Intraocular Lens (IOL) Materials

*Samir Čanović, Suzana Konjevoda, Ana Didović Pavičić and Robert Stanić*

### **Abstract**

In 1949, first intraocular lens (IOL) insertion after cataract surgery was performed by Sir Harold Ridley, in London. Only in the 1970s, the IOL insertion after cataract surgery began to be a standard procedure. The material the first IOL-s were composed of was polymethyl methacrylate (PMMA). The PMMA is a rigid material and the corneal incision had to be at least as big as the IOLs optic and it became its biggest disadvantage in the cataract surgery. The main goal of modern cataract surgery is as smallest incision possible, so the IOL-s had to be flexible and therefore foldable. This goal was achieved by improvements in the IOL design and materials that made them foldable. First foldable IOL-s were made of hydrogel but they were unstable and the development of the first silicone IOL-s overcame that problem. Foldable silicone IOL-s were first implanted in 1978 by Kai-yi Zhou. Foldable IOL's benefits are its compatibility with a small incision surgery that is self-sealing procedure and the possibility of insertion by a single-use applicators that made the surgery safer. In the future, we can expect some new, different and innovative approaches in the IOL design and materials.

#### **1. Introduction**

Intraocular lenses (IOL) are implanted in the eye in order to treat refractive errors produced by extraction of the lens as a standard procedure in cataract surgery.

IOL is designed and composed of optic—central part, and the haptics—side structures that keep the lens inside the capsular bag.

The first intraocular lens was inserted in 1949 after cataract surgery by Sir Harold Ridley in St Thomas Hospital in London [1]. The material the first IOLs were composed of was polymethyl methacrylate (PMMA). It was a rigid nonfoldable material making the placement of the IOL challenging [2]. In the 1970s, the new lighter posterior chamber IOLs were designed and had propylene haptics for better stabilization and ciliary sulcus fixation and the IOL insertion after cataract surgery began to be a standard procedure.

In the early 1980s, Epstein began to use lenses made of silicone with the intention to make them foldable. That way they could be inserted into the eye through the small incisions of 3 mm and less compared to 5–7 mm incisions needed for nonfoldable IOLs insertion [3, 4]. The practice of IOL implantation was revolutionized in 1984 when Thomas Mazzocco began folding and implanting the plate haptic silicone IOLs [5].

#### *Intraocular Lens*

Current materials used for IOL optics are of two types—acrylic and silicone. Acrylic materials can be rigid (PMMA) and foldable made of hydrophobic acrylic materials (AcrySof - Alcon Laboratories, Sensar – Advanced Medical Optics – AMO) and hydrophilic acrylics (Centerflex, Akreos).

Each foldable acrylic lens design is made from a different copolymer acrylic with a different refractive index, glass transition temperature, water content, mechanical properties and other attributes.

Hydrophobic acrylic lenses and silicone lenses have very low water content (less than 1%). But there are hydrophobic acrylic materials with higher water content about 4% also available. Hydrophilic acrylic lenses are made from copolymers with higher water content ranging from 18 to 38%.

The first silicone material that was used in the industry of IOLs was polydimethylsiloxane, with refractive index of 1.41 while the new silicone materials have higher refractive indexes.

Refractive index in foldable acrylics is 1.47 or greater, and for silicone lenses is lower—1.41 and higher. Therefore acrylic lenses are thinner than silicone ones with the same refractive power.
