1. What happens to your glasses after surgery?
Cataracts occur when the crystalline lens inside the eye becomes cloudy, making vision difficult. During surgery, this cloudy lens is removed and replaced with an artificial intraocular lens (IOL). The most commonly used lenses are monofocal, meaning they focus at only one distance. If set for distance, you may still need glasses to read nearby text.
Can a single lens create focus for both distance and near vision? This is the goal of multifocal intraocular lenses.
2. How one lens focuses at two places by splitting light
Multifocal lenses work by splitting incoming light into different paths, creating focus at multiple distances, such as far and near [2]. There are two main ways this is done. The first is the refractive type, which divides the lens surface into zones, with each zone dedicated to a specific distance. The second is the diffractive type, which uses concentric microscopic steps on the lens surface to split light through diffraction [2].
However, splitting light means that less light reaches any single focal point compared to a monofocal lens [2]. While this does not make vision disappear, this distribution of light causes specific visual quirks that are discussed later.
3. Do you really need fewer glasses? What studies say
A Cochrane Review, which collects and analyzes multiple studies, reported that multifocal lenses tend to improve near vision and may reduce reliance on glasses. The risk ratio for glasses dependence was 0.63, which is lower than the monofocal group, though the certainty of this evidence is rated as low [1].
For distance vision, there was little difference between multifocal and monofocal lenses, with moderate certainty [1]. Therefore, it cannot be said with certainty that multifocal lenses eliminate the need for glasses entirely.
4. Seeing rings around lights: Halos and glare
The same review reported that unpleasant visual phenomena are more common and more noticeable with multifocal lenses [1]. Seeing rings around streetlights or car headlights at night is called a halo, while feeling dazzled or uncomfortable is called glare. The incidence of halos was about 3.5 times higher with multifocal lenses than with monofocal ones [1]. This number compares likelihood; it does not mean every patient will experience it.
Whether the convenience of reduced glasses use outweighs these visual quirks depends on the individual. People who drive at night and people who do detailed close-up work may prioritize different visual qualities [1].
5. Can design changes reduce visual side effects?
To address these issues, new lens designs have been developed. These include trifocal lenses that focus at three distances (far, intermediate, and near), lenses with continuous focus extension, and Extended Depth of Focus (EDOF) lenses that extend the range of clear vision from far to intermediate [4].
EDOF lenses are introduced as being developed to have less halo and glare, though they provide less additional focus for near vision [4]. The choice of lens depends on whether a patient prioritizes the range of vision or the absence of visual quirks.
The history of intraocular lenses began on November 29, 1949, when Harold Ridley implanted the first one in a London hospital [3]. His idea was initially rejected by the medical community and only gained acceptance in the late 1970s. Multifocal lenses appeared in the late 1980s, with refractive types launched in the UK in 1986 and diffractive types by a US company in 1987 [2].
6. How costs are handled in Japan
In Japan, starting in April 2020, cataract surgery using multifocal lenses aimed at reducing glasses use became eligible for "selective medical treatment" defined by the Ministry of Health, Labour and Welfare [5]. The surgery itself is covered by health insurance, but the difference in cost between the multifocal lens and a standard lens is paid entirely out-of-pocket by the patient [5].
The extra cost varies by hospital. One hospital’s 2026 guide listed a trifocal lens at approximately 250,000 yen per eye, though costs vary by location and time, with several hundred thousand yen being a rough estimate [6]. Decisions about halos, near vision needs, and cost should be made through thorough discussion with a doctor based on one’s lifestyle.
7. Try this experiment yourself
If you want to understand how your eye focuses, try this simple experiment. Hold your index finger in front of your face and look alternately at the finger and a distant sign. When you focus on the finger, the distance blurs. When you focus on the distance, the finger blurs. This demonstrates that the eye struggles to focus on two distances at the same instant.