GP lens eye Rounds

PRESBYOPIA: Troubleshooting Corneal GP Multifocals

Thomas G. Quinn, OD, MS, FAAO, FSLS

Aspheric Corneal GP Multifocals

Aspheric corneal GP multifocals provide simultaneous optics to meet the needs of many presbyopes and are the most commonly employed corneal GP design.1 Most of these designs are center-distance with increasing add toward the periphery of the lens.

Back Surface Aspheric Designs

Back surface aspheric designs can employ either high eccentricity (rapid rate of base curve flattening from center to periphery) or low eccentricity optics.

High Eccentricity Back Surface Designs

Potential Problem: Spectacle Blur
Due to the rapid rate of flattening occurring on the back surface, these lenses need to be fit as high as 3 D steeper than “K”. 2 Such a steep fitting lens may lead to corneal molding resulting in spectacle blur following lens removal.
Solution:
Flattening the base curve of the lens may help but may create problems with centration. If this occurs, consider refitting with a different design.

Low Eccentricity Back Surface Designs

Potential Problem: Poor Near Vision
Poor near vision may result due to the limited add created by the low eccentricity back surface.
Solution:

1. Push plus in the lens worn on the non-dominant eye
2. Promote lid attachment by modifying the fit, usually by flattening the base curve, at minimum, 0.50 D. This helps the upper lid hold the lens up (lid attachment), promoting translation of the lens when in down gaze. This moves the line-of-sight to view through a more peripheral portion of the lens where there is higher add power.
3. If most needs are met but some assistance is needed for very fine detail at near, occasional use of over-spectacles (readers) may be satisfactory
4. Change to a different aspheric design that offers additional add power on the front surface of the lens
5. Change to a translating design if lower lid tangent or slightly above lower limbus

Front Surface Aspheric Designs

Excellent centration is critical for a lens design featuring add power on the front surface of the lens.
Potential Problem: Poor Distance Vision
Solution:

1. Enhance centration by modifying base curve radius (BCR), overall diameter (OAD) or reducing center thickness
2. Increase central distance zone diameter
3. Reduce add power

Potential Problem: Poor Near Vision
Solution:

1. Enhance centration by modifying BCR, OAD, or reducing center thickness
2. Decrease central distance zone diameter
3. Increase add power

Combined Front and Back Surface Add Designs

See troubleshooting strategies for Front Surface Aspheric Designs

Translating Bifocal/Trifocal Designs
Potential Problem: Poor Near Vision
Solution:

1. If the seg does not translate in down gaze or rotates excessively (particularly problematic if it does so in temporal direction), flatten fit by, at minimum, 0.50D, increase prism by, at minimum, 0.50D, and/or add truncation
2. If seg is too low (test by seeing if near vision improves in extreme down gaze), raise seg height

Potential Problem: Poor Distance Vision
Solution:

1. If seg is too high, lower seg.
2. If distance blur occurs immediately after the blink, increase prism and/or lower seg line
3. If fit looks good, perform an over-refraction to ensure proper distance power

Potential Problem: Poor Intermediate Vision with Bifocal Translating Design
Solution:

1. Fit with modified powers (one distance or near seg set to intermediate)
2. Refit with a segmented trifocal (especially with higher add)
3. Refit with progressive translating design
4. Wear +1.25D spectacles over bifocal translating design; view computer through distance portion of the contact lens; fabricating glasses with bottom of spectacle lenses cut off allows for usual use of add portion of the contact lens for near viewing.

Sources

1. Bennett ES. GP Annual Report 2017. Contact Lens Spectrum. 2017;32(10):22-25, 27, 28, 45.
2. Bennett ES, Henry VA, Richdale K, Benoit DP. Multifocal Contact Lenses. In Bennett ES, Henry VA. Clinical Manual of Contact Lenses (5th Ed.), Wolters Kluwer Publishers, 2020; 440-491.