Replacement lenses within the eye...
Replacement lenses within the eye...
An intra-ocular lens (IOL) is an artificial aid surgically implanted in the living eye to restore sharpness of vision, frequently after the removal of a cataract. It has to be transparent, tolerable material of an appropriate size, shape and power for the individual patient. Somehow it also has to remain in place.
In 1765 Casanova's Memoirs record a meeting with an Italian itinerant oculist, Tadini, at a dinner in Warsaw. Tadini showed him some polished crystal spheres in a box and claimed he could implant them underneath the cornea to replace the crystalline lens: 'A substance which I can place in the cornea to supply the loss of the crystalline matter'. The great lover's reply was 'There's a great difference between a tooth and the crystalline humour; and though you may have succeeded in putting an artificial tooth into a gum, this treatment will not do with the eye'. (Memoirs of Jacques Casanova de Seingalt, Vol 6b). A fellow guest, an unnamed German ophthalmologist, ridiculed the claim in print and Tadini never mentioned the spheres again, but Casanova may have been responsible for conveying the idea to the Court at Dresden where, according to a publication of 1795 by the Swiss surgeon Rudolph Schiferli (1773-1837), the Court Oculist Casaamata had tried to insert a glass lens underneath a corneal wound but this had fallen into the bottom of the eye. In other words this was the first failed attempt to correct aphakia via artificial lens implantation.
In 1948 the British ophthalmic surgeon, (Sir) Harold Ridley (1906-2001) of St Thomas' Hospital and the Moorfields Eye Hospital, consulted John Pike (1902-1983), the senior optical specialist at the Rayner Optical Company about designing and manufacturing an implantable lens. He had been stimulated in this by a chance remark of a medical student, F. S. (Steve) Perry, who had commented during a cataract extraction the year before that it was a pity that the diseased lens could not be replaced. Ridley had the humility and the foresight to take on board this idea from a student. The first operation, on a 45-year old female, took place at St Thomas' on 29 November 1949 though, as a two-stage process, the IOL was only implanted permanently three months later, on 8 February 1950. The procedure was highly controversial and apparently St Thomas' was chosen because it provided better security.
Ridley discounted glass as too heavy a material. The first IOL was made of a perspex called Transpex 1. This was a specially recreated plastic, copying that used in the windows of RAF fighter aircraft during the Second World War. Doctors had observed that when these windows shattered the eye injuries suffered by airmen, though otherwise horrific, were that bit less severe due to the inert properties of the perspex within the body, which therefore experienced no secondary inflammation. ICI resumed production of this form of perspex at Ridley's request. They made all of his lenses and charged only about £1 each. At 100mg in weight they were about twenty times heavier than modern intra-ocular lenses. In the 1950s, by now called Perspex CQ (Clinical Quality), the material was made using a compression moulding process. The lens blanks were then profiled and polished by hand.
The first few operations were conducted out of the glare of publicity and when the wider ophthalmological profession became aware of the revolutionary procedure, opinion was sharply divided as to its wisdom. As the lenses had to be sterilised in a Cetrimide solution at the point of insertion several patients suffered severe post-operative reactions. By 1957 all lenses were supplied by the manufacturer pre-sterilised in sodium hydroxide. Early patients were often left highly myopic. When Ridley performed his last operation in 1964 it was judged that 20% of his patients had experienced long-term failure and the main obstacle remained that of secure positioning. By the late 1960s fixation lenses were devised using loops of nylon 66 but, even then only, a few hundred IOLs were supplied each year. Nylon also degraded when it absorbed water. During the 1970s demand from the USA spurred the growth of the IOL manufacturing industry in Britain and elsewhere.
Some early types of IOL:
IOLs were designed with flanges (later fenestrated) by Copeland, but these became associated with chronic uveitis. 'Claw' designs were tried though sometimes an additional suture was deemed necessary to hold the lens in place. Fantastic shapes were produced, notably the 'Pregnant 7'.
In the 1980s design developments were influenced by viscoelastic technology. Posterior chamber lenses became much more popular and extracapsular cataract extraction surgery was refined. Harold Ridley even underwent a successful operation himself, in his old hospital of St Thomas'. Since 1993 their standard of manufacture has been governed by the European Medical Devices Directive. The perspex material now included an anti-UV absorbing agent preventing light-induced damage to the back of the eye. Several multinational optical corporations acquired IOL manufacturing divisions.
The implantation of modern IOLs requires minimally invasive surgery. A silicone folding lens can be inserted through a tiny incision or injected into the eye. The technology has close parallels with the contact lens industry and soft hydrophilic materials such as acrylic have been adapted for IOL use. Today there are in excess of 1500 designs and it is estimated that over 200 million people have benefited from an intra-ocular lens.