Ординатура / Офтальмология / Английские материалы / Mastering theTechniques of Lens Based Refractive Surgery (Phakic IOLs)_Garg, Alio, Dementiev_2005

the new NuVita MA20 lens was taken off the market. The reasons for this decision are not really known but it seems that the optical zone continued to cause problems such as glare and severe monocular diplopia at night.6 At the beginning of the 1990’s, starting from Kelman’s Multiflex anterior chamber implant, Pérez-Santonja and Zato7 developed a first generation phakic lens designated ZSAL-1 and marketed by IOLtech© (La Rochelle, France). This was an angle-support, monoblock PMMA anterior chamber lens with a convex-concave optic, a haptics angulation of 15° and optical zone of 5.5 mm. Out of this lens, emerged the second generation ZSAL- 2 in 1992 with a haptics angle of 17° and optical zone of 5.5 mm, but effective zone of 5.0 mm. However, the distance from the posterior side of the optic to the surface of the iris was too short so it was decided to launch the third generation ZSAL-3, with a haptics angle of 18° to try to increase the distance to the iris surface but the desired effects were not achieved. The further development of these models led to our current ZSAL-

4 and ZSAL-4/Plus designs (Fig. 2.3).

sutured to the iris — The Medaillon lens9 This was to be followed in 1978 in Pakistan by the development by Worst9 himself of a lens for aphakic eyes, the iris claw, from the Medaillon. Nevertheless, this lens was not to be implanted in a phakic eye until 1980, when the first implant of an opaque lens was undertaken to treat severe monocular diplopia.10

After several modifications, 1986 saw the birth of the lens known as the Artisan phakic lens for the correction of myopic refractive errors. This lens, initially with a biconcave optic, was redesigned by Fechner and Worst11 in 1990, to include a meniscus profile with a concave posterior and slightly convex anterior. In 1992 was designed the first Artisan model to correct hyperopia and in 1999 the first Artisan toric lens (Fig. 2.4). Early in 2002, the first foldable model was implanted, which combines a silicon optic with claw-shaped haptics made of PMMA in the Artiflex lens. This last model, set to be launched on the market in the middle of 2005, combines the technologies of Ophtec© (Boca Raton, Fl, USA) and Advanced Medical Optics, Incs (Santa Ana, Ca, USA).

Figure 2.3: Fourth generation lenses ZSAL-4 and ZSAL-4/Plus

IRIS-FIXATED ANTERIOR CHAMBER

PHAKIC LENSES

The original design of iris-fixated lenses was that of Cornelius Binkhorst.8 His first design was called the fourloop Binkhorst lens, and was used as a secondary implant after intracapsular cataract surgery. Owing to a tendency to luxate during pupil dilation, the four-loop lens was replaced by the two-loop Binkhorst lens.

In 1972, Professor Jan Worst tried to improve the design of this last lens by designing a model that was

Figure 2.4: Development of the Artisan lens: (A) “Lobsterclaw” for aphakic eyes (1978); (B) First biconcave phakic Artisan (1986); (C) Artisan concave-convex (1990); (D) Artisan hyperopic (1992); E)- Artisan toric (1999).

POSTERIOR CHAMBER PHAKIC LENSES

In 1985, Fyodorov and Zuev12 proposed a new silicon phakic lens to correct myopia designed to be implanted in the posterior chamber. Given its shape, this lens was named the Mushroom lens although it was also known as the “collar button” (Fig. 2.5). In practice, it was not completely implanted in the posterior chamber since its butterfly-shaped haptics and 11.5 to 12.5 mm of length were placed on the crystalline lens in the posterior chamber, while its 3.5 to 4.5 mm diameter optic extended beyond this through the pupil into the anterior chamber. These lenses provoked considerable night vision disturbances due to the small diameter of the optical zone, as well as photophobia in conditions of bright light since the pupil cannot constrict beyond 3.5 mm. With time, they gave rise to complications such as cataract, glaucoma and corneal decompensation, probably because the material was not of optimal quality, the lens damaged the endothelium and also because viscoelastic substances had not made their appearance yet.13,14

The Mushroom lens developed by Fyodorov underwent numerous design changes. The optic was enlarged, and the haptics were flattened and made rectangular. These improvements made the lens switch position to become a lens implanted exclusively in the posterior chamber between the iris and the natural lens. The main problem with this lens was decentering due to its small diameter of under 11.0 mm conferring the lens poor stability. Its easy displacement upwards or

Figure 2.5: Mushroom lens

sidewards induced significant secondary visual problems.14 This lens was the first prototype of most posterior chamber phakic lenses and was created to surgically correct high myopia.

From 1992, posterior chamber lenses continued their development as three lines of research according to the materials they were made of: (a) the silicon posterior chamber phakic IOL (later known as the Phakic Refractive Lens-PRL); (b) the collamer posterior chamber phakic IOL (later called the Implantable Contact Lens-ICL); and (c), the silicon-elastomer PC Phakic IOL (ChironAdatomed).15

En 1987, the firm Medenium, Inc© (Irvine, CA, USA) started developing the silicon Phakic Refractive Lens (PRL) based on one of Fyodorov’s designs (Fig. 2.6). This lens was launched worldwide by CIBA Vision© (Duluth, GA, USA), that later sold the patent to IOLtech© (La Rochelle, France), its current marketing company.

Figure 2.6: Phakic refractive lens (PRL)

In 1993, the company Staar© (Monrovia, CA, USA) having acquired the rights for one of Fyodorov’s lenses, started to market a posterior chamber lens. This lens composed of a collagen polymer (collamer), was given the name Implantable Contact Lens (ICL). The first of these models was IC2020-M with a biconcave 3.5 mm optic from which the following models were derived: ICM(H)V1, ICM(H)V2, ICM(H)V3 and the last generation ICM(H)V4 (Fig. 2.7).

Outside of Russia, Fechner16 in collaboration with the company Adatomed (Germany), started implanting a posterior chamber lens manufactured, as mentioned

Figure 2.7: Implantable contact lens (ICL)

before, out of silicon-elastomer. This lens had an optical zone of 5.5 mm, with a power up to –22.50 D and a length of up to 12.5 mm. The problem with these lenses was that they induced the opacification of the crystalline lens. Their hydrophobic silicon component along with their low refraction index meant they had a very thick periphery such that they eroded the natural lens leading to cataracts. This lens has been taken off the market.

REFERENCES

1.Strampelli B. Lentilles camerulaires après années d’expériences. Acta Cong Ohthal Belgica (Brussels) 1958; 11:1692-98.

2.Barraquer J. Anterior chamber plastic lenses. Results and conclusions from five years’ experience. Trans. Ophthalm. Soc. UK, 1959; 79:393-424.

3.Drews RC. The Barraquer experience with intraocular lenses. 20 years later. Ophthalmol Soc U.K. 1959; 79:393442.

1980; 6:166-67.

10.Worst J, Los L. Some aspects of implant surgery. Eur J Implant Ref Surg 1991; 3:157-67.

11.Fechner PUU, Worst JGF. A new concave intraocular lens for the correction of myopia. Eur J Implant Ref Surg 1981; 245-48.

12.Fyodorov SN, Zuev VK, Azanabayev BM. Intraocular correction of high myopia with negative posterior chamber lens. Ophthalmosurgery 1991; 3:57-58.

13.Tumanian E. Surgical correction of high myopia by the method of implantation of negative phakic IOL. Diss Kand Medic 1989; 158-64.

14.Carlo F Lovisolo, Paolo Pesando. ICL Posterior Chamber Phakic IOL. In: Jorge L. Ali©, Juan J. Pérez-Santoja, Eds. Refractive Surgery with Phakic IOLs. Fundamentals and Clinical Practice. Panama: Highlights of Ophthalmology International 2004; Chapter 11:133-165.

15.Dementiev D, Hoffer KJ. Phakic Refractive Lens (PRL): Indications and Techniques. In: Ashok Garg, Suresh K Pandey, Vidushi Sharma, David J Apple, Eds. Advances in Opthalmology 1. New Delhi: Jaypee Brothers 2003; 295-304.

16.Erturk H, Ozcetin H. Phakic posterior chamber intraocular lenses for the correction of high myopia. J Refract Surg Sept 1995; 11(5):338-91.

Jairo E Hoyos-Chacón

Melania Cigales

Jairo E Hoyos (Spain)

INTRODUCTION

The use of phakic lenses for the correction of high ametropia has recently gained popularity, owing to the poor efficacy of corneal techniques used to treat large refractive errors and the good visual quality achieved with intraocular lenses, along with the benefit of preserving the patient’s accommodation ability. Since the middle of the last century, when Strampelli1 implanted the first phakic intraocular lens, the materials and designs used have undergone extensive development. Phakic lenses may be implanted in the anterior chamber (between the cornea and iris) or the posterior chamber (between the iris and crystalline lens). The evolution of ophthalmologic microsurgery towards the small incision has been a determining factor for the widespread use of flexible phakic lenses, to the detriment of rigid lenses.

ANTERIOR CHAMBER PHAKIC LENSES

These lenses are implanted in the anterior chamber of the eye, that is, in the space between the iris and the cornea. Strampelli1 implanted the first anterior chamber lens in the middle of the 20th century. In the years to follow, many researchers improved this initial design by evaluating different materials in an effort to increase biocompatibility and thus reduce the incidence of both chronic iridocyclitis and cataract. New models also emerged designed to enlarge the optical zone and smoothen the lens edges to minimize visual disturbances. The angulation of the haptics was gradually modified to increase the distance between the lens and endothelium and try to resolve the problem of corneal decompensation, and different designs were worked on to attempt to avoid secondary glaucoma, which occurred in most implant series.

During this development process, many lenses entered the market only to quickly be discontinued, while others survived due to the constant improvements made in successive generations. Today, we have at our disposition anterior chamber lenses supported by the iridocorneal angle, denoted angle-supported lenses, or fixed at the iris, known as iris-fixated lenses. Let us briefly review the anterior chamber phakic lenses available at present.

Vivarte/GBR Lens

These two lenses are practically the same, but were initially marketed by two different companies. Ciba Vision© (Duluth, GA, USA) sold the Vivarte, while the GBR was distributed by IOLtech© (La Rochelle, France), which currently markets both lenses under the same name.

Designed by Baikoff, this is a one-piece anglesupported lens that has a foldable hydrophilic acrylic optic and haptics made of a rigid hydrophobic acrylic material (Fig. 3.1). The lens is implanted through a 3.2 mm clear corneal incision. It has soft acrylic angle support bearings, improving contact at the iridocorneal angle, to diminish local fibrosis, which can lead to iris retraction and consequently produce pupillary distortion. The lens has an optical zone of 5.5 mm and is available in three lengths (12.0, 12.5 and 13.0 mm). The manufacturing company recommends a minimum safety distance between the lens and endothelium of 1.55 mm and proposes a minimum anterior chamber depth depending on the lens power (Table 3.1).

Table 3.1: Minimum recommended anterior chamber depth (ACD) for the implantation of a Vivarte /GBR lens according to lens power

There are two current models, one for myopia with powers in the range –7.00 to –22.00 D, and a multifocal lens to correct presbyopia.

The multifocal lens is marketed under two names,

Vivarte Presbyopic and Newlife, but at present both are dependent on the company IOLtech© (La Rochelle, France). The multifocal model (Fig. 3.2) has three optic zones: the central and more peripheral zones for distance vision and the intermediate zone for near vision, and is available in powers of –3.00 to +3.00 D, with an addition for near vision of +2.5 D.

Safety Flex Phakic 6 Lens

This lens was developed by several modifications made by Dr Alessio to Baikoff’s ZB lens and is marketed by

Ophthalmic Innovations International© (Claremont, CA, USA).

The lens has an optical zone of 6.0 mm, a very flexible haptics that rest on the angle and it is supplied in lengths of 12.0 to 14.0 mm (Fig. 3.3). The distance of the lens to the anterior crystalline lens capsule has to be 1 mm, such that the manufacturers recommend a minimum anterior chamber depth of 3.2 mm. The powers available to correct myopia range from –2.00 to –25.00 D and to treat hyperopia from +2.00 to +10.00 D.

a curved step (Fig. 3.4). It has an overall optical zone of 6.0 mm and effective zone of 5.5 mm, and can be obtained in four different lengths (12.0, 12.5, 13.0 and 13.5 mm). To calculate lens power a constant “A” of 115.5 is used and it is available in powers between – 5.00 and –25.00 D in increments of 1.0 D.

Figure 3.3: Safety Flex Phakic 6 lens (Ophthalmic Innovations International©-Claremont, CA, USA)

The lens surface is treated with heparin, which being an endogenous carbohydrate is not recognized by the immune system as foreign yet impairs bacterial adhesion to the lens surface, thus reducing the risk of endophthalmitis.

JMJ Lens

This lens was designed by J García-Sánchez, MT Iradier and J García-Feijoo, and is produced by the company AJL© (Vitoria, Spain).

The JMJ is a polymethylmethacrylate (PMMA) anglesupported lens for the correction of myopia that has a plano-concave optic and haptics in the shape of a Z with

Figure 3.4: JMJ lens (AJL©-Vitoria, Spain)

LN-2000 Lens

This one-piece angle-supported lens was designed to correct myopia and is manufactured by Lenstec© (St. Petersburg, Fl, USA). The angulation of its haptics is 0º and its optic is meniscus-shaped with a diameter of 5.0 mm (Fig. 3.5). It is available in powers of –7.00 to – 20.00 D and there are four different models depending on the length of the lens: LN-2010 (12.0 mm), LN2020 (12.5 mm), LN-2030 (13.0 mm) and LN-2040 (13.5 mm).

ZSAL-4 Lens

This lens was developed by JJ Pérez-Santonja and JL Alió from Kelman’s Multiflex anterior chamber implant. Its development started in the mid 1990s, during which several modifications to the angulation of the haptics and to the size of the optical zone were made until the fourth generation model ZSAL-4 was created, marketed by Morcher GMBH© (Stuttgart, Germany).

This lens is a one-piece PMMA angle-supported implant with a plano-concave optic and haptics angulation of 19º (Fig. 3.6). Its Z-shaped haptics are 0.18 mm thick and very flexible, promoting the

Figure 3.5: LN-2000 lens (Lenstec©-St. Petersburg, Fl, USA)

dispersion of compression forces on the angular structures as an attempt to reduce the incidence of pupillary distortion. The size of the optical zone is 5.5 mm total and effective 5.0 mm, and has a triple-surface edge to minimize glare.2 The mean distance from the endothelium achieved is 1.54 mm. It comes in two diameters (12.5 and 13.0 mm) and powers in the range –6.00 to –22.50 D in steps of 0.50 D.

From the development of this lens emerged the ZSAL- 4 /Plus (Fig. 3.7), marketed by the same company. In this model, the optical zone is larger (overall optic zone size 5.8 mm, effective 5.3 mm) in an attempt to reduce halos and night vision problems. In the periphery, the transition zone still has three surfaces to reduce halos and reflections. Its haptics are thin and long in the shape of a Z to enhance flexibility and their geometry is such that they reduce compression of the angle structures and therefore diminish the risk of pupillary ovalization.8 Its total height is 1.2 mm, which avoids possible contact with the iris and allows a central distance from the crystalline lens of 1.0 mm. The mean distance between the lens border and the endothelium is 1.5 mm. It is manufactured in two diameters (12.5 and 13.0 mm), and powers of –6.00 to –22.50 D (in increments of 0.50 D; additional dioptric powers can be ordered).

ICARE Lens

This is the first fully foldable anterior chamber anglesupported lens. It was designed by Professor Sourdille

Figure 3.6: ZSAL-4 lens (Morcher GMBH©-Stuttgart, Germany)

Figure 3.7: ZSAL-4/Plus lens (Morcher GMBH©-Stuttgart, Germany)

and the engineers of the company Corneal© (Paris, France) that markets the lens.

It is a one-piece lens that may be inserted through a clear corneal incision of 3.0 to 3.2 mm with the help of an injector. Comprised of hydrophilic acrylic material (water content 26%), it has four symmetrical footplates for placement at the angle and an optical zone of

5.75 mm (Fig. 3.8). It is available in four lengths from 12.0 to 13.5 mm in 0.5 mm increases. The mean distance from the optic center to the endothelium is 2.07 mm, from the lens border to the endothelium is 1.85 mm and from the posterior lens surface to the crystalline lens is 0.84 mm. It is supplied in powers from –5.00 to –20.00 D in –0.25 D increments. A new model for the correction of hyperopia is soon to be launched.

For this type of anterior chamber lens, unlike the case for the previous lenses, it is recommended that two peripheral iridotomies be conducted at 10:00 and 2:00 hours (personal communication by Dr. Alessandro Mularoni).

separately introduced and fitted together once inside the anterior chamber (Fig. 3.9).

The Kelman Duet lens has a foldable silicon 5.5 mm optic and rigid PMMA haptics. It is available in lengths of 12.0, 12.5, 13.0 and 13.5 mm. For their implant, first, the haptics are inserted through an incision under 2.0 mm and, once rested on the angle, the lens optic is injected and connected to the haptics inside the anterior chamber (Fig. 3.10). The lens is presently available for the correction of myopia in powers of –8.00 to –20.00 D. In the future, the company intends to produce toric lenses, low power lenses for myopia and lenses for hyperopia.

Kelman Duet Lens

This lens, designed by CD Kelman and marketed by Tekia© (Irvine, CA, USA), is an anterior chamber, anglesupported two-piece model, whose two sections are

Figure 3.8: ICARE lens (Corneal©-Paris, France)

Artisan Lens

The Artisan lens is marketed by Ophtec© (Boca Raton, Fl, USA) but is also sold under the name of VerysiseTM by Advanced Medical Optics, Incs (Santa Ana, Ca, USA). It is a one-piece PMMA design supplied in only one length, 8.5 mm. Its concave-convex optic can be 5.0 or 6.0 mm in diameter. The optic-endothelium distance varies from 1.5 to 2.0 mm, according to the lens dioptric power. Maximum lens height with respect to the iris plane differs depending on its power, but it does not exceed 0.96 mm for myopic lenses and 1.0 mm for hyperopic lenses. The manufacturers recommend a minimum anterior chamber depth of 2.6 mm for its implantation. The lens design allows four outflow points for aqueous humor to pass from the posterior to the anterior chamber (Fig. 3.11), but it is still recommended that a surgical iridectomy or Yag laser iridotomy be undertaken.

The lens is introduced through a scleral-corneal tunnel 5.0 to 6.0 mm long. The haptics are secured at the midperiphery of the iris, which is the avascular zone and also the “mute” zone of the pupil’s dilatory muscle, such that pupillary excursions are not impeded;3 they can be fixed across a horizontal, vertical or oblique axis. The lens powers available for the correction of myopia span from –5.00 to –20.00 D, and for hyperopia from +3.00 to +13.00 D, with the option of correcting astigmatism with toric lenses.

Figure 3.9: Kelman Duet Implant lens (Tekia©-Irvine, CA, USA)

The latest generation of the Artisan family is Artiflex, a foldable lens that can be implanted through a 3.2 mm clear corneal incision. Its optic is made of silicon (soft and foldable) and PMMA haptics are rigid allowing them to extend their securing function to the iris stroma (Fig. 3.12). This lens arose from the merging of the technologies of Ophtec© (Boca Raton, Fl, USA) and Advanced Medical Optics, Incs (Santa Ana, Ca, USA),

Figure 3.10: Insertion technique for the Kelman Duet Implant: A): Introduction of the haptics. B): Introduction of the optic. C): Joining the optic to the haptics inside the anterior chamber

Figure 3.11: The Artisan lens design allows four points for aqueous humor to pass from the posterior to the anterior chamber

since the silicon used for the optic was patented by Advanced Medical Optics, Incs. Its launching on the international market is forecast for the middle of 2005 after clinical trials.

POSTERIOR CHAMBER LENSES

These lenses are implanted in the posterior chamber of the eye, that is, between the iris and the crystalline lens. The first phakic posterior chamber lens was the Mushroom lens designed by Fyodorov and Zuev4 in 1985. However, in practice this lens was not only implanted in the posterior chamber since its butterflyshaped haptics were placed on the crystalline lens in the posterior chamber, while the optic extended beyond this through the pupil. The Mushroom lens subsequently underwent many design changes to become a posterior

Figure 3.12: Artiflex lens (Ophtec©-Boca Raton, Fl, USA) (Advanced Medical Optics, Incs-Santa Ana, Ca, USA)

chamber lens exclusively, and the first prototype of most posterior chamber phakic lenses. We will now review the posterior chamber phakic lenses available today. Since they are implanted in the posterior chamber, all these lenses can produce acute glaucoma due to pupillary block, such that two Yag laser iridotomies or a wide surgical iridectomy need to be undertaken before the implant procedure.

Implantable Contact Lens (ICL)

It was in 1993, when the company Staar© (Monrovia, CA, USA) acquired the marketing rights to one of the lenses developed by Fyodorov, that a posterior chamber lens appeared on the market. This lens made of a collagen polymer (collamer) was given the name “Implantable Contact Lens” (ICL).

The first implants in the western world were performed by Paolo Pesando, Vincenzo Assetto, Guido Caramello and Christian Skorpik using the model IC2020-M.5 This lens had a biconcave 3.5 mm diameter optic and gave rise to the subsequent models: ICM(H)V1, ICM(H)V2, ICM(H)V3 and the last generation ICM(H)V4 (Fig. 3.13). In its development, the intention has always been to try to increase the diameter of the optical zone, and the space between the posterior surface of the lens and the anterior surface of the crystalline lens (the vault). This new design was prompted by reports of the development of cataract6,7 in eyes with a small vault,

provoked by the inherent hydrophilic nature of the lens material.

The collagen polymer from which the lens is manufactured (63% polyhydroxymethylethylacrylate, 34% water, 0.2% porcine collagen, 3.4% benzophenone) confers the lens 37.5 percent hydrophilia and good permeability to gases and nutrients. It allows 99 percent light transmission and has a refraction index of 1.452.

The ICL is implanted in the posterior chamber and has four small platforms at the end of the haptics so that it can rest on the sulcus. The posterior lens surface is concave and adopts the shape of a dome over the anterior crystalline capsule to create a space for the free movement of aqueous humor. This avoids contact with the crystalline lens inducing cataract formation.

The five lengths available: 11.5, 12.0, 12.5, 13.0 and 13.5 mm, mean the lens can be adapted to the different white-to-white measures (approximately the sulcus-to-sulcus distance). The optical zone varies from 4.5 to 5.5 mm depending on the lens power. The thickness of the optic is 100 to 600 microns and the thickness of the haptics is 60 to 80 microns. It has the advantage that it can be implanted using an injector through a self-sealing 3 mm corneal incision. The lens powers available for myopia run from –3.00 to –23.00 D and for hyperopia from +3.00 to +22.00 D (in 0.50 D increases).

There is currently also a toric lens, Toric ICL, that allows us to correct astigmatism associated with the spherical myopic defect. The lens has marks to help align the lens as it is implanted on the sulcus (Fig. 3.14). It can be purchased in the same length as the lens for spherical correction and is available for a myopia of – 6.0 to –23.0 diopters with +1.0 to +6.0 diopters of cylinder in 0.5 diopter increments.

Phakic Refractive Lens (PRL)

Developed by the company Medenium Inc© (Irvine, CA, USA) since 1987 from one of Fyodorov’s designs,8 the PRL was internationally launched by CIBA Vision© (Duluth, GA, USA), which then sold the patent to IOLtech© (La Rochelle, France), its current marketing company.