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Keywords:

  • central corneal thickness;
  • infant cornea;
  • pachymetry;
  • ultrasonic pachymetry

Abstract.

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Subjects and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Purpose:  To establish a standard of normal central corneal thickness (CCT) in normal full-term Saudi newborn. These values could be used as a reference in the early diagnosis and control of the fairly common primary congenital glaucoma in Saudi newborns.

Methods:  The CCT was measured in 100 normal full-term Saudi newborns (200 eyes) during the first 6 days of the postnatal period. All measurements were carried out by one investigator using ultrasonic pachymeter DGH-1000.

Results:  The mean CCT of 200 eyes (right and left) was 616 ± 61 μm. The mean CCT of the right and left eyes was similar (CCTRE was 617 ± 62 μm, and mean CCTLE was 616 ± 60 μm), with no statistically significant difference (p = 0.417). The mean CCT for males was 631 ± 66 μm and for females 600 ± 50 μm. This difference was statistically significant (p = 0.01). The mean CCT decreases significantly by age [day-1: 626 ± 65 μm, day-2: 601 ± 48 μm and day-3: 574 ± 45 μm (p = 0.049)]. No correlations were found between CCT and gestational age, birth weight, birth length and head circumference.

Conclusion:  The average CCT in full-term Saudi newborns was found to be 616 ± 61 μm. The mean CCT in males was significantly higher than in females. There was no correlation between CCT and gestational age, birth weight, birth length and head circumference. There were borderline significant differences between CCT in 1-day-, 2-day-, and 3-day-old babies.


Introduction

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Subjects and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

The histological structure of the cornea changes during development from the embryonic stage to adult life. It is known that the five corneal layers undergo significant changes during embryonic development. The adult structure of the cornea is reached at about 6 months after birth (Lesueur et al. 1994).

Corneal thickness can be measured by optical methods of which the most commonly used method employs an attachment to the Haag–Streit Slit lamp biomicroscope developed by Maurice & Giardini (1951) and later modified by Mishima & Hedbys (1968). Nowadays, measurements of corneal thickness are easier, more reproducible and more accurate when using ultrasonic pachymeters [first developed by Kremer (1980) with the advent of radial keratotomy] (Rapuano 1993), computer-assisted laser pachymetry and laser Doppler interferometry (Gritz & McDonnell 1990; Hitzenberger et al. 1992; Rapuano et al. 1993). Gordon et al. (1990) found good reproducibility of ultrasonic central corneal thickness (CCT) measurements that also were found to be less variable and more reproducible by Higgins et al. (1993). Thus, knowing the normal value of the CCT in newborn babies can be used as a reference in the early diagnosis and control of corneal oedema in some ocular disease such as primary congenital glaucoma. Applanation tonometry in adults as well as in infants and newborns is significantly influenced by CCT (Autzen & Bjornstrom 1989; Uva et al. 2011). When the thickness is below or above normal, the applanation reading is lower or higher, respectively (Ehlers et al. 1975).

Previous studies have shown that the CCT in full-term newborns and premature infants is significantly thicker than in adults (Autzen & Bjornstrom 1989, 1991; DeSilva et al. 2011). Ultrasonic pachymetry did show that the CCT of premature babies decreases significantly to the same level previously reported in full-term newborns at 3 months of age (Autzen & Bjornstrom 1991; Kirwan et al. 2005).

In recent years, the infant corneas have been the subject of increasing scientific studies. Having high endothelial cell densities ensured successful use of these infant donor corneas for penetrating keratoplasty (Wood & Nissenkorn 1981). The mass culturing of the neonatal corneal endothelium was also an interesting achievement step (Insler et al. 1987).

Endothelial dysfunction results in a corneal swelling, and because all the collagen fibrils in the stroma are along the plane of the cornea and no fibrils are present running across the corneal lamellae, measurement of cornea thickness allows the degree of endothelial damage and its repair processes to be evaluated. Central corneal thickness was found to be significantly thinner in children with congenital glaucoma. This finding may be another confounding factor when measuring IOP in those patients. So pachymetry should be considered during the examination and follow-up of those diagnosed to be suspect or well-established cases of congenital glaucoma (Henriques et al. 2004; Wygnanski-Jaffe & Barequet 2006).

Aims

To measure the CCT in normal full-term Saudi newborns. Also to investigate whether there is correlation between CCT and gestational age, gender, birth weight, birth length and head circumference of the baby. Additionally to find out whether there are differences in CCT with respect to different eyes or in relation to the gender or age of the babies.

Subjects and Methods

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Subjects and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

The CCT was measured in 100 normal, full-term Saudi newborns (200 eyes) during the first 6 days of the postnatal period. The subjects were from the normal newborn nursery unit at King Fahad Hospital of the University – Al-Khobar, Saudi Arabia. The average gestational age ± SD was 39.5 ± 1.3 weeks (range: 36–42 weeks). Most of the babies were born by uncomplicated delivery (92%), caesarian section (5%), assisted breech (2%) and ventouse (1%). There were 46 girls and 54 boys. The mean birth weight was 3196 ± 458 g (range: 1990–4620 g). The mean birth length was 49 ± 2 cm (range: 44.5–53.5 cm). The mean head circumference was 34.1 ± 1.4 cm (range: 31–37.5 cm). The mean age of the babies was 21.4 ± 22 hr (range: 0.5–135 hr) (Table 1). Ultrasonic pachymeter DGH-1000 with sound velocity of 1630 m per second was used for the CCT measurements that were taken in the afternoon shift, at 1–3 pm in most cases, and all by the same examiner. All of the babies were receiving prophylactic gentamicin eye drops, four times a day in both eyes, and none of them had any sign of ocular disease. Benoxinate (BNX) minims 0.4% drops were used as topical anaesthetic prior to the application of the ultrasonic probe to the corneal surface. All measurements were taken with the babies in the supine position. The eyelids of the baby were held apart widely by thumb and index of the examiner, which also allowed closure of the eyelids in between measurements to preserve the normal wetting of the corneal surface. Several measurements were taken (about five measurements for each eye), and the lowest reading was chosen as the CCT. The right cornea was measured first. Isopropyl alcohol swab was used for sterilization of the ultrasonic probe tip before application to each eye. Other data about babies and their mothers were completed from the clinical files. All data were entered in to a personal IBM compatible computer. The mean and standard deviations were calculated and compared by paired t-test. The correlation between CCT and gestational age, gender, birth weight, birth length, head circumference and age of the babies was tested by analysis of variance (anova) together with post hoc using the least significant difference between means.

Table 1.   Descriptive for some characteristics of newborns.
 RangeMean ± SD
MinimumMaximum
Age (hr)0.513521.4 ± 22
CCTRE (μm)496823617 ± 62
CCTLE (μm)491808616 ± 60
Gestational age (weeks)364239.5 ± 1.3
Head circumference (cm)3137.534.1 ± 1.4
Length (cm)44.553.549 ± 1.9
Weight (gm)199046203196 ± 458

Ethical approval

The study was approved by the ethical committee of King Fahad Hospital of the University. Informed consent +/or verbal approval of the parent was obtained.

Results

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Subjects and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

The mean CCT of the 200 eyes was 616 ± 61 μm (range: 491–823 μm). The mean CCT of the right eyes (100 eyes) was 617 ± 62 μm (range: 496–823 μm). The CCT of the left eyes (100 eyes) was 616 ± 60 μm (range: 493–808 μm) (Table 2). Nine infants (18 eyes) had CCT ≥ 700 μm. All of them were aged ≤24 hrs. Only two infants (four eyes) had very high CCT (≥800 μm) values recorded, one of them was 2.5 hrs old while the second was 20 hrs old. There was no statistically significant difference between CCT of the right eyes and the left eyes (p = 0.417) (Table 3).

Table 2.   Age distribution in relation to central corneal thickness (CCT) in newborns.
AgeNo.Right eyesRangeNo.Left eyesRangeNo.Both eyes
Mean CCT ± SDMean CCT ± SDMean CCT ± SD
Group (hr)EyeμmμmEyeμmμmEyeμm
0–630648 ± 61545–82330648 ± 57555–80460647 ± 59
7–1210605 ± 48535–66910601 ± 42529–65020603 ± 44
13–242611 ± 73496–82126611 ± 73491–80852611 ± 72
25–4827600 ± 47498–82127601 ± 49503–68854601 ± 48
49–725572 ± 43515–6265576 ± 46519–62510574 ± 42
>722604 ± 37577–6302595 ± 50559–6304599 ± 37
Total100617 ± 62496–823100616 ± 60491–808200616 ± 61
Table 3.   Comparison of the mean central corneal thickness (CCT) between eyes, gender and age.
ItemNo. of eyesMean ± SDp-Value
Eye
 Right100617 ± 620.417
 Left100616 ± 60
Gender
 Male108631 ± 66<0.001
 Female92600 ± 50
Postnatal period
 1-day132626 ± 650.049
 2-days54601 ± 48
 3-days10574 ± 45

The mean CCT in males (54 newborns) was 631 ± 67 μm in RE and 630 ± 65 μm in LE. The mean CCT in females (46 newborns) was 601 ± 52 μm in RE and 559 ± 49 μm in LE. There was no statistically significant difference between the CCT of RE and LE in males (p = 0.855), or in females (p = 0.307). However, there was statistically significant difference between CCT in males and females (p < 0.001).

Using post hoc (LSD) method shows a borderline statistically differences between CCT in these different age groups (p = 0.049). But the difference was higher between 1-day and 2-day age groups (Table 3), or even higher between 1-day and 3-day age groups.

There was no correlation between CCT and gestational age (r = 0.004, p = 0.97), birth weight (r = 0.01, p = 0.89), birth length (r = −0.10, p = 0.32) and head circumference (r = 0.014, p = 0.89).

Discussion

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Subjects and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Corneal oedema (thickness) is a very sensitive parameter in early diagnosis and control of primary congenital glaucoma. As far as we know, there is no published data on corneal thickness in Saudi newborns. This information is very vital, recalling the fact that primary congenital glaucoma is quite common among Saudis (1 in 2500 births compared with 1 in 10 000 births in western societies) (Jaafar 1988).

In this study, the mean CCT in 200 eyes of 100 newborn was found to be 616 ± 61 μm with a range between 491 and 823 μm. This is higher than that found in several previous studies (Insler et al. 1987; Autzen & Bjornstrom 1989; Portellinha & Belfort 1991; Remon et al. 1992). The differences were statistically significant (Table 4). This finding suggests that the baseline normal CCT for Saudi newborns is higher than other ethnic groups. It is well established that the CCT is significantly thinner in children with congenital or childhood glaucomas (Henriques et al. 2004; Wygnanski-Jaffe & Barequet 2006). Attention should be paid to the CCT in the examination and follow-up of those suspected or well-established cases of childhood glaucomas for interpretation of intraocular pressure. This holds valid for both acute cases with or without corneal oedema as well as chronic ones.

Table 4.   Comparison between this study and other study results.
StudyCases No.PeriodRight eyeLeft eyeBoth eyes
Mean CCT ± SDNo.Mean CCT ± SDNo.Mean CCT ± SDNo.
  1. * Previous studies’ results are significantly differing from this study result (p < 0.001).

This study1006 days617 ± 62100616 ± 60100616 ± 61200
Insler et al. (1987)193 weeks568 ± 58*19570 ± 55*19
Autzen & Bjornstrom (1989)301 week581 ± 47*30
Portellinha & Belfort (1991)743 days573 ± 52*148
Remon et al. (1992)1526 days585 ± 52*132585 ± 52*132

There was no statistical difference between the CCT of the right eyes and the CCT of the left eyes in these different age groups. There was borderline statistically significant difference between the CCT in 1-day, 2-day and 3-day age groups (p = 0.049). Remon found significant differences between the corneal thickness of the 1-day-old group and that of the other age groups. Table 5 shows comparison between mean CCT in 1-day-, 2-day- and 3-day-old newborn babies in this study and that found by Remon et al. (1992). There was statistically significant difference between the two studies in 1-day and 2-day age groups but with no significant difference in 3-day age groups. Autzen & Bjornstrom (1989) found no correlation between the CCT and the age of the babies. The increase in corneal thickness in the 1-day-old group may have resulted from the fact that the eyes remain closed for a long time (Portellinha & Belfort 1991; Remon et al. 1992). The decreasing thickness after birth as observed by Ehlers (1976), Portellinha & Belfort (1991), Remon et al. (1992) and Kirwan et al. (2005) as well as in this study may suggest that the corneal hydration control becomes operative.

Table 5.   Comparison between the mean central corneal thickness (CCT) in 1-day-, 2-day- and 3-day-old newborn babies in this study and that by Remon et al.
 Mean CCT ± SD
1-day2-day3-day
This study626 ± 65 (132 eyes)600 ± 48 (54 eyes)574 ± 42 (10 eyes)
Remon’s study611 ± 58 (108 eyes)573 ± 60 (114 eyes)567 ± 36 (28 eyes)
 p = 0.045p < 0.05p > 0.05

The mean CCT of the right eyes was similar to that of the left eyes with no significant difference (p = 0.417). The mean CCT in male babies was significantly higher than that in female babies of comparable age [males were 20.6 (SD = 21.4) hours old, and females were 22.5 (SD = 23.6) hours old; p-value 0.651]. This is in contrast to the observation of Alsbirk (1978) who found that the CCT was higher in females. Several previous studies (Portellinha & Belfort 1991; Remon et al. 1992) showed similar result of no significant difference between the right and the left eyes but also no significant difference between male and female babies, which differ from our study. Autzen & Bjornstrom (1991) found that the CCT in premature babies decreased significantly by 12% in the first few months to 0.566 mm that is slightly less than that 0.581 mm previously reported in full-term newborns in the first postnatal week. (The difference between these two is not statistically significant.) Also they noted that no correlation could be demonstrated between CCT and gestational age, birth weight and length in premature babies.

Conclusion

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Subjects and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

The mean CCT in full-term Saudi newborns was found to be 616 ± 61 μm. The mean CCT in males was significantly higher than in females. There was no correlation between CCT and gestational age, birth weight, birth length and head circumference. There were borderline significant differences between CCT in 1-day-, 2-day- and 3-day-old babies.

References

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Subjects and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References