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NR 4-6/2006
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Comparison of
contrast sensitivity after implantation of diffractive lens
SA60D3 and monofocal lens MA60BM
Porównanie czułości
kontrastu po wszczepieniu soczewki dyfrakcyjnej SA60D3 oraz
monofokalnej MA60BM
Marek Rękas, Beata Żelichowska
From the Departament of Ophthalmology, Military Health Service
Institute in Warsaw
The Head of the Clinic: professor Andrzej Stankiewicz, Ph.D.,
M.D. |
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| Summary: |
Purpose: Comparison
of CSF in groups with diffractive lens SA60D3 and with
monofocal lens MA60BM, and applying results to healthy
population.
Material and methods: The study included 3 groups
of patients. First group consisted of 10 patients, who
have undergone implant surgeries with diffractive lenses
SA60D3 in both eyes; second group included 9 patients
after implant surgeries with monofocal lenses MA60BM in
both eyes. Third group included 10 patients with clear
own lens. Groups were homogenous to number of patients,
age and gender structure, as well as BCVA. CSF was
determined for each eye. In the case of operated
patients studies were performed 6 months after surgery.
Homogeneity of groups was determined with Kruskal-Wallis
test, but results of the studies were tested with
variance. Results were shown in normalized CSF version.
Results: In conducted studies there was no
statistical difference in specific evaluated cpd (3, 6,
12, 18) between SA60D3 group and MA60BM group after 6
months from surgery (p=0.892, p=0.926, p=0.564,
p=0.9953). The above results were obtained by testing
variance at confidence level p≤0.01. At the higher
confidence level p≤0.05 there was significant difference
between SA60D3 group, MA60BM group and healthy control.
Conclusions: Diffractive lenses SA60D3 decrease
CSF in comparable range as monofocal MA60BM lenses,
which does not change acceptable standard for quality
vision for monofocal lenses, that is currently accepted. |
| Słowa kluczowe: |
wieloogniskowa soczewka
wewnątrzgałkowa, dyfrakcyjna soczewka wewnątrzgałkowa,
chirurgia zaćmy, CSF |
| Key words: |
multifocal intraocular
lens, diffractive intraocular lens, cataract surgery,
CSF. |
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Phacoemulsification
with implant of foldable monofocal lens is currently a standard
in cataract surgery in the world. Advantages and faults of this
method are commonly recognized. The most important disadvantage
is dependence on glasses for far sight or near sight correction
depended on original lens calculation. This problem is important
especially for people with active lifestyle, being in high
position for the company, public administration or working with
close objects. Multifocal lenses with refractive or diffractive
characteristics seem to solve the problem with dependence on
corrective glasses after cataract surgery. Capability of visual
system and central nervous system to steer attention at
different foci in space without the use of accommodation was the
basis for construction of multifocal lenses. As a matter of fact,
lens is only a physical setting distributing light energy
between far sight and near sight foci and in-between foci, and
alternative visual capability that we posses allows, depending
on its construction, to take advantage with better or worse
effect. Both lenses refractive and diffractive allow for near
sight and in-between distances. Comparison of their virtue is
not the goal of this paper, but the question comes up whether
usage of this type of lenses has diminished quality of far sight
and is changing achieved standard?
Apodized diffractive lens SA60D3 by Alcon is one part lens
constructed from hydrophobic acryl. Diameter of the optical part
is 6.0 mm. Central part of anterior surface with diameter of 3.6
mm is constructed according to diffractive lens technology by
Fresnel (1). Apodization is based on gradual reduction of the
height of particular diffractive zones from 1.3 um in the center
to 0.4 um on the periphery of the zone. Thanks to used
technology the addition in its plane was achieved in the
magnitude of 4,0 D. Large addition makes possible division by
retina and cortical centers created on retinal surface energetic
foci responsible for far sight and near sight (2, 3). The most
important advantage from the point of quality vision is
achievement of proportional light distribution responsible for
creation of far sight picture on the retina determined by pupil
diameter. With the pupil diameter of 1.0 mm light is divided 1:1
(far sight-near sight), and with enlargement of the pupil ratio
is higher, so at pupil diameter 3.0 mm is around 3:2. Such
construction is determined to eliminate or diminish lighting
side effects that appear with large contrast between the viewing
object and little illumination of the background (e.g. driving
at night). Monofocal lens MA60BM by Alcon, the entire light
energy focusing in one place, but at the same time is
introducing to the optical system of the eye as a spherical lens
aberration spherical and chromatic (2). It is important, to note
that clear lens has compensating property from positive
spherical aberration of the cornea (1, 2). This fact is not
considered in construction of MA60BM lens, but apodization
corrects the degree of light refraction dependent on refractive
zone, and the lens is behaving similar to aspherical lens (1).
The goal of this paper is comparison of the quality of the
vision for far sight based on contrast sensitivity function (CSF)
curve in the group of eyes after lens MA60BM implantation and
SA60D3 implantation, and applying results to healthy population.
Material and methods
Three groups of patients were studied. First group consisted of
10 patients, who received binocular pseudoaccomodative lens
SA60D3 implant; second group included 9 patients after monofocal
lens MA60BM implant in both eyes. Third group included 10
patients with clear lenses of their own. Excluding criteria from
group SA60D3 and MA60BM included eye diseases besides cataracts,
which were the indication for surgery. They included diseases of
the cornea, optic nerve with neuropathy characteristic, age
related macular degeneration, diseases of the retina,
uncontrolled glaucoma, and pupil reaction abnormalities. In the
case of SA60D3 patients were selected according to motivation
for surgery, willingness to be independent from corrective
glasses for near sight and the level of daily activity. Diseases
of the visual system were also the exclusion from the third
group of patients. Patients with corneal astigmatism greater
than 1.5 D were also excluded from all the groups.
Groups were homogenous considering structure, age, number of
patients, sex as well as best corrected visual acuity (BCVA).
There was no statistical difference between groups at tested
level of probability (p<0.05). Statistical analysis was
performed with Kruskal-Wallis test. Results are shown in tab. 1.
One surgeon performed cataract surgeries with ultrasound
phacoemulsification method using droplet anesthesia. The power
of intraocular lenses was calculated with SRK/T method. The main
opening with 2.8 mm diameter was done in clear temporal cornea.
Lenses SA60D3 and MA60BM were implanted with the Monarch system
by Alcon. There were no complications noted in post surgical
period.
Calculation of contrast sensitivity function (CSF) was done
using table CSV-1000 (Vector Vision, Dayton, OH USA). Visual
acuity was tested with the ladder formula in four spatial
frequencies (3, 6, 12, 18 cpd) with sinusoidal change of
stimulus illumination. Illumination of CSV-1000 table background
controlled by system of automatic calibration is held at the
same level 85 cd/m2 ±0.1 without consideration for surrounding
illumination, where tests are performed. The change of stimulus
contrast in each spatial frequency is done in logarithmic
progress by 0.15 in tests 1, 2, 3 and by 0.17 of the logarithmic
unit in tests 4, 5, 6, 7 and 8. The change between tests A, B,
C, D and 1 equal 0.3 of the logarithmic unit. Contrast is
defined with Michelson’s equation.
C- contrast in %
L – stimulus illumination in cd/m2
Tests were done from the distance of 3.0 m after correction of
refraction with glasses for far sight. Threshold of contrast
vision was tested for every spatial frequency. There are 17
wheels with 0.0381 m diameter each in every row. In the first
stage patient should recognize ladder formula with the high
contrast at the beginning of the row, marked, depending on
spatial frequency, with letters A, B, C or D. In the case of
identification of the ladder formula at the entrance level the
other levels were also tested. Every level out of eight was
presented to the patient as a choice test. The last correct
answer was determined, as a test result.
Testing was done for every eye separately in three groups. In
SA60D3 and MA60BM groups testing was done 6 months after surgery.
Results in particular spatial frequencies were shown in
logarithmic scale for statistical analysis. One way analysis of
variance (ANOVA) was done with the help of statistical packets
STATISTICA 6.0.
Results shown in decimal logarithm were normalized to show them
in the graph. Normalization was performed according to Boxer
Walcher and Krueger method (4).
Results
The results of one way analysis of variance of the Scheffer test
post-choc are collected in Tab. II, III, IV and V and Fig. 1.
The most important result of the analysis is lack of statistical
significance in all spatial frequencies between SA60D3 group and
MA60BM group, after 6 months from the surgery. In case of 6cpd
there was no statistical difference between SA60D3 group and the
third group and 12 cpd there was no statistical difference
between MA60BM group and third group. The above results were
obtained by testing variance at confidence level p<0.01 and they
have to be taken as significant. At the higher level of
confidence p<0.05 there’s significant difference between SA60D3
group, MA60BM group and the control group. Normalized graphs for
mean spatial frequencies in studied groups are shown in Fig. 2.
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Discussion
Human natural lens compensates positive spherical
aberrations of the cornea (1). Aging makes this natural balance
changed or completely imbalanced due to cataract development.
Quality vision depends on the quality of the eye optical system
on one side and from the other side its imperfections are
compensated by neuronal processes in the retina and central
nervous system (3). The optical eye system after lens implant,
either monofocal or multifocal is not perfect. Spherical lenses
increase positive aberrations, but multifocal lenses distribute
light energy into several foci (1, 5, 6). As a consequence of
these imperfections is lowering of contrast sensitivity function
(CSF) in relation to healthy population (7). Similar results
were obtained in our work (Fig. 2). Differences in low and
medium ranges cpd (3, 6, 12) after 6 months observation were
about 0.1 logarithmic units in comparison to healthy population
(p<0.05, Tab. II, III, IV). The difference of contrast vision
between group I, II and III within the range of 18 cpd was about
0.3 logarithmic units (p<0.01, Tab. V). Indeed lower contrast
sensitivity in the range of 18 cpd after implant of MA60BM and
SA60D3 as compared to healthy population confirms observations
by other authors (8). Montés-Micó et al. think, that decrease in
contrast sensitivity in the range of high spatial frequencies is
due to defocusing of the light energy and spherical aberrations
(8, 9).
Among many authors it is dominant belief, that multifocal lenses
either refractive or diffractive lower contrast sensitivity
function (CSF) (10, 11, 12, 13). There is no difference in
contrast sensitivity in particular spatial frequencies if we
compare two groups of lenses (14). Studies that were done did
not include diffractive, apodized lenses, but lenses
technologically inferior; therefore we cannot generalize this
tendency. Studies comparing multifocal lens AMO Array SA-40N
with unifocal lens AMO SI-40NB in 18 months observation did not
find any significant statistical differences in CSF in photopic
conditions (9). It is important to emphasize, that contrast
sensitivity for multifocal lenses was lower and CSF was in the
lower range of population standard (9). Montés-Micó et al.
performed studies in similar conditions as presented in our work,
but it is impossible to make comparison because they did not
show normalized CSF (9). Rocha et al. were comparing aberrations
of the optic system of the eye and contrast sensitivity in the
group of lenses SA60D3, MA30AC and SA60AT (1). The authors
concluded lower spherical aberrations in the group of patients
with implanted SA60D3 lens as compared to monofocal lenses
(p<0.05). But in testing of contrast sensitivity SA60D3 lens was
inferior to MA30AC and SA60AT lenses (p=0.02). Studies were done
only 2 months after surgery and included only one cpd. Similar
results were obtained by Schmitz et al. in the group of lenses
Array SA-40N after 5 months of observation (15). In other
studies with multifocal Array SA-40N lenses, significant
statistical differences in relation to monofocal SI-40NB were
seen in the range 1.5-18 cpd up to 6 months from surgery (5).
Neuroadaptation may be a process longer than 2 months. From the
other side low spatial frequencies do not seem to be the best
measure of the changes that occur in the optical system of the
eye with multifocal lens implantation (5, 8, 9). In cited
studies authors do not state statistical differences in all
tested spatial frequencies after 6 months from surgery between
the group of patients with multifocal lens implant and monofocal
lens implant (5). We established similar conclusions in our work
(p>0.05, Tab. II-V). However our studies included comparison of
SA60D3 lens with MA60BM, defocus and introduced aberrations into
the optical system, likely as in the case of multifocal lenses
are phenomena responsible for lowering of contrast sensitivity
(8, 9). Minimally lowered contrast sensitivity in the range 12
and 18 cpd of magnitude 0.05 logarithmic units in relation to
group MA60BM is preserved in our studies after 6 months from the
implant of SA60D3 lens (Fig. 2). Lowering of the contrast
sensitivity in high ranges cpd is not statistically significant
(p<0.05, Tab. IV, V)
Evaluation of contrast vision for far sight in patients with
diffractive SA60D3 lens implant and monofocal MA60BM lens
implant is comparable. Implant of SA60D3 lens does not change
the current standard in cataract surgery.
References
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Adres do korespondencji (Reprint
requests to):
dr n. med. Marek Rękas
ul. Trapezowa 51
08-521 Dęblin
e-mail: rekaspl@wp.pl |
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