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Contact Lenses > Toric RGPs > Flashcards

Toric RGPs Flashcards

1
Q

What are the types of astigmatism?

A

Regular
Irregular
Oblique
With-the-rule
Against-the-rule
Residual/lenticular
Induced
Corneal

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2
Q

What is regular astigmatism?

A

Meridians are at 90 degrees to each other

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3
Q

What is irregular astigmatism?

A

Meridians are not at 90 degrees to each other
(Normally due to disease, injury or congenital causes)

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4
Q

What is oblique astigmatism?

A

Meridians are more than 30 degrees from 90 or 180

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5
Q

What is with-the-rule astigmatism?

A

Vertical meridian has higher rx, steeper Ks (axis: 180 degrees +/- 30)

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6
Q

What is against-the-rule astigmatism?

A

Horizontal meridian has higher rx, steeper Ks (axis: 90 degrees +/- 30)

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7
Q

What is residual/lenticular astigmatism?

A

‘Leftover’ astigmatism when corneal astigmatism corrected by tear lens created by spherical RGP

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8
Q

What is induced astigmatism?

A

Astigmatism which is induced by a back surface toric RGP on a toric cornea - caused by differing refractive indices of RGP and tear film

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9
Q

What are the possible combinations of astigmatism?

A

Spherical cornea/spherical refraction
Spherical cornea/astigmatic refraction
Toric cornea/spherical refraction
Toric cornea/astigmatic refraction

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10
Q

Where is the majority of the astigmatism in spherical cornea/astigmatic refraction?

A

Lenticular

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11
Q

Where is the majority of the astigmatism in toric cornea/spherical refraction?

A

Corneal and lenticular astigmatism equal and opposite to each other (cancel each other out and give spherical refraction)

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12
Q

Where is the majority of the astigmatism in toric cornea/astigmatic refraction?

A

Corneal

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13
Q

Who should you fit with a toric lens?

A

Cyl over -0.75DC
If induced or residual astigmatism
Toric cornea which a spherical RGP fits poorly

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14
Q

What are the types of toric RGP?

A

Spherical
Back surface toric
Front surface toric
Spherical centre/toric periphery
Bitoric

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15
Q

What can a spherical RGP be used for in px’s with astigmatism?

A

To correct corneal astigmatism up to -2.50DC

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16
Q

When can a spherical centre/toric periphery RGP be used?

A

To correct astigmatism via the tear lens through spherical BOZR, toric periphery ensures more optimal fit on a toric cornea and allows even edge clearance

17
Q

When can a back surface toric be used?

A

Toric cornea/spherical refraction
Back surface should mimic corneal surface

18
Q

What should the fluorescein fit look like on a back surface toric?

A

Spherical alignment (bc tear lens spherical due to matching shape to cornea)

19
Q

When can a bitoric be used?

A

High levels of mixed astigmatism, if front or back surface torics produce lots of induced or residual astigmatism

20
Q

How does a bitoric work?

A

Both surfaces toric
Back surface helps physical fit
Front surface corrects astigmatism

21
Q

When can a front surface toric be used?

A

Spherical back surface
Toric front surface which corrects residual astigmatism

22
Q

What combination of astigmatism does a front surface toric correct?

A

Spherical cornea/astigmatic refraction

23
Q

Does a front surface toric need stabilisation?

A

Yes

24
Q

What are the types of stabilisation?

A

Toric back surface
Prism ballast
Truncation
Dynamic stabilisation

25
Q

What lid factors affect lens stabilisation?

A

Lower lid position
Lid angles
VPA
Lid tension
Force of blink
Direction of lens movement on blink

26
Q

What non-lid factors affect lens stabilisation?

A

Lens power
Gravity
Water content
Material elasticity
Lens thickness

27
Q

What can cause poor VA in a toric lens?

A

Lens fit too flat or steep
Rotation
Rotational instability
Incorrect rx

28
Q

What should you check if there is poor VA in a toric lens?

A

Lens rx
Specs rx
Lens fit
Rotation
Lens design (change stabilisation type)
Consider change from soft to RGP

Contact Lenses (13 decks)

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