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

Sunita Agarwal

Athiya Agarwal

Amar Agarwal

Ashok Garg (India)

INTRODUCTION

There are basically three methods to correct Presbyopia.1 The first comprises surgeries done on the sclera. This includes techniques like scleral bands or anterior ciliary sclerostomy. The second comprises surgeries done on the cornea like presbyopic lasik or Conductive keratoplasty. The third and most widely performed are surgeries done on the lens. This includes multifocal IOLs and the accommodating IOLs.

HUMANOPTICS

Humanoptics2 is a company in Germany, which has developed a pseudophakic accommodating foldable IOL. This is the Humanoptics accommodative 1 CU IOL, which helps correct both distance and near vision based on Helmholtz’s theory. This lens was developed on the work done by Khalil Hanna MD using finite element computer models.

ACCOMMODATIVE 1 CU IOL

This lens, which is an accommodating IOL, is a hydrophilic acrylic lens with a refractive index of 1.46. It has an integrated ultraviolet (uv) inhibitor. The lens has four square edge dynamic transition elements (Fig. 19.1) with an overall diameter of 9.8 mm and a biconvex optic of 5.5 mm. It comes in a diopter range of +16 to +26 D in 0.5 D increments. The lens functions by dynamic transition elements that enable the optical power of the lens to change during accommodation.

Figure 19.1: The Humanoptics Accommodative 1 CU IOL. Note the four haptics present in the lens, which have a hinge connection to the optics

MECHANISM OF ACTION

With the Accommodative 1 CU inserted into the bag, stimulus of accommodation leads to contraction of the ciliary muscle and relaxation of the zonules. The resultant mechanical energy stored in the capsular bag is transmitted to the implant during accommodation. This leads to a specific posterior deformation of the implant that increases its optical power, allowing near objects to focus on the retina. When accommodation ends, the ciliary muscle relaxes and zonular tension increases. The capsular bag is stretched and the Accommodative IOL returns to its unaccommodative state. This results in distant objects being focused on the retina.

BIOMETRY

If one uses an ultrasonic device, the measurement probe is applied directly to the anterior surface of the cornea. Due to the induced contact pressure the value of the axial length measurement may be smaller. It is thus recommended to add an average contact factor of 0.2 mm to the measured axial length. The K-readings are to be used in millimeters and not in dioptres as this can create an impact in the calculations. The target refraction should be 0 to – 0.5 D.

SURGICAL TECHNIQUE

The Humanoptics lens comes in a sterile package and is an acrylic hydrophilic IOL. The lens is taken from the package using a special forceps (model RS 211 from Humanoptics). This lens is the placed in a special cartridge (model RS 420 from Humanoptics). The lens is placed in such a way that the four haptics of the lens are outside the cartridge flange. Then using the same forceps parallel pressure is applied to fold the lens and the cartridge is partially closed. The forceps is then slowly removed and used to place the haptics into the loading chamber. When correctly positioned and ascertained that the lens and haptics are completely in the tunnel the wings can be fully closed. Using the other end of the same forceps, which has a special lens loader the lens, is pushed into the cartridge tunnel. For this one should apply light and constant pressure until the entire length of the loader is inserted into the cartridge. The cartridge is then placed in the injector (Fig. 19.2) (model RS 310 from Humanoptics).

Figure 19.2: The Humanoptics injector

The cartridge is now pushed in the positioning slot as well as down to ensure that the tunnel runs parallel to the tip of the injector. The lens is now ready (Fig. 19.3) to be implanted simply and reliably by slowly pushing the piston of the injector. The right hand holds the injector and the cartridge is passed through the incision inside the anterior chamber (Fig. 19.4). The incision size is 3.2 mm. The lens is gradually inserted

Figure 19.4: Cartridge inserted inside the eye. The lens is gradually implanted

inside the anterior chamber. The four haptics lie on top of the rhexis. Then using an Agarwal globe stabilization rod from Gueder (Germany) each of the four haptics is placed inside the capsular bag (Fig. 19.5). Once the entire lens is in the capsular bag (Fig. 19.6) the viscoelastic is removed by the irrigation aspiration probe.

POST-OPERATIVE CARE

The accommodative potential will be achieved after complete capsular bag shrinkage. This takes about a month after surgery.

Figure 19.5: The lens haptics are placed in the capsular bag using the Agarwal globe stabilization rod (Gueder, Germany)

Figure 19.6: The accommodating IOL is entirely in the capsular bag

REFERENCES

1.Agarwal A. Presbyopia: A Surgical Textbook; Slack; USA, 2002.

2.Gregory Pamel J. The Humanoptics Akkommodative 1CU IOL in A Agarwal’s Presbyopia: A Surgical Textbook. Slack USA, 2002; 211-14.

Tanuj Dada

Harinder Singh Sethi (India)

INTRODUCTION

The art and science of cataract surgery is undergoing a rapid evolution. The use of lenses implanted within the eye has been one of the major achievements of modern medicine. The intraocular lens technology has come a long way since the use of standard PMMA lenses for extracapsular surgery. The advent of small incision surgery made possible by phacoemulsification has ushered the era of foldables IOLs with silicone and acrylic materials. 1-3 In the last decade emphasis has shifted to lens based refractive surgery with the use of Phakic IOLs and recently the new technique of Micoincision cataract surgery (MICS) or Phakonit has been introduced with use of ultrathin lenses which can be inserted via sub 1.5 mm incisions. In addition to these advancements new IOL materials such as collagen polymers, specific blue light blocking IOLs, IOLs to decrease aberrations and restore accommodation have come into use. Research is one to create custom made IOLs for each individual based on wave front technology. The present text highlights the basic design and optical features of new IOL technologies.

PHAKIC IOLs

Phakic IOLs are increasingly being used for correction of high myopic errors (-8 to-20D). Recent studies have shown that that phakic IOLs are a safe alternative to corneal refractive surgery such as LASIK, but, they require a more surgical expertise. These IOLs are of two main types.3,4

1.Anterior chamber IOLs

a.Iris fixated e.g. Artisan/Verisyse IOLs (Fig. 20.1)

b.Angle fixated e.g. Kelman Duet/Vivarte IOLs and (Fig. 20.2)

2.Posterior chamber IOLs e.g. ICL /PRL

Figure 20.1: Iris claw phakic IOL

Figure 20.2: Vivarte IOL

Anterior Chamber IOLs

Anterior chamber phakic intraocular lenses have been used since 1950s but the surgical procedure failed due to lack of microsurgery devices and poor understanding of the endothelial function with a high rate of bullous keratopathy. The last decade has seen a comeback of these lenses and today phakic intraocular lenses are an important area of refractive surgery.

Criteria for Patient Selection

The following the selection criteria to be strictly followed before selecting a patient for phakic anterior chamber IOL:

1.Patient should be more than 18 years old

2.Moderate to high myopes (> 9.00D) and Hyperopes (> 4.5 D)

3.Also indicated in lesser degrees of ametropia especially if LASIK is contraindicated, as in conditions like corneal thickness less than 500 microns, steep or flat corneas, Topographic change suggestive of kerato-conus, etc.

4.Endothelial cell density of more than 2000 cells/ mm2

5.Pupil smaller than 6 mm in scotopic luminance.

6.Stable refraction for atleast 1 year.

7.Anterior chamber depth (excluding corneal thickness) of at least 2.8 mm

8.Angle width at least 30 degrees

9.No eye pathology except refractive error

10.No systemic pathology such as diabetes, collagen diseases, etc.

Iris Fixated IOLs

Iris fixated IOLs have haptics in the form of a lobster claw that fixate the lens to the mid peripheral iris. The classical type of this phakic IOL is the Artisan from Ophtec, and Verisyse from AMO).3,4 The Artisan lens is a onepiece UV wavelength absorbing PMMA compression molded lens with a diameter of 8.5 mm. The optic is vaulted suitably (0.5 mm) to stay clear of the iris cone. It is available in 5.0 mm optic (for myopia –3.00 to

–23.00 and hyperopia + 3.0 to + 12.00) or 6.0 mm (available for myopia –3.0 to –14.5 D). There is also a Toric Artisan available in 5.0 mm model, which corrects astigmatism of upto 7.0 D. Two models are available: Model A: axis of cylinder in the axis of IOL and Model B: Axis of cylinder 90 degrees to the axis of the IOL. The Artisan lens requires a 5- 6 mm incision and thus may be associated with significant astigmatism. Verisyse lenses has several different models: aphakic, myopic, hyperopic and toric. The FDA has recently given approval for the use of the Verisyse phakic IOL for myopia ranging from –5 to –20 D in patients above the age of 21 years. The toric and hyperopic lenses are not yet approved.. This IOL requires a large incision and thus can also induce an astigmatic error. Anterior chamber depth for Artisan or Verisyse must be greater than 3.0 mm. The iris and angle fixated lenses require a laser iridotomy to be performed prior to the lens insertion.4,5 An Iris claw phakic IOL, such as Artisan/Verisye, is attached to anterior iris surface through enclavation of peripheral iris into the claws of lens. A fold of iris tissue underneath the haptic apex is created by an enclavation needle. By lifting the iris fold slightly or pushing the lens downward with the implantation forceps, both sides of the haptics made to open and enclose the fold in the iris. These IOLs are available in a universal size as they are independent of the dimensions of the anterior chamber.

These lenses have the following advantages:

•The angle of the anterior chamber, the crystalline lens, and the corneal endothelium are not at risk because they are far away from the iris fixated IOL.

•The Pupil can be dilated for fundus examination. Iris claw lens does not affect the movements of the iris

and the pupil, except at the point where the iris passes through the claw.

•The crystalline lens is not affected since the implanted lens remains far away from it.

•These lenses are very easy to explanted if needed and new lenses can be implanted at any time if necessary.

Complications with these IOLs include decentration, corneal endothelial cell loss, chronic inflammation, elevated IOP, pupillary block glaucoma, iris atrophy, implant dislocation and glare.3,4,11

Angle supported IOLs (Table 20.1)

First generation angle supported IOLs were developed by Baikoff and Ioly in 1997. The first model (ZBDOMILENS) was a modified the Kelman type lens with a 4.0 mm optic and 2 haptics an with a 4-point fixation in the angle. However, this lens had a high vault and was close to the endothelium. In the line of Kelman type angle supported anterior chamber phakic IOL, the only available at present is PHAKIC 6 which is made of PMMA, has a 6.0 mm optic and 2 haptics with four point fixation in the angle.

The foldable intraocular lenses in this group can be classified into two groups11:

1.Vivarte (Ciba Vision, Switzerland) and the Duet (Tekia, USA) and

2.ICARE (Corneal, France) and Acrysof (Alcon, USA) Vivarte and Duet have a foldable optic (acrylic) of 5.5 mm and 2 haptics made of PMMA with 3 points for the angle fixation. The difference between these two IOLs is that in the Duet the haptic and optic are implanted separately in the bag and the lens is

assembled in the eye, whereas in the ICARE and Acrysof the folding occurs outside the eye.3,6,7 The Vivarte IOL from Ciba Vision is a foldable phakic

IOL which has three angle supports.6 It is an acrylic, 5.5 mm diameter, lens with refractive index of 1.47. It is now available in a multifocal form for presbyopic patients with a +2.5 D add for near correction. For Vivarte, the anterior chamber depth must be greater than 3.2 mm with refractive errors of –7 D to –13 D, greater than 3.4 mm with refractive errors of –13 D to –18 D or greater than 3.6 mm with refractive errors greater than –18 D.

The Kelman Duet is a unique IOL in that it is inserted through a 1-1.5 mm incision as a two phase procedure.7 The haptics are inserted separate from the optics and are attached to the optic within the anterior chamber. An additional advantage of this lens is that one can change the optic as the patient ages and the refractive error changes.7

NuVita ZB 5M is a slightly convex lens, 5 mm diameter anterior chamber angle supported IOL. NuVita MA 20 offers better results than the NuVita ZB 5M because the optic, inclination angle and haptics are redesigned to eliminate glare and reduce pressure at the iris that might lead to alteration in the pupil. Potential disadvantages include pupillary ovalization from fibrosis around the footplate in the anterior chamber angle and the potential for chronic compromise of the anterior chamber angle leading to glaucoma.5,8

Selection of angle supported IOL

To select an IOL we need to calculate the power and the size of the implant. As these IOLs are supported by the angle and the size of the anterior chamber varies from patient to patient, the correct size of the anterior, chamber must be assessed. Most surgeons measure horizontal or vertical white to white with the help of the calipers, Holladay discs or Orbscan. To this white-to- white, a correction factor is added to determine the correct length. For example 1 mm in Phakic 6, 0.5-1.0 mm in Vivarte and 1.5 mm in Acrysof.

To calculate the lens power one can use Van der Heijde nomogram, which takes into account the spherical

equivalent, the corneal power and the anterior chamber depth.

For the anterior chamber phakic IOLs, endothelial cell count must be more than 2,000 cells/mm2, patients must be older than 18 years of age and anterior chamber depth must be preferably measured with an IOL Master (Zeiss Humphrey Systems, Dublin, USA). Various contraindications for anterior chamber phakic IOLs include cataracts, retinal detachment, abnormal pupils and/or corneas, an endothelial cell count of less than 2,000 cells/mm, pre-existing macular degeneration or retinopathy, anterior chamber depth less than 3 mm and IOP greater than 21 mmHg. The potential complications of these lenses are glare, sizing error, pupil irregularity, pigment loss, endothelial loss. Iris root ischemia, surgically -induced astigmatism related to the incision, etc. One concern with the use of rigid anterior chamber phakic IOLs is that if the patient develops a cataract you require a large incision to remove the phakic IOL and this compromises the small incision cataract surgery in addition to inducing astigmatism.3,8,11

Prior to IOL implantation of an anterior chamber phakic IOL, one requires to do a gonioscopy to assess the anterior chamber angle, evaluate the corneal endothelial count and perform an indirect ophthalmoscopy to look for any abnormalities in the retinal periphery. In addition an accurate estimation of the axial length is essential for which the IOL master can be used. A new toric phakic IOL has also been introduced for keratoconus patients.

Posterior Chamber Phakic IOLs (Table 20.2)

The Phakic Refractive Lens (PRL) (Novartis, Basel, Switzerland) and the Implantable Contact Lens (ICL) (Staar Surgical, Monrovia, USA) are two posterior chamber phakic IOLs. The Intraocular Contact Lens (ICL) from STAAR surgical and the Phakic Refractive Lens (PRL) form Ciba Vision are both posterior chamber phakic IOLs that vault over the crystalline lens and do not require sulcus fixation.6,9,11 The ICL requires a 3-mm incision and is made of porcine collagen and a copolymer of hydroxyethylmethacrylate. Anterior chamber depth should be more than 2.8 mm.

However, ultrasound biomicroscopic studies have documented an IOL-crystalline lens touch leading to cataract formation with these IOLs.10 Complications associated with phakic posterior chamber IOLs can include decentration, pupillary block (which is prevented by performing two laser iridotomies one week prior to insertion or one surgical peripheral iridectomy), pigment dispersion from chafing and anterior subcapsular cataract because of contact with the crystalline lens, inverted implantation, endothelial cell damage and lens induced uveitis.

Customised Phakic IOLs

Carlo Francesco Lovisolo from Milan, Italy, reported his preliminary results with a new Phakic IOL, the ICLV5 from Staar Surgical.12 The dimensions of the new lens are individually customised to match each patient’s optics and intraocular anatomy. The overall length of each IOL is calculated on the basis of VHF echographic measurements of anterior chamber geometry including the irido-corneal angle width and sulcus-to-sulcus distances. The IOLs optic diameter is based on measurements of mesopic papillary diameter, and optic geometry is based on individual wavefront analysis. The major improvement of this lens in both safety and efficacy is represented by the customised features. The optic size covers the pupil’s mesopic size which prevents halos and glare. The overall length perfectly fits sulcus dimensions as measured with VHF echography. This in turn means high vault height predictability with ideal clearances from central and mid-peripheral crystalline lens to prevent iatrogenic cataract. Moreover, the lens has adequate

toricity to correct astigmatism, thus providing better visual acuity.

SMART LENS

The lens has been developed by Medennium Inc.,Irvine, California.13 The Smart lens uses a thermodynamic hydrophobic acrylic material that is packaged as a solid rod 30 mm long and 2 mm wide. When implanted into the eye via a small incision, the rod is transformed at body temperature into a soft gel like material that has the shape of a full sized biconvex lens that completely fills the capsular bag. The entire transfomation takes less than 30 seconds. The material is entirely cohesive and does not leak out of the capsular bag through the capsulorhexis. The main advantage of the lens is that it can restore accommodation. When inserted into the eye, it reconfigures to its original size, shape, and imprinted diopter power, totally filling the capsular bag. Because of its hydrophobic acrylic nature and the fact that it fills the capsular bag, this lens should theoretically suppress posterior capsular opacification. It also will totally eliminate decentration, tilt, and glare from edge effects, and because it is a stable gel at body temperature with a high refractive index, it will be capable of a large amplitude of accommodation.

COLLAMER IOL

The collamer IOL from Staar Surgical Inc. (USA) is a pure polymer of collagen is thus the most biocompatible IOL (Fig. 20.3). The collagen attracts a monolayer of fibronectin on the surface of the lens, which in turn inhibits

the deposition of other proteins on the surface of the lens. Once the monolayer is formed the lens is not recognized as a foreign body inside the eye and thus it is the most biocompatible IOL. The material has a refractive index of 1.44 and is available both as a single piece and multipiece IOL.14,15

Figure 20.3: The Staar Collamer IOL

MULTIFOCAL INTRAOCULAR LENSES

The intraocular lenses commonly in use have a fixed focus which can be adjusted by adjusting the IOL power to serve for near, intermediate or distance vision. It is not possible to see near and distant objects clearly with these lenses and thus patients are always dependent on spectacles.16 Over the past decade, a variety of multifocal intraocular lenses (MIOLs) have been introduced and enjoyed a widespread clinical use. Both refractive and diffractive models have been shown to be effective in allowing each eye to achieve quality, uncorrected distance and near acuity after cataract surgery. The major concerns with the use of these lenses are the loss of contrast sensitivity and the inducement of glare and halos from light sources during night vision.17 All MIOLs require careful attention to IOL power calculations and the creation of a relatively planospherical result after surgery. The multifocal intraocular lenses can be classified into following types.1-3

Refractive MIOLs

Two-Zone/Target or Center Surround MIOL

The IOLAB NuVueTM is an example of an MIOL with the central near add in the middle of the optic

surrounded by a distance optical power. A new model made of silicone with PMMA haptics has shown surprisingly good clinical results despite the potential for visual blur with pupillary miosis. The NuVueTM is considered to be a “near dominant” MIOL and some surgeons use it in a monovision capacity for the near eye. It has a 2 mm near zone in the center of a 5.5 mm optic which provides 4.0 D of added power.

Three-zone MIOL

A variety of three-zone MIOLs providing distance and near vision by using a near annulus at various distance from the central distance component have been popular. The Storz True VistaTM and the Domilens Progress ThreeTM are examples of this style. Normal pupil patients do enjoy both near and distance vision but smaller pupils can obstruct the near component with some three zone MIOLs. One advantage of this lens design is that even though there is pupil dependency, distance vision is always preserved despite the loss of near acuity with miosis. The Storz True Vista IOL has a 1.5 mm central zone, 2.6 mm midperipheral zone and an overall diameter of 6 mm. Thus, these lenses have 3 concentric refractive zones. Central and peripheral zones provide distance power while the midperipheral zone provides near add power.

Five-zone Spherical Curve MIOL

The AMO ArrayTM SA40N is a lens designed with five zones of near and distance powers on the anterior surface of the optic. These power rings help to reduce pupillary dependency. The ArrayTM is considered a “distance dominant” lens and provides near acuities without correction in the J-3 range or better, offering good midrange and near acuity for most tasks. The lens has a 4.7 mm central zone with 5 annular refractive zones. Some patients will prefer the addition of a bifocal add for finer print and especially under low-light conditions. The AMO ArrayTM is available in a foldable silicone material with PMMA haptics. A new injectable delivery system allows for greater ease of insertion. The AMO ArrayTM lens is currently the most popular multifocal IOL in current use.

Diffractive MIOLs

Diffractive optics multifocal technology is slowly gaining wide acceptance. The major advantage of this lens is less pupil dependency and the ability to provide an even distribution of near and distance vision. However, manufacturing techniques are more difficult and critical with these lenses due to difficulties with making of the diffractive plate. The Alcon ReSTOR diffractive multifocal IOL is one such IOL which has an anterior conventional refractive surface which provides the distant power and a posterior concentric diffractive plate which provides additional power ranging from 2.5 to 4.5 D. Pharmacia has also developed a diffractive MIOL, the CeeonTM 811E. Addition of a diffractive component to the popular AcrysofTM acrylic IOL is also under consideration.

PRESBYOPIC LENS EXCHANGE

PRELEXSM is a term used to describe presbyopic lens exchange with a multifocal intraocular lens. While the application of the technology is new, the surgical techniques employed are proven successful over many years of use.18,19 The onset of presbyopia has traditionally meant that use of glasses for clear vision. Even those individuals who have received laser vision correction will eventually become presbyopic and need glasses or contacts to restore their full range of sight. Unlike procedures that focus on changing the shape of the cornea, PRELEXSM works on the lens inside the eye. Consequently, vision after the procedure will be stable and unlikely to change over time. In addition, cataract surgery will not be necessary later in life. The multifocal lens that are used to replace eye’s natural lens will provide with clearer vision at all distances, giving little or no dependence on traditional or progressive bifocal glasses.

ACCOMMODATING INTRAOCULAR LENS

The ability to implant a new lens within the original capsular bag of the crystalline lens and restore the physiologic accommodation is a concept being investigated by many research workers all over the

globe.12,20 Kamman and Cumming have modifed the traditional plate haptic silicon IOL to allow for movement of the IOL within the capsular bag after insertion. This intriguing design has demonstrated initial success in restoring presbyopic accommodation. Accommodative amplitudes of approximately 2 to 3 diopters have been observed. However, long-term studies have to be done before the clinical efficacy of these lenses is established. C and C Vision crsytalens model AT-45 accommodating IOL20 (Fig. 20.4) has been shown in initial studies to provide 2.5 to 2.75 D of accommodation. The lens flexes back and forth and moves upto 1.5 mm with contraction of the ciliary muscle.16

Humanoptics, a German company has developed a new pseudophakic accommodating foldable IOL.12 This is the Humanoptics accommodative 1 CU IOL, which helps correct both distance and near vision based on Helmholtz’s theory.3 It is a hydrophilic acrylic lens with a refractive index of 1.46. It has an integrated ultraviolet (uv) inhibitor. The lens has four square edge dynamic transition elements (Fig. 20.5) with an overall diameter of 9.8 mm and a biconvex optic of 5.5 mm. It comes in a diopter range of +16 to +26 D in 0.5 D increments. The lens functions by dynamic transition elements that enable the optical power of the lens to change during accommodation. With the Accommodative 1 CU placed into the bag, stimulus of accommodation leads to

Figure 20.4: C and C Vision crystalens model AT-45 accommodating IOL