Introduction

The first intraocular lens was inserted on the 29th November 1949 and made out of polymethyl methacrylate (PMMA). The lenses were manufactured by Rayner in the United Kingdom and the name of the surgeon Harold Ridley became synonymous with innovation in ophthalmic surgery1. The lens was a disc inserted into the posterior chamber after extra-capsular cataract extraction (ECCE).

There was much skepticism about these lens implants, which were not accepted by the general ophthalmological population. However, development continued with anterior chamber lenses inserted after intracapsular cataract extraction (ICCE) designed by Choyce, followed by iris clip lenses designed by Strampelli, Boberg-Ans and Binkhorst.

The next generation of lenses returned to placement in the posterior chamber, supported by extensions or haptics in the ciliary sulcus, and were developed by Shearing, Kratz, Sinskey, Arnott and Pearce. The development of intraocular lenses paralleled the methods of cataract extraction. These lenses were also made of PMMA, but with the advent of small incision phacoemulsification cataract extraction, developed by Kelman, the subsequent generation of lenses has been made of some form of foldable material.

Requirements of intraocular lenses

The intraocular lens has to replace a complex structure that has variable focus due to the zonules allowing a change in shape of the elastic capsule through muscle interaction, variable refractive index to correct optical aberrations and astigmatism, and a filter to remove harmful wavelengths.

Therefore, the requirements of any intraocular lens and the material from which it is manufactured are that it has to be biocompatible over decades, have as good an optical function as possible in various optical roles, be easy to insert, minimize the development of posterior capsule opacification, and designed taking into account the anatomy and dimensions of the anterior segment.

Materials for lens implant manufacture

The original material was polymethyl methacrylate, chosen because it was found to remain in the eye without causing inflammation (as evidenced by fragments of the shattered windshield from Spitfire fighter planes lodging in the pilot’s eyes), but its principal failing was that it was not foldable.

Silicone was used because it was foldable, and various designs including three-piece with central silicone optic and PMMA haptics, or plate haptic in a one-piece design were developed. They suffered from the problem of greater postoperative inflammation, although this is not an issue with the second generation silicone lenses. The plate haptic designs were relatively unstable and were associated with posterior capsule opacification.

The most popular material used today is an acrylic material which is divided into hydrophilic and hydrophobic variants. These lenses are usually one piece, but can be a three-piece with PMMA haptics. The advantage of this material is better biocompatibility, reduced posterior capsular opacification, and the ability to modify the surfaces to provide toric, aspheric, and multifocal and bifocal intraocular lens implants.

A further development has been the light adjustable lens, in which the surface and shape of the lens can be modified postoperatively to fine tune the refraction and optical properties of the lens, and then fixed using UV light.

There have also been problems with lens implants with the hydrogel lenses causing opacification/calcification (Fig. 15.1) and glistenings/trapped fluid in vacuoles occurring in the hydrophobic acrylic lenses although these do not seem to cause visual symptoms2,3.

Fig. 15.1 (A) Calcification in an IOL. (B) Glistenings in an IOL.

Optical design

Intraocular lens design has to minimize posterior capsule opacification, by the incorporation of a square edge at the junction of the posterior surface and lateral surface, which provides a mechanical barrier to lens epithelial cell migration onto the posterior capsule (Fig. 15.2