Intraocular lens implantation - Optometry Today

Intraocular lens implantation - Optometry Today

Intraocular lens implantation - Optometry Today


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ot<br />

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Emma J. Hollick BA, FRCOphth, MD<br />

<strong>Intraocular</strong> <strong>lens</strong><br />

<strong>implantation</strong><br />

In the 18th century, Casanova first suggested that an<br />

artificial <strong>lens</strong> implant could be inserted into the eye to<br />

replace the crystalline <strong>lens</strong> after cataract extraction 1 .<br />

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The College of<br />

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Theoretically, replacement of the crystalline<br />

<strong>lens</strong> with an artificial <strong>lens</strong> is the optimal form<br />

of aphakic correction, as the majority of<br />

aberrations and distortions from spectacles<br />

derive from their placement anterior to the<br />

pupillary plane. Indeed, image magnification<br />

is a major disadvantage with aphakic<br />

spectacles as they increase the image size by<br />

20-35%, which leads to spatial disorientation.<br />

Other distortions include ring scotomata,<br />

peripheral distortion, the “jack-in-the-box”<br />

phenomenon, and a reduction in useful<br />

peripheral field.<br />

Contact <strong>lens</strong>es bring the refractive<br />

correction nearer to the nodal point of the<br />

eye, with a corresponding decrease in these<br />

distortions. Aphakic contact <strong>lens</strong>es increase<br />

Figure 1<br />

APMMA posterior chamber IOL seen<br />

through a widely dilated pupil. The whitish<br />

ring at the edge of the IOL optic is the<br />

opacified anterior capsule with a continuous<br />

curvilinear capsulorhexis<br />

the image size by 7-12%. However, many<br />

people cannot tolerate contact <strong>lens</strong>es –<br />

elderly people often find it difficult to<br />

manipulate <strong>lens</strong>es, and extended wear<br />

contact <strong>lens</strong>es are associated with a higher<br />

incidence of microbial keratitis. <strong>Intraocular</strong><br />

<strong>lens</strong>es are placed in a much more<br />

physiological position with obvious optical<br />

benefits.<br />

The first intraocular<br />

<strong>lens</strong> implant (1950)<br />

Harold Ridley implanted the first intraocular<br />

<strong>lens</strong> (IOL) in 1950 at St Thomas’ Hospital 2 .<br />

This followed the observation that intraocular<br />

fragments of Perspex seemed to cause little<br />

long-term inflammation in the eyes of pilots<br />

who had suffered penetrating eye injuries<br />

from the shattered Perspex windows of<br />

aeroplanes 3 .<br />

The original Ridley <strong>lens</strong> was made of<br />

Perspex (rigid Polymethylmethacrylate<br />

(PMMA)) and implanted behind the iris after<br />

extracapsular cataract surgery. The heavy <strong>lens</strong><br />

was placed between the iris and the<br />

remaining posterior capsule. Thousands were<br />

implanted, however, 15% needed to be<br />

explanted due to the high rate of<br />

complications, which included uveitis,<br />

secondary glaucoma, hyphaema and<br />

decentration or dislocation 4 . That said, some<br />

patients still have these IOLs in situ today,<br />

with relatively successful results 3 .<br />

Table 1<br />

Five generations of <strong>lens</strong> implants<br />

Early anterior chamber IOLs<br />

(1952-1962)<br />

The second generation of <strong>lens</strong>es were rigid,<br />

closed loop <strong>lens</strong>es, supported by the anterior<br />

chamber angle. The long-term results of these<br />

early anterior chamber <strong>lens</strong>es were universally<br />

poor due to their instability in the anterior<br />

chamber. This resulted in corneal endothelial<br />

damage, reducing the endothelial cell count of<br />

all patients with these implants, leading to a<br />

large number of patients suffering corneal<br />

decompensation and oedema. Progression to<br />

pseudophakic bullous keratopathy was<br />

frequent, with many patients requiring a<br />

corneal graft. The presence of these <strong>lens</strong>es<br />

increased the risk of graft failure, so many<br />

were explanted. Anterior chamber IOLs were<br />

also associated with iris complications such as<br />

iris chafing leading to blood aqueous barrier<br />

breakdown, iris erosion and pupil block. As a<br />

result, it was necessary to perform a peripheral<br />

iridectomy when implanting an anterior<br />

chamber IOL to reduce the risk of pupil block.<br />

These <strong>lens</strong>es were also associated with cystoid<br />

macular oedema (CMO), uveitis, the UGH<br />

syndrome (uveitis, glaucoma, hyphaema), and<br />

subluxation or dislocation.<br />

Iris-fixated IOLs (1953-1973)<br />

As instability of IOLs in the anterior chamber<br />

resulted in so many complications, greater<br />

support of the <strong>lens</strong> was sought by transferring<br />

the support from the anterior chamber angle<br />

Type of IOL Date Characteristics<br />

Figure 2<br />

The IOL has dislocated upwards in the eye<br />

Ridley posterior chamber IOL 1950 Heavy PMMA<br />

Early anterior chamber IOLs 1952 to 1962 PMMA, rigid design, closed loop<br />

Iris-supported IOLs 1953 to 1973 PMMA<br />

Modern anterior chamber IOLs 1970 to present day PMMA, Flexible haptics, open loop<br />

Modern posterior chamber IOLs 1975 to present day Standard PMMA designs<br />

Foldable <strong>lens</strong>es – silicone<br />

– hydrogel<br />

– acrylic<br />

Scleral-sutured IOL<br />

Multifocal IOLs<br />

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to the iris. The third generation of IOLs,<br />

independently produced by Epstein and<br />

Binkhorst, used the pupillary part of the iris<br />

diaphragm for anatomical fixation. However,<br />

this led to luxation of the <strong>lens</strong> if the pupil<br />

dilated unexpectedly. These pupillary fixated<br />

IOLs are now obsolete. A second development<br />

was the use of a Medallion <strong>lens</strong> fixed to the<br />

iris by a suture, however late degradation of<br />

the suture led to dislocation of the <strong>lens</strong>es. The<br />

next development was the Iris-claw <strong>lens</strong> with a<br />

fixating mechanism based on the capture<br />

of a fold of iris tissue at the two ends of the<br />

IOL.<br />

Modern anterior chamber<br />

IOLs (1970 to present day)<br />

For an anterior chamber <strong>lens</strong> to be safe and<br />

effective there should be minimal contact with<br />

the drainage angle, stability within the<br />

anterior chamber with no movement in the<br />

angle, no iris chafing and no endothelial<br />

touch.<br />

Modern anterior chamber IOLs were<br />

designed to achieve this by using flexible open<br />

loop <strong>lens</strong>es made of PMMA. They have the<br />

advantage of not requiring an intact posterior<br />

capsule for <strong>implantation</strong> and can be implanted<br />

into eyes even after posterior capsule rupture<br />

(occurring during complicated cataract surgery<br />

or after intracapsular surgery). Modern<br />

anterior chamber IOLs allow far better fixation<br />

Table 2<br />

Advantages and disadvantages of the IOL types<br />

www.optometry.co.uk<br />

than the early anterior chamber IOLs and<br />

corneal complications are rare. However, they<br />

are associated with a higher incidence of CMO<br />

and retinal detachment than posterior<br />

chamber IOLs.<br />

Modern posterior chamber<br />

IOLs (1975 to present day)<br />

The first posterior chamber IOLs were made of<br />

PMMA with either PMMA, polypropylene or<br />

polyamide haptics. They require the presence<br />

of a posterior capsule and can either be placed<br />

in the sulcus or the capsular bag. Capsular bag<br />

placement has been shown to be superior to<br />

sulcus placement in terms of centration and<br />

the rate of posterior capsular opacification<br />

(PCO). The advantage of posterior chamber<br />

IOLs is that they are placed in the position of<br />

the original crystalline <strong>lens</strong> leading to a more<br />

physiological situation with optical benefits.<br />

An additional advantage is that posterior<br />

chamber IOLs are situated away from the<br />

delicate structures of the anterior chamber<br />

including the cornea, the aqueous outflow<br />

channels, the iris and the ciliary body. This<br />

leads to a lower incidence of corneal problems,<br />

UGH and pupil block. When the IOL is placed<br />

within the capsular bag, contact with uveal<br />

tissues is completely avoided. The intact<br />

posterior capsule is associated with a<br />

decreased incidence of CMO and retinal<br />

detachment 5 .<br />

Type of IOL Advantages Disadvantages<br />

Ridley PC IOL optical uveitis<br />

secondary glaucoma<br />

hyphaema<br />

decentration/dislocation<br />

Early AC IOLs do not require posterior capsule - corneal complications:<br />

(rigid, closed loop) capsule usually removed therefore (decompensation, oedema,<br />

no PCO<br />

pseudophakic bullous<br />

keratopathy, IOL corneal touch)<br />

CMO, uveitis, UGH<br />

subluxation, dislocation<br />

Iris-supported IOL do not require posterior capsule iris complications: (iris chafing and<br />

erosion, pupil changes, pupillary block,<br />

PAS - Peripheral Anterior Synechiae)<br />

Modern AC IOLs do not require posterior capsule CMO retinal detachment<br />

(flexible, open loop) better fixation corneal complications rare<br />

Modern PC IOLs less corneal problems require intact zonules & posterior capsule<br />

less CMO<br />

less retinal detachment<br />

less UGH<br />

less pupil block<br />

optical<br />

Foldable IOLs small incision expensive<br />

less astigmatism<br />

decentration<br />

quicker rehabilitation<br />

rupture bag when unfolding<br />

safer<br />

spontaneous dislocation<br />

IOL material<br />

PMMA is the gold standard material for use in<br />

IOL manufacturing. It was the first material<br />

to be used, and has withstood the test of<br />

time as the majority of IOLs implanted<br />

worldwide today are still made of it. PMMA<br />

benefits from inducing a minimal intraocular<br />

inflammatory reaction, is not adversely<br />

affected by ultraviolet light and is not<br />

biodegradable in the eye. Because of this, it<br />

maintains a smooth surface even when in<br />

contact with vascular and metabolically<br />

active tissue. PMMA is also relatively<br />

inexpensive. However, one disadvantage is<br />

that it is rigid and so requires a larger<br />

incision for insertion than the newer foldable<br />

materials. Surface modifications of PMMA<br />

with heparin have been found to reduce the<br />

inflammatory cell precipitates found on the<br />

anterior IOL surface post-operatively,<br />

therefore, this <strong>lens</strong> modification is useful in<br />

patients expected to have more precipitation,<br />

such as uveitics.<br />

With the development of small incision<br />

phacoemulsification surgery, a whole new<br />

range of foldable <strong>lens</strong> implant materials have<br />

been developed. Early foldable IOLs, however,<br />

were not successful, because they elbowed<br />

and folded as the capsular bag contracted.<br />

The use of capsulorhexis dramatically reduces<br />

this decentration of foldable materials.<br />

The advantages of foldable IOLs are due<br />

to the smaller incision size required for their<br />

insertion. They are usually self-sealing and<br />

do not require suturing. Smaller incisions<br />

produce less astigmatism, allow quicker<br />

visual rehabilitation with stable refraction<br />

after a couple of weeks compared to six to<br />

eight weeks for larger wounds, and are safer<br />

with less iris prolapse and dehiscence. The<br />

disadvantage of foldable IOLs is that they are<br />

more expensive than PMMA and have a<br />

higher incidence of decentration if a<br />

continuous curvilinear capsulorhexis is not<br />

used.<br />

When a new IOL material is developed, its<br />

biocompatibility needs to be studied. IOL<br />

biocompatibility within the human eye has<br />

three major aspects. These are the effect on<br />

the blood aqueous barrier, the cellular<br />

reaction on the anterior surface of the <strong>lens</strong>,<br />

and the effect on the <strong>lens</strong> capsule. Blood<br />

aqueous barrier changes can be assessed by<br />

the amount of inflammation (flare and cells)<br />

within the anterior chamber, which can be<br />

quantified using the laser flare and cell<br />

meter. Cells on the anterior surface of the<br />

implant can be examined post-operatively<br />

using specular microscopy and have been<br />

used extensively as a method of assessing<br />

the foreign body response to the IOL. The<br />

effect of the IOL on the capsule consists of<br />

<strong>lens</strong> epithelial cell proliferation and<br />

metaplasia leading to anterior and posterior<br />

capsular opacification, and IOL decentration.<br />

PCO occurs in 20-50% of patients two years<br />

after cataract surgery (Figure 3). It leads to a<br />

progressive deterioration in visual acuity and<br />


ot<br />

Figure 3<br />

This IOL shows a dramatic amount of<br />

opacification of the posterior capsule.<br />

The patient’s vision was significantly<br />

reduced and they required a Nd: YAG laser<br />

posterior capsulotomy<br />

contrast sensitivity, and in many cases patients<br />

do not seek medical attention, fearing that this<br />

is an untreatable age-related change. PCO can<br />

be relatively easily treated with Nd<br />

(neodymium):YAG laser posterior capsulotomy,<br />

where the Nd:YAG laser is used to make a hole<br />

Table 3<br />

Posterior chamber intraocular <strong>lens</strong> design features<br />

Design feature<br />

Number of pieces<br />

Loop material<br />

Loop shape<br />

Optic design<br />

Surface modification<br />

IOL material<br />

Variations<br />

• One piece (disc or plate haptic)<br />

• Three piece (disc)<br />

Figure 4<br />

A diamond shaped posterior capsulotomy<br />

can be seen in the central posterior<br />

capsule of this patient with significant PCO<br />

in the posterior capsule to clear the visual axis<br />

(Figure 4). This procedure, however, can be<br />

associated with a number of complications such<br />

as pitting of the IOL, intraocular pressure<br />

spikes, inflammation, CMO and retinal<br />

detachment. Many IOL manufacturers are<br />

concentrating their research on ways to prevent<br />

PCO, and there are now certain IOLs which are<br />

associated with a lower incidence of PCO.<br />

• Polypropylene (flexible, possible higher incidence of endophthalmitis)<br />

• PMMA (rigid)<br />

• Polyacrylic<br />

• Angulation (forward angulation increases pressure on posterior capsule<br />

and may decrease PCO, and increases distance of optic from iris.<br />

Less angulation may facilitate insertion)<br />

• J or C loops<br />

• Convex plano, plano convex, biconvex (Biconvex associated with<br />

the least image degradation with decentration and tilt and less PCO)<br />

• Length of the IOL (14mm for sulcus fixation, 12-12.5mm<br />

for in-the-bag fixation)<br />

• Size of optic (4.5-7mm. Larger optics may be better for patients with large<br />

pupils but need bigger incisions. Smaller optics for bag fixation)<br />

• Holes (to facilitate dialling into capsular bag)<br />

• Ridges (designed to facilitate laser capsulotomy, but associated<br />

with more PCO)<br />

• Sharp or round optic edge (less PCO when optic has a square edge than<br />

round, due to barrier to <strong>lens</strong> epithelial cell migration, e.g. Alcon AcrySof IOL;<br />

Pharmacia & Upjohn CeeOn 911; Rayner Centerflex IOLs)<br />

• Binding of hydrogels or heparin to the IOL surface (to make IOL more<br />

hydrophilic, found to reduce inflammatory cell precipitate)<br />

• Surface passivation (to make IOL more hydrophobic and oleophilic,<br />

aiming to repel lipids such as cell membranes and ocular tissues)<br />

• PMMA<br />

• Silicone<br />

• Hydrogel/hydrophilic acrylic<br />

• Hydrophobic acrylic<br />

Silicone elastomers (elastic polymers) are<br />

composed of highly cross-linked polysiloxane<br />

chains. They are compressible and can<br />

therefore be inserted through a small incision<br />

by folding. Silicone <strong>lens</strong>es are homogeneous,<br />

heat-resistant, autoclavable, moldable and<br />

compressible and highly transparent to visible<br />

light. The specific gravity of the material is<br />

low and therefore the <strong>lens</strong> is nearly weightless<br />

in aqueous. Silicone has excellent tensile and<br />

tear strength, and is extraordinarily flexible.<br />

Silicone IOLs can be either three pieces, with<br />

open loop prolene, polyamide or PMMA<br />

haptics, or plate haptic.<br />

Silicone has a lower refractive index<br />

(1.41-1.46) than PMMA (1.49) and<br />

consequently the <strong>lens</strong> is thicker, which may be<br />

an impediment to very high powers. Although<br />

the silicone <strong>lens</strong> is transparent to Nd:YAG<br />

laser radiation, the <strong>lens</strong> can be pitted when<br />

hit by the laser beam 6 . In fact, silicone IOLs<br />

have been shown to have the lowest threshold<br />

for laser-induced damage compared to PMMA<br />

and acrylic IOLs, and to suffer the greatest<br />

damage depth at each energy level tested 7 .<br />

Furthermore, the surface of a silicone IOL is<br />

hydrophobic and it has been shown that a<br />

higher percentage of cellular reactions occur<br />

on hydrophobic surfaces than hydrophilic<br />

ones 8 .<br />

A further disadvantage is that they<br />

become slippery when wet and, as a result,<br />

become difficult to handle. An additional<br />

clinical complication occurs if silicone oil is<br />

used to help re-attach the retina following a<br />

retinal detachment in a pseudophakic patient,<br />

as the oil adheres to silicone IOLs. In<br />

addition, silicone IOLs with flexible haptics or<br />

plate haptic design have a higher incidence of<br />

decentration than other IOL types. Plate<br />

haptic silicone IOLs are also at increased risk<br />

of anterior capsule opening contraction 9 .<br />

Incidences of capsular bag rupture have also<br />

been reported during IOL unfolding, and<br />

spontaneous dislocation of IOLs into the<br />

vitreous after YAG capsulotomy, particularly<br />

with the plate haptic design.<br />

More recent silicone IOLs are made of<br />

second-generation silicone and appear to be<br />

associated with less inflammatory cell<br />

precipitate than the earlier first-generation<br />

<strong>lens</strong>es. A recent silicone IOL design,<br />

CeeOn 911 (Pharmacia & Upjohn) has been<br />

manufactured with a square optic edge, which<br />

has been shown to be associated with a low<br />

incidence of PCO compared to many other IOL<br />

types.<br />

Hydrophilic acrylics include a broad class<br />

of polymer materials which swell extensively<br />

in water but are not water-soluble (previously<br />

referred to as hydrogels). These materials<br />

have variable size and physical properties<br />

according to the state of hydration. An<br />

example is polyhydroxyethylmethacrylate<br />

(PHEMA), which has a 38% water content.<br />

High-water content hydrogels are<br />

cross-linked polymers based on a hydrophilic<br />

monomer. They are soft and resemble living<br />

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tissues in their physical properties and the<br />

smooth, hydrophilic nature minimises<br />

mechanical friction with ocular tissues and<br />

contributes to superior biocompatibility 10 . This<br />

is reported to produce less damage to the<br />

corneal endothelium after inadvertent touch<br />

on <strong>implantation</strong> than PMMA 11 . The hydrophilic<br />

nature of the <strong>lens</strong> surface causes low<br />

interfacial tension (wettability) of the<br />

hydrogel in aqueous solution and reduces the<br />

tendency of proteins to denature on the<br />

surface of the polymer, thus reducing<br />

biological rejection mechanisms. This possibly<br />

also prevents adhesion between the <strong>lens</strong> and<br />

the capsular bag. As the dimension of the<br />

hydrogel changes in direct proportion to the<br />

degree of water saturation, it enables<br />

<strong>implantation</strong> of a semi-hydrated <strong>lens</strong> through<br />

a small incision, for it to later expand in the<br />

eye as it becomes fully hydrated.<br />

Hydrophilic acrylics have the advantage of<br />

undergoing less damage during YAG laser<br />

capsulotomy. When there is direct impact of<br />

the YAG laser beam on the <strong>lens</strong>, mild to<br />

moderate localised pitting occurs, without the<br />

radial fracturing seen on a PMMA implant. This<br />

is due to the resilience of the material and its<br />

ability to act as a shock absorber rather than<br />

cracking under stress.<br />

Although high water-content polymers are<br />

usually mechanically weak, the hydrogels can<br />

be very strong owing to certain changes of the<br />

polymer produced during the process of<br />

polymerisation. Examples of hydrophilic<br />

acrylic IOLs are the Hydroview <strong>lens</strong>, EasAcryl,<br />

Inject-A, Centerflex and the Memory Lens.<br />

Studies on the Hydroview IOL (Bausch & Lomb)<br />

have shown that it is associated with fewer<br />

surface inflammatory cells than PMMA and a<br />

second-generation silicone IOL. However, a<br />

significant <strong>lens</strong> epithelial cell (LECs) reaction<br />

on the anterior IOL surface was reported in<br />

addition to a higher incidence of PCO 12,13 .<br />

AcrySof (Alcon) is an example of a<br />

hydrophobic acrylic IOL, which has become the<br />

most commonly inserted IOL in the USA. The<br />

AcrySof polymer was developed from the same<br />

backbone used in PMMA. It has a higher<br />

refractive index (1.55) than PMMA or silicone.<br />

This means that <strong>lens</strong> implants made from<br />

AcrySof are thinner, thereby facilitating<br />

folding and insertion through a smaller<br />

incision 14 .<br />

Acrylic polymers change their mechanical<br />

properties with temperature, being hard and<br />

glassy at low temperature, and soft and fluid<br />

at high temperature. This means that an IOL<br />

inserted at room temperature unfolds slowly<br />

and in a controlled manner 14 . This avoids the<br />

rapid, explosive opening which can be seen<br />

with three-piece silicone IOLs which may cause<br />

iatrogenic damage to the capsule or other<br />

anterior segment structures. The AcrySof IOL<br />

is, however, found by many surgeons to be<br />

more difficult to fold than silicone <strong>lens</strong>es, as<br />

the <strong>lens</strong> is more rigid if cool.<br />

In addition, due to its tacky nature, the<br />

AcrySof IOL has a tendency to stick to forceps<br />

or between two parts of the IOL on insertion 15 .<br />

This characteristic may mean that the IOL<br />

sticks to the capsular bag (which is discussed<br />

later and may have advantages), however, the<br />

adhesion means that the IOLs are more<br />

difficult to explant in cases of anisometropia<br />

or incorrect power calculation 16 . The IOLs are<br />

not slippery when wet in contrast to silicone<br />

IOLs.<br />

The AcrySof IOL has been found to be<br />

associated with dramatically reduced rates of<br />

PCO 17 . This is thought to be due to both<br />

mechanical and material features. This was the<br />

first <strong>lens</strong> implant to be manufactured with a<br />

square optic edge, and it is thought that this<br />

edge acts as a barrier to the migration of LECs<br />

onto the posterior capsule, reducing PCO. The<br />

tacky nature of the implant leads to increased<br />

adhesion of the IOL to the capsule which also<br />

probably limits the migration of LECs onto the<br />

posterior capsule.<br />

An IOL may have excellent cytological<br />

biocompatibility (a limited/nil inflammatory<br />

reaction), but poor capsular biocompatibility<br />

(the effect on anterior capsule and PCO), for<br />

example, the Hydroview IOL. Therefore, the<br />

goal is to find an IOL which has both<br />

cytological and capsular biocompatibility.<br />

Design features, such as a sharp optic edge,<br />

and material composition appear to be equally<br />

important. To date, the second-generation<br />

silicone IOLs and AcrySof IOLs appear to have<br />

the best biocompatibility.<br />

Table 4<br />

Advantages and disadvantages of the IOL types<br />

IOL Type Advantages Disadvantages<br />

PMMA Long term experience Rigid so need large incision<br />

Good biocompatibility<br />

Pits with YAG laser<br />

Cheap<br />

High incidence of PCO<br />

The prevalence of <strong>lens</strong> materials in the<br />

1997 survey of the American Society of<br />

Cataract and Refractive Surgery was 38%<br />

acrylic, 20% silicone, and 40% PMMA (Kohnen,<br />

1998). The <strong>implantation</strong> of foldable IOLs in<br />

Australia rose from 1% in 1991 to 67% in<br />

1997 18 .<br />

Multifocal IOLs<br />

Standard IOLs are monofocal and so the loss of<br />

accommodation which increases with age<br />

becomes absolute with surgery, and the need<br />

to correct the resultant presbyopia is apparent.<br />

Multifocal and bifocal IOLs have been designed<br />

in an attempt to provide both distance and<br />

near vision without additional spectacle<br />

correction, as they form separate images of<br />

near and distance objects. The goal of<br />

multifocal implants has been to enable<br />

patients to be less dependent on spectacles<br />

following surgery. Multifocal IOLs are based on<br />

the simultaneous vision principle – if the<br />

power difference between two optical systems<br />

is 3.00DS or more, then the images are<br />

dissimilar enough for the brain to interpret<br />

them as separate.<br />

An example is the ARRAY multifocal IOL by<br />

Allergan which has concentric rings of varying<br />

optical power around a central power for<br />

distance. The rings of power are for near<br />

distances, while the central distance power is<br />

dominant. Fifty per cent of the <strong>lens</strong> is<br />

dedicated to distance vision, 36% to near<br />

Silicone Foldable - small incision Low refractive index - thicker IOLs (first generation silicone)<br />

Fairly low incidence of PCO High refractive index - thinner IOLs (second generation silicone)<br />

(particularly second<br />

Pits with YAG laser<br />

generation silicone)<br />

Rapid unfolding in the eye<br />

Dislocation after YAG<br />

More decentration<br />

More anterior capsule contraction<br />

Slippery when wet<br />

Cannot use with silicone oil<br />

AcrySoft Foldable - small incision Short experience<br />

High refractive index - thin IOLs Tacky surface - sticks to forceps<br />

Very low incidence of PCO More difficult to fold<br />

LEC regression<br />

?Glistenings<br />

Biocompatible<br />

?Glare<br />

Fewer pits with YAG laser<br />

Slow uncontrolled folding<br />

Hydroview Foldable - small incision LECs on anterior IOL surface<br />

Good biocompatibility<br />

High incidence of PCO<br />

- low inflammatory cell reaction<br />

Fewer pits with YAG laser<br />

Controlled unfolding<br />

Less endothelial cell damage<br />

with cornea touch<br />

www.optometry.co.uk<br />


ot<br />

vision and 14% to intermediate distances.<br />

One study compared 100 patients implanted<br />

with the ARRAY <strong>lens</strong> in both eyes after<br />

bilateral cataract surgery with 100 patients<br />

with a standard monofocal IOL implanted<br />

bilaterally 19 . It was reported that 41% of<br />

patients with the ARRAY <strong>lens</strong> did not wear<br />

spectacles compared to 12% of patients with<br />

monofocal IOLs. For near tasks, 38% of<br />

multifocal patients did not wear spectacles<br />

compared to 10% of monofocal patients. In<br />

addition, 85% of those with multifocal IOLs<br />

did not wear spectacles for distance compared<br />

to 52% with monofocal IOLs.<br />

The downside was that patients with<br />

multifocal <strong>lens</strong>es were more bothered with<br />

glare and haloes from oncoming headlights at<br />

night and found night driving more difficult<br />

than the patients with monofocal IOLs. This<br />

“halo-effect” can also occur with other<br />

bright/dark contrast situations.<br />

An additional disadvantage of multifocal<br />

<strong>lens</strong>es is that they reduce contrast sensitivity.<br />

This results in loss of sharpness of vision<br />

particularly under poor visibility conditions<br />

such as low light or fog. Therefore, patients<br />

who spend their lives in a twilight<br />

environment and night-time work conditions<br />

may be disturbed by this loss of contrast<br />

sensitivity. Patient selection is a crucial step<br />

when considering whether a multifocal or<br />

monofocal <strong>lens</strong> should be implanted. Suitable<br />

candidates are those whose myopic<br />

astigmatism does not exceed 1.00D, spend<br />

most of their lives in normally lit<br />

environments and have no other ocular<br />

diseases. Bilateral <strong>implantation</strong> results in the<br />

most satisfying outcome, and leaving the<br />

patient emmetropic or slightly hypermetropic<br />

minimises glare and visual disturbances.<br />

Accommodative IOLs<br />

Certain research groups are studying ways of<br />

refilling the capsular bag with flexible IOLs<br />

capable of accommodation. One study<br />

removed <strong>lens</strong>es from a group of rabbits and<br />

primates, and refilled the capsular bag with<br />

an inflatable endocapsular balloon 20 .<br />

Accommodation could be demonstrated<br />

following this technique in primates 21 ,<br />

however, the incidence of PCO was reported to<br />

be very high (94%). The post-operative<br />

amplitude of accommodation was small and<br />

decreased with time, which was likely to be<br />

due to the increase in PCO with capsular<br />

fibrosis leading to a loss of capsular pliability.<br />

The use of a soft injectable liquid to fill<br />

the bag has been attempted in rabbit eyes 22<br />

and primates 23 : after making a minicapsulorhexis,<br />

phacoemulsification was<br />

performed with a tiny tip. Silicone material<br />

was then injected into the capsular bag, and<br />

the bag then closed with a silicone plug.<br />

Some accommodation appeared to be present<br />

postoperatively. However, all eyes suffered<br />

thick PCO soon after surgery. YAG laser<br />

capsulotomy would obviously not be<br />

appropriate as this could annul the attained<br />

accommodation. However, research has<br />

continued in this field and two prototypes will<br />

be marketed for use in humans next year<br />

(see previous CPD article, Outcome in Cataract<br />

Surgery, 05/10/01).<br />

Conclusion<br />

IOL design has developed through the years<br />

and has now become extremely successful<br />

with very few complications. The<br />

complications of corneal decompensation,<br />

glaucoma, hyphaema and uveitis have largely<br />

been resolved with the use of posterior<br />

chamber IOLs placed within the capsular bag.<br />

Similarly, <strong>lens</strong> decentration and dislocation is<br />

much rarer with the in-the-bag positioning of<br />

the <strong>lens</strong> implant with capsulorhexis. However,<br />

one complication remains, despite<br />

improvements in surgical technique – PCO.<br />

Nevertheless, developments in intraocular<br />

<strong>lens</strong> design are having a dramatic effect on<br />

reducing the incidence of PCO.<br />

About the author<br />

Emma Hollick works at Moorfields Eye<br />

Hospital. She recently carried out research at<br />

St Thomas’ Hospital looking at intraocular<br />

<strong>lens</strong> implant biocompatiblity and posterior<br />

capsular opacification.<br />

References<br />

1. Marcher A. Memoirs of Giacomo Casanova<br />

de Seingalt. 8, 45-50, R&R Clarke for<br />

Limited Editions Club 1940.<br />

2. Spalton DJ. Harold Ridley’s first patient.<br />

J Cataract Refract Surg 1999; 25: 156.<br />

3. Letocha CE, Pavlin CJ. Follow-up of three<br />

patients with Ridley intraocular <strong>lens</strong><br />

<strong>implantation</strong>. J Cataract Refract Surg 1999;<br />

25: 587-591.<br />

4. Ridley H. Intra-ocular acrylic <strong>lens</strong>- past,<br />

present and future. Trans Ophthalmol Soc<br />

UK 1964; 84: 5-14.<br />

5. Smith RT, Campbell CJ, Koester CJ et al. The<br />

barrier function in extracapsular cataract<br />

surgery. Ophthalmology 1990; 97: 90-95.<br />

6. Newland TJ, Auffarth GU, Wesendale TA,<br />

Apple DJ. Neodymium: YAG laser damage on<br />

silicone intraocular <strong>lens</strong>es. A comparison of<br />

lesions on explanted <strong>lens</strong>es and<br />

experimentally produced lesions. J Cataract<br />

Refract Surg 1994; 20: 527-533.<br />

7. Newland TJ, McDermott ML, Eliott D,<br />

Hazlett LD, Apple DJ, Lambert RJ, Barett<br />

RP. Experimental neodymium:YAG laser<br />

damage to acrylic,<br />

poly(methylmethacrylate) and silicone<br />

intraocular <strong>lens</strong> materials. J Cataract<br />

Refract Surg 1999; 25: 72-76.<br />

8. Amon M, Menapace R. In vivo<br />

documentation of cellular reactions on <strong>lens</strong><br />

surfaces for assessing the biocompatibility<br />

of different intraocular <strong>lens</strong> implants. Eye<br />

1994: 8: 649-656.<br />

9. Dahlauser KF, Wrolewski KJ, Mader TH.<br />

Anterior capsule contraction with foldable<br />

silicone intraocular <strong>lens</strong>es. J Cataract<br />

Refract Surg 1998; 24: 1216-1219.<br />

10. Blumenthal M. The use of high water<br />

content hydrogels as intraocular <strong>lens</strong>es. In:<br />

Soft implant <strong>lens</strong>es in cataract surgery.<br />

Mazzocco TR, Rajacich GM, Epstein E (eds),<br />

New Jersey, Slack Inc, 1986; pp107-117.<br />

11. Blumenthal M, Yalon M. Interaction of soft<br />

and hard intraocular <strong>lens</strong>es with cat cornea<br />

endothelium. Cornea 1982; 1: 129-132.<br />

12. Hollick EJ, Spalton DJ, and Ursell PG.<br />

Surface cytology on intraocular <strong>lens</strong>es:<br />

Can increased biocompatibility have<br />

disadvantages? Archives Ophthalmol<br />

1999a; 117: 872-878.<br />

13. Hollick EJ, Spalton DJ, Ursell PG, Meacock<br />

WR, Barman SA, Boyce JF. Posterior<br />

capsular opacification with Hydogel, PMMA<br />

and Silicone intraocular <strong>lens</strong>es: two-year<br />

results of a prospective randomised clinical<br />

trial. Am J Ophthalmol 2000;<br />

129: 577-584.<br />

14. Anderson C, Koch DD, Green G, et al. Alcon<br />

AcrySof acrylic intraocular <strong>lens</strong>. In: Martin<br />

RG, Gills JP, Sanders DR, eds, Foldable<br />

<strong>Intraocular</strong> Lenses. Thorofare, NJ, Slack,<br />

1993; 161-177.<br />

15. Komatsu M. Soft acrylic <strong>lens</strong>. In: Tobari I,<br />

ed. Textbook of Ophthalmic Surgery. Vol 2,<br />

Tokyo, Kanehara, 1995; 346-348.<br />

16. Neuhann TH. <strong>Intraocular</strong> folding of an<br />

acrylic <strong>lens</strong> for explantation through a<br />

small incision cataract wound. J Cataract<br />

Refract Surg 1996; 22: 1383-6.<br />

17. Hollick EJ, Spalton DJ, Ursell PG, Pande<br />

MV, Barman SA, Boyce JF, Tilling K. The<br />

effect of PMMA, silicone and polyacrylic<br />

intraocular <strong>lens</strong>es on posterior capsular<br />

opacification three years after cataract<br />

surgery. Ophthalmology 1999b;<br />

106: 49-54.<br />

18. Loughnan M. <strong>Intraocular</strong> <strong>lens</strong> materials<br />

and styles. Aust NZ J Ophthalmol<br />

1997; 25: 251.<br />

19. Javitt MD et al. Outcomes of cataract<br />

surgery with multifocal intraocular <strong>lens</strong><br />

<strong>implantation</strong>: Functional status and quality<br />

of life. Ophthalmology 1997; 104: 589-599.<br />

20. Nishi O, Nakai Y, Mizumoto Y, Yamada Y.<br />

Capsule opacification after refilling the<br />

capsule with an inflatable endocapsular<br />

balloon. J Cataract Refract Surg 1997a,<br />

23: 1548-1555.<br />

21. Nishi O, Nakai Y, Yamada Y, Mizumoto Y.<br />

Amplitudes of accommodation of primate<br />

<strong>lens</strong>es refilled with two types of inflatable<br />

endocapsular balloon. Arch Ophthalmol<br />

1993; 111: 1677-1684.<br />

22. Nishi O, Nishi K, Mano C, Ichihara M,<br />

Honda T. Lens refilling with injectable<br />

silicone in rabbit eyes. J Cataract Refract<br />

Surg 1998a, 24: 975-982.<br />

23. Nishi O, Nishi K, Mano C, Ichihara M,<br />

Honda T. Accommodation amplitude after<br />

<strong>lens</strong> refilling with injectable silicone by<br />

sealing the capsule with a plug in primate<br />

eyes. Arch Ophthalmol 1998b, 116: 1358-<br />

1361.<br />

32<br />

November 2, 2001 OT<br />


Sponsored by<br />

Module 3 Part 11<br />

Multiple choice questions<br />

<strong>Intraocular</strong> <strong>lens</strong> <strong>implantation</strong><br />

Please note there is only one correct answer<br />

1. All of the following statements concerning<br />

aphakic spectacle and contact <strong>lens</strong>es are<br />

correct except?<br />

a. Image magnification with aphakic<br />

spectacles is 50%<br />

b. Distortions with aphakic spectacles<br />

include ring scotoma<br />

c. Image magnification with aphakic contact<br />

<strong>lens</strong>es is 7-12%<br />

d. Spatial disorientation with aphakic<br />

spectacles can be a problem<br />

2. All of the following statements concerning<br />

the first IOL are correct except?<br />

a. It was manufactured from<br />

polymethylmethacrylate<br />

b. It was placed in the anterior chamber<br />

c. It had a high rate of complications<br />

d. Some patients can still be seen with these<br />

IOLs in situ today<br />

3. Which one of the following complications<br />

was not seen with early anterior chamber<br />

IOLs?<br />

a. Corneal oedema<br />

b. Uveitis<br />

c. Hyphaema<br />

d. Posterior capsular opacification<br />

4. The main difference between modern<br />

anterior chamber IOLs and early anterior<br />

chamber IOLs was?<br />

a. Material<br />

b. Loop flexibility<br />

c. Optic edge<br />

d. Insertion technique<br />

6. Which one of the following intraocular<br />

<strong>lens</strong>es does not have a square optic edge?<br />

a. AcrySof hydrophobic acrylic<br />

b. Centerflex hydrophilic acrylic<br />

c. CeeOn 911 second-generation silicone<br />

d. Hydroview hydrophilic acrylic<br />

7. Haptics can be made with all of the<br />

following materials except?<br />

a. Polypropylene<br />

b. PMMA<br />

c. Hypromellose<br />

d. Polyamide<br />

8. Binding of which one of the following<br />

materials to the IOL surface will make the<br />

IOL more hydrophilic?<br />

a. Heparin<br />

b. Silicone<br />

c. AcrySof<br />

d. Nitrate<br />

9. All of the following statements about IOL<br />

optics are correct except?<br />

a. The <strong>lens</strong> configuration of the <strong>lens</strong> optic<br />

may be convex plano, plano convex or<br />

biconvex<br />

b. Ridges in the IOL are associated with a<br />

high incidence of PCO<br />

c. The size of the optic varies from 4.5 to<br />

7mm in diameter<br />

d. A small optic may be better tolerated in<br />

patients with large pupils<br />

10. Advantages of foldable IOLs compared to<br />

rigid PMMA IOLs include all of the<br />

following except?<br />

a. Less astigmatism<br />

b. Cheaper<br />

c. Usually no need to suture incision<br />

d. Earlier stability of refraction<br />

11. Which one of the following IOL materials<br />

has been shown to suffer the most pits in<br />

its optic when a Nd:YAG laser posterior<br />

capsulotomy is performed?<br />

a. Silicone<br />

b. Acrylic<br />

c. PMMA<br />

d. Hydrogel<br />

12. All of the following statements regarding<br />

the refractive index of an IOL material are<br />

correct except?<br />

a. The higher the refractive index<br />

the thinner the optic can be<br />

b. Hydrophobic acrylics have a higher<br />

refractive index than either PMMA or<br />

silicone<br />

c. The refractive index depends on the<br />

dioptric power of the <strong>lens</strong><br />

d. IOLs with very high refractive<br />

indices can be inserted through<br />

smaller incisions<br />

5. Which one of the following features is the<br />

least important in the reduction of PCO?<br />

a. Capsular bag placement of the IOL<br />

b. Square optic edge<br />

c. IOL insertion technique<br />

d. IOL material<br />

An answer return form is included in this issue. It should be completed and<br />

returned to: CPD Initiatives (c2983i), OT, Victoria House, 178–180 Fleet Road,<br />

Fleet, Hampshire, GU51 4DA by November 28, 2001.<br />

www.optometry.co.uk<br />


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