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Optics Block 8 > Biometry/ Ocular Imaging > Flashcards

Biometry/ Ocular Imaging Flashcards

1
Q

Measurement of basic data relating to the anatomical dimensions of the eye

A

Biometry

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2
Q

Is biometry quantitative or qualitative

A

Quantitative

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3
Q

Is ocular imaging qualitative or quantitative

A

Qualitative

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4
Q

Techniques that provide imaging of any part of the eye. Help document and facilitate diagnosis and treatment

A

Ocular imaging

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5
Q

What is the oldest form of ocular imaging

A

Slit lamp

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6
Q

What is now an integral part of the eye exam today

A

Ocular imaging

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7
Q

One dimensional depth plot

A

The A scan

  • A=axial
  • time of flight converted to distance
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8
Q

Axial resolution

A

-smallest distinction we can make along axis of propagation

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9
Q

Things we can measure with A scan

A
  • axial length
  • AC depth
  • corneal thickness
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10
Q

What is axial resolution dependent on

A

Wavelength

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11
Q

Two-D plot for anatomical resemblance

A

B-scan

B for brightness

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12
Q

Combination of multiple A scans

A

B scan

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13
Q

What is all different between optical and acoustical

A

Wavelength, physics, results

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14
Q

What are some constraints on ocular imaging

A
  • absoprtion by tissue
  • wavelength
  • focal length
  • F#
  • resolution
  • depth range
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15
Q

What is the F#

A

Related to the resolution of the eye

F# of the eye=8.3

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16
Q

What is confocal good for

A

Powerful to show you cell morphology of the cornea

  • limited to thin layer
  • not as much depth
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17
Q

Acoustical modalities of imaging

A
  • ultrasound waves (8-80MHz)
  • axial res dependent on wavelength
  • good penetration
  • high speed in dense material
  • signal dependent on change in impedance
  • res better for small wavelengths (higher freq)
  • time of flight measurement converted to depth
  • requires immersion coupling and is often contact technique
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18
Q

What the main difference between acoustical vs optical modalities

A

Acoustical is contact, optical is noncontact

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19
Q

Optical modalities

A
  • visible or infrared
  • axial res dependent on wavelength
  • poor penetration
  • signal depended on change in refractive index
  • slower speed in dense media
  • res is better for smaller wavelengths, typically better than acoustical
  • interferometric measurements converted to depth
  • no contact
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20
Q

what is a qualitative mode of imaging that detects tumors

A

MRI

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21
Q

Reflection of elastic wave due to different elastic modulus

A

Ultrasound/ultrasonography

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22
Q

Is sound slower or faster in water

A

Faster

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23
Q

Is light slower or faster in water

A

Slower

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24
Q

An ultrasound system operating at 10MHz has axial resolution of 120 microns. A high frequency US operates at 30 HMz. It’s axial res is

A

40 microns

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25
Q

What kind of sound does ultrasound use

A

Very high frequency, 1000x higher than what humans can hear

26
Q

What happens to wavelength when frequency increases

A

Decreases

27
Q

What happens to resolution when wavelength is lower

A

Increased

28
Q

A scan or B scan: quantitative, numbers

A

A scan

29
Q

A scan or B scan: cross section, morphology, qualitative, shapes

A

B scan

30
Q

Traditional ultrasound

A
  • 8-20MHz sound waves
  • contact
  • no sublayer pach
  • low res, no 2D
  • not reliable peripherally
  • most common method used clinically
  • fast, simple technique
  • not accurate for edematous corneas
  • difficult to reposition
31
Q

Pros of ultrasound

A
  • penetration through opaque ocular media
  • portability
  • fast, simple
  • widely established, common clinical method
32
Q

Cons of ultrasound

A
  • repeatability, dissimulation to reposition, stadaradized
  • not reliable for periphery
  • possible risk of corneal abrasion
  • requires contact (need for anesthetic)
33
Q

Traditionally employed for axial length measurements and corneal pachymetry

A

Ultrasound imaging

34
Q

Uses a probe stylus and requires immersion coupling and applanation

A

Ultrasound

35
Q

Helps assess various ocular and orbital diseases

A

Ultrasound

36
Q

What can penetrate behind the iris

A

Ultrasound

37
Q

A UBM system operates on a 30 micron wavelength, its axial resolution is

A

30

Should be about the same as wavelght

38
Q

In UBM, what is the reflection amplitude proportional to

A

Impedance gradient

39
Q

Resolution of UBM

A

Dependent on wavelength; the higher the frequency, the better the resolution

40
Q

What is the limitation of optica imaging

A

Can’t penetrate tissue

41
Q

Visualization of the iridocorneal angle, anterior lens, ciliary sulcus

A

UBM

42
Q

LASIK flap and epithelial visualization

A

Epithelium is the small layer on top
Flap is about 2x thick as epithelium
CCT is the whole thing

43
Q

When you add the epithelial thickness and the stromal thickness in the center, what do you get on the pentacam

A

CCT

44
Q

Pros of arcscan UBM

A
  • high res
  • epithelial and stromal thickness maps
  • corneal sublayer pachymetry, lamellar graft, and flap imaging
45
Q

Cons of arcscan UBM

A

Patient uncomfortable data acquisition process

  • difficult to maintain centration, long acquisition time
  • significant capital acquisition cost
46
Q

What’s the difference between A scan and optical lower coherence reflectomerty

A

Optical low coherence reflectometyr is higher res

47
Q

How is the time of flight measure in optical low coherence reflectometery

A

Interferometry

48
Q

Examples of optical low coherence reflectometry

A
  • IOL master

- LenSta Ls900

49
Q

Infrared interferometry (similar to OCT), non contact

A

Optical low coherence reflectometry

50
Q

Sublayer pachymetry and optical low coherence reflectomerty

A

Limited potential

51
Q

What does optical low coherence reflectometry provide

A

A number of biometry data including axial length, anterior chamber depth, and pachymetry

52
Q

Tight focusing and increased contrast through equal-optical length illumination and detection optical paths

A

Confocal microscopy

53
Q

What is the confocal microscopy important for

A

Cellular morphology, detects microbial presence

54
Q

Can confocal microscopy do pachymetry?

A

Yes, but VERY slowly

55
Q

Things about confocal microscopy

A

-tight focus though corneal structures
-contact
-high res with sublayer pachymetry and cellular debris
-2D
=periphery requires repositioning
-cellular morphology; detects microbial presence
-high res, can quantify haze/scatter
-slow, poor penetration of opacity

56
Q

Which modality to use for intraorbital features

A

MRI

57
Q

Which modality or use to image cell morphology

A

Confocal microscopy

58
Q

Which modality to sue to image the epithelial layer

A

Ultrasound biomicroscopy

59
Q

Which modality to use for quick pachymetry

A

Ultrasound

60
Q

Which modality to use to image the vitreous when corneal opacity is present

A

If you want numbers: ultrasounds

If you want pictures: UBM

61
Q

Which modality to sue to image the ciliary sulcus structures

A

UBM

62
Q

Which modality to use to measure axial length with the best precision

A

Optica low coherence interferometry

Optics Block 8 (9 decks)

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