by Jay Stockman
Cataract surgery has been performed for many years, and new developments have dramatically improved the post-op vision. The lens is a normal structure of the internal part of the eye. We are all born with clear, natural lenses whose function is to focus light onto the retina, and also absorb dangerous wavelengths of light. Over time, this clear lens will become yellow, as its chemical structure changes as a result of years of light absorption, and general oxidative stress on the body.
Cataract surgery has been performed for many years, and new developments have dramatically improved the post-op vision. The lens is a normal structure of the internal part of the eye. We are all born with clear, natural lenses whose function is to focus light onto the retina, and also absorb dangerous wavelengths of light. Over time, this clear lens will become yellow, as its chemical structure changes as a result of years of light absorption, and general oxidative stress on the body.
Early cataract surgery involved simply removing the cloudy lens from the eye. In order to see, the patient then had to wear very thick eye glasses, or a contact lens. As technology advanced, anterior chamber Intraocular lenses(IOL) were developed. These were artificial lenses that were placed in front of the iris to replace the removed lens. They worked very well, but over time the corneas were damaged in most of these patients. These anterior chamber lenses vibrated as a result of aqueous humor (fluid) flow from the back of the eye toward the front. These vibrations over time damaged the endothelial (bottom) layer of the cornea resulting in swollen corneas, and cloudy vision.
The next big change was the development of posterior chamber IOLs. These are placed behind the iris, and thus eliminated the vibrations; sparing the cornea from trauma. Over time, improvements were made to these lenses; smaller, better quality and flexible so they could be implanted with very small suture-less incisions. The basic problem with all of these implants was that unlike the natural lenses of the eye, only distance correction could be achieved. Reading glasses were necessary to see objects up close. This brings us to the next big change in the IOL implants. In an effort to meet the challenges of allowing patients to see distance and near post surgically, multi-focal implants have been developed.
The major new players in this game of multi-focal IOLs include Restore by Alcon, Rezoom by AMO, Array and Tecnis also by AMO and Crystalens by Eyeonics. They are all designed to give the patients a full range of vision from distance to near without the need for any eyeglasses. Each type achieves this goal through different modalities.
The Restore implant is manufactured with multiple small concentric rings, similar to the rings of a dart board. These concentric rings alternate between distance and near vision. Multiple images are projected onto the retina, and the brain must then decide which image it wants to see clearly. Most patients say that they see adequately in the distance, and usually test to about 20/40 vision. Near vision is a bit better in most patients. The primary complaint, aside from less then perfect distance vision is glare at night. Approximately 80% of these patients do not wear any type of glasses post surgically.
The Rezoom lens works in the same manner as the Restore, but has larger concentric rings. This improves the distance vision, but reduces the near vision. 81% of these patients are happy with their reading vision, but 29% still require reading glasses to see at near. With both the Restore and Rezoom implants, Alphagan eye drops are employed to reduce bothersome glare by reducing the pupil size. The Tecnis IOL is not as yet available, but since it is made as an Aspheric lens and not concentric rings, there is less glare and halos and better reading in dim light. It also permits reading with a greater range. More research will bring to light the true value, and short comings of this implant.
The Crystalens is the first IOL that has an adjustable focusing ability, much like the natural lens of the eye. The implant is placed behind the iris, and has 2 flexible hinges 180 degrees apart from each other. As the ciliary muscle contracts, and relaxes it causes the implant to move forward and back changing the effective power of the lens. This mimics the natural lens's power change with focusing. It is therefore the first and only Accommodating implant that allows for bothe near and far vision. Substantial adaptation is required, and may take weeks to even months to reach an acceptable level of vision. There is, however a decrease in contract sensitivity ,and some distortion may be induced. Reading glasses may be required for the intermediate distances, and in patients with larger pupils night time vision issues may be present.
Which implant would be best for any given patient will vary, and depend on factors such as expectations, side effects, need for bilateral surgeries (since some implants work best when each eye has one) and cost. Insurance plans do not pay for these specialty implants, and the combined costs with the doctor's fees may be over $2000.00 per eye.
Finally, some patients have astigmatism following cataract surgery. Since the implants do not correct for this, corneal incisions can be made post surgically to reduce or eliminate that component.. When deciding to have cataract surgery it is important to see an experienced surgeon who is knowledgeable with all these new developments, and can best asses which implant would be best for which patient.
About the Author
Dr. Jay B Stockman is a practicing doctor for http://newyorkvisionassociates.com, and a contributing expert for VisionUpdate.net.
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