13. How to: Soft Toric Lens Fitting

Question 1

What 2 things are being observed in a push- up test?

Answer 1

1. How easy it is to move a lens
2. How well the lens recovers

Question 2

What mag is used when doing corneal staining?

Answer 2

16X

Question 3

Describe the process of observing corneal staining- illumination, beam size, mag, any filter used? and examined in how many positions of gaze?

Answer 3

Max illumination
Thin- medium beam width
Wratten filter
16X
3 position of gaze examined

Question 4

When recording lens fit, how do you record vision?

Answer 4

If it is clear and stable, does it change when patient blinks?

Question 5

What is the most accurate predictor of soft contact lens fit?

Answer 5

Push-up test

Question 6

What amendment is done to lenses with a steep fit?

Answer 6

1. Increase BC if possible
2. Try different manufacturer with same/ similar base curve as sag is likely to be different

Question 7

What amendment is done to lenses with flat fit?

Answer 7

1. Reduce BC if possible
2. Try different manufacturer with same/ similar base curve as sag is likely to be different

Question 8

Why are patients given toric lenses?

Answer 8

To correct astigmatism

Question 9

What 2 components give total astigmatism?

Answer 9

Corneal and lenticular astigmatism

Question 10

4 situations where patients are given toric lenses

Answer 10

1. When astigmatism present (-0.75 and more).
2. When astigmatism is a factor for VA
3. When adequate vision can not be. achieved with spherical lenses.
4. Visual quality vs cost factor

Question 11

What form of stability is required to keep toric lens in the correct position?

Answer 11

1. Dynamic/ accelerated stability
2. Prism ballast

Question 12

Toric lens availability starts at what Rx? And they come in how many diopter steps?

Answer 12

Starts at -0.75DC and steps of: -0.50DC

Question 13

In the ACLM book what does it means when:
1. Power range is written as: Plano to -6.00 (0.25)?
2. Which axis are available if written as 90+/-20 (10)?

Answer 13

1. This is the range of spherical lenses available in 0.25 diopter steps.
2. 110, 100, 70, 80, 90

Question 14

What do you do if toric Rx is not available ? (2 solutions)

Answer 14

1. Monthly lenses have more options available over daily lenses.
2. If some cyl powers are not available: sacrifice some cyl by over-minusing the sphere to compensate for the cyl lost.

Question 15

In lens selection when is BVD considered?

Answer 15

When sphere/ cyl or cross cyl power is above +/-4.00D

Question 16

What rule is used if an Rx is not available for a given brand and you do not want to change the brand?

Answer 16

Round down values: of axis, cyl, sphere.
ALWAYS ROUND DOWN

Question 17

How do you decide between the availability of 2 different axis or 2 different cyls, how do you know which one to order?

Answer 17

Place the 2 different Rx in the patients trial frame and let them decide which one is better

Question 18

How do you assess rotations on a toric lens?

Answer 18

Toric lenses have markings on them that help assess the rotation

Question 19

What causes rotation in toric lenses?

Answer 19

Rotation due to lens- cornea/ lid interaction

Question 20

What do the markings on toric lens indicate?

Answer 20

They do not indiacte cyl axis!
The markings only let you know how the lens is sitting and allow you to assess the degree of rotation

Question 21

Are all the marking on toric lens the same?

Answer 21

No it varies from manufacturer to manufacturer

Question 22

Describe the 3 positions you expect toric lens markings to be at?

Answer 22

3, 6 and 9 o’clock position

Question 23

How do you identify the degree of rotation incase a lens has moved??

Answer 23

Align the observation and illumination system. Rotate the beam to dissect the pupil and lens markings and read the amount of rotation off the slit lamp scale.

Question 24

Procedure of soft toric lens fit assessment before assessing with slit lamp?

Answer 24

As patient to look around, blink abit then assess the lens rotation and lens stability

Question 25

What mnemonic is used to help correct toric lens rotation? And when can these be used?

Answer 25

LARS: left Add, right subtract
CAAS: Clockwise add, anticlockwise subtract
It can only be used if lens is stable

Question 26

3 methods when a lens is not stable, and the axis of the toric lens keep moving about?

Answer 26

1. Choose a flatter/ steeper BC
2. Changing manufacturer
3. Change to a lens with a different method of stabilization

Question 27

How is movement of blink recorded?

Answer 27

In mm

Question 28

How can optometrists help patients decide if they need toric lenses or they can use lenses with mean sphere?

Answer 28

In the trail frame in one eye give patient mean sphere Rx and in other eye give patient full toric Rx and let the patient pick preference.