SILICONE HYDROGELS
Daily
Wear Experience with Two Silicone Hydrogel Lenses
This
study evaluated the performance of two silicone hydrogel lenses worn for two weeks
of daily wear.
By D. Priya Janakiraman, OD, & Joseph
M. Rappon, OD, MS, FAAO
|
TABLE
1 |
|
Lens Specifications
|
|
|
O2OPTIX |
ACUVUE
ADVANCE |
|
Base curve (mm) |
8.6 |
8.3/8.7 |
|
Diameter (mm) |
14.2 |
14.0 |
|
Material |
lotrafilcon B |
galyfilcon
A |
|
% H2O |
33 |
47 |
|
FDA Group |
I |
I |
|
Center thickness at
�3.00DS (mm) |
0.08 |
0.07 |
|
Dk |
110 |
60 |
|
Dk/t at �3.00DS |
138 |
86 |
During
their commercial release in 1999, silicone hydrogel lenses were primarily marketed
as extended wear lenses. Since then practitioners have also recognized the clinical
advantages of prescribing silicone hydrogel lenses on a daily wear basis. Many practitioners
began switching their established two-week HEMA disposable lens wearers into silicone
hydrogel lenses as well as fitting these lenses on their neophyte wearers. According
to a 2006 Health Products Research survey, silicone hydrogel lenses accounted for
40 percent of new soft contact lens fits in the United States during the fourth
quarter of 2005, compared to just 17 percent in the first quarter of 2004. This
change that is still underway indicates a massive shift in practitioners' dispensing
habits and has presumably resulted from advantageous clinical properties of silicone
hydrogel lenses.
This article reports the performance of
two silicone hydrogel contact lenses, O2Optix (lotrafilcon B, CIBA Vision)
and Acuvue Advance with Hydraclear (galyfilcon A, Vistakon), during a two-week period
of daily wear usage. Table 1 lists the specifications for the two study lenses.
Methods
An Ethics Committee approved this study and all
subjects underwent informed consent in accordance with the Declaration of Helsinki.
Researchers carried out a single-center, open label, parallel group, staggered enrollment
(non-randomized) study in which we enrolled 92 subjects based on the inclusion/exclusion
criteria outlined in Table 2; 43 to wear O2Optix and 49 to wear Acuvue
Advance bilaterally. The age, gender, refractive error, corneal curvature and lens
wear experience of the subjects was representative of the normal contact lens population
and similar between the two study groups.
|
 |
|
Figure 1. Subjects reporting lens-wear attributes
at two weeks. |
Researchers
prescribed a daily wear schedule with overnight disinfection using Clear Care (CIBA).
All subjects were instructed to rinse the lenses for five seconds through the basket
of the lens case with Clear Care and, if significant deposits were present, a rub/rinse
step was recommended on lens removal at the clinician's discretion. Patients were
required to wear their lenses for a minimum of six hours per day and at least five
days per week. We set no restriction on the maximum hours of wear per day or the
number of days per week that patients could wear their lenses, but we required that
they not sleep in their lenses. Three subjects didn't meet the inclusion criteria
and were not dispensed lenses, two in the O2Optix group (astigmatism
outside of parameter range; lid papillae) and one in the Acuvue Advance group (viral
keratoconjunctivitis). We fit all other subjects with the range of parameters commercially
available.
After two weeks of wear, subjects
completed questionnaires to rate a variety of subjective variables such as comfort,
dryness, vision and handling on a 1 to 10 scale, in which 1 was poor and 10 was
excellent. We also sampled satisfaction with the lenses using a five-point scale
with choices of "strongly agree," "somewhat agree," "neither agree nor disagree,"
"somewhat disagree," and "strongly disagree." We asked subjects for the average
number of hours that they were able to wear the lenses on a daily basis as well
as the average number of hours they felt that the lenses were comfortable to wear
on a daily basis.
|
TABLE 2 |
|
Inclusion/Exclusion
Criteria INCLUSION
CRITERIA
• Signed subject informed consent
• Be at least 18 years old
• Have a need for correction in both eyes
• Correctable to at least 20/40 distance
visual acuity with spherical hydrogel contact lenses
• Have ocular findings considered to be
within normal limits and which would not prevent the subject
from safely wearing contact lenses
• Stable and distortion-free keratometric
readings
EXCLUSION CRITERIA
• Any active corneal infection
• Acute or sub-acute inflammation or infection
of the anterior chamber
• Any eye disease, injury or abnormality
of the cornea, conjunctiva or eyelids that would
affect the wearing of contact lenses
• Severe insufficiency of lacrimal secretion
(dry eyes)
• Corneal hypoesthesia
• Any systemic disease or use of medications
that may affect the eye or be exaggerated by
wearing contact lenses
• Subjects who have undergone corneal refractive
surgery
|
Other measurements included contact
lens surface assessment and corneal physiology, recorded using a 0 to 4 scale in
which 0 indicated a score of "none" and 4 indicated a score of "severe," with descriptors
for each variable.
For subjective data we present average
subjective ratings, the percentage of subjects that fully or somewhat agreed that
they were satisfied to predetermined questions and the average total comfortable
wearing time. We present frequency distributions of the clinical grades for the
objective results.
We analyzed the subjective ratings
data with linear mixed models using restricted maximum likelihood method of estimation.
We set overall differences between lens types at 5 percent level of significance
and analyzed it using the t-test. We compared the severity of symptoms data using
the Fisher's exact test at each visit and set the level of significance also at
5 percent. Physiological, lens and vision variables were analyzed as eye-specific
data. The methods and principles of data analysis for these variables were similar
to the subjective ratings with a few exceptions: We compared baseline physiological
variables between the two lens groups for similarity. We did not consider variables
that were significantly different at baseline for further analysis. We also performed
visit-specific analysis using mixed models due to correlated eye data within each
subject.
Subjective Results
Eight subjects discontinued lens wear prior to
the two-week visit, two wearing O2Optix (both for discomfort) and six
wearing Acuvue Advance (one patient couldn't adapt to lens wear, one had near vision
and handling difficulties, one withdrew consent for an unknown reason and three
were lost to follow up). Of the 81 subjects who finished the study, we excluded
the data from 21 of these subjects in the analysis because the subjects presented
for examination at two weeks not wearing the study lenses, wearing the lenses inside
out or they presented outside the specified visit window period of 10 days to 19
days from lens dispensing. A total of 60 subjects (28 with O2Optix and
32 with Acuvue Advance) successfully completed the study and were included in the
analysis. Table 3 accounts for all subjects.
Comfort O2Optix
wearers rated their lenses significantly better than did Acuvue Advance wearers
in terms of comfort during the day, lens awareness, dryness (overall and at the
end of the day) and burning (Table 4).
At two weeks, a higher percentage of
subjects wearing Acuvue Advance lenses reported dissatisfaction with lens awareness
compared to those wearing O2Optix lenses (p=0.05). A trend also occurred
for a higher percentage of subjects wearing O2Optix lenses to agree that
they were satisfied with comfort (p<0.10). Although not statistically different,
more than 20 percent more subjects wearing O2Optix lenses than those
wearing Acuvue Advance agreed that the lenses didn't make their eyes feel dry overall
(Figure 1). Comfort tended to decline less throughout the day with O2Optix
lenses than with Acuvue Advance lenses (Figure 2).
|
TABLE
3 |
|
Subject Accounting |
|
|
O2OPTIX |
ACUVUE
ADVANCE |
|
Enrolled |
43 |
49 |
|
Enrolled, not dispensed |
2 |
1 |
|
Discontinued |
2 |
6 |
|
Missed or not evaluable |
11 |
10 |
|
Successfully completed |
28 |
32 |
The average number of hours of total
and comfortable wear time was 1.4 and 1.7 hours greater for O2Optix wearers
and Acuvue Advance wearers respectively (p<0.10), with 68 percent of O2Optix
wearers reporting a comfortable wearing time of nine hours or more compared to 47
percent of Acuvue Advance wearers (p=0.12).
Other Subjective Results
O2Optix wearers also rated subjective eye redness better (less redness)
than did Acuvue Advance wearers (9.1 ±1.3 vs. 7.9 ±2.9, p<0.05). Subjective
ratings and satisfaction ratings for vision and handling were not different between
the two lens types.
Other Results
Lens Surface O2Optix
lenses attracted less front surface deposits compared to Acuvue Advance lenses (p<0.05).
The percentage of lenses with these deposits for each grade appears in Figure 3
for both study lenses.
|
|
|
Figure 2. Subjects reporting good comfort throughout
the day at two weeks.
|
At
two weeks, four (6.3 percent) Acuvue Advance lenses accumulated raised linear front
surface deposits. None of the O2Optix lenses developed such deposits.
At dispensing, eight (7.4 percent)
Acuvue Advance contact lenses had star-shaped fractures (Figure 4). We didn't observe
these fractures with any O2Optix lenses.
Physiological Response and Visual
Acuity We observed less corneal staining in O2Optix wearers
compared to Acuvue Advance wearers (p<0.05), and there was a trend for less conjunctival
staining with O2Optix lenses (p<0.10). We found no differences in
objective redness measurements (Table 5). The lenses performed equally well for
both high and low contrast visual acuity.
|
 |
|
Figure
3. Front surface deposits at two weeks. |
Discussion
The prime reason for discontinuation of contact
lens wear is discomfort, particularly dryness-related discomfort. In addition, many
patients may decrease their wearing time during the day because of discomfort and
thus have a lower expectation of contact lens performance.
Corneal physiology and long-term eye health
are paramount particularly with respect to busy lifestyles and the desire to wear
contact lenses for longer periods during the day. Maintaining and improving comfort
and vision are also key motivators in the contact lens industry. We believe O2Optix
lenses address all of these issues.
A compromise of the corneal epithelium
may place contact lens wearers at a higher risk for complications such as bacterial,
viral or fungal infections. Although typical for contact lens wearers, both lenses
in this study caused a low degree of corneal and conjunctival staining, but staining
did tend to be higher with Acuvue Advance lenses.
|
TABLE
4 |
|
Subjective Ratings* |
|
|
O2OPTIX
|
ACUVUE
ADVANCE |
P
|
|
Comfort
during the day |
8.6
± 1.2 |
7.8
± 2.2 |
0.05
|
|
Lens Awareness |
8.7
± 1.1 |
7.1
± 2.9 |
0.01
|
|
Overall Dryness |
8.5
± 1.1 |
6.9
± 2.6 |
<0.01
|
|
Dryness at the end
of the day |
7.9
± 1.8 |
6.3
± 2.9 |
0.01
|
|
Burning |
9.3
± 1.0 |
8.0
± 2.9 |
0.03
|
|
* Subjective Rating (1 to 10) (1 = "poor,"
10 = "excellent") |
Schnider and Steffan (2004) cited better
vision, comfort and overall satisfaction with Acuvue Advance lenses compared to
O2Optix lenses, but presented results after one week of wear despite
having a two-week wearing period for the study. The recommended replacement schedule
for both Acuvue Advance and O2Optix is two weeks. Our study, which we
believe is more indicative of real world conditions, shows the impact of the full
two-week wearing schedule.
A
Note about Oxygen Transmissibility An average of 9 percent of daily disposable
subjects in clinical studies sleep in their lenses, and the industry estimates that
84 percent of patients nap in their lenses. We also know that corneal oxygen requirements
vary among individuals. O2Optix lenses provide additional oxygen transmissibility
(62 percent higher) than Acuvue Advance lenses, which may be beneficial for many
patients including those who have higher oxygen requirements, patients who occasionally
sleep in their lenses, those who have higher prescriptions and those under some
environmental conditions such as higher altitudes. This is vital not only for the
thicker plus and toric lenses, but also for higher myopic lenses where peripheral
lens thickness can be significant.
|
 |
|
Figure
4. Example of star-shaped fractures on Acuvue Advance lens (magnified 50X). |
Papas (1998) indicated that
even for daily wear, a recommended Dk/t level of 125 is required to minimize limbal
redness. Papas reported that the 95 percent confidence intervals around that value
are from 56 to 274, and recommends that at a minimum, lenses should provide a Dk/t
of at least 56 at the lens periphery. Having a central Dk/t of 86 and a peripheral
lens thickness of 240μm, Acuvue Advance has a Dk/t of 25 in the periphery for
a –3.00D lens. However, O2Optix has a central Dk/t of 138 and a
peripheral lens thickness of 150μm, which creates a peripheral Dk/t of 73 for
a –3.00D lens. This may explain why O2Optix wearers felt they had
whiter eyes and wore their lenses longer than did the Acuvue Advance group. Although
we found no difference between the lenses in terms of objective limbal and bulbar
redness, increased redness with Acuvue Advance as compared to O2Optix
may have been evident had we examined the patients at the end of the day. In addition,
this study was only two weeks in duration. Possible long-term differences would
need further evaluation.
It's also important to note that Papas'
work recommending these minimum peripheral levels has been cited as very important
to the long-term growth and repair functions of the eye. Being the only source of
new corneal epithelial cells, hypoxic stress on the limbal stem cells, which are
covered by the peripheral portion of a soft contact lens, may have serious long-term
corneal health implications.
|
TABLE 5 |
|
Physiology
(0 to 4) |
|
|
O2OPTIX
|
ACUVUE
ADVANCE |
P
|
|
Corneal
staining |
0.5
± 0.5 |
0.9
± 0.6 |
0.01
|
|
Conjunctival Staining |
1.1
± 0.5 |
1.3
± 0.5 |
0.09
|
|
Bulbar redness |
0.9
± 0.6 |
0.8
± 0.6 |
0.75
|
|
Limbal redness |
0.7
± 0.6 |
0.8
± 0.7 |
0.75
|
Deposits While protein
deposition on silicone hydrogels is known to be low, studies have noted increased
lipid spoilation compared to conventional hydrogel materials. The prominent, raised
shiny deposits we found on some Acuvue Advance lenses in this study appeared to
be lipid in nature.
Higher deposit levels on soft contact
lenses are connected with poorer comfort performance, impacting lens awareness,
disrupting wettability and potentially leading to increased dryness and decreased
wearing time. Deposits may also cause a mechanical irritation of the palpebral conjunctiva,
and lens surface defects have been shown to harbor microbes.
Conclusion
Our results indicate that O2Optix lenses
outperformed Acuvue Advance lenses in terms of comfort, dryness, lens awareness,
subjective redness, deposit resistance and corneal staining over two weeks of daily
wear. Both lenses performed well in terms of vision and handling. We feel that the
performance of O2Optix lenses combined with its high Dk/t positions it
as an outstanding lens for both daily and occasional overnight wear (up to six nights).
For references, please visit
www.clspectrum.com/references.asp
and click on document #133.
Dr. Janakiraman is a Senior Principal Scientist
at CIBA Vision Research and Development division. She holds a Doctor of Optometry
degree from New England College of Optometry and completed a clinical fellowship
at the prestigious L.V. Prasad Eye Institute in India. Currently, her main area
if interest is to study comfort and visual responses to various silicone hydrogel
lenses.
Dr. Rappon is the manager of medical marketing for CIBA Vision,
North America. He is a member of the American Optometric Association and is the
co-chair of the Georgia Optometric Association's CE committee. He was also named
Georgia's Young OD of the Year for 2005.
Contact Lens Spectrum, Issue: December 2006