Intraocular lens implantation - Optometry Today

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Emma J. Hollick BA, FRCOphth, MD
Intraocular lens
implantation
In the 18th century, Casanova first suggested that an
artificial lens implant could be inserted into the eye to
replace the crystalline lens after cataract extraction 1 .
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Theoretically, replacement of the crystalline
lens with an artificial lens is the optimal form
of aphakic correction, as the majority of
aberrations and distortions from spectacles
derive from their placement anterior to the
pupillary plane. Indeed, image magnification
is a major disadvantage with aphakic
spectacles as they increase the image size by
20-35%, which leads to spatial disorientation.
Other distortions include ring scotomata,
peripheral distortion, the “jack-in-the-box”
phenomenon, and a reduction in useful
peripheral field.
Contact lenses bring the refractive
correction nearer to the nodal point of the
eye, with a corresponding decrease in these
distortions. Aphakic contact lenses increase
Figure 1
APMMA posterior chamber IOL seen
through a widely dilated pupil. The whitish
ring at the edge of the IOL optic is the
opacified anterior capsule with a continuous
curvilinear capsulorhexis
the image size by 7-12%. However, many
people cannot tolerate contact lenses –
elderly people often find it difficult to
manipulate lenses, and extended wear
contact lenses are associated with a higher
incidence of microbial keratitis. Intraocular
lenses are placed in a much more
physiological position with obvious optical
benefits.
The first intraocular
lens implant (1950)
Harold Ridley implanted the first intraocular
lens (IOL) in 1950 at St Thomas’ Hospital 2 .
This followed the observation that intraocular
fragments of Perspex seemed to cause little
long-term inflammation in the eyes of pilots
who had suffered penetrating eye injuries
from the shattered Perspex windows of
aeroplanes 3 .
The original Ridley lens was made of
Perspex (rigid Polymethylmethacrylate
(PMMA)) and implanted behind the iris after
extracapsular cataract surgery. The heavy lens
was placed between the iris and the
remaining posterior capsule. Thousands were
implanted, however, 15% needed to be
explanted due to the high rate of
complications, which included uveitis,
secondary glaucoma, hyphaema and
decentration or dislocation 4 . That said, some
patients still have these IOLs in situ today,
with relatively successful results 3 .
Table 1
Five generations of lens implants
Early anterior chamber IOLs
(1952-1962)
The second generation of lenses were rigid,
closed loop lenses, supported by the anterior
chamber angle. The long-term results of these
early anterior chamber lenses were universally
poor due to their instability in the anterior
chamber. This resulted in corneal endothelial
damage, reducing the endothelial cell count of
all patients with these implants, leading to a
large number of patients suffering corneal
decompensation and oedema. Progression to
pseudophakic bullous keratopathy was
frequent, with many patients requiring a
corneal graft. The presence of these lenses
increased the risk of graft failure, so many
were explanted. Anterior chamber IOLs were
also associated with iris complications such as
iris chafing leading to blood aqueous barrier
breakdown, iris erosion and pupil block. As a
result, it was necessary to perform a peripheral
iridectomy when implanting an anterior
chamber IOL to reduce the risk of pupil block.
These lenses were also associated with cystoid
macular oedema (CMO), uveitis, the UGH
syndrome (uveitis, glaucoma, hyphaema), and
subluxation or dislocation.
Iris-fixated IOLs (1953-1973)
As instability of IOLs in the anterior chamber
resulted in so many complications, greater
support of the lens was sought by transferring
the support from the anterior chamber angle
Type of IOL Date Characteristics
Figure 2
The IOL has dislocated upwards in the eye
Ridley posterior chamber IOL 1950 Heavy PMMA
Early anterior chamber IOLs 1952 to 1962 PMMA, rigid design, closed loop
Iris-supported IOLs 1953 to 1973 PMMA
Modern anterior chamber IOLs 1970 to present day PMMA, Flexible haptics, open loop
Modern posterior chamber IOLs 1975 to present day Standard PMMA designs
Foldable lenses – silicone
– hydrogel
– acrylic
Scleral-sutured IOL
Multifocal IOLs
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to the iris. The third generation of IOLs,
independently produced by Epstein and
Binkhorst, used the pupillary part of the iris
diaphragm for anatomical fixation. However,
this led to luxation of the lens if the pupil
dilated unexpectedly. These pupillary fixated
IOLs are now obsolete. A second development
was the use of a Medallion lens fixed to the
iris by a suture, however late degradation of
the suture led to dislocation of the lenses. The
next development was the Iris-claw lens with a
fixating mechanism based on the capture
of a fold of iris tissue at the two ends of the
IOL.
Modern anterior chamber
IOLs (1970 to present day)
For an anterior chamber lens to be safe and
effective there should be minimal contact with
the drainage angle, stability within the
anterior chamber with no movement in the
angle, no iris chafing and no endothelial
touch.
Modern anterior chamber IOLs were
designed to achieve this by using flexible open
loop lenses made of PMMA. They have the
advantage of not requiring an intact posterior
capsule for implantation and can be implanted
into eyes even after posterior capsule rupture
(occurring during complicated cataract surgery
or after intracapsular surgery). Modern
anterior chamber IOLs allow far better fixation
Table 2
Advantages and disadvantages of the IOL types
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than the early anterior chamber IOLs and
corneal complications are rare. However, they
are associated with a higher incidence of CMO
and retinal detachment than posterior
chamber IOLs.
Modern posterior chamber
IOLs (1975 to present day)
The first posterior chamber IOLs were made of
PMMA with either PMMA, polypropylene or
polyamide haptics. They require the presence
of a posterior capsule and can either be placed
in the sulcus or the capsular bag. Capsular bag
placement has been shown to be superior to
sulcus placement in terms of centration and
the rate of posterior capsular opacification
(PCO). The advantage of posterior chamber
IOLs is that they are placed in the position of
the original crystalline lens leading to a more
physiological situation with optical benefits.
An additional advantage is that posterior
chamber IOLs are situated away from the
delicate structures of the anterior chamber
including the cornea, the aqueous outflow
channels, the iris and the ciliary body. This
leads to a lower incidence of corneal problems,
UGH and pupil block. When the IOL is placed
within the capsular bag, contact with uveal
tissues is completely avoided. The intact
posterior capsule is associated with a
decreased incidence of CMO and retinal
detachment 5 .
Type of IOL Advantages Disadvantages
Ridley PC IOL optical uveitis
secondary glaucoma
hyphaema
decentration/dislocation
Early AC IOLs do not require posterior capsule - corneal complications:
(rigid, closed loop) capsule usually removed therefore (decompensation, oedema,
no PCO
pseudophakic bullous
keratopathy, IOL corneal touch)
CMO, uveitis, UGH
subluxation, dislocation
Iris-supported IOL do not require posterior capsule iris complications: (iris chafing and
erosion, pupil changes, pupillary block,
PAS - Peripheral Anterior Synechiae)
Modern AC IOLs do not require posterior capsule CMO retinal detachment
(flexible, open loop) better fixation corneal complications rare
Modern PC IOLs less corneal problems require intact zonules & posterior capsule
less CMO
less retinal detachment
less UGH
less pupil block
optical
Foldable IOLs small incision expensive
less astigmatism
decentration
quicker rehabilitation
rupture bag when unfolding
safer
spontaneous dislocation
IOL material
PMMA is the gold standard material for use in
IOL manufacturing. It was the first material
to be used, and has withstood the test of
time as the majority of IOLs implanted
worldwide today are still made of it. PMMA
benefits from inducing a minimal intraocular
inflammatory reaction, is not adversely
affected by ultraviolet light and is not
biodegradable in the eye. Because of this, it
maintains a smooth surface even when in
contact with vascular and metabolically
active tissue. PMMA is also relatively
inexpensive. However, one disadvantage is
that it is rigid and so requires a larger
incision for insertion than the newer foldable
materials. Surface modifications of PMMA
with heparin have been found to reduce the
inflammatory cell precipitates found on the
anterior IOL surface post-operatively,
therefore, this lens modification is useful in
patients expected to have more precipitation,
such as uveitics.
With the development of small incision
phacoemulsification surgery, a whole new
range of foldable lens implant materials have
been developed. Early foldable IOLs, however,
were not successful, because they elbowed
and folded as the capsular bag contracted.
The use of capsulorhexis dramatically reduces
this decentration of foldable materials.
The advantages of foldable IOLs are due
to the smaller incision size required for their
insertion. They are usually self-sealing and
do not require suturing. Smaller incisions
produce less astigmatism, allow quicker
visual rehabilitation with stable refraction
after a couple of weeks compared to six to
eight weeks for larger wounds, and are safer
with less iris prolapse and dehiscence. The
disadvantage of foldable IOLs is that they are
more expensive than PMMA and have a
higher incidence of decentration if a
continuous curvilinear capsulorhexis is not
used.
When a new IOL material is developed, its
biocompatibility needs to be studied. IOL
biocompatibility within the human eye has
three major aspects. These are the effect on
the blood aqueous barrier, the cellular
reaction on the anterior surface of the lens,
and the effect on the lens capsule. Blood
aqueous barrier changes can be assessed by
the amount of inflammation (flare and cells)
within the anterior chamber, which can be
quantified using the laser flare and cell
meter. Cells on the anterior surface of the
implant can be examined post-operatively
using specular microscopy and have been
used extensively as a method of assessing
the foreign body response to the IOL. The
effect of the IOL on the capsule consists of
lens epithelial cell proliferation and
metaplasia leading to anterior and posterior
capsular opacification, and IOL decentration.
PCO occurs in 20-50% of patients two years
after cataract surgery (Figure 3). It leads to a
progressive deterioration in visual acuity and
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Figure 3
This IOL shows a dramatic amount of
opacification of the posterior capsule.
The patient’s vision was significantly
reduced and they required a Nd: YAG laser
posterior capsulotomy
contrast sensitivity, and in many cases patients
do not seek medical attention, fearing that this
is an untreatable age-related change. PCO can
be relatively easily treated with Nd
(neodymium):YAG laser posterior capsulotomy,
where the Nd:YAG laser is used to make a hole
Table 3
Posterior chamber intraocular lens design features
Design feature
Number of pieces
Loop material
Loop shape
Optic design
Surface modification
IOL material
Variations
• One piece (disc or plate haptic)
• Three piece (disc)
Figure 4
A diamond shaped posterior capsulotomy
can be seen in the central posterior
capsule of this patient with significant PCO
in the posterior capsule to clear the visual axis
(Figure 4). This procedure, however, can be
associated with a number of complications such
as pitting of the IOL, intraocular pressure
spikes, inflammation, CMO and retinal
detachment. Many IOL manufacturers are
concentrating their research on ways to prevent
PCO, and there are now certain IOLs which are
associated with a lower incidence of PCO.
• Polypropylene (flexible, possible higher incidence of endophthalmitis)
• PMMA (rigid)
• Polyacrylic
• Angulation (forward angulation increases pressure on posterior capsule
and may decrease PCO, and increases distance of optic from iris.
Less angulation may facilitate insertion)
• J or C loops
• Convex plano, plano convex, biconvex (Biconvex associated with
the least image degradation with decentration and tilt and less PCO)
• Length of the IOL (14mm for sulcus fixation, 12-12.5mm
for in-the-bag fixation)
• Size of optic (4.5-7mm. Larger optics may be better for patients with large
pupils but need bigger incisions. Smaller optics for bag fixation)
• Holes (to facilitate dialling into capsular bag)
• Ridges (designed to facilitate laser capsulotomy, but associated
with more PCO)
• Sharp or round optic edge (less PCO when optic has a square edge than
round, due to barrier to lens epithelial cell migration, e.g. Alcon AcrySof IOL;
Pharmacia & Upjohn CeeOn 911; Rayner Centerflex IOLs)
• Binding of hydrogels or heparin to the IOL surface (to make IOL more
hydrophilic, found to reduce inflammatory cell precipitate)
• Surface passivation (to make IOL more hydrophobic and oleophilic,
aiming to repel lipids such as cell membranes and ocular tissues)
• PMMA
• Silicone
• Hydrogel/hydrophilic acrylic
• Hydrophobic acrylic
Silicone elastomers (elastic polymers) are
composed of highly cross-linked polysiloxane
chains. They are compressible and can
therefore be inserted through a small incision
by folding. Silicone lenses are homogeneous,
heat-resistant, autoclavable, moldable and
compressible and highly transparent to visible
light. The specific gravity of the material is
low and therefore the lens is nearly weightless
in aqueous. Silicone has excellent tensile and
tear strength, and is extraordinarily flexible.
Silicone IOLs can be either three pieces, with
open loop prolene, polyamide or PMMA
haptics, or plate haptic.
Silicone has a lower refractive index
(1.41-1.46) than PMMA (1.49) and
consequently the lens is thicker, which may be
an impediment to very high powers. Although
the silicone lens is transparent to Nd:YAG
laser radiation, the lens can be pitted when
hit by the laser beam 6 . In fact, silicone IOLs
have been shown to have the lowest threshold
for laser-induced damage compared to PMMA
and acrylic IOLs, and to suffer the greatest
damage depth at each energy level tested 7 .
Furthermore, the surface of a silicone IOL is
hydrophobic and it has been shown that a
higher percentage of cellular reactions occur
on hydrophobic surfaces than hydrophilic
ones 8 .
A further disadvantage is that they
become slippery when wet and, as a result,
become difficult to handle. An additional
clinical complication occurs if silicone oil is
used to help re-attach the retina following a
retinal detachment in a pseudophakic patient,
as the oil adheres to silicone IOLs. In
addition, silicone IOLs with flexible haptics or
plate haptic design have a higher incidence of
decentration than other IOL types. Plate
haptic silicone IOLs are also at increased risk
of anterior capsule opening contraction 9 .
Incidences of capsular bag rupture have also
been reported during IOL unfolding, and
spontaneous dislocation of IOLs into the
vitreous after YAG capsulotomy, particularly
with the plate haptic design.
More recent silicone IOLs are made of
second-generation silicone and appear to be
associated with less inflammatory cell
precipitate than the earlier first-generation
lenses. A recent silicone IOL design,
CeeOn 911 (Pharmacia & Upjohn) has been
manufactured with a square optic edge, which
has been shown to be associated with a low
incidence of PCO compared to many other IOL
types.
Hydrophilic acrylics include a broad class
of polymer materials which swell extensively
in water but are not water-soluble (previously
referred to as hydrogels). These materials
have variable size and physical properties
according to the state of hydration. An
example is polyhydroxyethylmethacrylate
(PHEMA), which has a 38% water content.
High-water content hydrogels are
cross-linked polymers based on a hydrophilic
monomer. They are soft and resemble living
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tissues in their physical properties and the
smooth, hydrophilic nature minimises
mechanical friction with ocular tissues and
contributes to superior biocompatibility 10 . This
is reported to produce less damage to the
corneal endothelium after inadvertent touch
on implantation than PMMA 11 . The hydrophilic
nature of the lens surface causes low
interfacial tension (wettability) of the
hydrogel in aqueous solution and reduces the
tendency of proteins to denature on the
surface of the polymer, thus reducing
biological rejection mechanisms. This possibly
also prevents adhesion between the lens and
the capsular bag. As the dimension of the
hydrogel changes in direct proportion to the
degree of water saturation, it enables
implantation of a semi-hydrated lens through
a small incision, for it to later expand in the
eye as it becomes fully hydrated.
Hydrophilic acrylics have the advantage of
undergoing less damage during YAG laser
capsulotomy. When there is direct impact of
the YAG laser beam on the lens, mild to
moderate localised pitting occurs, without the
radial fracturing seen on a PMMA implant. This
is due to the resilience of the material and its
ability to act as a shock absorber rather than
cracking under stress.
Although high water-content polymers are
usually mechanically weak, the hydrogels can
be very strong owing to certain changes of the
polymer produced during the process of
polymerisation. Examples of hydrophilic
acrylic IOLs are the Hydroview lens, EasAcryl,
Inject-A, Centerflex and the Memory Lens.
Studies on the Hydroview IOL (Bausch & Lomb)
have shown that it is associated with fewer
surface inflammatory cells than PMMA and a
second-generation silicone IOL. However, a
significant lens epithelial cell (LECs) reaction
on the anterior IOL surface was reported in
addition to a higher incidence of PCO 12,13 .
AcrySof (Alcon) is an example of a
hydrophobic acrylic IOL, which has become the
most commonly inserted IOL in the USA. The
AcrySof polymer was developed from the same
backbone used in PMMA. It has a higher
refractive index (1.55) than PMMA or silicone.
This means that lens implants made from
AcrySof are thinner, thereby facilitating
folding and insertion through a smaller
incision 14 .
Acrylic polymers change their mechanical
properties with temperature, being hard and
glassy at low temperature, and soft and fluid
at high temperature. This means that an IOL
inserted at room temperature unfolds slowly
and in a controlled manner 14 . This avoids the
rapid, explosive opening which can be seen
with three-piece silicone IOLs which may cause
iatrogenic damage to the capsule or other
anterior segment structures. The AcrySof IOL
is, however, found by many surgeons to be
more difficult to fold than silicone lenses, as
the lens is more rigid if cool.
In addition, due to its tacky nature, the
AcrySof IOL has a tendency to stick to forceps
or between two parts of the IOL on insertion 15 .
This characteristic may mean that the IOL
sticks to the capsular bag (which is discussed
later and may have advantages), however, the
adhesion means that the IOLs are more
difficult to explant in cases of anisometropia
or incorrect power calculation 16 . The IOLs are
not slippery when wet in contrast to silicone
IOLs.
The AcrySof IOL has been found to be
associated with dramatically reduced rates of
PCO 17 . This is thought to be due to both
mechanical and material features. This was the
first lens implant to be manufactured with a
square optic edge, and it is thought that this
edge acts as a barrier to the migration of LECs
onto the posterior capsule, reducing PCO. The
tacky nature of the implant leads to increased
adhesion of the IOL to the capsule which also
probably limits the migration of LECs onto the
posterior capsule.
An IOL may have excellent cytological
biocompatibility (a limited/nil inflammatory
reaction), but poor capsular biocompatibility
(the effect on anterior capsule and PCO), for
example, the Hydroview IOL. Therefore, the
goal is to find an IOL which has both
cytological and capsular biocompatibility.
Design features, such as a sharp optic edge,
and material composition appear to be equally
important. To date, the second-generation
silicone IOLs and AcrySof IOLs appear to have
the best biocompatibility.
Table 4
Advantages and disadvantages of the IOL types
IOL Type Advantages Disadvantages
PMMA Long term experience Rigid so need large incision
Good biocompatibility
Pits with YAG laser
Cheap
High incidence of PCO
The prevalence of lens materials in the
1997 survey of the American Society of
Cataract and Refractive Surgery was 38%
acrylic, 20% silicone, and 40% PMMA (Kohnen,
1998). The implantation of foldable IOLs in
Australia rose from 1% in 1991 to 67% in
1997 18 .
Multifocal IOLs
Standard IOLs are monofocal and so the loss of
accommodation which increases with age
becomes absolute with surgery, and the need
to correct the resultant presbyopia is apparent.
Multifocal and bifocal IOLs have been designed
in an attempt to provide both distance and
near vision without additional spectacle
correction, as they form separate images of
near and distance objects. The goal of
multifocal implants has been to enable
patients to be less dependent on spectacles
following surgery. Multifocal IOLs are based on
the simultaneous vision principle – if the
power difference between two optical systems
is 3.00DS or more, then the images are
dissimilar enough for the brain to interpret
them as separate.
An example is the ARRAY multifocal IOL by
Allergan which has concentric rings of varying
optical power around a central power for
distance. The rings of power are for near
distances, while the central distance power is
dominant. Fifty per cent of the lens is
dedicated to distance vision, 36% to near
Silicone Foldable - small incision Low refractive index - thicker IOLs (first generation silicone)
Fairly low incidence of PCO High refractive index - thinner IOLs (second generation silicone)
(particularly second
Pits with YAG laser
generation silicone)
Rapid unfolding in the eye
Dislocation after YAG
More decentration
More anterior capsule contraction
Slippery when wet
Cannot use with silicone oil
AcrySoft Foldable - small incision Short experience
High refractive index - thin IOLs Tacky surface - sticks to forceps
Very low incidence of PCO More difficult to fold
LEC regression
?Glistenings
Biocompatible
?Glare
Fewer pits with YAG laser
Slow uncontrolled folding
Hydroview Foldable - small incision LECs on anterior IOL surface
Good biocompatibility
High incidence of PCO
- low inflammatory cell reaction
Fewer pits with YAG laser
Controlled unfolding
Less endothelial cell damage
with cornea touch
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vision and 14% to intermediate distances.
One study compared 100 patients implanted
with the ARRAY lens in both eyes after
bilateral cataract surgery with 100 patients
with a standard monofocal IOL implanted
bilaterally 19 . It was reported that 41% of
patients with the ARRAY lens did not wear
spectacles compared to 12% of patients with
monofocal IOLs. For near tasks, 38% of
multifocal patients did not wear spectacles
compared to 10% of monofocal patients. In
addition, 85% of those with multifocal IOLs
did not wear spectacles for distance compared
to 52% with monofocal IOLs.
The downside was that patients with
multifocal lenses were more bothered with
glare and haloes from oncoming headlights at
night and found night driving more difficult
than the patients with monofocal IOLs. This
“halo-effect” can also occur with other
bright/dark contrast situations.
An additional disadvantage of multifocal
lenses is that they reduce contrast sensitivity.
This results in loss of sharpness of vision
particularly under poor visibility conditions
such as low light or fog. Therefore, patients
who spend their lives in a twilight
environment and night-time work conditions
may be disturbed by this loss of contrast
sensitivity. Patient selection is a crucial step
when considering whether a multifocal or
monofocal lens should be implanted. Suitable
candidates are those whose myopic
astigmatism does not exceed 1.00D, spend
most of their lives in normally lit
environments and have no other ocular
diseases. Bilateral implantation results in the
most satisfying outcome, and leaving the
patient emmetropic or slightly hypermetropic
minimises glare and visual disturbances.
Accommodative IOLs
Certain research groups are studying ways of
refilling the capsular bag with flexible IOLs
capable of accommodation. One study
removed lenses from a group of rabbits and
primates, and refilled the capsular bag with
an inflatable endocapsular balloon 20 .
Accommodation could be demonstrated
following this technique in primates 21 ,
however, the incidence of PCO was reported to
be very high (94%). The post-operative
amplitude of accommodation was small and
decreased with time, which was likely to be
due to the increase in PCO with capsular
fibrosis leading to a loss of capsular pliability.
The use of a soft injectable liquid to fill
the bag has been attempted in rabbit eyes 22
and primates 23 : after making a minicapsulorhexis,
phacoemulsification was
performed with a tiny tip. Silicone material
was then injected into the capsular bag, and
the bag then closed with a silicone plug.
Some accommodation appeared to be present
postoperatively. However, all eyes suffered
thick PCO soon after surgery. YAG laser
capsulotomy would obviously not be
appropriate as this could annul the attained
accommodation. However, research has
continued in this field and two prototypes will
be marketed for use in humans next year
(see previous CPD article, Outcome in Cataract
Surgery, 05/10/01).
Conclusion
IOL design has developed through the years
and has now become extremely successful
with very few complications. The
complications of corneal decompensation,
glaucoma, hyphaema and uveitis have largely
been resolved with the use of posterior
chamber IOLs placed within the capsular bag.
Similarly, lens decentration and dislocation is
much rarer with the in-the-bag positioning of
the lens implant with capsulorhexis. However,
one complication remains, despite
improvements in surgical technique – PCO.
Nevertheless, developments in intraocular
lens design are having a dramatic effect on
reducing the incidence of PCO.
About the author
Emma Hollick works at Moorfields Eye
Hospital. She recently carried out research at
St Thomas’ Hospital looking at intraocular
lens implant biocompatiblity and posterior
capsular opacification.
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16. Neuhann TH. Intraocular folding of an
acrylic lens for explantation through a
small incision cataract wound. J Cataract
Refract Surg 1996; 22: 1383-6.
17. Hollick EJ, Spalton DJ, Ursell PG, Pande
MV, Barman SA, Boyce JF, Tilling K. The
effect of PMMA, silicone and polyacrylic
intraocular lenses on posterior capsular
opacification three years after cataract
surgery. Ophthalmology 1999b;
106: 49-54.
18. Loughnan M. Intraocular lens materials
and styles. Aust NZ J Ophthalmol
1997; 25: 251.
19. Javitt MD et al. Outcomes of cataract
surgery with multifocal intraocular lens
implantation: Functional status and quality
of life. Ophthalmology 1997; 104: 589-599.
20. Nishi O, Nakai Y, Mizumoto Y, Yamada Y.
Capsule opacification after refilling the
capsule with an inflatable endocapsular
balloon. J Cataract Refract Surg 1997a,
23: 1548-1555.
21. Nishi O, Nakai Y, Yamada Y, Mizumoto Y.
Amplitudes of accommodation of primate
lenses refilled with two types of inflatable
endocapsular balloon. Arch Ophthalmol
1993; 111: 1677-1684.
22. Nishi O, Nishi K, Mano C, Ichihara M,
Honda T. Lens refilling with injectable
silicone in rabbit eyes. J Cataract Refract
Surg 1998a, 24: 975-982.
23. Nishi O, Nishi K, Mano C, Ichihara M,
Honda T. Accommodation amplitude after
lens refilling with injectable silicone by
sealing the capsule with a plug in primate
eyes. Arch Ophthalmol 1998b, 116: 1358-
1361.
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November 2, 2001 OT
www.optometry.co.uk

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Module 3 Part 11
Multiple choice questions
Intraocular lens implantation
Please note there is only one correct answer
1. All of the following statements concerning
aphakic spectacle and contact lenses are
correct except?
a. Image magnification with aphakic
spectacles is 50%
b. Distortions with aphakic spectacles
include ring scotoma
c. Image magnification with aphakic contact
lenses is 7-12%
d. Spatial disorientation with aphakic
spectacles can be a problem
2. All of the following statements concerning
the first IOL are correct except?
a. It was manufactured from
polymethylmethacrylate
b. It was placed in the anterior chamber
c. It had a high rate of complications
d. Some patients can still be seen with these
IOLs in situ today
3. Which one of the following complications
was not seen with early anterior chamber
IOLs?
a. Corneal oedema
b. Uveitis
c. Hyphaema
d. Posterior capsular opacification
4. The main difference between modern
anterior chamber IOLs and early anterior
chamber IOLs was?
a. Material
b. Loop flexibility
c. Optic edge
d. Insertion technique
6. Which one of the following intraocular
lenses does not have a square optic edge?
a. AcrySof hydrophobic acrylic
b. Centerflex hydrophilic acrylic
c. CeeOn 911 second-generation silicone
d. Hydroview hydrophilic acrylic
7. Haptics can be made with all of the
following materials except?
a. Polypropylene
b. PMMA
c. Hypromellose
d. Polyamide
8. Binding of which one of the following
materials to the IOL surface will make the
IOL more hydrophilic?
a. Heparin
b. Silicone
c. AcrySof
d. Nitrate
9. All of the following statements about IOL
optics are correct except?
a. The lens configuration of the lens optic
may be convex plano, plano convex or
biconvex
b. Ridges in the IOL are associated with a
high incidence of PCO
c. The size of the optic varies from 4.5 to
7mm in diameter
d. A small optic may be better tolerated in
patients with large pupils
10. Advantages of foldable IOLs compared to
rigid PMMA IOLs include all of the
following except?
a. Less astigmatism
b. Cheaper
c. Usually no need to suture incision
d. Earlier stability of refraction
11. Which one of the following IOL materials
has been shown to suffer the most pits in
its optic when a Nd:YAG laser posterior
capsulotomy is performed?
a. Silicone
b. Acrylic
c. PMMA
d. Hydrogel
12. All of the following statements regarding
the refractive index of an IOL material are
correct except?
a. The higher the refractive index
the thinner the optic can be
b. Hydrophobic acrylics have a higher
refractive index than either PMMA or
silicone
c. The refractive index depends on the
dioptric power of the lens
d. IOLs with very high refractive
indices can be inserted through
smaller incisions
5. Which one of the following features is the
least important in the reduction of PCO?
a. Capsular bag placement of the IOL
b. Square optic edge
c. IOL insertion technique
d. IOL material
An answer return form is included in this issue. It should be completed and
returned to: CPD Initiatives (c2983i), OT, Victoria House, 178–180 Fleet Road,
Fleet, Hampshire, GU51 4DA by November 28, 2001.
www.optometry.co.uk
33