13. How to: Soft Toric Lens Fitting Flashcards
What 2 things are being observed in a push- up test?
- How easy it is to move a lens
- How well the lens recovers
What mag is used when doing corneal staining?
16X
Describe the process of observing corneal staining- illumination, beam size, mag, any filter used? and examined in how many positions of gaze?
Max illumination
Thin- medium beam width
Wratten filter
16X
3 position of gaze examined
When recording lens fit, how do you record vision?
If it is clear and stable, does it change when patient blinks?
What is the most accurate predictor of soft contact lens fit?
Push-up test
What amendment is done to lenses with a steep fit?
- Increase BC if possible
- Try different manufacturer with same/ similar base curve as sag is likely to be different
What amendment is done to lenses with flat fit?
- Reduce BC if possible
- Try different manufacturer with same/ similar base curve as sag is likely to be different
Why are patients given toric lenses?
To correct astigmatism
What 2 components give total astigmatism?
Corneal and lenticular astigmatism
4 situations where patients are given toric lenses
- When astigmatism present (-0.75 and more).
- When astigmatism is a factor for VA
- When adequate vision can not be. achieved with spherical lenses.
- Visual quality vs cost factor
What form of stability is required to keep toric lens in the correct position?
- Dynamic/ accelerated stability
- Prism ballast
Toric lens availability starts at what Rx? And they come in how many diopter steps?
Starts at -0.75DC and steps of: -0.50DC
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)?
- This is the range of spherical lenses available in 0.25 diopter steps.
- 110, 100, 70, 80, 90
What do you do if toric Rx is not available ? (2 solutions)
- Monthly lenses have more options available over daily lenses.
- If some cyl powers are not available: sacrifice some cyl by over-minusing the sphere to compensate for the cyl lost.
In lens selection when is BVD considered?
When sphere/ cyl or cross cyl power is above +/-4.00D
What rule is used if an Rx is not available for a given brand and you do not want to change the brand?
Round down values: of axis, cyl, sphere.
ALWAYS ROUND DOWN
How do you decide between the availability of 2 different axis or 2 different cyls, how do you know which one to order?
Place the 2 different Rx in the patients trial frame and let them decide which one is better
How do you assess rotations on a toric lens?
Toric lenses have markings on them that help assess the rotation
What causes rotation in toric lenses?
Rotation due to lens- cornea/ lid interaction
What do the markings on toric lens indicate?
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
Are all the marking on toric lens the same?
No it varies from manufacturer to manufacturer
Describe the 3 positions you expect toric lens markings to be at?
3, 6 and 9 o’clock position
How do you identify the degree of rotation incase a lens has moved??
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.
Procedure of soft toric lens fit assessment before assessing with slit lamp?
As patient to look around, blink abit then assess the lens rotation and lens stability
