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Contact lens Year 2 > Unit 3 > Flashcards

Unit 3 Flashcards

1
Q

Diagnostic instruments

A

-Dry eye testing
-Corneal sensation
-Specular microscopy
-Slit lamp assesment
-Burton lamp
-Corneal topography
-Corneal tomography

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2
Q

Diagnostic images

A

Anterior segment OCT
-Images of cross sections of diseased cornea and sclera lens

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3
Q

Radius of curvature

A

-Describes the curve of a surface by referring to the length of the curves radius
-Measured in mm

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4
Q

Short radius means..

A

Small number
Steep CURVE

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5
Q

Long radius means..

A

Large number
Flat curve

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6
Q

Relationship of Corneal power

A

P=(n-1) / r
P= corneal power
n= 1.3375
r= radius of curvature (m)

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7
Q

FOZR

A

Front optic zone radius

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8
Q

BOZR

A

Back optic zone radius
-determins the tear lens between the back surface of the RGP and cornea

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9
Q

BOZD

A

Back optic zone diameter
-Should be 1.5mm large than pupil size

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10
Q

TD

A

total diameter

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11
Q

OAD

A

overall diameter

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12
Q

BVP

A

back vertex power

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13
Q

CT

A

Centre thickness

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14
Q

RGP tear lens - On K (apical alignment)

A

-Zero powered tear lens
balanced tears on end and middle

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15
Q

RGP tear lens - steeper than K (apical clearance)

A

Plus powered tear lens
flatter tears at the end, bigger tears in the middle

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16
Q

RGP tear lens -flatter than K (apical bearing)

A

Minus powered tear lens
larger tears at the end , thinner tears in middle

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17
Q

Ideal GP fit

A

-centered over pupil
-Visual axis remains BOZD
-TD at least 1.4mm less than HVID (promotes tear exchange)
-Movement 1 to 1.5mm with each blind which allows tear exchange and removes debris in tear lens
-Edge clearance less than 1mm width
-Lid attachment vs interpalpebral fit

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18
Q

SAM rule

A

Steeper Add Minus

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19
Q

FAP rule

A

Flatter add plus

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20
Q

General rule

A

For every 0.05mm the rgp base curve is changed, the tear lens increased or decreased by 0.25D

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21
Q

If we steepen a lens we create a plus powered tears lens so what do we do…

A

Add minus power to final BVP

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22
Q

If we flatten a lens we are creating a minus powered tear lens so we…

A

Add plus power to final BVP

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23
Q

When the flat k is on the verticle meridian what type of astigmatism is this

A

ATR astigmatism

24
Q

Characteristic of steeper lens

A

tight fit
less movementc

25
Q

characteristic of flatter lens

A

looser fit
more movement

26
Q

what does radiuscope measurment?

A

BOZR of RGP

27
Q

when you increase lens diameter what happens?

A

-sag increases
-fit is tighter/steeper

28
Q

when you decrease lens diameter what happens

A

-sag decreases
-fit is looser/flatter

29
Q

when a lens is to flat with fluroscein how does it look?

A

pooling on the outside / peripheral

30
Q

when a lens is too steep how does it look with fluroscien?

A

pooling on the inside centre / apical

31
Q

how does a proper contact lens fit look with fluroscein?

A

pupil is visible , little bit of fluroscien along the peripheral

32
Q

when do you vertex a power

A

higher than +/- 4.00D

33
Q

when do you preform spherical equivalence?

A

if less than -0.75 astigmatism

34
Q

Spherical abberation

A

Longitudinal spread of focus

35
Q

positive spherical abberation

A

rays further from the principal axis are refracted more than central rays
ex; distance centre multifocal contact lenses, orthokeratology lens

36
Q

negative spherical abberationt

A

-rays further from the principal axis are refracted less than central rays
ex; near centre multifocal contact lens

37
Q

true or false; aspehric lenses reduce spherical abberations?

A

true

38
Q

myopia management

A

-reduce perihperal defocus with plus power periphery in lenses
-multifocal CLs
-OrthoK

39
Q

key concept in myopia management

A

slow axial length elongation

40
Q

Shape Factor

A

Cornea is usually aspheric
SF= 1 - e2

41
Q

Proloate cornea

A

flattens towards periphery

42
Q

oblate cornea

A

steeper towards peripehry

43
Q

Contact lens magnification formula

A

CLM: image corrected w/ contact lenses / image corrected with spectacles

44
Q

Myopes accomodation

A

accomodative demand is higher with contact lenses compared to gls

45
Q

hyperopes accomodation

A

accomodative demand is lower with contact lenses compared to gls

46
Q

how can prismatic effect occur?

A

decentered lenses

47
Q

how can induced astigmatism occur?

A

flexure = bending of lens on a toric cornea
-eyelids can induce astigmatism for the reason when you blink the contact lens can flex which creates more asitg

48
Q

halo effect

A

bright circles or rings around a light source
most noticeable in a dim or dark area
large pupil with a smaller optic zone

49
Q

coma abberation

A

higher order lens abberation
off axis points appear distorted with a tail

50
Q

Flexure on a lens results in..

A

the lens will bend in the steeper meridian
the change in shape of the lens causes astigmatism

51
Q

what should the edge clearnece be for alignemnt RGP fit?

A

less than 1mm width

52
Q

normal amount of Shape factor

A

0.13 to 0.35

53
Q

borderline amount of shape factor

A

0.02 to 0.12 and 0.36 0.46

54
Q

abnormal amount of shape factor

A

0.00 to 0.01 and 0.47 to 1.0

55
Q
A

Contact lens Year 2 (8 decks)

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