IOLs were traditionally made of an inflexible material (PMMA) though this largely been superseded by the use of flexible materials. Most IOLs fitted today are fixed monofocal lenses matched to distance vision. However, other types are available, such as multifocal IOLs which provide the patient with multiple-focused vision at far and reading distance, and adaptive IOLs which provide the patient with limited visual accommodation.
Insertion of an intraocular lens for the treatment of cataracts is the most commonly performed eye surgical procedure. The procedure can be done under local anesthesia with the patient awake throughout the operation. The use of a flexible IOL enables the lens to be rolled for insertion into the capsule through a very small incision, thus avoiding the need for stitches, and this procedure usually takes less than 30 minutes in the hands of an experienced ophthalmologist. The recovery period is about 2–3 weeks. After surgery, patients should avoid strenuous exercise or anything else that significantly increases blood pressure. They should also visit their ophthalmologists regularly for several months so as to monitor the implants.
IOL implantation carries several risks associated with eye surgeries, such as infection, loosening of the lens, lens rotation, inflammation, night time halos. Though IOLs enable many patients to have reduced dependence on glasses, most patients still rely on glasses for certain activities, such as reading.
History
Sir Harold Ridley was the first to successfully implant an intraocular lens on November 29, 1949, at St Thomas' Hospital at London. That first intraocular lens was manufactured by the Rayner company of Brighton, East Sussex, England from Perspex CQ made by ICI. It is said that idea of implanting an intraocular lens came to him after an intern asked him why he was not replacing the lens he had removed during cataract surgery. The first lenses used were made of glass, they were heavy and were prone to shatter during Nd:YAG laser capsulotomy. Plastic materials were used later, when Harold Ridley noticed that they were inert, after seeing pilots of World War II with pieces of shattered windshields in their eyes. The intraocular lens did not find widespread acceptance in cataract surgery until the 1970s, when further developments in lens design and surgical techniques had come about. Currently, more than a million IOLs are implanted annually in the United States.
Materials used for intraocular lenses
Polymethylmethacrylate (PMMA) was the first material to be used successfully in intraocular lenses. British ophthalmologist Sir Harold Ridley observed that Royal Air Force pilots who sustained eye injuries during World War II involving PMMA windshield material did not show any rejection or foreign body reaction. Deducing that the transparent material was inert and useful for implantation in the eye, Ridley designed and implanted the first intraocular lens in a human eye.
Advances in technology have brought about the use of silicone and acrylic, both of which are soft foldable inert materials. This allows the lens to be folded and inserted into the eye through a smaller incision. PMMA and acrylic lenses can also be used with small incisions and are a better choice in people who have a history of uveitis, have diabetic retinopathy requiring vitrectomy with replacement by silicone oil or are at high risk of retinal detachment. Acrylic is not always an ideal choice due to its added expense. New FDA-approved multifocal intraocular lens implants allow most post operative cataract patients the advantage of glass-free vision. These new multifocal lenses are not a covered expense under most insurance plans (In the United States, Medicare decided to stop covering them in May 2005) and can cost the patient upwards of $2800 per eye. Latest advances include IOLs with square-edge design, non-glare edge design and yellow dye added to the IOL.
In the United States, a new category of intraocular lenses was opened with the approval by the Food and Drug Administration in 2003 of multifocal and accommodating lenses. These come at an additional cost to the recipient beyond what Medicare will pay and each has advantages and disadvantages.
Multifocal IOLs - provide for simultaneous viewing of both distance vision and near vision. Some patients report glare and halos at night time with these lenses.
Accommodating IOLs - allow for both distance vision and midrange near vision. These IOLs are typically not as strong for closer vision as the multifocal IOLs.
To incorporate the strengths of each type of IOL, eye surgeons are increasing using a multifocal IOL in one eye to emphasize close reading vision and an accommodating IOL in the other eye for further midrange vision. This is called "mix and match." Distance vision is not compromised with this approach, while near vision is optimized.
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