by Jay Stockman,
published October 5, 2008
syndicated: 0 | total views: 114 |
word count: 581
laesbarhedsindex readability score: Difficult Readability
website: http://visionupdate.net
T
he evolution of cataract surgery has changed significantly over the years. It began with simply opening a large wound to remove the cataract, and then closing the hole leaving a void where the natural lens was. The only way a patient could then see was with the aid of very thick post surgical eye glasses. Eventually, contact lenses were developed that would correct the high power required to permit these folks to see well after surgery.
With the invention of the post cataract implant, these thick eye glasses and contact lenses became obsolete. Intraocular implants were initially developed with the goal of correcting distance vision, but still required eyeglasses to permit near vision. As time passed, an implant was needed that would permit both distance and near vision without the need for reading glasses. The first multi focal implant attempts were very poor, and were quickly discarded as useless appliances.
With almost 3 million cataract surgeries being performed annually, and that number expected to double in the next 5-10 years, better alternatives needed to be introduced. A very promising implant that permits both distance and near vision is the Crystalens by Bausch and Lomb. Unlike standard multifocal implants, the Crystalens is an accommodative lens that changes focus as the individual needs to see up close, or far away. It works on the premise that best simulates the natural lens’ ability to accommodate when reading is attempted. That is to say, the lens flexes forward when reading, and backward when viewing in the distance. This implant does however have its limitations. Most surgeons are happy when the implant achieves 20/30 in the distance, and some clarity at near.
This ability for the Crystalens to change focus is accomplished with the aid of the eye’s cilliary body; which pulled on the eye’s natural lens prior to its extraction resulting in its change in thickness. The cilliary body muscle continues to function throughout life and has even demonstrated greater contractile force after cataract surgery. The Crystalens is attached surgically to this muscle to assist in its function.
As this muscle contracts and rotates, the implant flexes and it alters the anterior chamber depth which results in the internal gel of the eye (vitreous) moving forward. Current research has shown that a 1 mm anterior movement will result in an increase of 1.3 diopters in accommodative ability. The Crystalens implant has hinges which allow the implant greater flexibility to move for accommodation.
The Crystalens AT- 45 had a 4.5 mm optic zone, while the Crystalens 5.0 has a 5 mm optic zone. These implants do work quite well, but still received patient complaints of poor near and night vision. The latest development is the Crystalens HD which supports a 5.0 OZ and increases the center thickness to 1.5 mm in the central zone of the lens. This increase in thickness permits a greater arching of the lens and thus better near focusing. The results have been outstanding according to Dr Thierry Hufnagel, a New York eye surgeon at the Stahl Eye Center. This increase in accommodative arching appears to be the answer to better near vision with these post cataract patients.
The FDA’s trial of this lens implant has demonstrated at least 2.OO diopters of accommodation in most patients (enough to read at arm’s length), and as much as 4.00 diopters of accommodation in some of these patients. An additional benefit of this new lens is a decrease in poor night vision as well.
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