Intra Ocular Lenses–Biomedical Article

Cataract surgery in the desert

Ridley’s implantation (1949) of the first intraocular lens (IOL) marked the beginning of a major change in the practice of ophthalmology. The IOLs are microlenses placed inside the human eye to correct cataracts, nearsightedness, farsightedness, astigmatism, or presbyopia. There are two types of IOLs: anterior chamber lenses,which are placed in the anterior chamber of the eye between the iris and the cornea, and posterior chamber IOLs, which are placed in the posterior chamber behind the iris and rest against the capsular bag. Procedures for implanting the IOLs and technologies for manufacturing them in various sizes, thicknesses, and forms as well as with various materials progressed tremendously in the last decade. Multifocal IOLs are one of the important signs of this progress. While monofocal IOLs, the most commonlyused, are designed to provide clear vision at one focal distance, the design of multiple optic (multifocal) IOLs aims to allow good vision at a range of distances.

INTRAOCULAR LENSES: WHAT AND WHY?

An intraocular lens, commonly called IOL, is a tiny artificial lens implanted in the eye. It usually replaces the faulty (cataractous) cristalline lens. The most common defect of the natural lens is the cataract, when this optical element becomes clouded over. Prior to the development of
IOLs, cataract patients were forced to wear thick coke bottle glasses or contact lenses after the surgery. They were essentially blind without their glasses. In addition to IOLs replacing the crystalline lenses, a new family of IOLs, generally referred to as phakic lenses, is nowadays subject of active research and development. (Phakos is the Greek word for lens. Phakic is the medical term for individuals who have a natural crystalline lens. In Phakic IOL surgery, an intraocular lens is inserted into the eye without removal of the natural crystalline lens.) These IOLs are placed in the eye without removing the natural lens, as is completed in cataract surgery. They are used to correct high levels of nearsightedness (myopia) or farsightedness (hyperopia). An IOL usually consists of a plastic lens with plastic side struts called haptics to hold the lens in place within the capsular bag. The insertion of the IOL can be done under local anesthesia with the patient awake throughout the
operation, which usually takes <30 min in the hands of an experienced ophthalmologic surgeon (Fig. 1).

HISTORICAL OVERVIEW

The idea of the IOL dates back to the beginning of modern cataract surgery when Barraquer developed keratomileusis. However, the first implantation of an artificial lens in the eye was probably attempted in 1795 . References to the idea of the IOL before World War II in ophthalmic literature are rare. There has been mention of limited animal experiments using both quartz and plastic material
performed in the 1940s, but nothing had come of these efforts .

The most important step toward the implantation of IOLs came as a result of World War II pilots, and the injuries sustained when bullets would strike the plastic canopy of their aircraft  causing small shards of plastic to go into their eye. In the late 1940s, Howard Ridley was an RAF ophthalmologist looking after these unfortunate pilots and observed, to his amazement, little or no reaction in cases in which the material had come from Spitfire planes. He then concluded the poly(methyl methacrylate) (PMMA) material of the canopies (windshield) was compatible with eye tissue.

This observation sparked the idea for inserting an artificial lens in the eye. Ridley, who was convinced this lens should be placed in the posterior chamber, designed a disk-shaped lens, much like the natural lens, with a small peripheral flange allowing him to hold the lens with forceps.

The artificial lens, made entirely of PMMA, weighed slightly >100 mg in air and was 8.35 mm in diameter. In several cases, he attempted to implant the lens following intracapsular surgery using the vitreous base for support. On November 29, 1949, the first successful IOL implantation was performed at St. Thomas Hospital in London. While far from perfect, the procedure worked well enough to encourage further refinement. Then, over a decade, Ridley implanted several hundred IOLs. Though Ridley was ahead of his time, his method was subject to serious criticism. Complications were common and failure rates > 50% were often contemporaneously quoted. Fixation was dependent on the formation of adhesions between the iris and the capsule. Several ophthalmologists strongly opposed to his procedure. Implantation in the anterior chamber was technically easier and was compatible with intracapsular surgery. Also, fixation could be achieved at the time of implantation by adding haptic struts to the lens that could be wedged into the angle. The first anterior chamber lens was implanted by Baron in 1952.
To make intraocular lens implantation safe, developments in lens design and surgical techniques were required. Lens implantation did not become widely adopted as an integral part of cataract surgery until the 1980s. Key advances were the introduction of viscoelastic fluids to
protect the cornea during implantation and flexible haptics to enhance long term stability of the IOL. With traditional single vision monofocal IOLs, people generally experience good vision after surgery at a single focal point, either near or at a distance. The multifocal IOL was designed in the mid-1990s to provide a full range of vision with independence from glasses in most situations. Besides, the invention of phakic lenses is no less important than Ridley’s invention. These IOLs were introduced by Strampelli and later popularized by Barraquer in the late 1950s. Phakic IOLs are becoming more popular because of their good refractive and visual results and because they are easy to implant in most cases. In the beginning, the design was a biconcave angle-supported lens.

These lenses were abandoned following serious angleand endothelium-related complications. By the late 1980s, Baikoff introduced a myopia lens with Kelman-type haptics. This design had many problems, leading to its design modification a number of times. Fyodorov, the inventor of radial keratotomy, introduced the concept of a soft phakic lens in the space between the iris and the anterior surface of the crystalline lens. Based on earlier works of Worst, winner of the Binkhorst
Award for innovation in ophthalmology in 1976, Fechner introduced phakic myopia lens of iris claw design in 1986. This IOL is then referred to as Worst–Fechnerlens. Many companies around the world manufactured it in various models. Today, people usually identify it by the
name of Artisan IOL.

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