Astigmatism-Correcting Intraocular Lenses

The front of the eye serves as a focusing element to bring a sharp image upon the retina.  Creating a sharp retinal image requires that the cornea and lens each create a single focal point.  Generating a single focal point for the cornea requires that the cornea has a round "dome" shape with the same degree of curvature for 360 degrees, therefore no matter what place light enters the cornea, it is bent to the same degree en route to the lens.  Astigmatism, specifically corneal astigmatism, may be described as the condition where the cornea has at least two radii of curvature.  Less technically explained, the outer window of the eye has a more oval or "football" shape.  The two different curvatures of the cornea generate tow different focal points because light rays are bent differently depending upon which part of the cornea they enter; as a result even a perfectly symmetric crystalline lens or standard IOL will not be able to bring the light rays to a single retinal focal point, so the eye does not create a clear image for the patient. 

Before the advent of advanced technology implants removing the cataract involved exclusively removing and replacing the eye's lens and if the eye had significant corneal astigmatism before cataract surgery, the condition would exist after surgery.  The introduction of astigmatism-correcting or toric intraocular lenses finally gave astigmatic patients an answer to correct their vision, no only reversing the effects of the cataract, but actually making their uncorrected vision better than it had been for years - typically decades!  Toric lenses correct vision in a manner that standard single focus lenses cannot - the toric lens, like the astigmatic eye's particular corneal curvature so that the toricity of the IOL neutralizes the patient's corneal astigmatism. 

Correcting or "neutalizing" the corneal astigmatism creates a more precise focal image, thereby reducing or totally eliminating the cornea-induced blur (in ophthalmology speak" this is called "collapsing the Conoid of Sturm" or reducing the distance between the two corneal focal points.