of thick cornea

A
  • endothelial cell damage, Fuchs dystrophy
  • corneal edema, bullus keratopathy, posteiror polymorphous dystrophy
  • herpes keratitis, DM, hyperglycemia
51
Q

Principle of operation of scheimpflug image pachymetry

A

High resolution, high depth of field imaging

52
Q

What did scheimpflug do

A

Tilt the lens

Optics Block 8 (9 decks)

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