AcrySof® Toric Intraocular Lens (TIOL)

The Natural Crystalline Lens

The crystalline lens is a refractive structure within the eye consisting of a transparent membrane filled with a transparent protein. The crystalline lens is responsible for approximately 40% of the eye's focusing power and can change its curvature in order to focus images of nearby objects in 
our environment. 

As part of the normal aging process, the crystalline lens progressively loses its clarity and elasticity. This hardening of the natural lens begins very early in life, but tends not to interfere with clear near vision until after the age of 40. At this approximate age, when the lens tissue has hardened and lost its ability to change its curvature sufficiently enough to focus for reading vision, the condition is called presbyopia. When presbyopia occurs, individuals require reading spectacles to fine-tune vision for near tasks such as reading or sewing.

Another aging process that occurs within the natural lens is the progressive loss of transparency in the transparent protein. When the lens opacity begins to impair an individual's functional vision or block vision, we describe the condition as cataract, which can be surgically extracted. However, once the lens tissue is removed, spectacles, contact lenses or an intraocular lens (IOL) implant must replace the lost optical power of the natural lens to achieve visual correction. Today, ophthalmologists use the intraocular lens device as the most typical method of restoring optical power after natural lens extraction. NOTE: Cataracts may also develop as the result of exposure to ultraviolet (UV) rays, eye trauma, medications, disease, genetics or infection prior to birth and/or other factors. 

Astigmatism

Astigmatism refers to an optical irregularity of the eye caused by unequal curvatures of the natural crystalline lens and/or the cornea (i.e., the clear front window of the eye responsible for ~60% of the eye's focusing power). Since an astigmatic lens or cornea has more curvature in one direction than another (similar to a football shape), as light enters the eye, the eye is unable to bend the light equally to focus images at any distance clearly. Though no cornea is perfectly shaped, the astigmatic distortion for most eyes is so slight that it does not significantly affect vision. However, when astigmatism is present in large amounts, it can blur functional vision.

Astigmatism can occur alone or along with myopia (i.e., nearsightedness) or hyperopia (i.e., farsightedness). If astigmatism is caused by an eye's natural lens having different curvatures on one or both its surfaces, it is referred to as Lenticular Astigmatism, which is resolved when the crystalline lens is removed at the time of lens extraction surgery (e.g., Cataract or Refractive Lens Exchange). Corneal Astigmatism refers to a variation in corneal curvature. In larger amounts, corneal astigmatism will continue to have an effect on vision quality after lens exchange surgery (if it is not corrected by incision placement, Astigmatic Keratotomy, Limbal Relaxing Incisions or excimer laser refractive surgery).

Restoring Optical Power & 
the AcrySof Toric Intraocular Lens (TIOL)

Until now, the most commonly manufactured IOL implants were spherical monofocal lenses, which offer a fixed-range of focus and correct myopia and hyperopia only. This means, after lens extraction and spherical monofocal lens insertion, a patient is reliant upon spectacles to fine-tune some ranges of focus (i.e., near, intermediate and/or distance vision — depending on patient preference) and correct corneal astigmatism, if more than a small degree 
is present.

Using principles similar to toric contact lenses, Alcon Laboratories has developed the AcrySof Toric intraocular lens to provide individuals with distance vision and astigmatic correction after natural lens extraction surgery. This type of IOL enables many patients with corneal astigmatism to function adequately without spectacle dependence for distance vision.

Basic Information About the AcrySof TIOL

• It has a toric back-surface design intended to neutralize corneal astigmatism.

• It can provide sharper vision than a spherical IOL and may reduce dependency on corrective lenses.

• It is the same hydrophobic acrylic lens material as the the original AcrySof intraocular lens, which has been inserted in over 16 million human eyes since 1991. This material provides the surgeon with a high level of rotational stability, which is important for accurate positioning of the implant lens during surgery.

• It offers a fixed-range of focus — providing near, intermediate or distance vision — depending on patient preference. After lens extraction and AcrySof TIOL 
  insertion, patients require spectacles to fine-tune tasks at other distances.