Which eye gets the distance correction in monovision?

The dominant eye receives the distance correction and the non-dominant eye receives the near correction. This is because distance vision is more critical for safety (driving, spatial awareness), and the brain preferentially relies on the dominant eye for these tasks. Ocular dominance is determined through tests like the sighting dominance (Miles) test or the plus lens blur test.

What is the main disadvantage of monovision?

The primary disadvantage is reduced stereoacuity (depth perception). Because each eye focuses at a different distance, the binocular system cannot process stereoscopic depth cues as effectively. The reduction is proportional to the add power used. Approximately 25-40% of patients who trial monovision find this trade-off unacceptable. Patients requiring precise depth perception for work or activities may not be good candidates.

What is modified monovision?

Modified monovision combines traditional monovision with multifocal lens technology. Common approaches include fitting the dominant eye with a single-vision distance lens and the non-dominant eye with a multifocal, or fitting both eyes with multifocal lenses at different add configurations. This provides better stereoacuity and intermediate vision than traditional monovision while still addressing near vision needs.

Monovision: Fitting Strategy, Dominant Eye, and Modified Approaches

What Is Monovision?

Monovision is a contact lens fitting strategy for managing presbyopia in which one eye is corrected for distance vision and the other eye is corrected for near vision. Each eye receives a single-vision contact lens with a different power, and the brain learns to preferentially use the eye that provides the clearest image for the task at hand.

This approach is conceptually simple and uses standard single-vision lenses, making it straightforward to implement and cost-effective. However, its success depends entirely on the patient's ability to neurally adapt to seeing different images in each eye.

Dominant Eye Determination

In traditional monovision, the dominant eye is corrected for distance and the non-dominant eye is corrected for near. Determining ocular dominance is therefore an essential step in the fitting process.

Common methods for determining the dominant eye:

Sighting dominance (Miles test): The patient extends both arms, creates a small triangular opening with overlapping hands, and views a distant target through the opening with both eyes open. When each eye is closed alternately, the dominant eye is the one where the target remains in the opening
Hole-in-card test: Similar to the Miles test but using a card with a small hole. The patient holds it at arm's length and views a target, then each eye is alternately covered
Plus lens test (blur dominance): Add +1.50 to +2.00 D in front of each eye alternately while the patient views a distance target with both eyes. The dominant eye is the one that causes more disturbance (blur) when fogged

The dominant eye gets the distance correction; the non-dominant eye gets the near correction. The rationale is that distance vision is more critical for safety (driving, navigation, spatial awareness), and the dominant eye is the one the brain preferentially relies on for these tasks.

How Monovision Works

With monovision, the brain receives two slightly different images:

The distance eye sees distant objects clearly but near objects are blurred
The near eye sees near objects clearly but distant objects are blurred

Through a process called interocular suppression, the brain learns to suppress the blurred image and attend to the clear one. When looking at distance, the brain emphasizes input from the distance eye and suppresses the blurred near eye. When reading, the brain reverses this emphasis.

This process is usually not conscious. Most adapted patients are not aware of which eye they are using and simply perceive generally clear vision at most distances.

Benefits of Monovision

Simplicity: Uses standard single-vision lenses without specialized multifocal designs
Cost-effective: Single-vision lenses are typically less expensive than multifocal lenses
Wide availability: Any single-vision lens can be used, providing maximum material and parameter options
Predictable optical quality: No simultaneous image blur from competing zones as with multifocal designs

Limitations and Trade-offs

Reduced Stereoacuity

The most significant trade-off is reduced stereoacuity (depth perception). Because each eye has a different focal point, the binocular visual system cannot process stereoscopic depth cues as effectively. The degree of stereoacuity reduction depends on the add power:

Low add (up to +1.25 D): Minimal stereoacuity reduction; most patients adapt easily
Medium add (+1.50 to +2.00 D): Moderate reduction; most patients still function well
High add (+2.25 D and above): Significant reduction; some patients may struggle with depth-dependent tasks

Intermediate Vision

Standard monovision provides clear distance and near vision but may leave a gap at intermediate distances (computer screen, dashboard). Neither eye is optimally focused at these distances, which can be problematic for patients who spend significant time at intermediate distances.

Adaptation Failure

Not all patients can adapt to monovision. Approximately 60-75% of patients who trial monovision find it acceptable. Those who cannot adapt typically report persistent blur, difficulty judging distances, or a general sense of visual discomfort. A trial period before prescribing is essential.

Always perform a monovision trial before prescribing. Fit the patient with trial lenses and have them wear them for at least several days (ideally 1-2 weeks) during normal activities before deciding. In-office testing alone does not reliably predict real-world success. Patients who drive frequently should test their distance vision through the monovision setup, especially at night.

Modified Monovision

Modified monovision combines elements of monovision with multifocal lens technology to reduce the limitations of traditional monovision:

Single-vision distance + multifocal near: The dominant eye wears a single-vision distance lens while the non-dominant eye wears a multifocal lens. This provides clear distance vision through the dominant eye and both near and partial distance through the non-dominant eye, improving binocularity
Multifocal + multifocal with different adds: Both eyes wear multifocal lenses, but with different add configurations. The dominant eye might have a center-distance design with a low add, while the non-dominant eye has a center-near design with a higher add
Reduced near power: Using a lower add than the full near prescription on the near eye. This reduces the interocular difference and preserves more stereoacuity while still providing functional near vision

Modified monovision typically provides better stereoacuity and intermediate vision than traditional monovision, at the cost of slightly more complex fitting and potentially higher lens cost.

Prescribing the full near add for the near eye in monovision without considering the impact on stereoacuity and adaptation. Starting with a lower add (undercorrecting the near eye slightly) improves the chance of successful adaptation. The add can be increased gradually as the patient adapts or as presbyopia progresses.

Patient Selection

Good candidates for monovision:

Motivated patients who understand the trade-offs
Patients with low to moderate adds (up to +2.00 D)
Patients who do not rely heavily on precise depth perception for work or hobbies
Patients who have previously adapted to monovision

Poor candidates for monovision:

Patients requiring precise stereoacuity (surgeons, pilots, athletes in ball sports)
Patients with existing binocular vision problems (strabismus, amblyopia)
Patients uncomfortable with the concept after thorough explanation

Key Takeaways

Monovision corrects the dominant eye for distance and the non-dominant eye for near
The brain suppresses the blurred image through interocular suppression
Stereoacuity (depth perception) is reduced, proportional to the add power
Approximately 60-75% of patients successfully adapt to monovision
Modified monovision combines single-vision and multifocal lenses to reduce limitations
Always perform a trial period before prescribing; start with a lower add if possible