CENTRAL CORNEAL THICKNESS IN NEWBORNS AND CHILDREN
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A C T A O P H T H A L M O L O G I C A V O L . 5 4 1 9 7 6
T h e Department of Ophthalmology (Head: N . Ehlers)
and Department of Obstetrics and Gynaecology (Head: M . Ingerslev),
drhus Kommunehospital, University of Aarhus, Denmnrk
CENTRAL CORNEAL THICKNESS IN NEWBORNS AND CHILDREN
NlELS EHLERS, TORBEN SQRENSEN,
THORKILD BRAMSEN and ERIK HOLK POULSEN
Central corneal thickness was measured optically in premature and full- term babies, and in children. The thickness was found to dccrease from the values found in premature and full-term babies to those found in small children aged between 2-4 years. The thickness of the adult cornea is reached at the age of about 3 years. These findings are discussed with respect to the possible role of corneal thickness as a biometric parameter, to intraocular pressure measurement, and to corneal thickness steady state regulation.
Key words: biometry - corneal thickness - premature - newborn - children - intraocular pressure - hydration.
No age variation in central corneal thickness has been found in adults (van Bahr 1948; Lavergne & Kelecom 1962; Martolo & Baum 1968; Lowe 1969; Kruse Hansen 1971). This apparent stability of the thickness seems very interesting, as the thickness may prove to be an individual-specific measure, a biometric parameter. From this point of view the correlation of corneal thickness to other ocular dimensions was studied and it was found to be a relatively independent dimension (Ehlers, Kruse Hansen & Aasved 1975). The apparent stability of
Received April 14, 1976.
Niels Ehlers, Torben Ssrensen, Thorkild Brumsen and Erik Hoik Poulsen
the thickness is interesting when hydration and transparency control are con- sidered, as it suggests the existence of regulatory mechanisms.
Central corneal thickness is an important parameter in the determination of the intraocular pressure by applanation tonometry (Ehlers, Bramsen & Sperling 1975). Consequently, knowledge of corneal thickness in the small child would appear to be important in the diagnosis and control of buphthalmia.
In the literature no data on central corneal thickness in children could be found. It was therefore decided to study this aspect, and to include premature and full-term children. A change in thickness after birth might represent a further argument for the existence of regulating factors.
Material and Methods
The study comprised 61 children. There were 6 premature babies and 19 full-term babies, born at Fsdselsanstalten in Jylland. In these two groups corneal thickness and curvature of the mothers were also measured. Ten children aged from 2-4 years, 15 aged from 5-9 years and 11 aged from 10-14 years were also examined. These were mainly children of the hospital staff, all with a normal eye examination and re- fractions within & 2 D.
Central corneal thickness was measured optically with the Haag-Streit pachometer modified according to Mishima & Hedbys (1968) as previously described (Ehlers 1974). Horizontal corneal curvature was measured with a Haag-Streit keratometer. and thickness readings corrected according to this, using the correction table supplied by Haag-Streit. T h e small children were held in front of the slit-lamp and the kerato- meter by assistants.
Evaluation of the data was made according to the directions of Sokal & Rohlf (1969). Values are given as mean k standard error of mean, and significance tested by the t-test. Adult corneal thickness shows a frequency distribution which does not differ from the normal curve.
Central corneal thickness. The obtained data are shown in the Table I. The average thickness in the group of premature babies was 0.545 k 0.014 mm while in the group of full-term babies it was 0.541 & 0.006 mm. The difference between these two groups is not statistically significant. The three groups of children aged 2-4, 5-9, and 10-14 years respectively all showed an average thickness of 0.520 mm. The thickness in the group of full-term babies is signifi- cantly higher than in any of the other three groups of children ( P < 0.025, 0.01 and 0.025, respectively).
Corneal Thickness in Children
0 5 5 -
Table I . Central corneal thickness and curvature in newborns and children.
. . . . . . . . . *.: . 0 . . . 0 . 0 . . 0 . . . . . . . . .
Premature newborns 6 0.545 f 0.014 6.35 k 0.09 Mature newborns 19 0.541 ?L 0.006 7.11 k 0.07
Children 5- 9 years 15 0.520 f 0.005 7.81 f 0.09 Children 2- 4 years 10 0.520 k 0.007 7.73 k 0.09
Children 10-14 years I1 0.520 k 0.007 8.01 f 0.05
own groups and Adults data from literature N 0.52 N 7.8
The data apply to right eyes. Essentially similar values were found for left eyes.
Corneal curvature. The data appear from Table I. As expected the smaller eyes of the premature and full-term babies have a more curved cornea. Adult values are reached at about 3 years of age.
central corneal lhlckness mm
O 5 I 9
0 45 6 0 6 5 7 0 7 5 8 0
Fig. I Correlation between horizontal corneal radius and central corneal thickness in min.
There is a tendency towards decreasing thickness with increasing radius. ( r = -0.427, P < 0.01).
NicJlc Ehlers, Torbcn Ssrensen, Thorki ld h'ramsen and Erik I iolk Poulsen
mrn 60- central corneal thickness
0 5 5 -
central corneal thickness MOTHER
0 50 0 55 0 60 mrn
Fig. 2. Central corneal thickness (in mm) in mother and child. It is seen that the child has
the thicker cornea. There is a statistically significant correlation. (r = 0.611, P < 0.01).
Correlations. In adults no correlation was found between central corneal thick- ness and radius of curvature, although this correlation was evident in rabbits (Ehlers et al. 1975). The data obtained in the present study are shown in Fig. 1. The thickness tends to decrease with increasing radius. The correlation coeffi- cient is statistically significant (r = -0.427, P < 0.01).
In 17 cases of newborn children the corneal thickness of the child as well as that of the mother was measured. In this small group a significant correlation was found between thickness in child and mother (r = 0.611, P < 0.01). The data are shown in Fig. 2, from which it is also seen that the cornea was usually thicker in the child.
The possible correlation between thickness and weight was studied in all the 25 premature and full-term babies of the study. No significant correlation was found.
The central cornea in premature and full-term babies is thick but the adult level is reached within the first 2-4 years of life. The corneal curvature is greater
Corneal Thickness in Children
(smaller radius) at birth but also reaches the adult range within the first years of life. A parallel to the rabbit eye, where thickness increases with radius (Ehlers, Bramsen 8s Sperling 1975), is not found in this human material, rather the inverse correlation exists.
With regard to the applicability of the central corneal thickness as a bio- metric parameter, a t the present time it would seem that it is a dimension reached within the first 2-4 years and then maintained constant throughout life. This makes central corneal thickness a unique biometric dimension. How- ever, longitudinal studies are still not available. Possible seasonal, menstrual and diurnal variations will be discussed in another paper, but are not likely to affect the average values presented here. The significant correlation between the central corneal thickness in mother and child adds to the interest of this dimension. The genetic influence on thickness and the possible use of the thick- ness as a genetic marker will be considered in a future paper.
The decreasing thickness after birth may suggest that a hydration control becomes operative. Decreasing hydration during development is known from chickens, where it is possibly subjected to a hormonal control (Coulombre 8s Coulombre 1964; Masterson et al. 1975). The influence of evaporation is also a possibility. In this connection thickness or hydration studies in newborn rabbits or cats, where the eyes remain closed until after the first week, could be informative. A direct metabolic hydration control, would be supported by leptocurtosis of the frequency distribution curve, although the lack of this pro- perty, of course, does not prove the non-existence of regulating factors. U p to the present time our data has demonstrated a distribution which does not deviate from the normal curve. The study of the thickness of penetrating grafts (Ehlers 1974) showed that a minimum thickness was found after 3-6 months; later the thickness slowly rose to the normal level. This may be interpreted as a long-term regulation, possibly caused by the metabolism of the stroma.
Measurement of the intraocular pressure in the small child is important in the diagnosis of congenital glaucoma. Assuming that adult mechanical qualities exist in the child cornea, a correction due to thickness would be appropriate. In cases of buphthalmia, unless the thickness differs clearly from the normal, this correlation would amount to only a few mmHg and hardly be of practical importance. W e have only had occasion to study a few buphthalmic corneas, which showed thickness values within the normal range. I t is hoped in the future to extend these studies and to calibrate the applanation tonometer on eyes of still-born babies. This study, which still appears to be missing, will yield in- formation concerning the mec