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COT > Biometry 4% > Flashcards

Biometry 4% Flashcards

1
Q

What is used to calculate IOL power?

A

Axial length
K power(k curvature)
AC depth
White to White
Lens Constant (aka A constant

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2
Q

The distance from the front of the eye to the macula is—

A

Axial length in 100ths of mm

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3
Q

The measurement of K diameter

A

white to white

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4
Q

A number assigned to an IOL by the implant manufacturer depending on where the IOL sits in the capsular bag

A

Lens Constant (A constant)
Some designed to sit more posteriorly and some anteriorly.

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5
Q

Dr. can customize their IOL calculations based on _____

A

outcomes

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6
Q

All surgeons use the same generic IOL calculations. After a surgeon as performs a certain amount of cases they can do a retrorespective analysis of their refractive outcomes and make adjustments to these IOL calculations to customize them to their particular sx technique. This is called……..

A

Surgeons factor

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7
Q

What IOL calculation formulas are used for short eyes?

A

Hoffer Q
Haigis (multi-Variable Formula)

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8
Q

What IOL calculation formulas are used for longer eyes?

A

SRKT
Holladay II (multi-variable formula)

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9
Q

Which IOL calculation formulas are considered the most accurate? Why are they considered more accurate?

A

Haigis
Holladay II
Olsen
Barrett Universal II
(Because they use multi-variable formulas that take into account many different structures in the eye not just axial length and K readings)

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10
Q

What are the 3 main methods of A-scans?

A

Contact (ultrasound)
Immersion
Optical coherence (LASER light)

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11
Q

This method of Ascan uses ultrasound, there is no K compression, very accurate, uses Prager shell filled with BSS, requires training and skill.

A

Immersion

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12
Q

Ascan method that is not considered good enough anymore because K compression inevitable so it will always give a shorter axial length than any other method of Acan. Uses Topical anesthetic and is susceptible to operator error

A

Contact (ultrasound)

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13
Q

This method of Ascan uses LASER light

A

Optical Coherence (IOL Master)

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14
Q

What is the main advantage of ultrasound over LASER light Ascan?

A

Ultrasound can measure through dense media such a CAT or K opacification, LASER light can not.

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15
Q

These Ascan methods use Laser (not ultrasound), considered Good Standard, is non contact, no anesthetic needed, no risk of patient-patient contamination, very precise, Most accurate K’s, easy to operate, need good tear film, and intraocular lens calc software included.

A

IOL master and Lenstar

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16
Q

What do the peaks on the amplitude scan graph represent?

A

From left to right:
PCAPRS
probe, cornea, anterior lens, posterior lens, retina, sclera

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17
Q

IOL Master and Lenstar is also sometimes referred to as—-

A

Partial Coherence Inferometry
“Optical Biometry”

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18
Q

IOL and Lenstar uses _____to let you know accuracy of measurements.

A

Traffic Light Indicators (Red for bad, green for good)

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19
Q

IOL and Lenstar can measure through many types of media and eyes such as—-

A

Measures aphakic, silicone, and phakic eyes

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20
Q

IOL Master and Lenstar may have difficulty measuring through —-

A

very dense CATS and other media opacities due to using light beams

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21
Q

An Ascan is a ____measurement of the eye.

A

linear

22
Q

An Ascan is a _____dimensional scan

A

1

23
Q

An Ascan has scans in how many dimensions?

A

1

24
Q

A Bscan measures in how many dimensions?

A

2

25
Q

The standardized Ascan uses a _____

A

linear echo wave

26
Q

The standardized Ascan measures the ….

A

axial length of the eye the 100ths of a mm from K to macula

27
Q

A diagnostic Ascan is used to locate…..

A

intraocular FBs

28
Q

The purpose of an standardized Ascan is to ….

A

determine the axial length for IOL power calculations (usually emmetropia)

29
Q

What is measured to get the axial length

A

from corneal to macula

30
Q

In Ascan sound waves travel through _____at varying speeds depending on _______ of tissue.

A

tissue
density

31
Q

In Ascan, sound wave reflect to _______,impulses displayed electronically.

A

Transducer

32
Q

The standardized Ascan uses _____

A

ultrasound

33
Q

Standardized Ascan sends _____through the eye

A

sound waves

34
Q

Depending on the ______of the tissue the sound wave will bounce back to the transducer and make a _____representing different structures of the eye.

A

density
linear graph

35
Q

Ascan uses _____instead of light

A

sound

36
Q

Ascan is accurate even with dense media because…..

A

it uses sound instead of light

37
Q

Ascan measures….

A

axial length, AC depth, Lens thickness.

38
Q

What do the spikes correspond to in an Ascan?

A

structures of the eye

39
Q

The gain in an Ascan is measured in _____

A

decibles

40
Q

What does the gain in Ascan affect?

A

amplification and resolution of display

41
Q

When the gain is higher on Ascan…

A

you get better view of spike height but worse resolution

42
Q

When the gain is lower on Ascan…..

A

Spikes and display sensitivity decreased and improved resolution.

43
Q

In Ascan this is Essentially electronic calipers that measure between 2 points, Biometer sets this to specific anatomical landmarks.

A

Gate

44
Q

True of false:
All Ascans have a gate

A

false

45
Q

If you get more than 3mm difference axial lengths between the 2 eyes or more than 1/10 of a mm difference in a single eye consecutive measurements you should get….

A

another check.

46
Q

Normal axial length is…

A

23.5
range is 22-24.5

47
Q

Normal AC depth is…

A

3.24mm

48
Q

Normal lens thickness is….

A

4.63mm up to 6.9mm for cataractous lens

49
Q

Normal K readings are….

A

43.0-44.0

50
Q

Normal CCT(central K thickness)

A

555

51
Q

Thick K gives a ____reading on IOP

A

higher

52
Q

Thin K gives a ___reading on IOP

A

lower

COT (28 decks)

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