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Taiwan Journal of Ophthalmology 4 (2014) 129e132
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Original article
White-to-white corneal diameter of full-term Nigerian newborns
Victoria Ayodeji Olatunji a, *, Dupe Ademola-Popoola a, b, Feyi Grace Adepoju a, b,
Omotayo Olukemi Adesiyun c, d
a
Department of Ophthalmology, University of Ilorin Teaching Hospital, Ilorin, Kwara State, Nigeria
Department of Ophthalmology, University of Ilorin, Ilorin, Kwara State, Nigeria
c
Department of Paediatrics and Child Health, University of Ilorin Teaching Hospital, Ilorin, Kwara State, Nigeria
d
Department of Paediatrics and Child Health, University of Ilorin, Ilorin, Kwara State, Nigeria
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 April 2014
Received in revised form
16 May 2014
Accepted 19 May 2014
Available online 1 August 2014
Background: Measurement of corneal diameter (CD) in children is pertinent in the diagnosis and
monitoring of some ocular diseases, especially anterior segment anomalies and congenital glaucoma.
Data on normal values of CD in African children are scarce, and Caucasian values are mostly referred to.
The aim of this study was to determine the normative values of CD in full-term newborns and to assess
its relationship with some birth parameters.
Methods: Horizontal and vertical CDs were measured in 1000 eyes of 500 consecutive normal full-term
babies within their 1st week of life using calipers in a cross-sectional study. The relationship between CD
and different variables was assessed using multiple linear regression.
Results: A total of 254 (50.8%) male and 246 (49.2%) female babies were involved in the study. The values
(mean ± standard deviation) of horizontal and vertical CD were 9.87 ± 0.04 mm (range 9.00e10.75 mm)
and 9.62 ± 0.41 mm (range 8.75e10.75 mm), respectively. There was no statistically significant difference
between the mean horizontal CD for the right and left eyes (p ¼ 0.39). The mean horizontal CD in males
were not significantly different from that in females (p ¼ 0.21). The 95% range for horizontal CD
(mean ± 2 standard deviations) was 9.06e10.66 mm. Birth weight showed a positive correlation with CD
(r ¼ 0.59, p < 0.001).
Conclusion: From the results of this study, normative values of CD in full-term Nigerian newborns have
been established. This will enhance the ophthalmic care of newborns in Nigeria and Africa as a whole.
Copyright © 2014, The Ophthalmologic Society of Taiwan. Published by Elsevier Taiwan LLC. All rights
reserved.
Keywords:
birth weight
corneal diameter
first week
newborn
1. Introduction
Corneal diameter (CD) is an essential clinical diagnostic and
monitoring tool in the practice of ophthalmology and more
importantly in its pediatric subspecialty. Its measurement has also
been found useful in cataract, with refractive surgery being
particularly important when implanting intraocular lens and estimating anterior chamber width and ciliary sulcus size.1,2 Measurement of CD is particularly relevant in pediatric ophthalmology
because deviations from normal values play an important role in
the diagnosis of ophthalmic conditions such as relative anterior
Conflicts of interest: The authors declare that they have no conflicts of interest.
* Corresponding author. Department of Ophthalmology, University of Ilorin
Teaching Hospital, Private Mail Bag 1515, Ilorin, Kwara State, Nigeria.
E-mail address: [email protected] (V.A. Olatunji).
microphthalmos, corneal dystrophies, microcornea, and congenital
glaucoma.
Early diagnosis and appropriate intervention may be sight saving
in some causes of childhood blindness, one of which is congenital
glaucoma. CD value is usually greater than normal in eyes with
congenital glaucoma, and it is a sensitive parameter in diagnosis and
monitoring of such patients who sometimes present with haziness
of the cornea.3 However, neonates may sometimes be born with a
cloudy cornea in the absence of glaucoma, and determining the
diameter of the cornea in such cases may be crucial to diagnosis
because a corneal haze is present in other diseases such as sclerocornea and congenital hereditary endothelial dystrophy.4
At present, the frequently used reference values for Nigerian and
African children as a whole are often those obtained from studies of
Caucasian children even when racial variation has been reported in
general and ocular biometric parameters.5,6 The present study was
therefore designed to determine the normal values of CDs in
http://dx.doi.org/10.1016/j.tjo.2014.05.008
2211-5056/Copyright © 2014, The Ophthalmologic Society of Taiwan. Published by Elsevier Taiwan LLC. All rights reserved.
130
V.A. Olatunji et al. / Taiwan Journal of Ophthalmology 4 (2014) 129e132
2. Methods
determined using Student t test. To analyze the association between birth parameters and CD, Pearson's correlation coefficients
were calculated. For simple and multiple linear regression analyses,
p < 0.05 was considered statistically significant.
2.1. Patients
3. Results
This was a cross-sectional study. We included healthy full-term
newborns (37e42 weeks of gestation) delivered between August
2011 and October 2011 in a teaching hospital in the north central
geopolitical zone of Nigeria. The University of Ilorin Teaching
Hospital is a tertiary health center that also offers secondary health
care to all socioeconomic classes in its catchment areas. All fullterm babies born in the hospital within the study period constituted the study population. A total of 500 consecutive babies of
consenting mothers were recruited into the study. Babies with any
congenital anomalies (ocular or nonocular) or uncertain gestational
age were excluded, as were babies of mothers with antenatal
conditions likely to cause intrauterine growth retardation, products
of multiple pregnancy, and those with stillbirth. General examination was conducted by a pediatrician who certified them healthy
and excluded any congenital abnormalities prior to enrollment into
the study.
Ethical approval was obtained from the Ethical Review Committee of the hospital, and informed oral consent was taken from all
mothers. Anthropometric measurements (birth weight, head
circumference, baby length) were taken by trained staff within the
1st hour of life. Postnatal age and sex were also recorded. Gestational age was estimated from the last menstrual period and
recorded in days.
3.1. Neonatal characteristics
Nigerian newborns and possible relationship with some birth
parameters.
2.2. Methods
CDs were measured by one of the authors (VAO, an ophthalmologist) within the 1st week of life while the infants were still on
the postnatal wards. Babies were placed in the supine position on
the examination couch, and the anterior segments of both eyes
were examined with a pen torch. A local anesthetic drop was
instilled into the eyes before a pediatric lid speculum was gently
applied to expose the limbus for proper measurement of the whiteto-white CD. A caliper was then used to measure the white-towhite vertical and horizontal CDs with the examiner standing at
the head end of the couch. Vertical diameter was measured from 12
o'clock to 6 o'clock limbus, whereas horizontal diameter was
measured from 3 o'clock to 9 o'clock limbus. Three readings
were taken of each eye, and an average of the readings was taken as
the CD.
Out of the 500 babies examined, there were 254 (50.8%) males
and 246 (49.2%) females, with a male/female ratio of 1:1. As shown
in Table 1, the gestational ages ranged from 259 days to 294 days
with a mean of 271.3 ± 10.8 days, and birth weight ranged from
2.2 kg to 4.5 kg with a mean of 3.06 ± 0.4 kg. Other birth parameters
are summarized in Table 1. There was no significant sex difference
in these parameters.
3.2. CD
Modal and median values for both vertical and horizontal CD in
both eyes were similar (Table 2). In males, the right mean vertical
diameter was 9.59 ± 0.40 mm and 9.60 ± 0.43 mm in the left, and
the right mean horizontal diameter was 9.84 ± 0.42 mm and
9.79 ± 0.44 mm in the left. Female newborns had a mean vertical
diameter of 9.60 ± 0.35 mm in the right and 9.62 ± 0.43 mm in the
left, whereas the right horizontal diameter was 9.89 ± 0.38 mm and
the left horizontal diameter was 9.88 ± 0.39 mm (Table 3). There
was no significant sex difference in the mean values of vertical or
horizontal CD as shown in Table 3. Differences in laterality of the
horizontal diameter also proved nonsignificant (p ¼ 0.39). Figs. 1
and 2 depict the distribution of horizontal CD in both eyes. The
95% range (mean ± 2SD) for horizontal CD using the mean value of
the left eyes was 9.06e10.66 mm. Based on this, 0.8% of the sample
had macrocornea and 9.6% had microcornea.
3.3. Birth parameters and CD
Table 4 shows the relationship between birth weight and CD. CD
was positively correlated with birth weight (r ¼ 0.59, p < 0.001). By
contrast, there were no significant associations with birth length,
sex, postnatal age, and head circumference. A multiple regression
model was generated, including birth weight, sex, postnatal age,
gestational age, length, and head circumference. In this model, it
was exhibited that birth weight was the strongest independent
predictor of CD (Table 5). The model showed that a 1-kg increase in
birth weight is associated with at least a 0.36- and 0.41-mm increase in vertical and horizontal CD, respectively (Table 5).
2.3. Statistical analysis
4. Discussion
Analysis of data was performed with SPSS version 16 (SPSS Inc.,
Chicago, IL, USA). Mean, standard deviation (SD), median, and range
were calculated. Differences between data sample means were
Our study aims at providing normative data on the CD among
newborn Nigerian children. To the best of our knowledge, this
Table 1
Birth parameters.
Number
Mean ± SD (range)
Postnatal age (h)
Gestational age (d)
Birth weight (kg)
Length (cm)
Head circumference (cm)
SD ¼ standard deviation.
Total
Males
Females
500
254 (50.8%)
246 (49.2%)
47.1 ± 4.9 (1.0e156.0)
271.3 ± 10.8 (259.0e294.0)
3.06 ± 0.4 (2.2e4.5)
50.7 ± 6.1 (42.0e62.0)
34.1 ± 1.8 (31.0e38.0)
52.7 ± 4.9 (1.0e156.0)
271.3 ± 10.9 (259.0e294.0)
2.98 ± 0.4 (2.2e4.0)
51.2 ± 5.9 (42.0e62.0)
34.4 ± 1.9 (31.0e38.0)
42.6 ± 4.7 (1.0e156.0)
270.8 ± 10.6 (259.0e294.0)
3.12 ± 0.5 (2.3e4.5)
50.2 ± 6.2 44.0e62.0)
34.2 ± 1.6 (31.0e38.0)
p
0.06
0.35
0.07
0.06
0.96
V.A. Olatunji et al. / Taiwan Journal of Ophthalmology 4 (2014) 129e132
131
Table 2
Vertical and horizontal corneal diameter (CD) in newborns.
Right eye (n ¼ 500)
Mode
Median
Mean
SD
Range
Left eye (n ¼ 500)
Vertical CD
Horizontal CD
Vertical CD
Horizontal CD
9.50
9.50
9.59
0.38
8.75e10.50
10.00
10.00
9.87
0.40
9.00e10.50
9.50
9.50
9.62
0.41
8.75e10.75
10.00
10.00
9.86
0.40
9.00e10.75
SD ¼ standard deviation.
Table 3
Vertical and horizontal corneal diameter (CD) by sex.
Right eye (n ¼ 500)
Male
(n ¼ 254)
Vertical CD
Mean
9.59
SD
0.40
Range 9.00e10.50
Horizontal CD
Mean
9.84
SD
0.42
Range 9.00e10.50
Left eye (n ¼ 500)
Female
(n ¼ 246)
p
Male
(n ¼ 254)
Female
(n ¼ 246)
p
9.60
0.35
8.75e10.50
0.89
9.60
0.43
8.75e10.50
9.62
0.43
9.00e10.50
0.86
9.89
0.38
9.00e10.50
0.37
9.79
0.44
8.75e10.75
9.88
0.39
9.00e10.75
0.21
Fig. 2. Frequency distribution of left horizontal corneal diameter (HCDL; mm).
SD ¼ standard deviation.
study provides the largest sample size of published data on CD in
newborn Nigerians/Africans.
The horizontal CDs in Caucasians at birth are approximately
10 mm, with the fastest growth rate occurring in the first few
months of life and attaining adult size at ages 1e3 years.7,8 The
mean horizontal CD in the present study is 9.87 ± 0.40 mm. This is
comparable to the value of 9.98 mm reported by Lagreze and
Zobor9 using the photography method. There are previous reports
that a very strong correlation exists between measurements by the
photography method and caliper.9,10 However, unlike the use of
calipers, the photography method also has the advantage of being
simple to perform, not requiring the use of anesthetic agent, and
providing permanent records for monitoring purposes.10 The result
of this study also agrees with the mean horizontal diameter value of
10.0 ± 0.4 mm in Asian newborns11 and 9.6 mm as reported by
Kirwan et al12 also measuring with calipers.
However, our result is slightly different from that
(10.26 ± 0.59 mm) reported by a previous study13 in Southwestern
Nigeria, which recruited 64 termed babies and also used the caliper
method. This difference may probably be attributable to a wide
difference in our sample size and that of the study.
In the present study, the mean birth weight of female infants
was greater than that of males. Accordingly, the mean horizontal
CD was found to be slightly higher in female infants, although the
mean values in both sexes showed no significant difference. This
insignificant sex difference in CD observed in the current study is
consistent with previous reports.13,14 However, a study in Middle
East Asia indicated significantly larger CDs in the male sex.15 The
mean horizontal CD of the right eyes was similar to that of the left
eyes with no significant difference.
Micro- and macrocornea in the newborn in this study can be
defined as horizontal CD less than 9.06 mm and greater than
10.66 mm, respectively, based on the 95% range obtained in our
study. Using this definition, less than 1% (0.8%) had macrocornea
and 9.6% had microcornea in this study. Furthermore, birth weight
was found to be positively correlated with CD in the 1st week of life.
This is in consonance with a previous study.16
Different methods have been described in the literature as
regards the measurement of CD. These include the use of manual
calipers, millimeter rule, slit lamp attachment, photographic measurement, orbscan II, IOL Master, EyeSys corneal analysis, and the
Table 4
Corneal diameter (CD) stratified by birth weight.
Birth weight
<2.5 kg
N
Mean
SD
Range
2.5e3.5 kg
N
Mean
SD
Range
>3.5 kg
N
Mean
SD
Range
Fig. 1. Frequency distribution of right horizontal corneal diameter (HCDR; mm).
Right eye
Left eye
Vertical CD
Horizontal CD
Vertical CD
Horizontal CD
24
9.00
0.26
8.75e9.50
24
9.08
0.19
9.00e9.50
24
8.96
0.10
8.75e9.00
24
9.04
0.10
9.00e9.25
416
9.60*
0.36
9.00e10.50
416
9.87*
0.37
9.00e10.50
416
9.62*
0.39
8.75e10.75
416
9.87*
0.37
9.00e10.75
60
9.80**
0.29
9.50e10.50
60
10.15**
0.20
10.00e10.50
60
9.88**
0.33
9.50e10.75
60
10.1**
0.26
9.50e10.50
N ¼ sample size; SD ¼ standard deviation.
*p < 0.05 compared with <2.5 kg group.
**p < 0.05 compared with <2.5 kg and 2.5e3.5 kg groups.
132
V.A. Olatunji et al. / Taiwan Journal of Ophthalmology 4 (2014) 129e132
Table 5
Multiple linear regression models of significant correlates of corneal diameter.
Determinant
Vertical corneal diameter
B (SE)
b
p<
Birth weight 0.36 (0.04)
0.39
0.0001
Model
p < 0.0001; adjusted R2 ¼ 0.33
summary
Horizontal corneal diameter
B (SE)
b
p<
0.41 (0.05)
0.43
0.0001
p < 0.0001; adjusted R2 ¼ 0.37
B ¼ unstandardized regression coefficient; b ¼ standardized regression coefficient;
SE ¼ standard error.
Galilei.10,17e19 CD was measured with the use of calipers in the
current study because it is readily available, easy to use, less technically challenging, and one of the most commonly used tools in
everyday practice. It is also more affordable in a developing economy such as Nigeria.
The strength of this study lies in the large sample size. However,
this study has several limitations. First, recall bias might have been
produced from the method of determining the gestational age by
confirming the last menstrual period from the mothers and introduced error in calculating the gestational age. Second, because the
majority (84%) of the babies belonged to one particular ethnicity,
the result may not be a true representation of the country, which is
composed of diverse ethnicities. Racial variation has been reported
in general and ocular biometric parameters.5,6
In conclusion, the mean horizontal CD in the 1st week of life as
found among Nigerian newborns was 9.87 ± 0.40 mm, whereas the
vertical CD was 9.62 ± 0.41 mm. There was no statistically significant difference in sex or laterality. There was no correlation between CD and sex, birth length, and head circumference. The
results also indicate that birth weight is a strong correlate of CD.
Acknowledgments
The authors are grateful to Dr L.A. Olatunji for statistical assistance as well as reviewing the manuscript and Mr Amos Salami for
assistance in data collection.
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