Spherical or aspheric lens in cataract surgery: does it make a difference at night?

"I was told an aspheric lens is better at night. Will I see more clearly when I drive after dark? And is the spherical lens I had implanted years ago lower in quality?" This is one of the questions that puzzle patients most, because the word itself is unfamiliar. The short answer: an aspheric lens does not let you read more letters on the eye chart, but it may improve your ability to make out faint detail, especially in dim light. This is a real difference, but it is moderate in size, and not every patient notices it to the same degree.

What do spherical and aspheric mean?

Imagine an ordinary magnifying glass. Light passing through its center comes together at one point, and light passing through its edges comes together at a point slightly closer. The result is an image that is clear overall, but with a faint halo of softness around it. This optical flaw is called spherical aberration.

Its effect grows when the pupil widens, that is, in dim light and at night, because light then also enters through the edges of the lens. The cornea itself usually adds some of this aberration. In an Egyptian study that measured the eyes of 1658 people awaiting cataract surgery, the cornea added a positive amount of this aberration on average, and the average pupil size in dim light was about 4.6 mm (Elkitkat et al., 2020).

A spherical lens has an evenly curved surface, so it adds some of this aberration on top of what the cornea adds. An aspheric lens has a surface designed with a curvature that changes gradually toward the edges, to reduce this aberration or offset part of what the cornea adds. Aspheric lenses also come in degrees: some offset the cornea's average aberration completely, some offset part of it, and some are "neutral," neither adding nor removing aberration.

What did studies in patients find?

The clearest evidence available is an analysis of 43 clinical trials in which aspheric lenses were implanted in 2076 eyes and spherical lenses in 2034 eyes. The difference in reading the letter chart with glasses was very small, about half a letter, and of no practical value. But contrast sensitivity, the ability to see faint detail such as shades of gray or the outline of a road in fog, was moderately better with the aspheric lens, especially in dim light. Patient questionnaires about satisfaction with the quality of vision, however, did not show a clear result in favor of either type (Schuster et al., 2013). Researchers explain this improvement by the smaller amount of spherical aberration and other fine optical flaws in the eye with an aspheric lens (Schuster et al., 2015).

The same picture appeared in studies from Egypt. In a trial at the Ain Shams University hospitals on 56 eyes, clarity of vision did not differ between the two lenses, while contrast in dim light was better with the aspheric lens (Assaf and Kotb, 2010). In another study from Cairo, the improvement in contrast appeared at only one level of the test and not at the others (Wahba et al., 2011). In other words, the benefit is real, but its size varies from study to study and from eye to eye.

In a trial that followed 200 eyes for two years, the contrast advantage of aspheric lenses persisted, and no difference appeared between two aspheric lenses from different companies (Caporossi et al., 2009).

Is more correction always better?

Not necessarily. In a Swedish trial in which each patient received, in one eye, a lens that fully offsets the cornea's aberration and, in the other eye, a neutral lens, the two eyes were equal in visual acuity and contrast. Aberration was lower with the fully correcting lens, but the neutral lens gave a greater depth of focus, a slightly wider range of clear distances. 28% of patients preferred the eye with the neutral lens, compared with 14% who preferred the other eye (Johansson et al., 2007). The researchers concluded that removing aberration as much as possible did not give the best sense of visual quality.

There is another consideration that appears in the laboratory. A study on an optical testing bench found that a lens that offsets more aberration is affected more if it does not sit exactly in the center, while a neutral lens is hardly affected (Pieh et al., 2024). This is a laboratory result, but it helps explain why one degree does not suit every eye.

The laboratory is one thing, the patient's eye another

Lenses are tested on optical benches that measure image quality very precisely, and clear differences between designs appear on them. But some of these studies were carried out by employees of the manufacturing companies (Alarcon et al., 2023). More importantly, a difference on the bench does not necessarily become a difference the patient notices. The eye is not a fixed instrument: the pupil changes, the cornea differs from person to person, and the brain adapts to the image. So we rely on trials in patients to judge, and treat laboratory results as a signal that needs confirmation.

Does an aspheric lens mean perfect night vision?

No. Night vision after surgery is affected by other factors that may be stronger than lens design. These include residual focusing error or astigmatism, the condition of the retina and the macula, and dryness of the eye surface. They also include capsule clouding behind the lens, which increases glare from lights long before it lowers the reading on the letter chart (Meacock et al., 2003).

Also, obvious halos around lights are clearly more common with multifocal lenses than with monofocal lenses (de Silva et al., 2016). We explain the different lens types in our article on choosing an intraocular lens.

Questions patients often ask

Will I read an extra line on the eye chart with an aspheric lens?

Usually not. The difference in visual acuity in the studies was only about half a letter (Schuster et al., 2013). The real difference is in contrast and vision in dim light.

I had a spherical lens implanted years ago. Is my vision worse than it should be?

Not necessarily. A spherical lens gives good visual acuity. The difference between the two types appeared in contrast tests, while patient questionnaires about the quality of vision did not settle the difference between them (Schuster et al., 2013). There is no reason to replace a healthy lens for this reason alone.

Does an aspheric lens suit every eye?

The cornea differs from person to person, which is why aspheric lenses come in different degrees. No single degree has been shown to be best for every eye. In one trial, the lens that fully offsets aberration did not come out ahead in patient satisfaction (Johansson et al., 2007), and in the laboratory it was affected more when the lens did not sit exactly in the center (Pieh et al., 2024).

Does this depend on the lens's country?

No. Aspheric design is a feature of the lens design, not of the company's name or country. We explain this in our article on American, European or Indian lenses. The material also matters over the long term, as covered in hydrophobic or hydrophilic lens.

Summary

An aspheric lens is designed to reduce an optical flaw that grows in dim light. Studies show that it moderately improves contrast, with no meaningful difference in reading the letter chart, and without guaranteeing perfect night vision. More correction is not always best for every eye. The aim is for patients to understand what this design can add for their own eye, and what depends on factors other than the lens.

This information is for health education and does not replace a medical examination.