Ridley Medal lecturer appraises past and future of hydrogel IOLs
Dermot McGrath
in Munich

DEVELOPMENTS in new materials and designs for intraocular lenses combined with advances in micro-incision surgery techniques and tools are paving the way to an exciting new era of cataract surgery, according to Australian ophthalmologist Graham Barrett, FRACO, FRACS.

Graham Barrett

"The future is bright for the next generation of intraocular lenses. I will always be grateful to have participated in this process and I think we will continue to see many exciting developments in the coming years," he said. Dr Barrett was reflecting on the past, present and future development of hydrogel lenses as the major theme of his Ridley Medal Lecture at the ESCRS XXI Congress in Munich . As one of the renowned innovators in the field of IOL technology and cataract surgery techniques, Dr Barrett's address paid tribute to the pioneering work of the first ophthalmologists who introduced lens implants and ultimately laid the groundwork for modern refractive surgery.

From Ridley to Refractive Surgery

He singled out Sir Harold Ridley – after whom the lecture is named – as the father of IOL implantation and said that the essential qualities that he brought to his work still served as an inspiration for present-day practitioners. He cited Dr Ridley's innovation, application and, above all, his conviction and self-belief in the face of widespread scepticism about IOL implantation from the medical establishment, as the chief cornerstones of his outstanding achievement. "Perhaps Harold Ridley's most important characteristic was his deep conviction that leaving patients aphakic after cataract surgery was simply unacceptable, and that an intraocular lens implant could restore quality of vision and quality of life. It was this conviction that gave him the courage to challenge the conventions of the time and perform that historic first IOL operation on 29 November 1949 ," said Dr Barrett.

Dr Barrett, current head of Department of Ophthalmology at Sir Charles Gardner Hospital in Perth , Western Australia and President of the Australian Society of Cataract and Refractive Surgeons, then surveyed his own career development and outlined his research interests in areas such as epikeratoplasty, fluidics in phacoemulsification, inlays for presbyopia and hydrogel IOLs.

Moving away from PMMA

He said much of his own interest in hydrogel IOLs stemmed from difficulties of biocompatibility that surgeons experienced with early IOLs made from PMMA material. Early anterior chamber, iris supported and posterior chamber PMMA lens designs often caused chronic inflammation and other secondary problems, noted Dr Barrett. "The issue of major concern at that time was biocompatibility of intraocular lens implants. From this starting point, I asked myself: ‘why not make IOLs from material other than PMMA?' That was the start of a long journey into exploring the possibilities of hydrogel material that continues to this day," he said. Dr Barrett's investigations in this area led him to develop his first hydrogel lens in the mid-1980s, the IOGEL PC12.

Hydrogels are soft hydrophilic materials with a water content varying from 18% to 38%. They are often referred to as "hydrophilic acrylics" and the refractive index varies from 1.44 to 1.47 depending on the water content. These materials are very compressible and unfold faster than hydrophobic acrylic materials and in a more controlled fashion than silicone. The new lens boasted several unique characteristics, noted Dr Barrett, including a hydrophilic surface, improved biocompatibility, thermal stability, and enhanced optical properties.

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Dr Barrett said that the mechanical properties of the hydrogel lens, which allowed it to be folded and inserted through a small incision, pointed the way forward for IOL implantation. "Because the lens was supple and foldable, it could be injected through a small incision, thereby reducing the incidence of astigmatism and limiting manipulations inside the eye," he said.

Growing pains for hydrogels

A photo of a patient with an IOGEL PC12 taken in 2003. As the lens was implanted in 1983-84 this is almost 20 years post op	A photo of an IOGEL 2000 lens being injected through a small incision in 1992
A photo of a patient with an IOGEL 2000 lens implanted taken at one week post op, and the same patient 12 months later. The photo demonstrates that a soft haptic has sufficient rigidity to support the lens within the capsulorhexis

Reflecting on some of the early problems encountered by the first generation of hydrogel implants, Dr Barrett remarked that all new lens types experienced some difficulties in their evolution, but that this was all part of the learning process."Reports from the United States of dislocation following early YAG capsulotomy limited the widespread use of the IOGEL lens. As with all plate haptic lenses, there is a need to avoid early YAG laser capsulotomy. We now know that post-YAG laser dislocation can be avoided if the capsulotomy is delayed for more than three months," he said.In order to tackle the problems of dislocation associated with the original plate haptic lenses, Dr Barrett set about developing a modified version, the IOGEL 2000. "The surgical technique of phacoemulsification and capsulorhexis provided a different support environment for an implant than that achieved by extracapsular cataract surgery in the early 1980s when most of the criteria for loop rigidity were derived," he noted.

Dr Barrett said that he remained convinced that a haptic design is adequate for modern cataract surgery with capsulorhexis so long as there is sufficient rigidity to support the weight of the implant within the capsular bag. "The haptic of the new lens, for example, is designed with sufficient rigidity to maintain centration in the early postoperative period and avoid posterior vaulting associated with earlier models," he said.

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Problems not unique to hydrogels

Dr Barrett touched on some of the problems that all IOL types, regardless of materials or design, have encountered over the years. "There have been problems of internal crazing with PMMA, discoloration and yellowing has occurred with certain silicone implants, we have seen glistening with hydrophobic acrylic lenses, and certain hydrophilic acrylic lenses have become opacified," he said. Dr Barrett predicted a bright future for hydrogel lenses. He paid tribute to the research of other innovators such as Philippe Sourdille MD from France and his work with the Concept 360 IOL, as paving the way towards improved safety and quality for the next generation of hydrogel IOLs. He said that micro-incision surgery opened up exciting new possibilities for the field of IOL implantation.

"To my mind the two most important roles of cataract surgery are improving safety levels and visual acuity. The widespread adoption of small incision cataract surgery, certainly in my career, has made a big impact on both these areas by improving wound integrity and reducing astigmatism."

Smaller incisions, better vision

However, Dr Barrett pointed out that while the incision size has diminished, the properties of many current hydrophobic and hydrophilic IOLS demand an incision size of between 2.8 mm to 3 mm. He reported on a study he conducted earlier this year, in which he measured higher-order aberrations in patients after cataract surgery and correlated the errors with the IOL material. "We measured the higher order aberrations in patients who had undergone cataract surgery and IOL implantation and we found that patients who have a high-refractive index acrylic IOL implanted appear to have a higher level of induced higher order aberrations following surgery."

H e believed that one of the biggest challenges now was to find a way to reduce the incision size while maintaining the optical quality of IOL implantation. He cited the ThinOptX lens, which could be inserted with a sub-2 mm incision, as an ex citing development but said that further evaluation of its safety and efficacy was needed before drawing any firm conclusions. Looking forward, Dr Barrett said that he was currently working on developing further improvements in hydrogel materials. "I am proposing the term hydro-elasto-gel to describe the unique properties of a new type of polymer which retains the best features of hydrogel and silicone materials." Dr Barrett said that one of the unique characteristics of this material is that it can be folded or injected when dry with an optic diameter of 5.0 mm. The lens can then be inserted through an incision 2 mm or less but unlike previous lenses, the optic will instantly unfold after insertion. It will then expand to a diameter of 6.0 mm. "The content of the next generation of hydrogel lens will be lenses that can be folded or injected through an incision size less than 2.0 mm and then expand to a full optic diameter, reducing astigmatism while maintaining visual quality," predicted Dr Barrett.

Graham Barrett FRACO, FRACS
b arrett@uniwa.edu.au