Contact Lens Solutions for Presbyopia
Multifocal contact lenses provide correction for both distance and near vision in a single lens, addressing the needs of presbyopic patients. Unlike progressive spectacle lenses where you look through different zones by moving your eyes, multifocal contact lenses use fundamentally different optical principles to deliver multiple focal points simultaneously or sequentially.
Simultaneous Vision Designs
Simultaneous vision is the most common approach in soft multifocal contact lenses. In these designs, both distance and near correction zones are present in front of the pupil at the same time. Light from both distances enters the eye simultaneously, creating multiple images on the retina. The brain then selects the clearest image and suppresses the others.
This process requires neural adaptation: the brain must learn to ignore the slightly blurred image from the zone not in use. Most patients adapt within 1-2 weeks, though some require longer.
Center-Near Design
In a center-near design, the central zone of the lens provides near correction, with distance correction in the surrounding zone:
- Works well in bright light (constricted pupil exposes mostly the near zone, aiding reading)
- In dim light (dilated pupil exposes more of the distance zone), distance vision improves
- Often preferred for patients who prioritize near vision tasks
- May compromise distance vision slightly, especially in bright conditions
Center-Distance Design
In a center-distance design, the central zone provides distance correction, with near correction in the surrounding zone:
- Provides better distance vision in most lighting conditions
- Near vision depends on pupil dilation to expose the peripheral near zone
- Often preferred for patients who prioritize distance activities (driving, sports)
- May require more lighting for comfortable near tasks
Aspheric Designs
Aspheric multifocal lenses use a gradual, continuous power change from the center to the periphery rather than distinct concentric zones. The power transitions smoothly, providing a range of corrections across the lens surface. This design often provides good intermediate vision in addition to distance and near.
Alternating (Translating) Vision Designs
Alternating vision (also called translating) designs work on a different principle: the lens physically moves (translates) on the eye so that different zones are positioned over the pupil depending on gaze direction.
- In primary gaze (looking straight ahead): The distance zone is centered over the pupil
- In downgaze (looking down to read): The lens translates upward on the eye (pushed by the lower lid), positioning the near zone over the pupil
Alternating designs function similarly to bifocal spectacles: you look through one zone at a time, not both simultaneously. This provides sharper vision at each distance because there is no competing blurred image.
Characteristics:
- More commonly implemented in GP lenses than soft lenses because the rigid material allows reliable translating movement
- Requires a lower lid position that supports lens translation
- Often uses truncation (flat inferior edge) to stabilize the lens on the lower lid
- Provides better visual acuity at each distance than simultaneous designs
- Requires more precise fitting than simultaneous designs
Add Power Selection
The add power is the additional plus power needed for near vision, compensating for the patient's lost accommodation. Add powers are specified either as a dioptric value or as a category:
- Low add: Approximately +0.75 to +1.25 D (early presbyopia, ages 40-45)
- Medium add: Approximately +1.50 to +2.00 D (moderate presbyopia, ages 45-55)
- High add: Approximately +2.00 to +2.50 D (advanced presbyopia, ages 55+)
Higher add powers create a greater difference between distance and near zones, which can reduce visual quality at intermediate distances and make neural adaptation more challenging.
Fitting Strategies
Successful multifocal fitting involves several considerations:
- Determine the dominant eye: This guides which design configuration to use on each eye (some fitting guides place center-distance on the dominant eye)
- Start with the lowest effective add: Over-adding creates unnecessary visual compromise
- Evaluate in real-world conditions: Test vision at different distances and lighting levels in the office before the patient leaves
- Allow adaptation time: Most patients need 1-2 weeks to neurally adapt. Set this expectation clearly at dispensing
- Consider pupil size: Large pupils expose more of the peripheral zones; small pupils may not access peripheral zones adequately
Key Takeaways
- Simultaneous vision designs present distance and near zones over the pupil at the same time; the brain selects the clearest image
- Center-near designs prioritize near vision in bright light; center-distance prioritize distance vision
- Alternating (translating) designs physically move the lens to position different zones over the pupil; more common in GP lenses
- Add power increases with age: low (early presbyopia), medium (moderate), high (advanced)
- Neural adaptation typically takes 1-2 weeks; managing patient expectations is essential
- Pupil size significantly affects which zones contribute to vision in simultaneous designs