Keywords
axial length - anterior chamber depth - lens thickness - normal Libyans
Introduction
The difference in refractive errors between people is due to the diversity in the
axial length (AL), the refractive power of the cornea, and the lens, in addition to
the anterior chamber depth (ACD) and lens thickness (LT).[1]
The AL and ACD are essential parameters needed for the calculation of the power of
the intraocular lens (biometry) and to define the refractive state of the eye before
cataract and refractive surgeries that had been advanced over previous years. These
eye parameters differ according to population due to race and genes variation.[2] The LT measurement is important in the study of myopia as well as in primary angle-closure
glaucoma.[3]
It is essential to know the normality of the ocular parameters in the healthy population,
in order to be able later to know what are the data that are out of normality. Currently,
we can assess these parameters by multiple noninvasive methods, very quickly and without
the need to use drugs.[4]
One of these noninvasive methods is the Aladdin that is a combination of a reflection-based
topographer and an optical biometer that can measure corneal curvature, AL, ACD, LT,
and intraocular lens calculation with a great accuracy.[5]
In spite of the importance of these eye parameters, there are not many studies on
this subject.[6] In Libya, although cataract and refractive surgeries are done on daily basis, there
is no information about these parameters in the literature; therefore, with the help
of a noninvasive method and without the use of drugs, this study aims to gain an idea
about the AL, ACD, and LT in normal Libyans.
Methods
A cross-sectional study was conducted at Benghazi teaching eye hospital in the period
between July 1 and August 31, 2021. The study involved 106 Libyans of both genders.
The participants were volunteering hospital's doctors, nurses, employees, and 4th
year medical students, in addition to patients attending the hospital specialty clinic
department with minor complaints like headache and minor refractive problem.
Medical history and ophthalmic history were taken from all participants. Complete
ophthalmic examination was done as best corrected visual acuity, slit-lamp examination
for both anterior and posterior segment (using +90D lens), and measurement of intraocular
pressure to rule out any eye pathology.
Inclusion Criteria
People aged 17 years and more having no ophthalmological diseases (cornea, lens, retina)
with no previous eye surgery, and people with refractive errors limited to ± 3.00D
sphere and less than 2.00D cylinder with decimal best corrected visual acuity of 1.0
were included in this study.
Exclusion Criteria
Diabetics, children less than 17 years of age, people with any ophthalmological disease
or having previous eye surgery or laser treatment were excluded.
Measurements
The Aladdin (Topcon, Tokyo, Japan), was used to measure the AL, ACD, and LT. Aladdin
machine was positioned carefully so that the examiner has a clear scene of the eye
with the presence of quality control image (green eye). The participant was asked
to fixate on a red target point then the examiner pressed the button of the joystick.
The AL, ACD, and LT measurements were obtained from only the right eye of all participants
by the same skilled ophthalmologist. A previous study confirmed the accuracy and reproducibility
of Aladdin.[5]
This study followed the rules of the Helsinki Declaration; it was approved by the
ethical committee of Benghazi teaching eye hospital and participants gave informed
consent after an explanation of the procedure was done for them.
Statistical Analysis
The Statistical Package for the Social Sciences (SPSS version 23.0; IBM Corporation,
Armonk, New York, United States) was used. Data were presented as mean ± standard
deviation and frequencies. Unpaired Student's t-test was used to test the differences
in the measured variables between gender. Analysis of variance (ANOVA) was used to
compare variables within age groups. A p-value ≤ 0.05 was considered statistically significant.
Results
[Table 1] shows gender of patients, their age, AL, ACD, and LT measures, participated in this
study. There were no significant statistical differences between male and female regarding
age distribution, AL, ACD, and LT measures using unpaired Student's t-test (p > 0.05).
Table 1
Mean gender analysis of age, axial length, anterior chamber depth, and lens thickness
|
Variable
|
Total
(n = 106)
|
Male
(n =50)
|
Female
(n = 56)
|
p-Value[a]
|
|
Age ± SD (y)
Range (y)
|
35.36 ± 13.35
17–75
|
33.64 ± 13.29
17–67
|
36.89 ± 13.34
19–75
|
0.77
|
|
Axial length ± SD (mm)
Range (mm)
|
23.79 ± 0.91
21.00–26.00
|
23.88 ± 1.04
21.00–26.00
|
23.72 ± 0.77
22.00–25.50
|
0.19
|
|
Anterior chamber depth (mm)
Range (mm)
|
2.96 ± 0.62
1.40–4.24
|
2.91 ± 0.68
1.40–4.24
|
3.01 ± 0.58
1.51–4.00
|
0.14
|
|
Lens thickness (mm)
Range (mm)
|
3.67 ± 0.62
2.11–5.00
|
3.69 ± 0.63
2.19–5.00
|
3.65 ± 0.62
2.11–5.00
|
0.85
|
Abbreviations: mm, millimeter; n, number of participants; SD, standard deviation.
a Differences between gender using unpaired Student's t-test.
[Table 2] shows descriptive statistics of ALs, ACD, and LT (mms) according to age groups.
ANOVA done on the mean differences in AL, ACD, and LT measures showed no significant
differences across the age groups.
Table 2
Descriptive statistics of axial lengths, anterior chamber depth, and lens thickness
(mms) according to age groups
|
Axial length (mm)[a]
|
Anterior chamber depth (mm)[b]
|
Lens thickness (mm)[c]
|
|
Age grouping years, (n)
|
Mean ± SD
|
Range
|
Mean ± SD
|
Range
|
Mean ± SD
|
Range
|
|
< 20 (10)
|
23.99 ± 0.51
|
23.07–25.00
|
3.12 ± 0.58
|
2.20–3.77
|
3.60 ± 0.39
|
3.11–4.11
|
|
21–40 (66)
|
23.83 ± 0.90
|
21.79–26.00
|
3.01 ± 0.65
|
1.40–4.24
|
3.67 ± 0.64
|
2.11–5.00
|
|
41–60 (24)
|
23.67 ± 0.69
|
22.03–24.77
|
2.77 ± 0.59
|
1.51–3.52
|
3.68 ± 0.69
|
2.59–5.00
|
|
>60 (6)
|
23.55 ± 2.01
|
21.00–25.50
|
2.83 ± 0.47
|
2.23–3.30
|
3.63 ± 0.59
|
3.06–4.37
|
|
Total (106)
|
23.79 ± 0.91
|
21.00–26.00
|
2.96 ± 0.62
|
1.40–4.24
|
3.67 ± 0.62
|
2.11–5.00
|
Abbreviations: ANOVA, analysis of variance; mm, millimeter; SD, standard deviation.
a ANOVA between age groups F = 0.46, df = 3.00, p = 0.70.
b ANOVA between age groups F = 1.18, df = 3.00, p = 0.32.
c ANOVA between age groups F = 0.06, df = 3.00, p = 0.98.
Discussion
This is the first published study done in Libya to obtain knowledge on the AL, ACD,
and LT in normal Libyans performed by the Aladdin optical biometer.
This study involved 106 normal Libyan participants, with a mean age of 35.36 ± 13.35
years; the mean AL in the total study population was 23.79 ± 0.91 mm; this was slightly
different from other studies from many countries that may be due to differences in
race, genes, and diversity in age between the studies.[7] However, our reported values fall near the midrange of these studies that range
between 22.96 and 24.7mm (see [Table 3)].
Table 3
Mean AL, ACD, and LT reported in previous studies compared to the present study
|
Author
|
Place
|
Mean age (y)
|
Age range (y)
|
Measurement technique
|
AL (mm)
|
ACD (mm)
|
LT (mm)
|
Lens status
|
|
Albashir and Saleem[8]
|
Sudan
|
62.86
|
18–107
|
Ascan ultrasonography
|
23.09
|
NR
|
NR
|
NR
|
|
Gessesse .et al[9]
|
Ethiopia
|
40.31
|
18–69
|
Compact touch AB Scan Biometer
|
22.96
|
2.91
|
4.29
|
Cataract+ clear lens
|
|
Abdelaziz and Mousa[10]
|
Egypt
|
57.4
|
43–75
|
IOL master
|
24.70
|
NR
|
NR
|
NR
|
|
Bamahfouz[11]
|
Saudi Arabia
|
58.1
|
14–103
|
IOL master
|
23.48
|
3.10
|
NR
|
Cataract
|
|
Hashemi et al[6]
|
Iran
|
50.9
|
40–64
|
LENSTAR/BioGraph
|
23.14
|
2.62
|
4.28
|
NR
|
|
Praveen et al[12]
|
India
|
52.48
|
25–71
|
Ascan ultrasonography
|
NR
|
NR
|
4.38
|
Clear
|
|
He et al[13]
|
China
|
64.4
|
> 50
|
Ascan ultrasonography
|
23.11
|
2.67
|
4.44
|
Cataract+ clear lens
|
|
Wong et al.[14]
|
Tanjong Pagar
|
NR
|
40–81
|
Ascan ultrasonography
|
23.23
|
2.90
|
4.75
|
Cataract+ clear lens
|
|
Palencia et al[15]
|
Colombia
|
27.59
|
8–56
|
Ascan ultrasonography
|
23.13
|
3.32
|
NR
|
NR
|
|
Lee et. al[16]
|
Beaver Dam (older Caucasian population
|
71.9
|
65–75
|
IOL master
|
23.69
|
3.11
|
NR
|
Cataract+ clear lens
|
|
Wojciechowski et al[17]
|
Eskimo
|
59.5
|
40–79
|
Ascan ultrasonography
|
23.70
|
2.96
|
4.74
|
Cataract+ clear lens
|
|
Mashige and Oduntan[18]
|
South Africa
|
28.15
|
10–66
|
Ascan ultrasonography
|
23.05
|
3.21
|
3.69
|
Clear
|
|
Mallen et al[19]
|
Jordan
|
NR
|
17–40
|
Ascan ultrasonography
|
23.13
|
3.19
|
3.85
|
Clear
|
|
Present study
|
Libya
|
35.36
|
17–75
|
Alladdin optical biometer
|
23.79
|
2.96
|
3.67
|
Clear lens
|
Abbreviations: mm, millimeter; AL, axial length; ACD, anterior chamber depth; IOL,
intraocular lens; LT, lens thickness; NR, not reported.
Although the AL for males was slightly more than females (23.88 ± 1.04 vs. 23.72 ± 0.77;
[Table 1]), this difference was statistically nonsignificant. It was also noticed that the
AL decreases nonsignificantly (p= 0.70) with aging in the total study population ([Table 2]); this observation goes well with some other studies that reported shorter AL with
older people.[14]
[17]
[20] Grosvenor explained the decrease in AL with aging by the tendency of the eye to
be emmetropic in order to counteract myopic shift caused by the increase in eye refractive
power.[20]
The mean ACD in our study is comparable with the studies from Ethiopia,[9] Alaskan Eskimos,[17] Tanjong Pagar[14] (see [Table 3]), but it is deeper than other studies done in Iran[6] and China.[13] The ACD shows decrease in size with aging in the total study population ([Table 2]) and a tendency to increase after 60 years of age (although number of participants
in this age group is small), a result that was explained previously by researchers
as a result of posterior rotation and atrophy of ciliary body by aging.[17]
The ACD unexpectedly was shallower in male participants than females (2.91 ± 0.68
vs 3.01 ± 0.58; [Table 1]), although this difference was not significant (p = 0.14); it is the opposite to many other studies. Hsu et al in their study found
that gender is not an associated factor with ACD; it was the age and body height.[21]
The mean LT in the present study is 3.67 ± 0.62 mm, which was similar to Mashige and
Oduntan study who reported a mean LT of 3.69 ± 0.25 mm in their study in South Africa;
although differently less than other studies, ([Table 3]), this difference could be explained based on that our study was done on younger
population with clear lens, while most other researchers work on older population
with cataractous lens. The males in the present study were having thicker lens than
females (3.69 ± 0.63 vs 3.65 ± 0.62 mm), a result that is similar to other researchers.[6]
[18]
We noticed that the LT increased with age up to 60 years old then it started to decrease;
this was statistically nonsignificant (p = 0.98; [Table 2]). We cannot rely on this decrease in thickness after 60 years of age because of
small number of participants in this age grouping (only six). It was reported by other
investigators that LT increases by age due to increase in the fibers formed inside
the lens.[6]
[17]
Limitation of the Study
This study was limited by the small number of subjects included, as well by the absence
of other information such as refractive errors, body height, and educational level
of participants, since other studies showed a significant association with these factors.[13]
[16]
[21]
Recommendation
A longitudinal study with larger number of participants is needed to confirm the present
study findings.
Conclusion
This study has shown that the AL, ACD, and LT in normal Libyans performed by the Aladdin
optical biometer was comparable with studies from other populations. Age and gender
differences have no effect on these parameters in Libyan patients.
