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- Evaluate tear film, pupil size and lower lid position
- Use diagnostic lenses
- Have available at least one aspheric and segmented diagnostic set
- Get a complete list of CLMA member labs
- Use trial lenses for over-refraction
- Evaluate the position of segmented designs to the lower lid
- Segment line should be at or near the lower pupil margin
- To evaluate the reading portion of a segmented design, lift up the lid as the patient looks down: the lens should be pushed up. This is referred to as translation.
- Some nasal rotation can be beneficial for reading
- High eccentricity aspheric lenses are usually fit up to 3D – 4D steeper than K
- Low eccentricity aspheric lenses are usually fit up to 1D – 2D steeper than K
- Aspheric lenses typically require good centration with minimal lag on blink (1mm)
- Some aspheric designs benefit from the lens positioning under the upper lid
- Aspheric multifocals benefit from some lens translation when patient looks down to read
- Use the CLMA lab consultants for fitting advice
Making Lens Design Changes
To improve the fitting relationship, make a significant change in lens design:
- Change BCR at least 0.50D
- Change diameter at least 0.3mm
- Change amount of prism at least 0.50D
- Consider switching lens design concepts if unsuccessful with one style