The Akreos® IOLs
Clinically Proven to Provide
Quality of Vision
By Anders Behndig, MD, PhD, Roberto Bellucci, MD,
Joel Pynson, MD (B&L), & Lindsay Brooks, PhD (B&L)
Ten Years of Innovation
The first Akreos® intraocular lens (IOL) was implanted by Professor
Jean-Louis Arné on 29th June, 1998, in Toulouse, France. Since then,
the Akreos IOL design has progressively evolved, culminating in the
latest fifth generation model, the Akreos AO Micro Incision lens,
which can be implanted through a 1.8mm incision.
In what will be the 10th year since the first Akreos IOL became
available in Europe, this is a timely opportunity to review the
amassed clinical evidence demonstrating the performance of the
Akreos IOLs. The rationales behind the key design elements of the
Akreos range, and the properties and function of the Akreos
material delivering the lenses’ clinical performance are considered
in terms of:
1.
2.
3.
4.
Quality of vision
Stability
Biocompatibility
PCO prevention
US publication, April 2009
02
The evolution of the five generations of
Akreos IOLs
The five generations of Akreos IOLs have undergone progressive
modifications designed to improve the safety and efficacy of the
lenses. The haptic design has been modified, the anti PCO features
have been enhanced and the latter models, the Akreos Advanced
Optics (Akreos AO) and the Akreos AO Micro Incision lens (Akreos
MICS) lenses both have an aspheric, aberration-free optic. This optic
is designed to give all patients enhanced quality of vision. The five
models are summarized in Table 1.
Although varying in design, the full range of Akreos IOLs are
composed of the same biocompatible, hydrophilic acrylic Akreos
material featuring a one-piece biconvex IOL. This material has a
long term record in safety and has been used in over 2 million
implants. It is the unique properties of the Akreos material which
provide optical clarity, biocompatibility and make it suitable as a
MICS IOL. These subjects will be discussed in more detail throughout
this document.
The Akreos MICS IOL is the latest, innovative Akreos IOL. It can be
implanted through a 1.8mm incision using a wound-assisted
technique, while maintaining an excellent optical performance. The
availability of this microincision lens enables surgeons to transition
to microincision cataract surgery (MICS™) using either a biaxial MICS
(B-MICS) or coaxial MICS (C-MICS) technique, when used in
conjunction with the Bausch & Lomb Stellaris™ Vision Enhancement
System.
Akreos IOL designs
Akreos IOL
Launch data
IOL image
Optic
diameter
Total diameter and
diopter range
Optic
Haptic
design
Implantation
Anti PCO
Akreos MICS
2006
6.2mm (0–15D)
6.0mm (15–22D)
5.6mm (22.5–30D)
11.0mm: 0.0–15.0D
10.7mm: 15.2–22.0D
10.5mm: 22.5–30D
Asymmetric, biconvex,
Aspheric, aberration-free
optic (Advanced Optic)
4-point
fixation
1.8mm wound
assisted technique
Single use injection
system
360° anti PCO
barrier, square
edge design, 10°
angulation
Akreos AO
2005
6.0mm
11.0mm: 0.0–15D
10.7mm: 15.5–22.0D
10.5mm: 22.5–30D
Asymmetric, biconvex,
Aspheric, aberration-free
optic (Advanced Optic)
4-point
fixation
2.8mm
AI 28 single use
injection system
360° anti PCO
barrier, square
edge design
Akreos Adapt
2000
6.0mm
11mm: 10–15D
10.7mm: 15.5–22D
10.5mm: 22.5–30D
Biconvex spherical
4-point
fixation
3.2mm
PS 27 single use
injection system
Square edge
Akreos Fit
1999*
5.7mm
11.5mm
Biconvex spherical
C-shaped
Akreos Folder
device
Square edge
Akreos Disc
1998*
6.0mm
10.7mm
Biconvex spherical
2
fenestrated
plate
haptics
Forceps
Square edge
Table 1
*
No longer commercially available
03
1. Quality of Vision
The Akreos lens material, the lens design and the high precision
machining process which is better than any molding process,
contribute to the quality of vision provided by the Akreos lenses. An
overview of material properties and lens design is provided below.
Therefore, the optical performance of the subsequent Akreos lenses
has been improved by using an optic free from spherical aberrations,
called the Advanced Optic. This is produced by essentially flattening
the spherical lens at the periphery of both optic surfaces to create an
optic without spherical aberrations. Both the Akreos AO and the
Akreos MICS feature this aberration-free, aspheric optic in order to
provide patients with improved quality of vision.
A. The Akreos material
i) Designed for biocompatibility
The Akreos material was developed in 1996–1997. It is a copolymer of
PHEMA (polyhydroxyethylmethacrylate) and PMMA
(polymethylmethacrylate). These polymers have a long record of use in
ophthalmology, demonstrating excellent biocompatibility. PMMA has
been used in IOLs since the first IOLs were introduced, whilst HEMA is
used both extraocularly in contact lenses and intraocularly for scleral
implants and IOLs. This Akreos copolymer has a 26% water content
which makes it compressible and foldable (see Section 3).
ii) Designed for quality of vision
The Akreos lens material is an extremely homogeneous material with
transparency across the optic and it is vacuole-free. The Akreos material
has a refractive index of 1.458 (hydrated) which limits internal and
external light reflection and prevents many dysphotopsic effects,1,2
discussed in further details in section 1.6.
iii) Designed for MICS
The mechanical properties of the Akreos material make it suitable as a
MICS lens. It has a thinner lens design without compromising optical
quality as it is extremely deformable, tear-resistant and easy to fold,
independent of temperature, making it appropriate for use in sub 2mm
incisions. The hydrophilic component, HEMA, allows the lens to be
easily compressed to fit through the microincision and unfold smoothly
once implanted in the eye. The mechanical resistance of the
hydrophobic acrylic component (PMMA) ensures the lens recovers its
initial shape without damage. The lens material can be machined with
high precision milling and lathe-cut machines to give very precise
optical surfaces, making it suitable for modern cataract surgery
techniques such as MICS.
B. Akreos lens design
i) Advantages of aspheric, aberration-free optics
The Advanced Optic lenses have an asymmetric biconvex shape,
with aspheric anterior and posterior surfaces that create no spherical
aberrations. The lenses are neutral to the cornea, making them
suitable for all patients regardless of corneal shape. This leaves the
eye with its natural degree of corneal positive spherical aberration,
with an improved contrast sensitivity, but still providing patients with
a good depth of field.9 Because it is truly aspheric, the lens also has
a uniform refractive power from the center to the edge of the optic.
These lens characteristics mean the lens performance is unaffected
by optical misalignment or pupil decentration, giving more
predictable, repeatable refractive outcomes.
ii) Issues with aspheric-aberrated IOLs
Other aspheric lenses which try to make adjustments for the natural
irregularities can cause problems as every patient has a unique
optical system. Aspheric lenses using aberrated optics can potentially
cause visual impairment if ocular misalignment occurs, leading to
higher order aberrations (HOA) such as coma.10 These lenses have
also been designed from an average of corneal profiles, so then
cannot fit with patients whose corneas deviate from the average
cornea e.g., those that have undergone refractive surgery.
(a)
(b)
The first generations of Akreos lenses with a spherical optic design have
a proven record of safety and optical performance provided by the
Akreos material and design. However, like other conventional IOLs, their
spherical optic adds positive spherical aberrations to the ocular system.3,4
Standard spherical lenses create positive spherical aberrations as the
peripheral rays come to a shorter focus than the central rays. This
results in degradation in retinal image quality, causing a loss in contrast
sensitivity. Pseudophakic patients’ eyes with standard IOLs have more
spherical aberrations than phakic patients’ eyes of the same age.
In the younger population, a negative spherical aberration of the
crystalline lens compensates for positive spherical aberrations of the
cornea. However, with age, this compensation is gradually lost, leading
to an increase in positive spherical aberrations.5–8 Implanting a spherical
IOL adds to the already positive spherical aberrations of the ocular
system and can impair the visual outcome with a loss of contrast
sensitivity in low light conditions.
(c)
Figure 1: (a) Standard Spherical IOL, (b) Aspheric Aberrated IOL
and (c) Aspheric Aberration-Free IOL
04
Summary Box
– Creates no new spherical aberrations
– Leaves the eye with its natural corneal positive spherical
aberration
– Improves contrast sensitivity
– Provides patients with a good depth of field
– Suitable for all patients regardless of corneal shape
– Performance unaffected by optical misalignment
Percent of Patients
Advantages of an aspheric, aberration-free optic:
40
30
20
10
0
Tecnis
Akreos AO
Supporting clinical evidence
The clinical data demonstrating the optical performance of the
Akreos IOLs is summarized below, first considering the studies on
the Akreos AO lens with the aspheric, aberration-free optic design.
Figure 2: Subjective patient preference for eye following IOL
implantation11
Note: 58% of patients reported no difference.
A prospective, double-masked, randomized bilateral, multicenter
comparative study compared the visual and optical performance of
the Akreos AO lens with the Tecnis Z9000 (Advanced Medical Optics,
AMO).11 The Tecnis lens is a 3-piece silicone IOL with a negative
spherical aberration produced using a molding process. It is
designed to neutralize the positive spherical aberration of the
cornea. This 80 patient study was conducted at 4 Swedish sites,
each site implanting the lenses in 20 patients.
At 10 to 12 weeks, patients were asked to comment on their
perceived quality of vision by completing a questionnaire based
upon the Tester questionnaire with two additional questions:12 (1) In
which eye do you perceive the best visual quality?, and (2) In which
eye do you perceive most visual disturbance? The second question
was only posed to the patients reporting a visual disturbance.
Percent of Patients
1.1 Preferred by patients
40
30
20
10
0
Tecnis
Akreos AO
Figure 3: Patient perception of eye with more pronounced
visual disturbances following following IOL implantation11
Note: 56% of patients reported no difference.
1.2 Improved depth of field
The results showed an overall high level of patient satisfaction with
either lens. However, 28% or twice as many patients expressed a
spontaneous preference for the Akreos AO IOL, compared with 14%
preferring the Tecnis Z9000 (P<0.001). Three-times as many
patients perceived visual disturbances with the Tecnis lens versus
the Akreos AO lens, at 33% and 11% respectively (P<0.001).
The Swedish study also studied the patient depth of field provided
by the two lenses, calculated using the Strehl ratio.13 The study
findings showed the depth of field was larger in the eyes implanted
with the Akreos AO than those implanted with the Tecnis Z9000.
This difference increased as pupil size increased and was
statistically significant at pupil diameters of 5mm and 6mm.
In the discussion, the authors comment “The differences in eye
preference and visual disturbance between the 2 IOLs favored the
Akreos AO”. They continued, “considering the results of the
wavefront analysis, in which HOA, in particular spherical aberration,
was significantly lower in eyes with Tecnis Z9000 IOL, it would
appear that maximum reduction of spherical aberration does not
correlate with the perceived visual quality of the eye having
surgery.” The authors consider that factors such as larger depth of
field may contribute to a higher perceived visual quality, and other
factors such as differences in lens design and material may also
affect results.
05
1.3 Improved contrast sensitivity
Studies by Porta and Ferentini and Takhchidi et al both examined
the contrast sensitivity of the Akreos AO lens.14,15 Porta conducted a
30 patient prospective, comparative, intra patient study assessing
3 different aspheric IOLs in terms of quality of vision. Porta reported
there is a statistically significant difference in the performance of
the Akreos AO in mesopic conditions at 2 months, compared with
spherical IOLS at all different spatial frequencies (Figure 4). The
study also demonstrates the excellent contrast sensitivity provided
by the Akreos AO in both day and night conditions, comparable with
other aspheric lenses available.
7
6
5
4
The Akreos AO reduced spherical aberrations (–0.2±0.03μ) compared
with the conventional AcrySof group (–0.41±0.02μ). A statistically
significant difference between the two IOLs was found in the
spherical aberration coefficient (Z4.0) of the whole eye for a 5mm
pupil of 0.038±0.011μ in the Akreos AO lens and 0.09±0.0015μ in
the AcrySof lens.
Takhchidi et al concluded “The aspheric Akreos AO yielded better
low contrast visual acuity and contrast sensitivity than the
conventional IOL (Acrysof). The difference was statistically
significant and much bigger in higher spatial frequencies. The
results of this study clearly indicate the advantages of Akreos AO in
improving functional vision in pseudophakic patients.”
1.4 Distance vision of a middle-aged phakic eye
3
2
1
0
frequencies of 3, 6, 12 and 18 cpd (P<0.05), with the biggest
difference between the two groups occurring at 12 cpd, equalling
21% in mesopic and 27% in photopic conditions.
1.5
3
6
12
18
Cycles/degree
Akreos AO
Spherical IOLs
According to Pfeifer, the Akreos AO may help provide the distance
vision of a middle-aged phakic eye in high and low contrast.16
Pfeifer conducted a prospective clinical evaluation of the Akreos AO
implanted in 50 eyes. High and low contrast visual acuity results for
the Akreos AO at 1 year are close to the normal phakic population
aged 43 years (see Figures 6 and 7).17 At one year, 93.5% of
patients were ≥20/20 (LogMAR mean –0.11±0.16 = 20/16). Ninetytwo percent of patients had a BCVA ≥20/40 (LogMAR mean
–0.12±0.13 = 20/25).
Figure 4: Performance of the Akreos AO in mesopic conditions14
1
LogMar
7
6
5
-1
-2
4
3
2
1
0
0
Akreos AO
(mean age:
70 years)
Normal phakic
population
(mean age:
43 years)
Figure 6: High contrast visual acuity of Akreos AO at 1 year16
1.5
3
6
12
18
Cycles/degree
Akreos AO
Tecnis
AS60 Ligi
Figure 5: Contrast sensitivity results for aspheric14
Takhchidi’s clinical work found the Akreos AO provides higher
contrast sensitivity than the AcrySof SA60AT (Alcon) during day and
night. Twenty eyes of 20 patients receiving the aspheric Akreos AO
lens were compared with 27 eyes of 25 patients receiving the
conventional AcrySof lens. Significantly better low contrast visual
acuity with glare was reported in Akreos AO group (0.25±0.12)
compared to Acrysof group (0.15±0.09). Contrast sensitivity was
better in eyes implanted with the Akreos AO lens at spatial
Pfeifer concluded “The new aberration-free Adapt AO aspheric IOL
combines cataract surgery with refractive principles to produce
good visual acuity comparable with that of younger phakic patients.
Unlike other aberrated aspheric lenses, the lens is tolerant of slight
misalignment along the visual axis.”
06
Percent of Patients
2.0
LogMar
0.3
0.2
0.1
0
-0.1
Akreos AO
(mean age:
70 years)
Normal phakic
population
(mean age:
43 years)
40
30
20
10
0
1 week*
Akreos Adapt
8 weeks
AcrySof SN60AT
*Statistically significant difference
Figure 7: Low contrast visual acuity of Akreos AO at 1 year16
Figure 8: Dysphotopsic effects in the Akreos Adapt and AcrySof
SN60AT25
1.5 Reduced dysphotopsic effects
1.6 Importance of refractive index and glare
The Akreos material’s refractive index of 1.458 avoids the unwanted
dysphotopsic effects such as glare, halos, internal and external
reflections, and improves resolution. Hydrophobic acrylic intraocular
lenses with a higher refractive index pose a higher risk of these
unwanted visual phenomena, which have been reported in a
number of studies.1,2,12,18–24
Studies by Erie et al1,2 demonstrated that a lens material such as the
Akreos IOL with a refractive index of 1.458 and the equi-biconvex
design of the optic minimized disturbing light reflection when
compared with the Alcon AcrySof IOLs which have a refractive index
of 1.55 and an unequal biconvex design. By reducing the retinal
glare image, which is a secondary light reflection from the IOL’s
anterior surface back towards the retina, the Akreos material and
optic design minimizes this phenomenon. The Relative Glare
Intensity Ratio* of the Akreos IOL material is ~17 compared with
~900 with the AcrySof lenses. These studies show the importance
of the refractive index when evaluating glare.
Radford et al investigated the dysphotopic effects occurring with
the Akreos Adapt lens compared with the AcrySof SN60AT IOL.25
Sixty-one patients, 29 of which had received the Akreos Adapt IOL,
and 32 patients with the AcrySof IOL, answered a questionnaire that
graded symptoms of positive and negative dysphotopsia.
1.7 Reduced glare
At one week postoperatively, 30% of patients reported both positive
and negative dysphotopsia, where negative dysphotopsia is defined
as a dark shadow or an absence of light in a portion of vision,19 and
is cited as being a more likely cause of IOL explantation.26 Incidence
of dysphotopsia was 24.1% in the Akreos group, compared with
37.5% in the AcrySof group, a statistically significant difference.
Regarding negative dysphotopsia, no patients in the Akreos group
had the symptoms, but 8 patients in the AcrySof group exhibited
symptoms.
Reports of dysphotopsia at 8 weeks fell to 26%, with an overall
incidence of 31.3% in the AcrySof group and 20.7% in the Akreos
group (see Figure 8). Three patients with AcrySof lens described
symptoms of negative dysphotopsia, while the incidence reported
in the patients with the Akreos lens remained at zero. One week
postoperative data on patient difficulties in reading in dim or low
light conditions also found a statistically significant difference
between the two lenses, with 1 patient (3.4%) from the Akreos
group and 6 patients (19%) from the AcrySof group displaying
symptoms.
In the conclusion, the authors said “our data indicates that early
symptoms of negative dysphotopsia after cataract surgery are
dependant on IOL type and that the Akreos Adapt lens appears to
be superior to the SN60-AT in this regard.”
The Akreos lens was shown to reduce severe glare by two thirds
compared with the AcrySof acrylic hydrophobic lenses in a 111patient study conducted by Shambhu et al.27 This study compared the
incidence of level of dysphotopsia in the AcrySof MA30 and MA60 BM
lenses, and the Akreos Fit lens. The level of lens dysphotopsia was
assessed using a patient questionnaire and a glare provocation test.
Patients’ levels of dysphotopsia were recorded on a grading system
from 0 to 6, where 0=no dysphotopsia and 6=the most severe
symptoms. Overall, the average dysphotopsia score was 1.56 with the
Akreos lens, and 2.43 and 2.65 for the AcrySof MA30 and MA60 BM
lenses. With eyes implanted with the Akreos Fit lens (65 eyes), 75%
of patients had mild or no symptoms of dysphotopsia, compared with
48% of the patients (92 eyes) which were AcrySof lenses. Although
less common, severe cases of dysphotopsia were found in 4.6% of
the eyes with the Akreos implant, as opposed to 13% with the
AcrySof IOLs. There was significantly less dysphotopsia in the Akreos
group at the 5% level compared with both the AcrySof MA30 and
MA60 lenses (P=0.005, and P=0.002).
An assessment of contrast sensitivity and glare conducted by
Drummond et al provides further evidence that the Akreos material
produces less glare than other IOLs.28 In this prospective comparative
study, 84 patients gave a subjective response to a glare questionnaire
on 6 different IOLs. The Akreos Adapt had less subjective glare than
any of the other lenses implanted in this study (Alcon AcrySof MA60
and SA60, AMO Array SN 40, AMO Clariflex Optiedge, Allergan Sensar
AR40). Better contrast sensitivity was also recorded with the Akreos
Adapt lens in this study.
*
Relative Glare Intensity Ratio = (IOL material reflectivity in %)
/ (Area of the retinal glare image in mm2)
07
1.8 Importance of refractive index and spherical aberration
The refractive index also affects the level of spherical aberration.
With a refractive index of 1.458, the RI of the Akreos material is
very close to the RI of the natural lens equalling 1.41.
Dr Bellucci discusses how using different lens materials of differing
refractive index has a consequence on the curvature of the lenses at
a given power, both of which affect the induced spherical
aberrations, whereby “one may therefore expect IOLs with a high
refractive index to induce more spherical aberration.29 Studies by
Smith and Atchison demonstrate a relationship between refractive
index and spherical aberration, as well as curvature and
aberration.30,31 Higher levels of induced spherical aberration were
observed for lenses with higher refractive index.32–34
1.9 Reduction of unwanted images and light sensitivity
Rozot analyzed the incidence of light related issues occurring with
the Akreos Adapt and Akreos Disc by means of a patient
questionnaire.35 The incidence of light related issues was then
compared with data from a study by Tester et al, which evaluated
different types of IOLs.12 Overall, 91.6% of patents were very
satisfied to neutral with the implants. Of the 150 best cases, 9 (6%),
experienced unwanted images. This compares very favorably with
the average 20% of the 352 patients experiencing unwanted images
in the study conducted by Tester on six conventional IOLs. Rozot’s
study also demonstrated a significant decrease in general light
sensitivity issues compared with the conventional IOLs analyzed in
Tester’s study. Thirty-three percent of patients experienced light
sensitivity issues compared with only 8% in the Rozot study.
1.10 Improved resolution
All of the Akreos lenses are lathe cut, producing an improved
quality of optical performance at the high powers required for IOLs
compared with IOLs produced with a molding process. This lathing
process also produces precise aspheric surfaces. Laboratory testing
of Resolution Efficiency in aqueous of a 3mm pupil with a 20.0D
lens demonstrated the Akreos performs with a 70% resolution
efficiency versus 55% with the hydrophobic acrylic material.36
Unlike the blue-blocking lenses available on the market, the Akreos
IOL range preserves visible blue light, which is helpful for vision in
low light conditions, only blocking the harmful ultraviolet radiation
(<400nm) part of the spectrum. Akreos IOLs do not impact on color
perception. Mainster conducted an evaluation of photoprotection
versus photoreception in blue-blocking and uv-blocking IOLs.
Compared to the uv-blocking IOLs, the blue-blocking 20D IOL
provides 14% less scotopic sensitivity and the blue-blocking 30D IOL
provides 21% less scotopic sensitivity.40
2. Akreos Stability
The haptic design of the Akreos IOLs has evolved to continue to
improve the lens stability and hence improve lens performance in
terms of stable refractive outcomes, while reducing the PCO rates.
The lens and haptic design modifications also reflect necessary
adaptations to cater for the continuing surgical trend for implanting
the lens through reduced incision size.
The five generations of Akreos IOLs have moved from the disc
design, onto a C-shaped design, culminating in a 4-point haptic
design. Multipoint stability is considered to be the current
benchmark. The latter Akreos models, the Akreos Adapt, AO and
MICS all use the 4-point haptic design.
The 4-point haptic design has demonstrated the real advantage of
its stability. In vivo decentration rates are up to 5 times lower than
in C-shaped haptics (0.1 vs 0.5mm). A further advantage stems
from the injection, as the 4 points are symmetrical and therefore
leave a space between the loops, so the plunger can position itself
on the optic. As haptics are more fragile than the optic, it is safer
for the plunger to be pushing on the optic. The loop design haptic
allows for compressions within the capsular bag. The Akreos AO
design is a prime example of how haptic shape deals with
compressions, providing immediate centration and optimized
capsular contact (see Figure 9).
1.11 Preservation of natural color vision
Blue light has been shown to contribute to contrast sensitivity in
mesopic and photopic conditions.37,38 Providing 7% of the cone-related
photopic vision and 35% of the rod-related scotopic sensitivity, blue
light plays a greater role in quality of vision in dim lighting conditions.
There is also growing acceptance of the role blue light plays in overall
general health, sleep patterns and emotional wellbeing.39
Blue-blocking lenses, (yellow lenses) have been introduced into the
market with the aim to reduce the incidence of age-related macular
degeneration (AMD). However, the clinical effectiveness in preventing
AMD remains to be proven. Surgeons are now questioning the benefit
of using a blue-blocking lens, which provides less photoprotection
than a middle-aged crystalline lens, and has not been clinically shown
to prevent AMD, potentially impairing patient vision and quality life.38,40
Figure 9: Akreos AO in an artificial 9.5mm capsular bag
08
Modifications for MICS
Supporting clinical evidence
To allow the implantation through a sub 2mm incision, the Akreos
MI-60 lens is 25% thinner than its parent Akreos AO design.
However, this reduction in thickness has an inherent effect on the
lens stability, renewing the risk of decentration and requiring
additional compensation for lens stability with a redesign of the
4-point haptic shape and behavior.
Decentration results from Davies and Amzallag demonstrate the
4-point haptic design of the Akreos Adapt IOL and the modified haptic
design of the Akreos MICS lens both provide long-term centration
(Figure 12).41,42 Davies’ prospective 30-patient study on the Akreos
Adapt and Amzallag’s 20-patient pilot study on the Akreos MICS lens
both measured IOL centration with 1-year follow-up. The results
compare favorably with the mean decentration reported with C-loop
designs which varies from 0.3–0.5mm. The refraction was also shown
to remain stable in the studies, evidence that the IOLs do not vault.
i.e. there is no anterior or posterior movement from the lens position
(see Figure 13). There is no significant difference in the decentration
and refraction over time. Long-term visual acuity is also evident from
the one-year UCVA and BCVA data (Figure 14). Many other studies and
lens implantations measuring UCVA and BCVA confirm lens stability
over time.
Novel haptic design for 3-dimensional stability
Decentration (mm)
The haptic design is slender, but ensures excellent stability of the
implant. The external portions of the haptics, known as the
absorption zone, undergo deformation in 3-dimensions in order to
limit any pressure which may be exerted on the optic. The base of
the haptics is rigid and thicker, and together with the optic, forms
the foundation zone (see Figures 10 and 11). It is the unique
deformable and tear-resistant properties of the Akreos material
which enables this lens to be produced. These properties mean the
optical performance of this Akreos MICS IOL is not compromised.
2.0
0.15
0.1
0.05
0
3 weeks
3 months
Akreos Adapt
6 months 1 year
Akreos MICS
Figure 12: One year centration data on the Akreos Adapt and
Akreos MICS41,42
Note: No statistically significant difference over time.
Refraction
2
1
0
-1
-2
Figure 10: Akreos MICS lens design
3 weeks
3 months
Akreos Adapt
6 months 1 year
Akreos MICS
Figure 13: One year refraction of Akreos Adapt and Akreos MICS
lenses41,42
Note: No statistically significant difference over time.
2.0
1
0.5
0
3 weeks
3 months
UCVA
Figure 11: Conforming haptics of the Akreos MICS lens
6 months 1 year
BCVA
Figure 14: Visual acuity of Akreos Adapt41
Note: No statistically significant difference over time.
09
As discussed earlier, the combination of the polymers used in the
Akreos material, comprising a pure PMMA-HEMA copolymer, provide
its mechanical and biochemical properties. The 26% water content
makes the Akreos material soft and bulky, giving flexibility, while
the PMMA component provides its mechanical resistance.
The Akreos material means it provides excellent optical clarity and
is vacuole-free. The glistening effect is caused by small droplets of
water inside other acrylic materials. Glistenings or so-called
“vacuoles” have been observed in 57% of the AcrySof optics,
reports Miyata.43 Other studies reported in the literature find
glistenings occurring in up to 93% of AcrySof lenses.44
Not all hydrophilic acrylic materials are the same
There are many kinds of hydrophilic acrylics. They differ in terms of:
– Water content
– Chemical structure (monomers, linking agent, crosslinkers,
uv blockers)
– Polymerization process
This means different hydrophilic materials exhibit different behavior,
in terms of:
– Mechanical and biochemical properties
– Interaction with lens epithelial cells
– Calcification
Supporting clinical evidence
3.1 Biomaterial suitable for MICS
The suitability of the Akreos material for a MICS IOL was shown in
investigations by Kamae and Mamalis on cadaver eyes.45,46 IOP
measurements recorded during IOL injection showed the Akreos
MICS lens produced a lower peak and mean intraocular pressure
measurement than the AcrySof SN60AT lens. The Akreos MICS lens
produced a mean IOP of 88.4mmHg (six cases) as opposed to
147.25mmHg with the AcrySof SN60AT lens (eight cases) when
wound assisted insertions through incisions varying from 1.8–2.5mm
in cadaver eyes were performed.
Peak IOP measurements of 118.71mmHg with the Akreos MICS lens
versus 306.05mmHg were recorded. An average smaller final
incision size of 2.2mm was recorded for the Akreos MICS lens versus
2.5mm for the AcrySof SNAT60 lens. The authors concluded “the
new small incision Akreos MICS IOL performed well with relatively
lower peak and mean intraocular pressure measurements during
lens injection, smaller incision sizes, and a higher success rate of
insertion compared to the AcrySof lens.”
IOLs suitable for sub 2mm also need the optical and mechanical
properties of the IOL to be preserved following implantation,
without any deformation.47 Laboratory testing has demonstrated the
Akreos material needs lower forces to be folded.48
Bending forces (N)
3. A Suitable Biomaterial
6.0
4.8
3.6
2.4
1.2
0
0
0.8
1.6
2.4
3.2
4
Bending of the lens (mm)
Akreos
Acrylics average
o
AcrySof 20
AcrySof 18o
Figure 15: Foldability tests results for different lens materials48
3.2 Biocompatibility: Less bacterial adhesion and less
inflammatory cell response
With a 26% water content, the Akreos material’s high hydrophilicity
may make it less susceptible to biocontamination compared with
hydrophobic lenses. Owing to the bacterial adhesion data obtained
by Schauersberger et al, the authors discussed how “the higher the
hydrophilicity of the IOL material, the lower the early adhesion and
bacterial density on the IOL surface.”49 The in vitro study found that
after bacterial contamination, hydrophobic materials have bacterial
densities 2 to 3 times greater than hydrophilic acrylic materials.
Having now been safely used in over 2 million implants, the Akreos
material’s record of biocompatibility is exemplary. Lenses comprising
the Akreos material have been shown to induce a lower
inflammatory response. Ursell performed an in vivo prospective,
randomized study on 60 patients to measure the surface cytology of
three different single piece acrylic intraocular lenses: Akreos Fit,
AcrySof SA30, and the Clariflex (AMO).50 The presence of small cells,
giant cells and lens epithelial cells (LEC) was measured using
specular microscopy of the IOL surface.
The hydrophobic IOL had significantly more LECs during the
post-operative period. Significantly more giant cells in the late
post-operative period were also produced with the hydrophobic IOL,
in agreement with the result also reported by Abela-Formanek et
al.51 Lower inflammatory cell attachment was also demonstrated by
the Akreos IOL compared with the hydrophobic lens. The results are
summarized in Table 2.
The authors concluded “the Akreos Fit IOL was associated with the
least small cell response and the AcrySof IOL was associated with
the most LEC proliferation, suggesting that the hydrophilic IOLs may
have greater biocompatibility.”
10
4. PCO Prevention
Surface cytology of different single-piece acrylic IOLs50
Small cells
(number of cells)
Lens epithelial
cells (LEC)
(Present/Absent, %)
Giant cells
(Present/Absent, %)
Follow-up
2W 2M 6M* 1Y*
2W* 2M 6M 1Y
2W 2M 6M* 1Y
Akreos Fit
3
10
0
0
0
0
0
0
0
AcrySof SA30
5.6 4.8 3.8 1.2
10
21
5
0
5
0
37
25
Clariflex
5
85
5
4
0
0
0
0
0
2.2 0.5 0
4
1.2 0.3
Table 2
The causes of PCO are multifactorial: patient-related factors, surgeryrelated factors and IOL-related factors all have an influence on PCO
formation.
A number of design modifications have been incorporated into the
Akreos lens models in order to best combat PCO.
First, the Akreos Adapt and subsequent models feature the square
edge, designed to minimize PCO.54–59 Studies by Nishi et al found no
substantial difference in levels of PCO in lenses comprising different
materials, where all the lenses incorporate a square edge design.56–59
*Statistically significant difference
3.3 Use in high risk patients: diabetic & uveitis
Diabetic patients were implanted with the Akreos Adapt, in a study
examining the clinical outcomes of implanting a hydrophilic acrylic
lens in this patient group, comprising 12 cases with type 1 and 27
cases with type 2 diabetes. In their conclusion, Tadayoni et al
commented “The clinical results of the hydrophilic acrylic intraocular
lens seem similar to other types of lens. No cases of severe
complication requiring a lens exchange was noted.”52
Mingels et al performed a prospective, randomized study on 96
patients undergoing simultaneous cataract and vitreoretinal surgery.
Patients were implanted with either the Akreos Adapt (48 patients)
or the Akreos Fit (46 patients). The authors concluded “Although
differing in intraoperative handling, BCVA, PCO, IOL-centration was
better with Akreos Adapt than with Akreos Fit after combined
phacoemulsification and pars plana vitrectomy”.53
The Akreos has also been used in patients with uveitis. According to
Manuchehri et al, biomaterial type has an association with the
incidence of brown deposits in uveitis patients, observing a link in
the degree of deposit and material type.44 Their clinical investigation
monitored the cross-sectional prevalence and risk factors for brown
deposits to form in foldable IOLs implanted in 54 consecutive
patients (71 eyes) with uveitis. A definite association between the
hydrophobic acrylic AcrySof MA60BM lens and incidence of the
brown deposits was recorded. The authors calculated this IOL was,
on average, “38.5 times more likely to have intraocular deposits
than the other types of foldable IOLs used in this study.” The nature
and cause of the deposits remain unknown.
Figure 16: Akreos Adapt with square edge design
However this sharp edge barrier excludes the optic-haptic junction. The
lack of sharp edge at this junction might be a gateway for LECs’
migration to the optic. The continuous 360° posterior barrier on the
Akreos AO IOL is designed to avoid this possible weak point (Figure 17).
Figure 17: Continuous 360° posterior barrier on the Akreos AO IOL
11
This additional provision of PCO inhibition was developed following
cell culture evaluations using an artificial capsular bag.60 Cell
proliferation and migration were evaluated in this standardized
environment. On the Akreos AO design, Stachs concluded “A 360°
barrier in ridge design seems to be a very effective method to
prevent cell migration and proliferation towards the central optic
region.”
EPCO Scores at 1 year for Akreos IOLs
Akreos IOL
PCO
prevention
EPCO
score
YAG
rate (%)
Cases
Akreos
Adapt63,64
Square edge
1.02 (overall
PCO score)
0.24 (central
3.5mm optic
area
0.2
390
Akreos
Adapt65
Square edge
/
0
250
Akreos
Adapt41
Square edge
/
3.3
30
Akreos
Adapt66
Square edge
/
0.7
141
Akreos AO16 Square edge;
360° barrier
(ridge)
0.048 (6mm
optic area)
0
50
Akreos
MICS42
0.03 (6mm
optic area
0
20
Additional contact between the lens optic and the capsular bag is
provided by a 10° angulation of the haptics in the Akreos MICS lens
(Figure 18).
Square edge;
360° barrier
(ridge); 10°
angulation
of haptics
Table 3
Figure 18: Akreos MICS lens with 10° angulation of the haptics
Supporting clinical evidence
4.2 PCO and YAG rates comparable with the hydrophobic
acrylic IOLs
The clinical data available at 1 year on the Akreos range of IOLs
shows all the lens designs provide a clinically acceptable level of
prevention against PCO.
PCO and YAG rate data available on the hydrophobic acrylic IOLs
shows the Akreos models all compare favorably with hydrophobic
IOLs at both 1 and 2 years follow up (Figure 19 and Table 4).
4.1 One year data on the Akreos IOLs
First, considering just the Akreos models themselves, the one year
data on EPCO scores and YAG rates are consistently low. The design
modifications to enhance the inhibition of PCO have been shown to
be effective at lowering PCO rates (Table 3).
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
Akreos Akreos
Adapt 63 AO16
Akreos
MICS 42
AcrySof AcrySof
SA30AL67
68
Figure 19: EPCO score of Akreos IOLs and hydrophobic acrylic
IOLs at one year
12
Weinstein et al’s study on the AcrySof SA30AL (111 cases) resulted
in EPCO scores of 0.074 at 1 year.67 Further laboratory data available
on 123 cases demonstrates EPCO scores of 0.114 for a 6mm optic
area.68 The available literature on YAG rates at one year of the
acrylic hydrophobic lenses also finds the results are comparable
with the Akreos IOL models, ranging from 0.7% to 3.3%.69–72
The two year data provides further supporting evidence to show the
Akreos hydrophilic IOLs provides rates of PCO which are comparable
with the hydrophobic acrylic lenses.
YAG and PCO rates of Akreos and AcrySof lenses at 2 years
Lens
YAG rate (%)
Cases
Akreos Adapt73
Akreos Adapt74
Akreos Adapt75
AcrySof76
AcrySof70
AcrySof61
3.7
4.1
9.4
2.2
2.7
8.0
27
1377
128
45
8540
45
Table 4
Other surgical-related factors affect PCO formation.61,62 PCO
prevention can be improved by:
– Performing hydrodissection with enhanced cortical cleanup
– Giving attention to careful cleanup of the posterior face of
the anterior capsule when implanting hydrophilic lenses
– Ensuring the continuous curvilinear capsulorhexis (CCC)
overlaps with the IOL optic in the capsular bag.
Conclusion
Clinical studies conducted on the Akreos IOLs demonstrate their
safety and efficacy. The Akreos material is proven to be
biocompatible and reduces dysphotopsic effects. Incorporating an
aspheric, aberration-free optic has been shown to improve quality
of vision and give greater patient satisfaction. Now, the availability
of the MICS Akreos AO Micro Incision lens, the Akreos MICS IOL,
offers the opportunity to further enhance patient outcome through
performing aberration-free cataract surgery.
13
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Clinical studies conducted with the Akreos Lenses to assess the effect of the aspheric surface on spherical aberration,
visual acuity and contrast sensitivity are currently under review by FDA.
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