Transcript Contact Lens Monthly - ОНЛАЙН магазин за контактни лещи

Contact Lens Monthly
Anewsiliconehydrogel
dailydisposablelens
16 | Optician |06.11.09
16-19CLMClariti 16
TAble 1 Parameters for Clariti 1 Day
Filcon II 3 (FDA group II)
56%
Advanced edge technology
(AET)
8.6mm
14.1mm
+8.00 to -10.00 (0.25 &
0.50DS steps)
0.5MPa
0.07mm
86
Material
Water content
Manufacturing
method
Base curve
Diameter
Power range
Modulus
Centre thickness
Dk/t (at -3.00)
until recent times, this type of contact
lens material has not been available in
a daily disposable product. Exceptional
oxygen transmissibility, coupled with the
improved hygiene expected with a single
use product offers distinct advantages
over most existing daily disposable
contact lens products available.
Major factors in achieving a daily
disposable silicone hydrogel lens
included the need for a dramatic
improvement in yield and of course
the development of a high volume
process. The base chemistry used for
the Clariti lens provided an excellent
starting point. For the daily product
Sauflon opted for the development of
a more rapid curing process, a more
efficient extraction and hydration
process, with the resultant high yield
which is an absolute requirement for
daily disposable manufacture.
Utilising the base chemistry of the
Clariti lens allowed Sauflon to optimise
lens properties that have the greatest
influence on comfort such as water
content, stiffness and wettability. The
changes made to the silicone monomer
and the cure cycle yielded a lens with
slightly lower water content than the
Clariti monthly lens.
Oxygen performance
For over 30 years the best known
methods for measuring oxygen
performance of contact lenses have
been:
● Oxygen permeability (Dk) of the lens
materials
●Oxygen transmissibility (Dk/t) of
the finished, manufactured lens which
takes lens thickness into consideration.
However, the important factor to
consider is how much oxygen the
cornea requires to maintain normal
100
Percentage corneal oxygen consumption
T
he first generation silicone
for daily wear. Although these lenses
provided high
levels oflenses
oxygen,
the
hydrogel
were
materials tended
to befor
stiffer,
not as
designed
monthly
wettable and
attracted wear
moreand
deposits
continuous
when
than conventional
hydrogel
lenses.
this modality did not take
Since theiroff
introduction
a decade
ago
they were then
adapted
silicone hydrogel lenses have evolved,
with the latest generation of materials
providing more comfortable contact
lens wear. Additionally, improvements
in materials and manufacturing
techniques have resulted in the launch
of daily disposable modalities of these
healthier materials.
From the beginning of Sauflon’s
research and development programme
into silicone hydrogel materials over
five years ago the objective had been
to produce a silicone hydrogel lens that
provided maximum ocular health using
a material that is less stiff, less prone
to deposits and with a more wettable
surface. This approach would clearly
improve wearer comfort by allowing
Sauflon toincludelower levelsof silicone
monomers in the Clariti formulation.
The level of silicone was optimised to
provide a lens with excellent oxygen
performance but keeping it low enough
so that it did not negatively impact
modulus, wettability, water content and
therefore comfort of the lens.
In September 2008 after five years
of research and development, Sauflon
launched Clariti, a monthly disposable,
daily wear silicone hydrogel lens with
a high water content and low modulus
which is sold exclusively to eye care
professionals.
Clariti 1 Day
Having developed the monthly silicone
hydrogel lens Clariti, the next step for
Sauflon was to develop a daily disposable
silicone hydrogel lens. It is considered
that silicone hydrogel contact lenses
are likely to dominate the contact lens
market in the years ahead. In some
markets, they already account for up to
70 per cent of new spherical (non-daily
disposable) contact lens fits1 however,
As Sauflon launches the Clariti 1 Day silicone hydrogel daily
disposable lens, Howard Griffiths reviews the development and
performance of this new product
90
80
70
60
50
40
30
20
Open eye
Closed eye
10
0
0
50
100
150
200
250
300
Dk/t x 10 2 (cm/sec) (mlg/ml.mmHg)
Figure 1 Corneal oxygen consumption vs lens oxygen transmissibility
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Contact Lens Monthly
1.5
Change in limbal redness
Figure 2
Change in
limbal
redness
during daily
wear of
various
contact lens
brands
1.0
0.5
0
-0.5
Acuvue 2
Acuvue Advance
Night & Day
No lens
Dk/t (Oxygen)
90
80
70
60
Dk/t
corneal physiology. Holden and Mertz
(1984)2 presented the best known value,
suggesting that a lens with a Dk/t of
24.1 would not induce corneal swelling
duringdailywear. Harvitt and Bonanno
(1999)3 subsequently proposed a value
of 35 units to avoid hypoxia through
the cornea.
Clearly for overnight wear more
oxygen is required and Holden and
Mertz found that a lens with Dk/t
of 87 would limit overnight corneal
swelling to 4 per cent, avalue considered
equivalent to a non-lens wearer. They
also suggested a compromise threshold
of 34 units which might induce some
additional swelling after overnight
wear but would allow the cornea to
return to normal thickness soon after
waking.
The guru of contact lens oxygen
measurement Irving Fatt4 considered
that the Dk/t measure failed to inform
how much oxygen actually gets to the
cornea. Consequently over the years
alternative methods of describing
corneal oxygenation have evolved
including oxygen flux (oxygen volume
reaching cornea during lens wear)
and corneal oxygen consumption. Fatt
himself advocated using flux as a better
measure of corneal oxygenation. More
recently, however, corneal oxygen
consumption has been considered as a
more important factor by researchers
such as Professor Noel Brennan.5 It is
considered to be abetter index of corneal
physiology because it reflects how much
oxygen the cornea metabolises.
It can be seen in Figure 1 below that
there is amarked flattening off of corneal
oxygen consumption as Dk/t increases.
In other words we have a situation of
diminishingreturnsbetweenincreasing
Dk/t and the amount of oxygen used
by the cornea. In turn this suggests that
the difference in percentage oxygen
consumption between an eye wearing
a lens with Dk/t of 56 and another
wearing a lens with a Dk/t of 300 is
surprisingly modest.
This relationship does explain why
Dk/t was appropriate in the era of low
Dk lenses. If we only consider values of
Dk/t up to 30 units then the near-linear
relationship between oxygenation
and Dk/t would mean that doubling
transmissibility would account for
approximately twice as much oxygen
consumed by the cornea. No such
relationship exists for lenses of higher
oxygen transmissibility.
Although mathematical diffusion
models such as those discussed above
provide a helpful indicator of the
theoreticalsituationatthecorneaduring
contact lens wear, it is also important
50
40
30
20
10
0
Proclear
1 Day
I Day
Acuvue
Moist
Dailies
Focus Dailies
Aqua
All Day
Comfort Plus
Comfort
SofLens
Daily
Disposable
Clariti 1 Day
Figure 3 Dk/t values for a range of daily disposable lenses
to relate this to clinical observations. A
good way to achieve this is to consider
the presence or absence of hypoxia
related clinical signs across a range
of lenses, one example here is limbal
hyperemia which is known to be an
indicator of corneal hypoxia.
In 2004 researchers at Eurolens
Research at the University of
Manchester6 performed a masked,
controlled study of neophyte subjects
in which they evaluated changes in
limbal redness during daily wear of
contact lenses. They found that limbal
redness increased during daily wear of
Acuvue 2 lenses by about half a clinical
grade compared to baseline whereas
there was no change in limbal redness
observed in patients wearing Acuvue
Advance or Focus Night & Day lenses
(Figure 2).
It is important tonotethat thefour-fold
difference in peripheral Dk/t between
the two silicone hydrogel lenses in this
study did not result in a difference in
limbal redness. This is presumably
because both lenses fall on the flat part
of the blue curve in Figure 1.
The Clariti 1 Day lens has a Dk of 60
and a Dk/t of 86 (Figure 3). Therefore
taking into account that Holden and
Mertz (1984) suggested a Dk/t value of
24.1 and the other estimates of oxygen
transmissibility to maintain normal
corneal physiology during daily (open
eye) wear, it is evident that the Clariti 1
Day lens comfortably provides enough
oxygen for optimum corneal health.
Comfort
One of the most important attributes
that patients demand from their contact
lenses today is comfort. By making their
objective a lens for daily wear Sauflon
was able to keep silicone levels in its
formulation lower. This in turn allowed
for the optimisation of lens properties
that have the greatest influence on
comfort such as surface wettability,
water content and stiffness.
Surface wettability – Inclusion of
silicone in a lens formulation makes
the surface extremely hydrophobic.
The first generation silicone hydrogel
lenses therefore required some form
of surface modification to overcome
the hydrophobicity. Bausch & Lomb’s
PureVision lenses rely on plasma
oxidation to render the surface more
hydrophilic. CIBA Vision’s Air Optix
Night & Day Aqua and Air Optix Aqua
also utilise plasma treatment to yield
a continuous hydrophilic surface for
their lenses.
J&J was the first company to move
away from surface treatment with its
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Contact Lens Monthly
TAble 2 Lens parameters for a clinical assessment of Clariti 1 Day
Lens 1
Clariti 1 day
Name
Manufacturer
Sauflon
Pharmaceuticals
Material
EWC (%)
BOZR (mm)
Diameter (mm)
Filcon II 3
56
8.6
14.1
Lens 2
1-Day Acuvue
TruEye
Johnson &
Johnson Vision
Care
Narafilcon A
46
8.5
14.2
Lens 3
Proclear
1-Day
CooperVision
Lens 4
Focus Dailies All Day
Comfort
CIBA Vision
Omafilcon A
60
8.7
14.2
Nelfilcon A
69
8.6
13.8
TAble 3 Subjective scores at follow-up
Parameter
TruEye
Proclear
1-Day
Focus Dailies
ADC
Clariti 1 day
p
Comfort after insertion
81.7 ± 17.6
82.0 ± 14.8
83.8 ± 15.1
89.6 ± 9.6
0.17
Comfort before removal 78.0 ± 18.8
73.1 ± 17.5
71.4 ± 20.9
77.4 ± 17.9
0.35
Comfort
82.3 ± 16.5
81.0 ± 14.3
78.4 ± 15.4
82.9 ± 15.7
0.34
Ease of insertion
90.9 ± 9.5
81.8 ± 16.7
86.2 ± 13.8
93.4 ± 7.8
0.003
Ease of removal
91.7 ± 8.6
85.1 ± 15.6
81.8 ± 16.3
84.9 ± 14.4
0.03
Overall score
81.7 ± 16.8
80.0 ± 12.9
78.3 ± 15.2
81.6 ± 10.6
0.18
Clariti
Figure 4
High
contrast
visual
0.1
Dispensing
Follow-up
Visual acuity
0.0
-0.1
-0.2
-0.3
TruEye Proclear Focus
Clariti
TruEye Proclear Focus
acuity
%
Acceptable
Optimum
100
90
80
70
60
50
40
30
20
10
0
TrueEye
Proclear 1 Day
Acuvue Advance and Oasys lenses
which relyon an internal wetting agent,
Polyvinyl pyrrolidone (PVP).
Sauflon’s Clariti lens does not use any
form of surface treatment or wetting
agents. Instead a patented process,
AquaGen, is used which produces a
unique silicone hydrogel lens material
with enhanced oxygen permeability
and superior levels of wettability and
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16-19CLMClariti 18
Focus ADC
Clariti 1 Day
biocompatibility. This is achieved by
controlling how the novel silicone and
hydrophilic materials are combined at
the molecular level to produce a surface
with unparalleled biocompatibility
and wettability without the need for
surface modification, while retaining
excellent clarity and low modulus to
achieve the uncompromised visual and
comfort standards required by the latest
Figure 5
Lens fit at
follow up
generation of SiH lens products.
Water content – Patients often cite
lens dryness and irritation as reasons
for removing lenses earlier in the day
and for dropping out of contact lens
wear altogether. The Clariti 1 Day
lens has a water content of 56 per cent
which is comparable to the mid water
conventional hydrogel lenses that have
been popular and preferred for their
comfort for many years prior to the
advent of silicone hydrogel lenses.
This higher water content provides
excellent biocompatibility with the
ocular surface.
Modulus – Incorporation of silicone
makes silicone hydrogel lenses ‘stiffer’
than conventional hydrogel lenses and
this rigidity has been implicated in
poorer comfort, papillary conjunctivitis
and in continuous lens wear superior
epithelial arcuate lesions (SEALs).
Higher modulus values can also
make switching to these lenses from
conventional hydrogels more difficult.
Clariti 1 Day has one of the lowest
modulus values for a silicone hydrogel
lens, measuring 0.5 MPa.
Clinical performance
Toassessthe Clariti 1 Daylensclinicallyit
was decided to evaluate its performance
against the only other marketed silicone
hydrogel daily disposable contact lens
(1-Day Acuvue TruEye) and two other
market leading daily disposable contact
lenses. These were the conventional
hydrogel Proclear 1-Day lens and Focus
Dailies All Day Comfort lens. The study
was conducted by an independent
clinical research group7 as a dispensing,
randomised, crossover clinical study
where the clinical performance and
subjective acceptance of the four lens
types were compared at a single study
site.
Thirty existing contact lens wearers
were recruited and each subject was
required to wear all lens types (as pairs)
for aone-week studyperiod. Lenseswere
worn on a daily wear, daily disposable
basis; that is, the lenses were worn
during the day and discarded at night.
Lenses were worn for a minimum of
eight hours a day, six days a week. The
lenses were also worn for a minimum of
two hours before attending for clinical
assessment. Subjects were examined
for a dispensing visit and a follow-up
visit for all four lens types.
Wearing patterns
There were no differences between
the four lens types in terms of ‘days
per week’ (p = 0.46), ‘hours per day’
of lens use (p = 0.59) or ‘comfortable
hours of wear’ (p = 0.63).
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Visual acuity
There were no differences between the
lenses for visual acuity (Figure 4) at
both the dispensing visit (high contrast
p = 0.20; low contrast p = 0.62) or the
follow-up visit (high contrast p = 0.81;
low contrast p = 0.09).
90
Subjective score
l ens fit
There was no difference between lenses
for proportion of optimum fits at the
dispensing visit. All four lenses fitted
all eyes acceptably at follow up (Figure
5). There were more optimum fits with
Clariti 1 Day than with the other three
lenses although this difference was not
statistically significant.
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16-19CLMClariti 19
60
50
30
Comfort
TruEye Proclear Focus
Vision
Overall score
Clariti TruEye Proclear Focus Clariti TruEye Proclear Focus Clariti
100
90
Subjective score
80
70
60
50
40
Figure 7
Subjective
scores at
follow-up
30
Comfort insertion
TruEye Proclear Focus
Comfort removal
Clariti TruEye Proclear Focus Clariti
Overall comfort
TruEye Proclear Focus Clariti
100
90
Subjective score
Summary
In terms of ‘days per week’ of wear
and ‘hours per day’ and ‘comfortable
hours per day’ of wear, there were no
differencesinwearingpatternsbetween
the study lenses.
Visual acuity was good for all lens
typesand no differenceswereestablished
between the lenses. Over-refraction and
dispensed lens powers were similar for
the all the study lenses.
All lenses fitted to at least an acceptable
level and there were no differences
between the lenses in this regard.
Subjective scores were generally
high. No differenceswereestablished at
dispensing. At follow up, lens handling
wasgenerallybetter with theClaritilens
and the 1 Day Acuvue TruEye lens.
Conclusion
With the benefits of exceptional
oxygen transmissibility, high levels of
patient comfort, added to the improved
hygiene expected with a single use
product, the Clariti 1 Day lens clearly
offers distinct advantages over most
existing daily disposable contact lenses
available. Due to its performance and
market positioning Clariti 1 Day is set
to be a very popular lens for the optical
practitioner. ●
70
40
Figure 6
Subjective
scores at
dispensing
Subjective scores at dispensing
Differences between the subjective
scores at dispensing (Figure 6) were
not statistically significant for comfort
(p = 0.91), vision (p = 0.75) or overall
score (p = 0.86).
Subjective scores at follow-up
At follow-up, subjective scores (Figure
7 and Table 3) were similar for the
four lens types except for lens handling
evaluations. For lens insertion (Figure 8
and Table 3), scores were significantly
higher with the Clariti lens than with
the Proclear 1-Day lens and the Focus
All Day Comfort lens.
80
80
70
60
Figure 8
Subjective
scores at
follow-up
Ease of insertion
Ease of removal
50
TruEye Proclear Focus
Clariti
References
1Morgan PB,Woods CA,Tranoudis IG,Efron
N,Knajian R,Grupcheve CN,Jones D,Tan
K-O,Pesinova A,Ravn O,Santodomingo J,
Vodnyanszky E,Montani G,Itoi M,Bendoriene
J,van der Worp E,Helland M,Phillips G,
Gonzalez-Meijome JM,Radu S,Belousov V,
Silih MS,Hsiao JC,Nichols J. International
contact lens prescribing in 2008. Contact Lens
Spectrum, 2009; 24(2):28-32.
2Holden B,Mertz G.Critical oxygen levels to
avoid corneal edema for daily and extended
wear contact lenses. Invest Ophthalmol Vis
Sci,1984: 25:1161-1167.
3Harvitt DM,Bonanno JA.Re-evaluation of
the oxygen diffusion model for predicting
minimum contact lens Dk/t values needed to
avoid corneal anoxia. Optom Vis Sci.1999:
TruEye Proclear Focus
Clariti
76: 712-719.
4Fatt I.New physiological paradigms
to assess the effect of lens oxygen
transmissibility on corneal health. CLAO J,
1996; 22: 25-29.
5Brennan NA.Beyond flux:total corneal
oxygen consumption as an index of corneal
oxygenation during contact lens wear.
Optom Vis Sci,2005: 82: 467-472.
6Maldonado-Codina C,Morgan PB,Schnider
CM et al.Short-term physiologic response in
neophyte subjects fitted with hydrogel and
silicone hydrogel contact lenses. Optom Vis
Sci,2004: 81: 911-921.
7 Data on file Sauflon.
●Howard Griffiths is technical director
of Sauflon Pharmaceuticals
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4/11/09 09:51:12
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