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Citation: Zhao HL,
Jiang J, Yu J, Xu HM. Role of short-wavelength filtering lenses in delaying
myopia progression and amelioration of asthenopia in juveniles. Int J
Ophthalmol 2017;10(8):1261-1267
Role
of short-wavelength filtering lenses in delaying myopia progression and
amelioration of asthenopia in juveniles
Hai-Lan Zhao, Jin Jiang, Jie Yu,
Hai-Ming Xu
Department of Ophthalmology, Zhejiang
Provincial People’s Hospital, Hangzhou 310014, Zhejiang Province, China
Correspondence to: Hai-Ming Xu.
Department of Ophthalmology, Zhejiang Provincial People’s Hospital, Hangzhou
310014, Zhejiang Province, China. xuhamin@163.com; bowen75@126.com
Received: 2017-02-12
Accepted: 2017-07-26
AIM: To
evaluate the positive effects of blue-violet light filtering lenses in delaying
myopia and relieving asthenopia in juveniles.
METHODS: Sixty
ametropia juveniles (aged range, 11-15y) were randomized into two groups: the
test group (30 children, 60 eyes), wearing blue-violet light filtering lenses;
and the control group (30 children, 60 eyes), wearing ordinary aspherical
lenses. Baseline refractive power of the affected eyes and axial length of the
two groups was recorded. After 1-year, the patients underwent contrast
sensitivity (glare and non-glare under bright and dark conditions),
accommodation-related testing, asthenopia questionnaire assessment, and adverse
reaction questionnaire assessment.
RESULTS: After 1y
of wearing the filtering lenses, changes in refractive power and axial length
were not significantly different between the two groups (P>0.05). Under
bright conditions, the contrast sensitivities at low and medium-frequency
grating (vision angles of 6.3°, 4.0°, and 2.5°) with glare in the test group
were significantly higher than in the control group (P<0.05), while the
contrast sensitivity at low-frequency grating (vision angles of 6.3° and 4.0°)
in the absence of glare in the test group was higher than in the control group
(P<0.05). Under glare and non-glare dark conditions, the contrast
sensitivities of various frequencies in the test group did not show significant
differences compared with those in the control group (P>0.05). In the test
group, the amplitude of accommodation, accommodative lag, and accommodative
sensitivity of patients wearing glasses for 6 and 12mo were significantly
elevated (P<0.05), while the asthenopia gratings were significantly
decreased (P<0.05). Nevertheless, in the control group, the amplitude of
accommodation, accommodative lag, and accommodative sensitivity after 12mo were
not significantly altered compared with baseline (P>0.05), and the
asthenopia grating was not significantly decreased (P>0.05). In addition,
after wearing glasses for 6 to 12mo, the asthenopia grating of patients in the
test group decreased significantly compared with the control group (P<0.05).
At 12mo, the constituent ratio of adverse reactions did not show significant
difference between the two groups (P>0.05).
CONCLUSION: A 1-year
follow-up reveal that compare with ordinary glasses, short-wavelength filtering
lenses (blue/violet-light filters) increase the low- and medium-frequency
contrast sensitivity under bright conditions and improved accommodation. They
effectively relieved asthenopia without severe adverse reactions, suggesting
potential for clinical application. However, no significant advantages in terms
of refractive power or axial length progression were found compared with
ordinary aspheric lenses.
KEYWORDS:
short-wavelength filtering lenses; asthenopia; juvenile myopia
DOI:10.18240/ijo.2017.08.13
Citation: Zhao HL,
Jiang J, Yu J, Xu HM. Role of short-wavelength filtering lenses in delaying
myopia progression and amelioration of asthenopia in juveniles. Int J
Ophthalmol 2017;10(8):1261-1267
Blue light is an important
component of natural light. Blue light hazard refers to the photochemical
action induced by radiant exposure to light with a wavelength of 400-500 nm
(short wavelength light), leading to retinal damage[1].
However, blue light plays an important role in perception and in distinguishing
graphics and colors, regulating hormone secretion in vivo, maintaining
circadian rhythms in animals, and maintaining refractive ability[2].
Therefore, the need for short-wavelength filtering lenses (blue/violet-light
filter) is still controversial. Nevertheless, short-wavelength filtering lenses
control light-sensitive stimulation, improve visual comfort and definition, and
play a positive role in alleviating asthenopia in humans[3].
In the meantime, it improves contrast sensitivity and visual acuity under
photonic vision, improves retinal image quality, and strengthens the
accommodative function, which may delay myopia progression. In this randomized
controlled study, we followed up patients for 1y to evaluate whether the
short-wavelength filtering lenses played a positive role in delaying myopia and
relieving asthenopia in juveniles. We selected the Sanlang medical protective
glasses (patent No.ZL201020301257.8 versatile anti-blue lenses), which were
designed using substrate absorption, including a substrate and a coating layer.
They absorb UV light shorter than 380 nm, as well as 400 to 500 nm high-energy
blue light. They transmit 90% of the light in the range of 500 nm to 780 nm to
ensure clear vision.
Subjects Between 2012 and 2014, 60 juveniles with
ametropia and aged 11-15y were followed up at our Outpatient department. These
60 juveniles were all from the same school. They exhibited a refractive power
of -1.0 to -5.0 D (astigmatism lower than -1.00 D, 50% of the astigmatism was
included in spherical equivalent). The patients were randomized using a random
number table to two groups (60 eyes of 30 patients for each group): the test
group, wearing blue-violet light filtering lenses; and the control group,
wearing ordinary aspherical lenses. The mean age of the patients in the test
and control groups was 13.7±1.1y (14 males and 16 females) and 13.3±1.3y (15
males and 15 females); there were no significant differences between the two
groups.
Patients with glaucoma, cataract,
retinal detachment or denaturation, and other ocular diseases affecting vision
were excluded. This study was approved by the hospital Ethics Committee.
Guardians of all the subjects signed informed consent.
Research Methods At the beginning of the experiment, the
patients in both groups were tested for initial visual acuity, optometry, and
axial length. After wearing glasses, contrast sensitivity and glare contrast
sensitivity were assessed at low, medium, and high frequencies under bright and
dark conditions. Accommodation-related tests (amplitude of accommodation,
accommodative lag, and accommodative sensitivity) and asthenopia questionnaire
were administered. The asthenopia questionnaire included nine items:
photophobia, foreign body sensation, burning sensation, blepharism,
ophthalmalgia, dizziness and headache, lachrymation, nausea, vomiting, and
hyperemia. Hyperemia was evaluated and recorded by the same clinician, and the
remaining subjective symptoms were self-assessed by the patients using the
method proposed by Liu et al[4] according to the severity of
symptoms (Table 1). Due to the significant differences in the appearance of
lenses between the two groups, blinding was not adopted in this study. Patients
in the test and control groups wore glasses for one year, and filled out the
adverse reaction questionnaire at the end of the experiment. Adverse reactions
included presence of headache, dizziness, nausea, sleep disorder, night vision
disorder, growth and developmental disorder, and dyschromatopsia (Table 2).
Table 1 Symptom assessment form
Grades |
Symptoms |
0 |
No
symptoms |
1 |
Occasional
symptoms (less than 3 times per week), and relieved after rest. |
2-4 |
Falls
between 1-5, assessment based on individual conditions. |
5 |
Recurrent
symptoms, affecting quality of life and work, and not relieved easily with
rest. |
6-8 |
Falls between
5-9, assessment based on individual conditions. |
9 |
Ongoing
symptoms seriously affecting quality of life and work, and not ameliorated
with rest. |
Table 2 Adverse reaction
assessment form
Grades |
Symptoms |
0 |
No
symptoms |
1 |
Occasional
symptoms (less than 3 times per week). Patients are tolerant, without a need
for termination of the experiment. |
2 |
Moderate
discomfort (less than 6 times per week). Patients are basically tolerant,
without a need for termination of the experiment. |
3 |
Frequent
symptoms affecting the quality of life and work. Patients are intolerant,
warranting cessation of the experiment. |
The patients in both groups were
reviewed every 3mo for one year. At each review, they were tested for visual acuity,
optometry, and axial length. All the examinations from the beginning until the
end of the experiment were conducted by the same expert. Refractive power
progression exceeding -0.50 D and the corrected visual acuity smaller than 5.0
suggested that the original lens was not consistent with the optometric
prescription (corrected visual acuity above 5.0), and warranted lens
replacement. All the subjects underwent accommodation-related detection and
asthenopia questionnaire again after wearing glasses for 6 to 12mo. All the
patients filled out the adverse reaction questionnaire after wearing the
glasses for 12mo.
During the experiment, patients
in both groups were required to avoid medications and physical therapy delaying
myopia progression, and not to work at close range for longer than 3h every
day. They were also asked to use the same type of eye-shield lamp.
Measurement of Contrast
Sensitivity Contrase sensitivity
was measured using a CGT-1000 Contrast Glare tester (Takagi Seiko, Nagano,
Japan). The size of the pupils was 2.5-4 mm at an examination distance of 35
cm. Under bright adaptation (85 cd/m2), bright adaptation combined with glare,
dark adaptation (3 cd/m2) and dark adaptation plus glare, monovision and glare
contrast sensitivity under the best corrected visual acuity were assessed after
the patients adapted to the darkroom for about 10min. In glare testing,
brightness of the glare source was set to the highest level (40 000 cd/m2), and
the duration for the presence of visual target was set to 0.2s, with an
interval of 2s. Hollow ring with visual targets of 6.3°, 4.0°, 2.5°, 1.6°,
1.0°, and 0.7° corresponded to visual angles of 28.6’, 18.0’, 11.4’, 7.2’,
4.5’, and 2.9’ respectively, with the corresponding circumference/degree of
1.0, 1.7, 2.6, 4.2, 6.6, and 10.4 cpd at 35 cm respectively. The visual angle
of 6.3°-4.0° represented low-frequency, 2.5°-1.6° was medium-frequency, and
1.0°-0.7° was high-frequency light. Contrast thresholds of each spatial
frequency were transformed using -lg contrast sensitivity for statistical
analysis.
Accommodation-related
Detection Amplitude of
accommodation was determined in patients of the two groups using a push-up
method after wearing different glasses. An object was gradually moved towards
the patient, which increased the divergence of the light and stimulated
accommodation, to determine the ability of the eye to change the diopter with
respect to the shape of proximal stimulants.
After wearing different glasses,
patients in both groups underwent accommodative lag examination using fused
cross cylinders (FCC) test to evaluate the status of the tested eye in
visualizing near targets.
Accommodative sensitivity refers
to the ability to control accommodative status. After wearing glasses, the
frequency of human eyes to effectively alter the accommodation within 1min was
tested using flippers (±2.0 D) to represent the accommodative sensitivity.
Statistical Analysis Statistical analyses were performed
using SPSS 17.0 (SPSS, USA). Normality of each group was tested using a
non-parametric approach (binomial test). Intragroup comparisons were performed
using paired t-test. Intergroup comparisons were conducted using
independent-samples t-test. Constituent ratios of gender and adverse reactions
were compared between the two groups using Chi-square test. P<0.05 was
considered statistically significant in all the tests.
According to sample size
calculation for mean comparison between two groups, N=[Zα/2+Zβ]σ/δ]2
(Q1-1+Q2-1), combined with our pre-experimental results, the sample size was
estimated as N=30. Therefore, we recruited 100 subjects in total, including 35
patients randomly selected in each group according to the inclusion criteria.
At the end of 1-year follow-up, 30 patients remained in each group, and the remaining
10 patients were lost to follow-up.
RESULTS
Patients’ Baseline Data There were no significant differences
between the two groups for age (independent-samples t-test: P=0.199) and gender
(Chi-square test: P=0.796) (Table 3).
Table 3 Patients’ age and gender
Groups |
Age (a) |
M (n) |
F (n) |
Test group |
13.67±1.09 |
14 |
16 |
Control
group |
13.27±1.29 |
15 |
15 |
Refractive Power and Axis
Oculi The baseline refractive powers
of the test group (60 eyes) and control group (60 eyes) were -2.81±0.96 D and
-2.67±0.93 D, respectively (P=0.442), and there were no significant differences
in refractive power after wearing glasses for 1y between the two groups (Table
4). The changes in refractive power of the two groups during the 1-year
follow-up (4 visits). The baseline axial lengths of the test and control groups
were 25.62±0.86 mm and 25.32±0.96 mm, respectively (P=0.071). The axial length
was not significantly different between the two groups after 1-year (P=0.108)
(Table 4).
Table 4 Changes in refractive
power and axis oculi at baseline and after 1-year in the two groups mean±SD
Parameters |
Test group |
Control
group |
P |
Baseline
refractive power (D) |
-2.81±0.96 |
-2.67±0.93 |
0.442 |
Refractive
power at 3mo (D) |
-2.95±0.93 |
-2.77±0.95 |
0.298 |
Refractive
power at 6mo (D) |
-3.10±0.98 |
-2.95±0.92 |
0.363 |
Refractive
power at 9mo (D) |
-3.14±0.99 |
-3.05±0.94 |
0.536 |
Refractive
power at 1a (D) |
-3.24±0.98 |
-3.15±0.95 |
0.638 |
Difference
of refractive power at
1a (D) |
0.47±0.40 |
0.43±0.34 |
0.461 |
Baseline
axis oculi (mm) |
25.62±0.86 |
25.32±0.96 |
0.071 |
Axis oculi
at 1a (mm) |
25.73±0.87 |
25.47±0.92 |
0.108 |
Difference
of axis oculi |
0.11±0.13 |
0.15±0.26 |
0.332 |
Independent-samples t-test.
Contrast Sensitivity Baseline contrast sensitivity with and
without glare under bright conditions was measured in patients of the test
group (60 eyes) and control group (60 eyes) wearing different glasses (Table
5). The contrast sensitivities at medium and low-frequency grating (visual
targets of 6.3°, 4.0°, and 2.5°) in the presence of glare were significantly
higher in the test group compared with those in the control group (P<0.05),
while the contrast sensitivity at low-frequency grating (visual targets of 6.3°
and 4.0°) in the absence of glare in the test group was also higher than in the
control group (independent-samples t-test, P<0.05). Meanwhile, there were no
differences in contrast sensitivities at each frequency grating under glare
dark as well as non-glare dark conditions between the two groups (Table 6;
independent-samples t-test, P>0.05).
Table 5 Contrast sensitivity and
glare contrast sensitivity under bright conditions between the two groups mean±SD
Visual
target |
Glare |
No glare |
||||
group |
Test group |
Control
group |
P |
Test group |
Control
group |
P |
6.3° |
1.89±0.12 |
1.84±0.17 |
0.031a |
1.97±0.07 |
1.92±0.14 |
0.025a |
4.0° |
1.89±0.12 |
1.83±0.17 |
0.042a |
1.92±0.02 |
1.87±0.16 |
0.048a |
2.5° |
1.79±0.19 |
1.72±0.20 |
0.046a |
1.82±0.19 |
1.83±0.16 |
0.906 |
1.6° |
1.50±0.26 |
1.47±0.17 |
0.501 |
1.64±0.17 |
1.67±0.19 |
0.340 |
1.0° |
1.25±0.15 |
1.27±0.26 |
0.565 |
1.39±0.21 |
1.32±0.21 |
0.095 |
0.7° |
0.89±0.29 |
0.84±0.31 |
0.399 |
0.89±0.26 |
0.86±0.19 |
0.365 |
aP<0.05. Independent-samples
t-test.
Table 6 Comparison of contrast
sensitivity and glare contrast sensitivity under dark condition between the two
groups mean±SD
Visual
target |
Glare |
No glare |
||||
group |
Test group |
Control
group |
P |
Test group |
Control
group |
P |
6.3° |
1.77±0.12 |
1.72±0.17 |
0.061 |
1.76±0.12 |
1.72±0.15 |
0.099 |
4.0° |
1.79±0.12 |
1.77±0.15 |
0.585 |
1.74±0.15 |
1.78±0.13 |
0.110 |
2.5° |
1.64±0.21 |
1.65±0.21 |
0.717 |
1.59±0.21 |
1.60±0.15 |
0.825 |
1.6° |
1.36±0.17 |
1.36±0.26 |
0.855 |
1.57±0.61 |
1.60±0.19 |
0.340 |
1.0° |
1.13±0.15 |
1.16±0.26 |
0.435 |
1.15±0.21 |
1.22±0.21 |
0.081 |
0.7° |
0.80±0.18 |
0.83±0.25 |
0.530 |
0.56±0.31 |
0.61±0.29 |
0.386 |
Independent-samples t-test.
Amplitude of Accommodation,
Accommodative Lag, and Accommodative Sensitivity There no differences in baseline
amplitude of accommodation, accommodative lag, and accommodative sensitivity between
the two groups (P=0.523, 0.701, and 0.080, respectively). In the test group,
after wearing the glasses for 6mo, the amplitude of accommodation was
significantly improved (P=0.001), accommodative lag was significantly decreased
(P=0.027), and accommodative sensitivities of both eyes were significantly
improved (P=0.034) compared with baseline. In the control group, the amplitude
of accommodation, accommodative lag, and accommodative sensitivity at 6 and
12mo after wearing glasses did not show significant differences compared with
baseline values (P>0.05). Six months after wearing glasses, the amplitude of
accommodation was significantly increased in the test group compared with the
control group (P=0.025), while accommodative lag and accommodative sensitivity
did not show significant differences between the two groups (P=0.216 and 0.154,
respectively). After wearing the glasses for 12mo, the amplitude of
accommodation was significantly increased (P=0.008) and the accommodative lag
was decreased (P=0.046) in the test group compared with the control group,
while the accommodative sensitivity did not show significant differences
between the two groups (P=0.448) (Table 7).
Table 7 Comparison of amplitude
of accommodation before and after wearing glasses in the two groups
mean±SD
Parameters |
Baseline |
Glasses
for 6mo |
P
(baseline vs after 6mo
of wearing
glasses) |
Glasses
for 12mo |
P
(baseline vs glasses for 12mo) |
Amplitude
of accommodation in test group (D) |
12.17±1.10 |
12.53±1.13 |
0.001a |
12.58±1.14 |
0.001a |
Amplitude
of accommodation in control group (D) |
12.05±0.87 |
12.10±0.95 |
0.370 |
12.07±0.95 |
0.709 |
P (test
group vs control group) |
0.523 |
0.025a |
|
0.008a |
|
Accommodative
lag in test group (D) |
0.45±0.23 |
0.39±0.25 |
0.027a |
0.37±0.46 |
0.006a |
Accommodative
lag in control group (D) |
0.46±0.25 |
0.45±0.26 |
0.582 |
0.46±0.22 |
0.748 |
P (test
group vs control group) |
0.701 |
0.216 |
|
0.046a |
|
Accommodative
sensitivity in test group (C/M) |
10.42±1.11 |
10.53±1.03 |
0.034a |
10.68±1.10 |
0.001a |
Accommodative
sensitivity in control group (C/M) |
10.78±1.17 |
10.82±1.13 |
0.532 |
10.83±1.08 |
0.659 |
P (test
group vs control group) |
0.080 |
0.154 |
|
0.448 |
|
aP<0.05. Independent-samples
t-test, paired t-test.
Asthenopia Grading All the patients underwent asthenopia
grading at baseline, as well as at 6 and 12mo after wearing glasses (Table 8).
At baseline, there were no differences in asthenopia grading between the two
groups (P=0.816). After wearing glasses for 6mo, the asthenopia grading in the
test group was significantly decreased compared with the control group
(P=0.024). Glasses significantly reduced the asthenopia grade in the test group
(P=0.016), while the difference in asthenopia grade before and after wearing
glasses was not significantly different in the control group (P=0.725).
Similarly, asthenopia grading was significantly decreased after wearing glasses
for 12mo in the test group compared with the control group (P=0.013). Glasses
significantly reduced asthenopia grade in the test group (P=0.01), while the
difference before and after wearing glasses was not significant in the control
group (P=0.596).
Table 8 Comparison of asthenopia
grading before and after wearing glasses between the two groups
mean±SD
Groups |
Baseline |
Glasses
for 6mo |
P
(baseline vs glasses
for 6mo) |
Glasses
for 12mo |
P
(baseline vs glasses
for 12mo) |
Test group |
10.23±1.55 |
9.10±2.11 |
0.016a |
8.80±1.79 |
0.01a |
Control
group |
10.13±1.76 |
10.03±1.77 |
0.725 |
9.97±1.73 |
0.596 |
P (test
group vs control group) |
0.816 |
0.024a |
|
0.013a |
|
aP<0.05. Independent samples
t-test, paired t-test.
Adverse Reactions At the end of the experiment, patients in
both groups filled out an adverse reaction questionnaire (Table 9). The results
showed that one patient in the test group occasionally manifested
dyschromatopsia (1 point) and another patient occasionally showed night vision
disorder (1 point), with a 6% constituent ratio of adverse reactions.
Meanwhile, in the control group, one patient occasionally manifested headache
(1 point), with a 3% constituent ratio of adverse reactions. There were no
differences between the two groups for the frequency of adverse reactions (χ2=
0.351, P=0.554).
Table 9 Comparison of constituent
ratios of adverse reactions between the test and control groups after wearing
glasses for 1y
Groups |
Headache |
Dizziness |
Nausea |
Sleep
disorder |
Night
vision disorder |
Growth and
development disorder |
Dyschromatopsia |
Constituent
ratio of adverse reactions |
Test group |
0 |
0 |
0 |
0 |
1 |
0 |
1 |
6% |
Control
group |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
3% |
P |
|
|
|
|
|
|
|
0.554 |
Chi-square test.
Foulds et al[5]
found that chicks with myopia caused by red light exposure progressed to
hyperopia after transfer to short-wavelength light, which indicated that blue
light affected the refractive development but also reversed the existing myopia
in an animal model. In addition, Jiang et al[6] found that
blue light interfered with the progression of optical defocused myopia in
guinea pigs, with thickened choroid membranes. Nevertheless, the impact of
blue-light filter on refractive development in juveniles has not been
investigated in clinical trials. The present study strongly suggests that
juveniles wearing glasses for 1y showed no significant differences in
refractive power and axial length between the test group wearing blue-violet
light filtering lenses and the control group wearing ordinary aspheric lenses.
Although short-wavelength filtering lenses improve accommodative function and
visual quality, they promoted defocused myopia, resulting in an insignificant
effect on myopia progression.
In order to investigate the
differences in contrast sensitivity between the blue-violet light filtering
lenses and ordinary lenses under bright and dark conditions, we simulated
night-time driving under glare. Glare testing has been widely used to detect
visual quality. In this experiment, contrast sensitivities with and without
glare were measured under bright and dark conditions. The results revealed that
the contrast sensitivities at medium- and low-frequency conditions of
brightness and glare in patients wearing short-wavelength filtering lenses were
significantly increased (P<0.05). Yap[7] studied the
change in contrast sensitivity after wearing yellow filter, and found that
yellow light filter significantly increased the sensitivity in normal
individuals in medium- and low-spatial frequency. Yuan et al[8]
and Niwa et al[9] investigated implantation of blue
light-filtering intraocular lens made of polymethylmethacrylate (PMMA) after
cataract surgery, and found that it was significantly better than the
non-blue-light filtering intraocular lens in terms of spatial contrast
sensitivity at medium and low frequencies, which was consistent with the
present study. Thus, under normal light and glare conditions, wearing
short-wavelength filtering lenses improves the medium- and low-frequency
contrast sensitivity, resulting in improved visual quality.
This study demonstrated that
under glare dark and non-glare dark conditions, the contrast sensitivities at
each frequency grating did not show significant differences between the test
(60 eyes) and control (60 eyes) groups (P>0.05). Night vision sensitivity
depends on the number of photons absorbed by the rhodopsin pigment in rod
cells. This absorption depends on wavelength and peaks at about 498 nm. With
age, the number of rod cells may be reduced by 30%[10],
leading to decreased night vision sensitivity[11]. Wirtitsch
et al[12] found that under 500, 5, and 0.5 lx brightness,
the blue-light filtering intraocular lenses decreased the visual contrast
compared with transparent intraocular lenses, and the difference was
significant under low brightness. Mester et al[13] conducted
a 12-month follow-up of patients implanted with blue-light filtering
intraocular lenses, and found decreased blue color vision under dark
conditions. In the present study, there were no significant differences between
the test and control groups for contrast sensitivities with gratings of
different frequencies under glare dark and non-glare dark conditions,
indicating that the medium- and low-frequency contrast sensitivity of the
short-wavelength filtering lenses did not display a significant advantage
compared with the ordinary aspheric lenses under dark condition. Nevertheless,
a previous study showed that contrast sensitivity was not significantly
decreased at different frequencies using blue-light filtering intraocular
lenses[14], but these subjects were elderly people with
decreased dark contrast sensitivity, while the subjects in the present study
were juveniles wearing glasses that filtered less blue-light compared with
intraocular lenses, resulting in insignificantly decreased contrast sensitivity
under dark condition.
Accommodation is one of the
important functions of eyes[15]. It facilitates clear focus
of objects at different distances on the retina by normal eyes corrected for
refractive error by changing the refractive state of the eyes. Parameters
reflecting accommodation include accommodative amplitude, lag value, and
sensitivity[16]. A few studies reported that subjective
symptoms of near vision discomfort were associated with various accommodative
parameters: a smaller accommodation of amplitude, worse accommodative
sensitivity, and smaller accommodative lag value suggest significant subjective
visual fatigue[17-18]. This study
revealed that wearing short-wavelength filtering lenses for 6mo increased the
accommodation of amplitude significantly, decreased the accommodation of lagged
value, and increased the accommodation of sensitivity in patients, which
significantly alleviated the onset of asthenopia. Therefore, asthenopia and the
total asthenopia score were significantly reduced in the group of patients
wearing short-wavelength filtering lenses for 6 and 12mo. On the other hand, in
the control group, the accommodation amplitude, lag values, and sensitivity
after wearing glasses for 6 and 12mo did not show significant differences
compared with baseline (P>0.05). The total asthenopia score was not changed
significantly. After wearing glasses for 6 and 12mo, accommodations of
amplitude were significantly increased in the test group compared with the
control group. Compared with the control group, accommodations of lag value in
the test group did not show significant difference after wearing glasses for
6mo, while it was significantly decreased after for 12mo. Furthermore, compared
with the control group, accommodation of sensitivity in the test group did not
show significant differences after wearing glasses for 6 and 12mo. This effect
might be attributed to the remarkable improvement in the accommodation of
amplitude in the test group, while the accommodations of lag value and
sensitivity showed greater differences at baseline between the two groups, and
were not improved significantly in the test group after wearing glasses, which
led to non-significant differences between the two groups. A previous study
revealed that yellow light stimulates the large cell system of the lateral
geniculate body as well as increases its activity[19]. It
improves the stability of the eyes, as well as the sensitivity of movement,
convergence, accommodation, reading abilities and other large cell functions,
and ultimately improves reading performance, which undoubtedly alleviates
visual stress and fatigue in juveniles engaged in long periods of reading. Ray
et al[20] studied dyslexia in children manifesting as
convergence and dys-adaptation, and found that the sensitivity of movement,
convergence, accommodation, reading ability and other large cell functions were
improved in children after wearing yellow light filter for 3mo, which was
associated with short- and long-term effects. In the present study,
accommodative function was improved in both eyes in the test group, and
asthenopia and reading stress were reduced, which is supported by Ray et al[20].
Since blue light filters may
alter the perception and discrimination to graphics and color, night vision,
and human circadian rhythm, an adverse reaction questionnaire was administered
to the subjects, and the results showed that there were no differences between
the two groups. Augustin[21] reviewed the impact of
blue-light filter on night vision, contrast vision, color vision, and circadian
rhythm and found that blue-filtering intraocular lens had no effect on these
parameters. In the present study, the patients in the test group did not show
severely decreased visual acuity, dyschromatopsia, dyscoimesis, or other
adverse reactions.
Finally, the present study showed
that short-wavelength-filtering lenses (blue/violet light filters) improved
medium- and low-frequency contrast sensitivity by optimizing ambient light into
the eyes, resulting in a better retinal image quality compared with ordinary
glasses. Furthermore, the short-wavelength-filtering lenses removed
glare-related light components from the natural light, resulting in a soft and
comfortable vision. It also improved the accommodative function of the eyes,
and alleviated asthenopia. In this experiment, patients in the test group did
not manifest severe decline in nocturnal visual acuity, dyschromatopsia,
dyscoimesis, or other adverse reactions.
Compared with ordinary aspheric
lens, short-wavelength-filtering lenses did not show significant advantages in
refractive power and axial length, possibly because of the short-term follow-up
and small sample size. Furthermore, no design data related to adverse reactions
were available. Thus, additional classification and analysis of adverse
reactions are needed. In addition, due to obvious differences in the lens
between the two groups, blinding was not possible. We hope to address this
limitation by improving lens technology in the future. Finally, the
questionnaire about adverse effects was subjective and a more reliable tool is
needed.
Foundation: Supported
by Projects of Medical and Health Technology Development Program in Zhejiang
Province (No.2011KYA020).
Conflicts of Interest: Zhao HL,
None; Jiang J, None; Yu J, None; Xu HM, None.
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