Reading in a dark with a aspheric IOL

Aspheric and Toric IOL Functions

Advanced cataract treatment options

Different types of intraocular lenses (IOLs) are available today. All of them can treat cataracts. However, modern IOLs are able to offer even more functions in addition to cataract treatment. For instance, aspheric lenses correct certain light phenomena and improve contrast, providing an optimized image quality.

Toric intraocular lenses enable the treatment of astigmatism, a common vision disorder affecting roughly one third of the global population and causing distorted vision.

Both IOL types have special characteristics to enable clear, crisp images. These additional functions are not always covered by the national health care system. Please check with your doctor if an aspheric and/or toric IOL is recommended in your case and discuss the potential extra costs of the lens.

Characteristics of Aspheric Lenses

Correcting spherical aberration for clear vision

Standard types of monofocal IOLs have a spherical optic, which is equally curved on both sides. However, the natural crystalline lens of the eye has a slightly aspherical (not completely round) shape at the front. This enables it to precisely focus the light rays entering the eye on one point of the retina.

Modern monofocal IOLs are available with an aspherical optic just like the shape of the natural lens, which allows you to have a vision as close as possible to natural vision.

Vision simulation with a spheric (left) and an aspheric IOL (right).

Vision simulation with a spheric (left) and an aspheric IOL (right).

How Aspheric Lenses Correct Vision

The special, not uniformly curved, design of the aspheric IOLs enables the correction of spherical aberrations.

What is a spherical aberration?

A spherical aberration is a visual defect that occurs when light rays passing into the eye are not precisely focused at one single focal point. When we are young, the cornea and lens of the eye work together to focus the entering light rays at exactly one point on the retina, optimizing image contrast.

As we grow older, that interaction deteriorates, causing reduced vision quality. This means:

  • Vision gets blurry, and
  • Contrast perception is decreased, leading to difficulty seeing in low-light conditions

With aspheric IOLs, light rays entering the eye are once again sharply focused at a single point on the retina. The result is improved contrast sensitivity and an enhanced image quality, especially during activities such as driving at night or reading in dim lighting conditions.

If you are already suffering from spherical aberration or you want to prevent this visual change, an aspherical IOL may be a suitable option for you. Discuss this option with your ophthalmologist.

A toric IOL implanted in the eye.

A toric IOL implanted in the eye.

Characteristics of Toric Lenses

Correcting irregularly shaped corneas for clear vision

Visual acuity is an important factor for patients. The possibility of correcting astigmatism using toric intraocular lenses (IOLs) during a cataract procedure is a great option for patients suffering from both conditions. Astigmatism is a refractive error like near- or farsightedness. This error is usually the result of an irregularly shaped cornea, which leads to light not being properly focused on the retina. It causes objects at different distances to appear skewed or distorted.

Vision simulation a) with astigmatism b) with a toric IOL.

Vision simulation a) with astigmatism b) with a toric IOL.

How Toric Lenses Correct Astigmatism

How the lens works

A toric lens is shaped in a certain way. The shape of toric lenses is significantly unlike other types of corrective lenses, as they feature two different curvatures.

The shape of toric lenses creates various refractive powers on the vertical and horizontal axis. The combination helps to focus all incoming light properly onto your retina to reduce or eliminate astigmatism.

How toric lenses are implanted in the eye

If you decide to have a toric IOL, the surgical procedure is slightly different to normal cataract surgery. The lens must be implanted in a very specific position in the eye, meaning:

  • Depending on the type of lens, just prior to cataract surgery, temporary markings may need to be placed on your cornea that identify the location of the most curved meridian.
  • During surgery, the toric IOL is implanted in your eye.
  • Once implanted, each toric lens is rotated until the markings on the lens are aligned with the markings on your cornea. 

If you have astigmatism and would like to correct it during cataract surgery, consult your doctor to discuss the implantation of toric IOLs.