Continuing Education

Author: Leon Davies, James Wolffsohn and Shehzad Naroo

Leon Davies, James Wolffsohn and Shehzad Naroo describe the development of modern intraocular lenses (C4664, one standard CET point)

This module has closed - you cannot earn any CET points

THIS ARTICLE IS BEST VIEWED ON A PDF FORMAT

View PDF

 

 

It has been projected that there could be an estimated 50 million people blind worldwide due to cataract by 2020.

Cataract does not discriminate between countries: there are currently over 1.5 million cataract operations performed in the US and there are approximately 250,000 procedures performed each year in the UK, making it the most commonly performed surgical procedure.

The World Health Organization (WHO) states that, in global terms, it will be necessary to increase the currently estimated 12 million annual cataract operations to 20 million by 2010. By the year 2020, the final target should be 32 million cataract surgeries annually.

Currently, once the lens has opacified there is no treatment for cataract other than surgery, with almost all eyes being fitted with intraocular lenses (IOLs). Early historical techniques used by ancient civilisations to treat cataracts, such as couching, where the dense lens was pushed back into the vitreous chamber, are no longer used but have been reported in tribal regions of developing countries.

In the modern era of implant surgery, mechanical problems have been the most prevalent, and it is in this area that most innovations have been made.

SURGICAL PROCEDURES

Intracapsular cataract extraction

Intracapsular cataract extraction (ICCE) first gained popularity in the 1960s and 1970s and is still widely used in developing countries.

The procedure involves the removal of the whole crystalline lens with the intact capsule from the eye. The function of the removed lens can be replaced either by the insertion of an IOL, usually in the anterior chamber, or by the use of aphakic spectacles or contact lenses.

The main advantage of ICCE is that it is a standardised technique that can be performed rapidly (often within five minutes) with minimal manipulation of the eye. Furthermore, the ubiquitous posterior capsular opacification (PCO) is negated with this procedure as both the lens and capsule are removed simultaneously.

Extracapsular cataract extraction

Extracapsular cataract extraction (ECCE) was first utilised over 50 years ago but was later abandoned in favour of ICCE. ECCE, however, was re-introduced with the development of microsurgical techniques in the early 1980s.

Here, the lens contents are removed, leaving the posterior lens capsule intact. A posterior chamber IOL can then be implanted in the capsular bag. If no IOL is implanted, aphakic spectacles or contact lenses must be used. Extracapsular cataract surgery has become the preferred method of extraction in developed countries and is beginning to be adopted by surgeons in developing countries.

Further advances in surgery have led to the development and use of sutureless ECCE.1 This surgery uses either a manual2 or mechanical fragmentation3 technique (phacoemulsification) of the lens nucleus for less dense opacities. Both suture and sutureless ECCE leave the posterior capsule of the lens in place. This maintains the anatomical barrier between the posterior and anterior segments of the eye. The barrier is important as it may reduce the risk of posterior segment complications. As mentioned earlier, however, the disadvantage of all extracapsular techniques is that the posterior lens capsule can become cloudy, with the need for a primary or secondary capsulotomy by surgery or by using an Yttrium-Aluminium-Garnet (YAG) laser. Typically, this increases the risk of secondary complications.4

IOL TECHNOLOGY

Generation I: The first IOLimplantation

On November 29, 1949, Sir Harold Ridley conducted the first IOL implantation procedure at St Thomas' Hospital, London.5

Interestingly, on examining the operating theatre records, Ridley recorded that the patient (a 45-year-old female) was in fact recalled for a 'lenticular graft' to correct anisometropa induced by a previously performed ECCE.6

The main theoretical concern with the Ridley procedure was the placement of a foreign body within the eye. However, the procedure was validated by the clinical observation that intraocular fragments of perspex seemed to cause little or no long-term inflammation in the eyes of aircraft pilots who had suffered penetrating eye injuries from the shattered perspex canopies of Royal Air Force aeroplanes.

The original Ridley intraocular lens, therefore, was made of rigid polymethylmethacrylate (PMMA), not glass as is often believed. Its shape resembled that of the natural human crystalline lens, but its weight was approximately eight times that of a modern PMMA IOL and 45 times more than an IOL of modern material, such as silicon. It did not include a haptic portion. The procedure required the surgeon to implant the IOL behind the iris and in front of the remaining capsular bag after ECCE. Operating microscopes were not used, nor was a visco-elastic agent.

Approximately 1,000 of Ridley's lenses were implanted worldwide. However, due to the high incidence of ocular complications (which included dislocation or decentration of the lens, uveitis and secondary glaucoma) approximately 15 per cent of lenses were explanted. Even so, there was a 10-year success rate in 70 per cent of cases with a number of patients still having these PMMA IOLs in situ today.7

Generation II: Early anteriorchamber IOLs (1953-1962)

In 1953, attention was directed to the anterior chamber as a suitable location for placement of the IOL implant by the surgeon Barton, who implanted an IOL into the anterior chamber of an eye for the first time. It was plano convex, with the steep anterior surface of the IOL in close proximity to the cornea. In September 1953, Strampelli, of Italy, and Danheim, of Germany, followed Barton's idea and developed anterior chamber implants of their own design.

The Strampelli lens was rigid and had three-point anterior chamber angle contact. It was markedly thinner and did not have the anterior surface convexity that the Barton lens had. The Danheim lens was a closed-loop, flexible lens having a 5mm optic with nylon loops. Interestingly, Ridley also developed an anterior chamber implant after he abandoned his original posterior chamber IOL.

The long-term results of these early anterior chamber IOLs were universally poor due to their instability in the anterior chamber. Invariably, this resulted in damage to the corneal endothelium, with many patients subsequently suffering from corneal decompensation and oedema due to the reduced endothelial cell count. The condition often progressed to pseudophakic bullous keratopathy, with many patients requiring a corneal graft.8 The presence of the anterior chamber lenses, however, increased the risk of graft failure, so many were explanted.

Anterior chamber IOLs were also associated with iris complications such as iris rubbing, often leading to hyphaema, iris erosion and pupil block. Consequently, it was often necessary to perform a peripheral iridectomy when implanting an anterior chamber IOL to reduce the risk of pupil block. The lenses were also associated with a raft of other secondary complications including cystoid macular oedema (CMO), uveitis, UGH (uveitis, glaucoma, hyphaema) syndrome, and IOL dislocation.

Generation III: Iris-supported IOLs(1957-1973)

Anterior chamber IOLs were inherently unstable and therefore resulted in many complications. As such, greater support of the lens was sought. This was achieved by transferring the support from the anterior chamber angle to the iris.

In 1957, Binkhorst designed the first of these iris clip lenses which used the pupillary part of the iris for anatomical fixation.9 Concurrently, but independently, Epstein designed the collar stud lens, which was also supported by the iris. Although these lenses initially reduced the rate of endothelial corneal dystrophy, they were far from perfect. Indeed, a large number of glaucoma cases developed owing to pupillary occlusion. Modifications were made to the lenses to aid the flow of aqueous through the pupil, but the pupillary-fixated IOLs soon became obsolete. Later, the Medallion IOL was introduced where the lens was fixed to the iris by a suture. Next to be developed was the Iris-claw lens which captured a fold of iris tissue at the two ends of the IOL to maintain its fixation.

Generation IV: Modern anteriorchamber IOLs (1970 to date)

In order for anterior chamber IOLs to be safe and effective there should be minimal contact with the drainage angle, stability within the anterior chamber with no movement in the angle, no iris chafing and no endothelial touch.

Modern anterior chamber IOLs were designed to achieve this by using flexible open-loop haptics attached to a PMMA lens. They have the advantage of not requiring an intact posterior capsule for implantation and can be implanted into eyes even after posterior capsular rupture.

Modern anterior chamber IOLs, therefore, allow far better fixation than the early anterior chamber IOLs, with very low incidence of corneal complications. They are, however, associated with a higher prevalence of CMO and retinal detachment than posterior chamber IOLs. Such clinical experiences helped to renew awareness of the advantages of the posterior chamber IOL as the site of implantation.

Generations V and VI: Posterior chamber IOLs and moderncapsular surgery (1975 to date)

In 1975, Dr John Pearce became the first surgeon to return to the posterior chamber IOL in a consistent and continuing manner.10 Posterior chamber IOLs require the presence of the posterior capsule and can be either placed in the sulcus or the capsular bag.11

Most fixation of the early posterior chamber IOLs was uveal (one or both haptics out of the capsular bag) often leading to an almost automatic decentration of the IOL optic.12 In addition, any contact with adjacent uveal tissues has the potential to cause tissue damage due to chafing.13 The lens material most commonly used was PMMA with either PMMA, polypropylene or polyamide haptics.

During this time, important new surgical techniques began to be applied. Most importantly, the transition to introducing a visco-elastic agent, used to inflate the anterior chamber,14 and the use of a continuous curvilinear capsulorrhexis, the entry incision into the anterior lens capsule.15 The enhanced cortical cleanup16 and modern phacoemulsification with a small sutureless incision made possible the future implementation of foldable IOLs.

The first attempts at implantation of IOLs of a softer material, the forerunners of today's modern foldable IOLs, began in the late 1970s. Here, surgical techniques moved toward consistent, secure, in-the-bag (capsular) fixation where mostly rigid lenses were inserted via large incisions.

Cataract surgery, as we know it today began in the late 1980s, and can be defined by modern foldable IOLs inserted through a small incision after phacoemulsification in contrast to the large semi-circular incisions made around the limbus as in ICCE and ECCE procedures.

Careful biometry is now applied to phacoemulsification so that the end point refractive status of the patient can be better determined. This has led to the development of clear lens extraction as a refractive surgery procedure. Phacoemulsification has also allowed the development of several specialised types of IOLs in addition to basic foldable lenses, including refractive IOLs and lenses designed to restore ocular accommodation.17-20

SUMMARY

Intraocular lenses have been implanted for only a relatively short period of time, but have developed greatly through pioneering surgeons to the more stable designs with less complications used in cataract surgery today.

Further developments of specialised IOLs will be discussed in a future article.

References

1 Norregaard JC, Bernth-Petersen P, Bellan L, Alonso J, Black C, Dunn E, Andersen TF, Espallargues M and Anderson GF. Intraoperative clinical practice and risk of early complications after cataract extraction in the US, Canada, Denmark, and Spain. Ophthalmol, 1999106:42-48.

2 Blumenthal M, Ashkenazi I, Assia E, Cahane M. Small-incision manual extracapsular cataract extraction using selective hydrodissection. Ophthalmic Surgery, 199223:699-701.

3 Alio J, Rodriguez-Prats JL, Galal A. Advances in microincision cataract surgery intraocular lenses. Curr Opin Ophthalmol, 200617:80-93.

4 Aslam TM, Devlin H, Dhillon B. Use of Nd:YAG laser capsulotomy. Surv Ophthalmol, 200348:594-612.

5 Rosen ES. The development and characterisation of the intraocular lens. In: Intraocular lens implantation (eds E S Rosen, W M Haining and E J Arnott) Mosby, St. Louis, Missouri, USA. 1984:50-58.

6 Spalton DJ. Harold Ridley's first patient. J Cataract Refract Surg, 199925:156.

7 Letocha CE and Pavlin CJ. Follow-up of three patients with Ridley intraocular lens implantation. J Cataract Refract Surg, 199925:587-591.

8 Cheng CL and Tan DTH. Lamellar corneal autograft for corneal perforation. Australian and New Zealand J Ophthalmol, 199927:437-439.

9 Binkhorst CD. Use of the papillary lens (iris clip lens) in aphakia. Our experiences based on the first 50 implantations. Br J Ophthalmol, 196246:343.

10 Pearce JL. Sixteen months experience with 140 posterior chambr intraocular lens implants. Br J Ophthalmol, 197761:310.

11 Vargas LG, Peng Q, Escobar-Gomez M, Schmidbauer JM and Apple DJ. Overview of modern foldable intraocular lenses and clinically relevant anatomy and histology of the crystalline lens. In: Complications of aphakic and refractive intraocular lenses (eds L Werner and DJ Apple) Lippincott, Williams & Wilkins, Philadelphia, Pennsylvania, US. 2001:1-15.

12 Tappin MJ and Larkin DF. Factors leading to lens implant decentration and exchange. Eye, 200014:773-776.

13 Miyake K, Asakura M and Kobayashi H. Effect of intraocular lens fixation on the blood aqueous barrier. Am J Ophthalmol, 198498:451-155.

14 Alpar JJ. On-the-table posterior capsulotomy and 1per cent sodium hyaluronate. J Cataract Refract Surg, 198612:391-393.

15 Gimbel H and Neuhann T. Development, advantages and methods of continuous circular capsulorrhexis techniques. J Cataract Refract Surg, 199016:31-37.

16 Fine IH. Cortical cleaving hydrodissection. J Cataract Refract Surg, 199218:508-512

17 Davies LN, Hunt OA, Wolffsohn JS, Naroo S, Hurcomb PG, Shah S, Cunliffe IA and Benson MT. Performance of the KH3500 accommodative intraocular lens. Optom Vis Sci, 200582:E-abstract 050437.

18 Dick HB. Accommodative intraocular lenses: current status. Current Opinion in Ophthalmology, 200516:8-26.

19 Wolffsohn JS, Hunt OA, Naroo S, Gilmartin B, Shah S, Cunliffe IA, Benson MT and Mantry S. Objective Accommodative Amplitude and Dynamics with the 1CU Accommodative Intraocular Lens. Invest Ophthalmol Vis Sci, 2006a47:1230-1235.

20 Wolffsohn JS, Naroo SA, Motwani NK, Shah S, Hunt OA, Mantry S, Sira M, Cunliffe IA, Benson MT. Subjective and objective performance of the Lenstec KH-3500 'accommodative' intraocular lens. Br J Ophthalmol, 2006b90:693-696.

◆ Dr Leon Davies is a lecturer in the School of Life and Health Sciences, Aston University. Dr James Wolffsohn is a reader in the School of Life and Health Sciences, Aston University, and immediate past-president of the British Contact Lens Association. Dr Shehzad Naroo is a lecturer in the School of Life and Health Sciences, Aston University, past-treasurer of the British Society for Refractive Surgery, and editor-in-chief of the BCLA's journal Contact Lens and Anterior Eye

Providing exclusive eye care news, information and educational needs every week, including a FREE CET programme. Subscribe to Optician Print Edition.