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NBEO Part 2 > Contact Lenses > Flashcards

Contact Lenses Flashcards

1
Q

What is the recommended extension of a soft contact lens beyond the limbus?

A

1-2mm 360 degrees

Insufficient coverage can lead to ocular redness and irritation.

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2
Q

What indicates that a soft contact lens may be too flat?

A

Decentered contact lens

Steepening the base curve can improve centration.

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3
Q

What is the acceptable movement range for a well-fitting soft contact lens during a blink?

A

0.50 - 2.00mm

Too tight lenses can cause irritation, while excessive movement can lead to discomfort.

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4
Q

What does ‘sag’ refer to in soft contact lens evaluation?

A

The amount the lens drops during upward gaze

Excessive sag is considered over -1.5mm.

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5
Q

What is the maximum acceptable lag for a soft contact lens?

A

1.5mm

Less than this indicates the lens fits too tight.

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6
Q

What is the purpose of the push-up test in soft contact lens fitting?

A

To observe the lens’ resistance to movement

This helps evaluate the fit when other measurements are minimal.

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7
Q

How is lens rotation measured for toric soft contact lenses?

A

By matching the slit-lamp light beam to the cylinder marking

Record the direction of rotation (right or left).

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8
Q

Fill in the blank: A soft contact lens should _____ over the entire cornea.

A

center

A decentered lens can affect vision and comfort.

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9
Q

True or False: A soft contact lens should not move at all during a blink.

A

False

Some movement is necessary for comfort and fit.

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10
Q

Soft contact lens evaluation protocol

A
  1. Coverage
  2. Centration
  3. MOB ( movement on blink)
  4. Sag
  5. Lag
  6. Push-up test
  7. Rotation (Toric soft CL)
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11
Q

What is the significance of the contact lens fitting in terms of movement during blinking?

A

Loose fitting leads to excessive CL movement with blink

This can indicate poor lens centration and may cause discomfort or irritation.

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12
Q

What are the characteristics of a loose fitting contact lens?

A
  • Excessive CL movement with blink
  • Poor CL centration
  • Lens edge bubbles
  • Lens edge stand-off
  • Superior eyelid irritation

A loose fitting lens may not provide adequate vision correction.

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13
Q

What are the characteristics of a tight fitting contact lens?

A
  • Minimal CL movement with blink
  • Indentation around limbus
  • Injection around limbus
  • Corneal edema
  • No comfort complaints

A tight fitting lens may cause discomfort or corneal issues.

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14
Q

How can you adjust the fit of a contact lens?

A
  • Increase sagittal height
  • Decrease sagittal height
  • Choose steeper base curve
  • Choose flatter base curve
  • Increase diameter
  • Reduce diameter

Adjustments depend on the fit characteristics observed.

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15
Q

What effect does a steep contact lens have on the lacrimal lens?

A

Creates a positive lacrimal lens

This requires adding minus to adjust the power of the lens.

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16
Q

What effect does a flat contact lens have on the lacrimal lens?

A

Creates a negative lacrimal lens

This requires adding plus to adjust the power of the lens.

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17
Q

What is the formula to calculate the Tear Lens?

A

Tear Lens = Base Curve - Keratometry

This equation helps determine the effective power of the contact lens.

18
Q

What is the mm to Diopter conversion formula?

A

mm = 337.5 / D

This is used to convert measurements for contact lens fitting.

19
Q

What is the Vertexing Equation for contact lenses?

A

CL Power = Spectacle Power / [1 - (Vertex Distance * Spectacle Power)]

This equation adjusts spectacle power for contact lens fitting.

20
Q

What is the formula for calculating Residual Astigmatism?

A

Residual Astigmatism = Total astigmatism of the eye - corneal astigmatism

This helps in determining the appropriate lens for astigmatism correction.

21
Q

What does SAM FAP stand for in contact lens fitting?

A

Steeper Add Minus, Flatter Add Plus

This guideline assists in adjusting lens power based on curvature.

22
Q

In the context of lens power adjustment, what does LARS stand for?

A

Left Add, Right Subtract

This indicates how to adjust the power based on the orientation of the lenses.

23
Q

What does apical touch in a lens indicate?

A

The lens is too flat and likely has excessive edge lift.

Apical touch can cause distortion of the central cornea and, in extreme cases, corneal scarring.

24
Q

How can apical touch be resolved?

A

By steepening the base curve of the lens or increasing the overall diameter of the lens or optic zone.

Steepening the base curve helps to prevent distortion and scarring.

25
Q

What does apical clearance indicate?

A

The lens has been fit too steeply.

This fitting relationship can result in central pooling of sodium fluorescein with peripheral touch.

26
Q

What can result from apical clearance?

A

Lens seal-off and lack of tear exchange.

Central pooling of sodium fluorescein indicates that the lens is not fitting properly.

27
Q

How can apical clearance be remedied?

A

By flattening the base curve, decreasing the overall lens diameter, or decreasing the optic zone diameter.

These adjustments help ensure proper fit and tear exchange.

28
Q

Fill in the blank: A lens that displays _______ is considered too flat.

A

apical touch

29
Q

True or False: Increasing the lens diameter can resolve apical touch.

A

True

30
Q

What is a common result of fitting a lens too steeply?

A

Central pooling of sodium fluorescein with peripheral touch.

31
Q

What does this RGP fluorescein pattern indicate?

A

ATR astigmatism
* FL will pool along the right and left side of lens with central touch vertically 12 to 6 o’clock band

32
Q

RGP FL pattern indicates?

A

WTR astigmatism
* bow tie on FL pattern
* FL will pool along top and bottom of lens with central touch across 3-9 o’clock band

33
Q

What is flexure in the context of RGP lenses?

A

Flexure occurs when an RGP becomes distorted while it is on the cornea, but assumes its normal shape when it is no longer on the cornea.

34
Q

How is irregular astigmatism measured with RGP lenses?

A

Irregular astigmatism is measured with keratometry or topography when the RGP is on the eye.

35
Q

What happens to the measurement of irregular astigmatism when the RGP is off the eye?

A

When the RGP is off of the eye, irregular astigmatism will not be measured.

36
Q

What typically causes flexure in RGP lenses?

A

Flexure is usually caused when the RGP is thin and so its shape is easily contorted.

37
Q

True or False: Flexure can be confirmed by rubbing the RGP during cleaning.

A

True

38
Q

Fill in the blank: Flexure occurs when an RGP becomes _______ while it is on the cornea.

A

[distorted]

39
Q

FDA Classes of SCL

A
  • Group 1 low water content, non-ionic
  • Group 2 high water content, non-ionic
  • Group 3 low water, ionic
  • Group 4 high water, ionic
  • Group 5 includes silicone hydrogels
40
Q

Which FDA group of SCL is least likely to develop deposits?

A

Group 1: low water content and non-ionic

41
Q
A

Dimple veiling
* tight RGPCL fit, bubbles get trapped under and imprint dimples into cornea which pool with FL when RGP is removed
Tx: fit into flatter RGP

NBEO Part 2 (15 decks)

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