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Contact Lenses > Practical > Flashcards

Practical Flashcards

1
Q

When looking at Kertaometry readings in Diopters what indicates steeper?

A

Higher the number, the steeper the curve

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2
Q

When looking at Kertaometry readings in mm of Radius what indicates steeper?

A

The lower the number, the steeper the curve

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3
Q

When using the keratometer, what happens if you cannot see the - signs?

A

This means that the eyes are not wide enough.

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4
Q

When using the keratometer, what happens if you cannot see the + signs?

A

This means that the occluder is in the way

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5
Q

When using the keratometer, what happens if there are irregular mires?

A

This means the eyes are dry, too wet or they have an irregular cornea

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6
Q

What is the average power of the cornea?

A

+43.00 D (or 7.85 mm)

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7
Q

What is the average power range of the cornea?

A

42.00 to 45.00 D
or
8.04 to 7.50 mm

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8
Q

What is a nomogram?

A

The manufacturer’s guide of how to fit THEIR lenses

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9
Q

What happens when you change the diameter of a SCL?

A

You change the fit because for every 0.5 step change in the diameter, you must compensate 0.3 mm BC

14.0 diam with 8.6 mm BC
fits the same as
14.5 diam with 8.9 mm BC

Anytime you make the lens smaller you are also flattening the fit

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10
Q

Define LARS

A

Lars is a fitting technique to compensate for the lens rotation on a toric soft or GP lens. It is based on the fitter’s point of view while looking at the eye in the slit lamp.

Every hour of the clock is 30º rotation

If the lens rotates L add 30º to the axis for every “hour”.
If the lens rotates R subtract 30º from the axis for every hour

Once refit, the lens will still rotate, but the patient will be seeing the correct prescription as you have compensated

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11
Q

Define SAM/FAP

A

A fitting technique used to compensate for the power created by the tear film under a GP lens

SAM - When fitting a GP lens steeper than the cornea, a plus tear film lens is created → Steeper Add Minus

FAP - When fitting a GP lens flatter than the cornea, a minus lens is created → Flatter Add Plus

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12
Q

Why are front Toric Lenses the worst option?

A
  • Cause fluctuating vision
  • Lots of Lens movement ∴ patient discomfort

As much as possible you should avoid these fits (ideally use bi/back toric or aspheric lens

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13
Q

How do you decide if you are going to use a bi/back toric?

A

if Tcyl is 1.5 then use a BACK TORIC

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14
Q

Why can you drop the residual cyl in a toric GP lens?

A

It is accounted for in the CL power

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15
Q

When using a back aspheric lens design, why would you choose the Steeper K?

A

This lens would have less movement ∴ more comfortable

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16
Q

When using a back aspheric lens design, why would you choose the Flatter K?

A

This lens would have better edge lift ∴ more tear exchange

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17
Q

What is Flexure?

A

A lens design used to try to avoid using a Front Toric Lens design

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18
Q

How does Flexure work?

A

A minimum centre thickness typically keeps the lens from bending with every blink which keeps the lens power consistent

Flexure takes advantage of this principle by reducing the centre thickness. You put a sphere lens on the eye and use each blink to bend the lens and induce the proper amount of cylinder

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19
Q

Why is Flexure not a popular design?

A

Now you can order a back aspheric!

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20
Q

What are the two fitting philosophies for GP lenses according to Robert Mandell?

A

Interpalpebral and Upper Lid Attachment

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21
Q

What is the main use of a slit lamp?

A

To look at the eye to check basic health and to check if the eye is healthy enough to wear contact lenses

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22
Q

What are the two categories of Illumination?

A 
Direct focal (in click stop)
Indirect focal (out of click stop)
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23
Q

Define Direct Focal Illumination. What is an example?

A

Both the light source and the oculars are focused on the same point of interest

Example: Parallel Piped

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24
Q

Define Indirect Focal Illumination

A

The light source ant eh oculars are NOT focused on the same point of interest

Example: Direct and Indirect Retro

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25
Q

In terms of using the slit lamp, define magnification

A

The magnification number read on the oculars

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26
Q

In terms of using the slit lamp, define focus

A

The point that the OCULARS are focused on

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27
Q

In terms of using the slit lamp, define light

A

The intensity of the light source

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28
Q

In terms of using the slit lamp, define slit width

A

How wide the beam of light is

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29
Q

In terms of using the slit lamp, define slit direction

A

Where the light source is directed

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30
Q

In terms of using the slit lamp, define angle

A

The angle between the light source and oculars

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31
Q

In terms of using the slit lamp, define click stop

A

Asking if this illumination direct focal or indirect focal

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32
Q

What is the relationship between light and magnification

A

Low light - use low mag.
Medium light - use medium mag.
High light - use high mag.

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33
Q

What is the purpose of a Diffuse Illumination?

A

A general overview of the health of the eye/cornea. Checking if there is anything that blatantly shows this person cannot wear contact lenses.

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34
Q

For a Diffuse illumination, what is the:

  1. Magnification
  2. Focus
  3. Light
  4. Slit width and direction
  5. Angle
  6. Click stop?
A
  1. Low (6-10x)
  2. Cornea
  3. Low
  4. Wide Open on the cornea
  5. 45-60º
  6. Direct Focal
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35
Q

Name 5 things can you detect using a Diffuse Illumination

A
  • Outer Adnexa
  • Pinguecula/Pterygium
  • Arcus
  • Entropion/Ectropion
  • Chalazion
  • Hordeolum
  • Ptosis
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36
Q

What is the purpose of a Parallel Piped Illumination?

A

To see the cornea /pathological condition in more detail. You can see the anterior and posterior at the same time. This is a good starting point for the other illuminations

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37
Q

For a Parallel Piped illumination, what is the:

  1. Magnification
  2. Focus
  3. Light
  4. Slit width and direction
  5. Angle
  6. Click stop?
A
  1. Start low then work up to Medium (10-16x)
  2. Cornea
  3. Medium
  4. 2-4 mm on the cornea
  5. 45-60º
  6. Direct Focal
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38
Q

Name 5 things can you detect using a Parallel Piped Illumination

A
  • CL Fit/Scribe Marks)
  • TBUT
  • Meibomian Orifices (raised or plugged)
  • Scars/Ulcers
  • Desiccation
  • Abrasions
  • Keratitis
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39
Q

What is the purpose of an Optic Section Illumination?

A

To view the corneal layers in detail/cross-section.

This is very similar to the parallel piped, but your beam is narrower because you are looking WITHIN the cornea and you will see 3 layers

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40
Q

For an Optic Section illumination, what is the:

  1. Magnification
  2. Focus
  3. Light
  4. Slit width and direction
  5. Angle
  6. Click stop?
A
  1. Medium (16x)
  2. Cornea
  3. Medium to High
  4. 02-1.0 mm on the cornea
  5. 45-60º
  6. Direct (in click)
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41
Q

Name 5 things can you detect using an Optic Section Illumination

A
  • Depth and location of scars
  • Vertical striae
  • Stromal Edema
  • Dellen
  • CL to cornea relationship
42
Q

What is the purpose of a Specular Reflection Illumination?

A

To view a section of the endothelial mosaic

43
Q

For a Specular Reflection illumination, what is the:

  1. Magnification
  2. Focus
  3. Light
  4. Slit width and direction
  5. Angle
  6. Click stop?
A
  1. High (16-40x)
  2. Obliquely on the cornea (set up monocularly (left eye in the right ocular) to make sure you are lined up properly)
  3. High (medium light while searching, then bump up mag and light)
  4. 2-4 mm on the cornea
  5. 60-90º (i=ii)
  6. Direct Focal (in click)
44
Q

Name 5 things can you detect using a Specular Reflection Illumination

A
  • Guttatae (age)
  • Blebs
  • Fuch’s dystrophy
  • Polymegathism/polymorphism
  • Crystaline lens
  • Tear Film
45
Q

What is the purpose of a Conical Beam Illumination?

A

To view any inflammation in the anterior chamber

46
Q

For a Conical Beam illumination, what is the:

  1. Magnification
  2. Focus
  3. Light
  4. Slit width and direction
  5. Angle
  6. Click stop?
A
  1. Medium (16x)
  2. Cornea
  3. Medium to High
  4. Pinpoint (1mm x 1mm or 2mm x 2mm) on the cornea (looking just behind the cornea)
  5. 45-60º
  6. Direct Focal (in click)
47
Q

Name 3 things can you detect using a Conical Beam Illumination

A
  • To look for aqueous flare (protein, WBC or RBC) - if left long enough it will turn into a hyphema
  • Look for haze/fog in front of a black background
  • Detect iritis or uveitis (aqueous flare is a symptom as well as photophobia and accommodation problems)
48
Q

What is the purpose of a Direct Retro Illumination?

A

To see things you cannot see with direct light

49
Q

For a Direct Retro illumination, what is the:

  1. Magnification
  2. Focus
  3. Light
  4. Slit width and direction
  5. Angle
  6. Click stop?
A
  1. Medium (16x)
  2. Cornea
  3. Medium
  4. 2-4 mm on the iris (the light reflects BEHIND the object of interest)
  5. ≥ 60º
  6. Indirect focal (out of click)
50
Q

Name 5 things can you detect using a Direct Retro Illumination

A
  • ***Microcysts and Vacuoles
  • Neovascularzation and Pannus
  • Scribe Marks
  • CL Depositcs
  • Edema
  • Infiltrates
  • Scars
51
Q

What is the purpose of an Indirect Retro Illumination?

A

To see things you cannot see with direct light

52
Q

For an Indirect Retro illumination, what is the:

  1. Magnification
  2. Focus
  3. Light
  4. Slit width and direction
  5. Angle
  6. Click stop?
A
  1. Medium (16x)
  2. Cornea
  3. Medium
  4. 2-4 mm on the iris (the light reflects BESIDE the object of interest)
  5. ≥ 60º
  6. Indirect focal (out of click)
53
Q

Name 5 things can you detect using an Indirect Retro Illumination

A
  • ***Microcysts and Vacuoles
  • Neovascularzation and Pannus
  • Scribe Marks
  • CL Depositcs
  • Edema
  • Infiltrates
  • Scars
54
Q

What is the purpose of a Sclerotic Scatter Illumination?

A

To look at corneal transparency. When using this illumination it creates a circumcorneal halo/limbal glow/crescentric halo

55
Q

For a Sclerotic Scatter illumination, what is the:

  1. Magnification
  2. Focus
  3. Light
  4. Slit width and direction
  5. Angle
  6. Click stop?
A
  1. Lowest/Naked Eye
  2. Cornea
  3. Low
  4. 2-4 mm at the limbus (temporal)
  5. 45-60º
  6. Indirect (out of click)
56
Q

Name 5 things can you detect using a Sclerotic Scatter Illumination

A
  • CCC : Edema in the central cornea due to GP lens hypoxia
  • Scars (RK or Pizza Slices)
  • Infiltrates
57
Q

Name 5 things can you detect using a Tangental Illumination

A
  • Raised areas on the iris
  • Iris scars
  • Coloboma
58
Q

Which anatomical features allows the sclerotic scatter to work?

A

The fact that Descemet’s membrane only covers the central 65% of the cornea. Thisouter gap allows the light to pass into the cornea

59
Q

What is unique about over-refracting presbyopic fits?

A

You always should over-refract binocularly

60
Q

What are some causes of poor distance vision when fitting multifocal contact lenses?

A
  • Wrong power
  • Incorrect Segment height
  • Large pupil with small optic zone
  • Small pupil with near-centre design
  • Low light
61
Q

What are some causes of poor near vision when fitting multifocal contact lenses?

A
  • Excessive lens movement
  • Incorrect Segment height
  • Improper blinking (dry lens)
  • Lens is too flat or too steep (especially GP lenses/tear lenses)
  • Residual Cyl
  • Lack of pupil constriction at near
  • Low light
62
Q

What are some causes of ghosting/doubling when fitting multifocal contact lenses?

A
  • Excessive lens movement
  • High riding lens
  • Too much plus the dominant eye
  • Too much of a difference between OD and OS
  • Too much segment rotation
  • Too Flat/Too steep
  • Poor segment blending
  • Residual Cyl.
63
Q

What are the 5 uses of a radiuscope?

A
  1. BC/Fitting Curves
  2. Front Curves
  3. Peripheral Curves
  4. Surface Quality
  5. Warpage
64
Q

How can you tell the difference between the aerial image and the real image when using a radiuscope?

A

The aerial image can “move” if someone bumps the table because the lens is floating on water

The real image usually appears brighter, sharper and clearer than the aerial image or star.

65
Q

How do you set up the radiuscope?

A

Place a drop of SCL solution in the mount but be careful to not get any solution inside the lens.

This is important and must be used to neutralize the optics on the front surface of the contact lens.

66
Q

Why use SCL solution, not GP solution?

A

Soft lens solution is used as it is less viscous than rigid lens solutions (No rule against using rigid lens solution, it is just very sticky).

67
Q

How do you determine if a radiuscope works by finding the top aerial image first or the bottom aerial image first?

A

Determine the method by looking at the clock dial outside of the oculars

If the clock dial goes CLOCKWISE from 0-90:

  1. Find the top aerial image,
  2. Zero the radiuscope
  3. Lower the platform DOWN through the filament until you reach the real image and then take the reading.

If the clock dial goes COUNTER CLOCKWISE from 0-90:

  1. Find the lowest aerial image
  2. Zero the radiuscope
  3. Move the platform UP through the filament until you find the real image and take the reading.
68
Q

How do you read a radiuscope clock dial?

A

You read the inner number first and the second outer dial are the decimal places!

69
Q

For a radiuscope that you start by finding the image at the top first, what is a trick

A

For any radiuscope that reads the top image first, lower the platform until you see the filament. .You are now approximately half way between the aerial image or star and the real image or star.

70
Q

For a radiuscope that you start by finding the image at the top first, what is a trick to determine where you are?

How do you do this?

A

For any radiuscope that reads the top image first, lower the platform until you see the filament. This is approximately half way between the aerial image and real image.

  1. Zero the clock (both hands have to be at zero)
  2. Lower the platform until you see the filament . You are now approximately half way between the aerial image and the toric lines.
71
Q

What will the images look like when you are measuring a bi-back toric?

A

One distinct spoke will come into focus first. Rotate the mount in order have this spoke come clearly into focus. At this point read the clock for the first base curve

Continue to lower the platform until the second line comes into focus. Read the clock for the second base curve of a back toric. All top to bottom radiuscopes work the same way.

72
Q

What are the steps for verifying a Spherical/Front Toric GP lens?

A
  1. Find the aerial image so all the mires are clear and crisp (centre the aerial image)
  2. Zero the radiuscope (with the silver dial) - the image should not change
  3. Turn the side knob away, go past the filament until the real image comes into focus
  4. Read BC off the dial
  5. Measure the diameter (Jeweller’s loupe or V-Gauge ruler)
  6. Measure centre thickness (Zero the gauge, place the lens into the gauge under the dial. Measure and record centre thickness)
  7. Find the prescription in the lensometer (place lens in concave side down)
73
Q

What are the steps for verifying a Bi/Back Toric GP lens?

A
  1. Find the aerial image of the one mire that is the closest to zero (coldest)
  2. Zero the instrument with the silver dial
  3. Turn the side knob past the other principle meridian , the filament and focus on the real image
  4. Record the first base curve
  5. Return back to zero and focus on the “warmer” principle meridian. Re-zero the radiuscope at this location
  6. Turn the side knob past the filament and focus on the real image and record this base curve
  7. Measure the diameter and centre thickness (Zero the gauge, place the lens into the gauge under the dial. Measure and record centre thickness)
  8. Find the prescription in the lensometer
74
Q

How do you determine the orientation of the axis of a Bi/Back toric GP lens?

A

The coldest power goes with the steepest curve (lower integer)

75
Q

What is a rule fo thumb when trying to determine the power of the tear lens?

A

For every difference of curvature of 0.05 mm the tear lens has a value of 0.25

76
Q

What are the signs and symptoms of a square GP edge?

A
  • Excessive lid awareness
  • Excessive lid/edge interaction
  • 3 and 9 o’clock staining
77
Q

What are the signs and symptoms of a sharp GP edge?

A
  • Lid discomfort
  • Discomfort with lateral movements
  • Discomfort when re-centring
78
Q

What are the signs and symptoms of a rolled-in GP edge? What causes this edge?

A
  • Constant lens awareness
  • Pain when re-centring
  • Arcuate abrasion staining
  • 3 and 9 o’clock staining

Dropped lens can cause a rolled in edge

79
Q

What are the signs and symptoms of a thick GP edge? What causes this edge?

A
  • Lid awareness
  • Slight lid/edge interaction
  • 3 and 9 o’clock staining

High minus prescriptions can cause this edge

80
Q

What are the signs and symptoms of a GP rolled-out edge ?

A
  • Excessive lid awareness
  • Erratic lens positioning by upper lid movements
  • Lens falls out easily
  • 3 and 9 o’clock staining
81
Q

What are the signs and symptoms of an ideal GP edge?

A
  • Minimal led awareness
  • Smooth profile
  • Gentle regression of the posterior zone
  • Well rounded ape
  • Allows for easy removal and minimal 3 and 9 o’clock staining
82
Q

Troubleshoot: GP lens rides too low

A
  1. Lens is too small → reduce thickness/weight

2. Too thick/too flat → steepen lens/use lenticular

83
Q

Troubleshoot: GP lens rides under the upper lid

A
  1. Lens is too flat → Reduce lens size/steepen base curve
84
Q

Troubleshoot: Lens Rides to the side

A
  1. Against the rule Astigmatism → Steepen the lens and reduce the optic zone. Use a bi/back toric
85
Q

Troubleshoot: Mucous on the lens

A
  1. Scratched surface → Polish lens

2. Deposits on the lens → Use enzyme cleaner

86
Q

Troubleshoot: Unusual change in refraction

A
  1. Lens is too flat/too steep → Compare K with the original reading. Refit after 506 days without wearing lens
87
Q

Troubleshoot: Deep corneal stain with pain

A
  1. Corneal ulcer → Stop wearing lens

2. Possible uveitis → Refer to OD

88
Q

Troubleshoot: 3 and 9 o’clock staining

A
  1. Too flat periphery → Steepen secondary curve

2. Wrong size lens → Flatten the base curve/alter size

89
Q

Troubleshoot: Zig-Zag Corneal Stain

A
  1. Foreign body under the lens → Clean the lens
90
Q

Troubleshoot: Fine Stippling

A
  1. Normal in adaptation → Flatten the base curve/clean the lens
  2. Insufficient circulation → Reduce optic zone
91
Q

Troubleshoot: H Fluorescein pattern

A
  1. Corneal Astigmatism → Refit to bi/back toric
92
Q

Troubleshoot: Excessive Edge Stand Off

A
  1. Peripheral curve is too flat or too wide → Make new lens with narrower and/or steeper peripheral curve
93
Q

Troubleshoot: Central Touch

A
  1. Lens is too flat → Steepen base curve
94
Q

Troubleshoot: Central Pool with ring touch inside bevel

A
  1. Lens is too steep → flatten base curve
95
Q

Troubleshoot: Bubbles under the lens

A
  1. Lens is too steep → flatten base curve
96
Q

Troubleshoot: Displacement by the lid

A
  1. Edges too thick/too large → Reduce edge thickness, make lens smaller
  2. Lens is too flat → Steepen base curve
97
Q

Troubleshoot: No movement

A
  1. Lens is too large/steep → Flatten base curve
98
Q

Troubleshoot: Excessive Movement

A
  1. Lens is too loose/too steep → Check fluorescein pattern

2. Excess tearing → check lens edge

99
Q

How do you prepare a GP for the radiuscope?

A
  1. Clean the lens
  2. Place a drop of solution in the mount and place the lens so it is floating in the liquid (be sure to not get any liquid in the lens)
100
Q

Why do hard lenses need to rock?

A

This creates a tear pump to keep the tear film circulating

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