A cataract describes a clouding of the eye lens, which focuses images on the nerve tissue at the back of the eye. A significant cataract causes loss of visual clarity and dimmed vision. The definitive treatment for a cataract is the removal of the clouded lens. In most cases, the diseased lens is replaced with a permanent artificial lens known as an intraocular lens. Different types of intraocular lenses offer varying advantages for people with nearsightedness, farsightedness and astigmatism.
Monofocal Lens
Monofocal lenses, also known as single vision fixed focus lenses, optimize visual focus for a single distance. Lenses that optimize distance vision cause blurry near vision. Conversely, lenses the provide optimum near vision cause blurry distant vision. People who choose monofocal cataract lenses typically require glasses or contacts to provide correction for visual distances outside the fixed focus of the implant, notes the patient information website All About Vision.
For people with a cataract in both eyes, monovision is an option in which correction is optimized for distance in one eye and near vision in the other. The brain adapts to the different focal points for each eye by relying more heavily on input from the focused eye in a given situation.
Toric Lens
A toric cataract lens is a monofocal lens that also corrects for astigmatism. The Bascom Palmer Eye Institute of the University of Miami explains that the astigmatism correction of a toric lens enhances the level of correction only for the chosen point of focus.
Accommodating Lens
An accommodating cataract lens attaches to the eye muscles that once controlled the natural lens. The eye muscles move the artificial lens in ways similar to the way the natural lens was moved. This enables a range of distances at which images can be seen clearly, explains the patient information website eyeSmart, sponsored by the American Academy of Ophthalmology.
Multifocal Lens
Multifocal cataract lenses have different areas within the lens that correct for different focal distances, similar to a progressive lens in a pair of eyeglasses. Typically, a multifocal cataract lens is implanted in each eye. The eyes and brain adapt to the lenses over a six to 12 week period, according to the website eyeSmart.
In a 2006 review article published by the "Cochrane Database of Systematic Reviews," Drs. Martin Leyland and Edward Pringle report that multifocal cataract lenses provide superior correction for near vision compared to monofocal lenses. The authors point out, however, that multifocal lenses are associated with an increased incidence of halos around bright lights and decreased contrast sensitivity compared to monofocal lenses.
References
- All About Vision: Cataract Surgery
- All About Vision: Intraocular Lenses (IOLs): Including Premium, Toric & Aspheric Designs
- eyeSmart: IOL Implants
- The Cochrane Collaboration: Multifocal Versus Monofocal Intraocular Lenses After Cataract Extraction
- Bascom Palmer Eye Institute, University of Miami Health System: Cataracts
