Aspheric Intraocular Lenses

What is the difference between a spherical and an aspherical intraocular lens?

To enable them to improve visual acuity, intraocular lenses must have a modified design.  There are currently various types of intraocular lenses on the market, including spherical and aspherical lenses.   The design of aspherical intraocular lenses seeks to improve or completely neutralise the spherical aberration which exists after extraction of the crystalline lens and which manifests itself especially in night vision. It also seeks to increase sensitivity to contrast and improve visual quality.

In a spherical lens, the rays which pass through the periphery do not converge on the same point as those which pass through the centre.

In an aspherical lens, the aim is to modify the radius of curvature of the lens from the centre to the periphery to make the rays all focus on a single point.

Comparison of Rays of Light crossing Spherical and Aspherical optics

Comparison of Rays of Light crossing Spherical and Aspherical optics (https://www.syscom.com.mx/)

In its natural state the cornea has a spherical aberration with a positive value.  Meanwhile, the crystalline lens has a negative value which compensates for this corneal aberration fully or partially.  When cataract surgery is performed the spherical aberration is increased even more, as the crystalline lens is removed.

The designs of the most innovative intraocular lenses with aspherical design seek to compensate the corneal spherical aberration.  Thanks to this design, visual quality is greatly improved.  Patients especially note a difference in nocturnal conditions.  This type of lens is also useful for activities requiring greater precision, such as golf.

Explanation of aspherical aberration

Explanation of aspherical aberration (https://www.acrysofrestor-la.com/)

What type of aspherical lenses are there on the market?

Today, there are monofocal, toric and multifocal aspherical lenses. There is a wide range to choose from depending on the visual requirements of the patient and individual refractive objectives.

Example of how optotypes are seen when there is aspherical aberration

Example of how optotypes are seen when there is aspherical aberration (https://www.lfmejia.com)