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

The Department of Ophthalmology (Head: N . Ehlers), Arhzis Kommunehosfiital, University of Aarhus, Denmark

FURTHER DATA ON BIOMETRIC CORRELATIONS OF CENTRAL CORNEAL THICKNESS

BY

NlELS EHLERS and FINN KRUSE HANSEN

Central corneal thickness measured in 126 young men aged from 18-21 years was correlated to a number of ocular and other parameters. The frequency distribution was skewed towards the lower end, but the deviation could not be statistically supported. No correlation between corneal thickness and birth weight was found. Other characteristics not correlated in this material to corneal thickness were corneal astigmatism, refraction, visual acuity, optic disc and retinal abnormalities, red-green colour vision defects, ABO and rhesus blood-groups, EEG abnormalities, chromosomal abnormalities, hearing defects, ear abnormalities and qua- lity of the hair. The findings in this study, although mainly of negative character, stress the relative independence of the central corneal thickness as a biometric parameter.

K e y zewrrls: biometry - corneal thickness - birth weight - blood-groups - astigmatism - refraction - ophthalmoscopy.

Since the development of good optical pachometers the biometric correlations of central corneal thickness (CCT) have been studied. No correlations have been found between CCT and depth of anterior chamber, lens thickness, length of vitreous body or axial length of the eyeball (Ehlers, Kruse Hansen & Aasved 1975). After a small but significant reduction during the first years of life (Ehlers, Sarensen, Bramsen & Poulsen 1976) the CCT has not been found

Received August 18, 1976.

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Bionietric Correlations of Central Corneal Thickness

to be correlated to age (Kruse Hansen 1971). In the study of Kruse Hansen ( 1 9 i l ) there was a tendency towards decreasing thickness with increasing body height, although this was not statistically significant.

The present report is concerned with data obtained on examining a number of young men, all prisoners at Msgelkxr, during the years 1969-71. Various data were available as the eye examination was part of a large socio-medical study, which will be presented in detail elsewhere.

Material and Methods

The study comprised 126 young men aged from 18-21 years, all prisoners at Msgelkier, a state-prison for young criminals. The series, therefore, cannot in all respects be considered as representative of young danish men. The 101 were included in the above- mentioned comprehensive socio-medical investigation performed in the period August 1969 -April 1971. Twentyfive were subjected to eye-examinations only, and were those already imprisoned at Msgelkier when the socio-medical study was started.

The eye-examination comprised determination of visual acuity, refraction, slit lamp biomicroscopy, ophthalmoscopy and campimetry 6/2000 white. The external eyes were inspected and the occurrence of squint was evaluated by the cover test. Central corneal thickness (CCT) was measured with a Haag-Streit pachometer and corneal curvatures and astigmatism by a Haag-Streit keratometer. Screening for red-green colour vision defects was made with the Ishihara plates.

As there is a strong right-left correlation for CCT, and additionally in this study a systematic difference between the two eyes, the left cornea being measured thicker, the numerical analysis presented below apply to right eyes only. Inspection of the figures for the left eyes, treated statistically in a similar manner revealed no new information.

Results

Central corneal thickness (CCT)

The average CTT was for right eyes 0.514 -t 0.0027 (mm ? SEM). The fre- quency distribution curve is shown in Fig. 1. The shape of the histogram might suggest some abnormal cases at the lower limit, but this cannot be supported statistically; the marginal items are at mean value minus 2 standard deviations, outside which some 2.5 O / O would be expected. Neither did the Kolmogorov- Smirnov test show any deviation from the normal curve.

Correlations of CCT

This part of the study comprised only the 101 subjects of the socio-medical study. The analysis was performed by cross-tabulating CCT against various

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Niels Elders and Finn Kruse Hansen

2000 2500 3000 3500 4000 4500 Birth weight grams

-2499 2999 3499 3999 4499 4999 >5000

Nuinbei

no inform. Total

Q Q Q Q Q

d 0 d

Corneal thickness

Fig. I . Frequency distribution for central corneal thickness in 126 young men.

Corneal thickness in mm.

Table 1. Central corneal thickness (CCT) and birth weight.

CCT

< 0.450 1 1 1 4 2 - - 3 12 0.480-0.499 - 1 2 3 1 - 1 2 10 0.500-0.539 l G 1 3 1 2 5 1 - 13 51 0.540-0.559 - 1 2 3 3 - - 4 13 > 0.560 - 2 4 3 - 1 - 3 13

2 no inform. - 1 - l - - - -

Total no. 2 12 22 26 11 2 1 25 101

111111

Data for right eyes

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Biometric Correlations of Central Corneal Thickness

Blood groups I A l B

properties, including all registered properties that might influence or be in- fluenced by the CTT.

Birth weight. Table I shows that there is no evident correlation between CCT and birth weight. This might have been expected as the cornea is thick at birth, and particularly thick in premature babies (Ehlers et al. 1976).

Ocrtlnr iiaranielers. Cross-tabulations revealed no correlation between CCT and astigmatism, refraction or visual acuity. Ophthalmoscopical abnormalities cf the optic disc, vessels or retina showed no correlation to CCT. Red-green colour vision defects were not correlated to CCT.

Othci chnrcictcristics. ABO and Rhesus blood-groups showed no correlation with CCT (Table 11). EEG-abnormalities were noted in 39 cases; no correlation to CCT could be demonstrated. Chromosomal abnormalities were found in 11 cases; normal thickness was found in cases characterized as 47XXY, 4iXY16GHL, 46XY9GH+, 46XYGP+. Six cases were 46XY,Q+, of these 3 had a normal CCT, while 3 showed a CCT below 0.48.

Hearing defects, ear abnormalities and quality of the hair (silky, normal, stiff) showed no correlation to CCT.

0 I AB

Discussion

In spite of the fact that most of the observations in this study are of a negative character, i. e. show no correlation to the CCT, it was found worth while to briefly present the results as part of our continued studies of corneal thickness.

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h'iels Ehlers and Finn Kruse Hansen

The average thickness conforms with previous findings (Kruse Hansen 1971 ; Ehlers et al. 1975). The frequency distribution although suggestive of a surplus of low values, did not differ from a normal distribution. The thickness distribu- tion has been studied in a group of 90 conscripts and in 146 recipients of kidney grafts. Deviation from a normal distribution could not be demonstrated, although in the latter group two maxima could be suggested (Ehlers et al. 1976).

A correlation between CCT and birth weight could have been expected when it is recalled that the newborn has a thicker cornea than children and adults. A particular thick cornea is found in premature babies. The lack of correlation suggests that general growth is not the factor determining the thickness change after birth, but rather that the thickness is controlled by more specific effects as previously discussed (Ehlers et al. 1976).

The correlations to the various ocular and other parameters were studied in a search for the characteristics of the CCT. The results have been negative, and as such hardly require further comment. It should, however, be stressed that the lack of correlation illustrates a relative independence of the CCT, which tends to make this an interesting and unique parameter.

Acknowledgments

Drs. Frode Henriksen and Ole Bentzen are thanked for the kind permission to use their data. The valuable statistical assistance of Mr. Th. Bjerre is acknowledged.

References

Ehlers N., Kruse Hansen F. & Aasved H. (1975) Biometric correlations of corneal thick-

Ehlers N., Ssrensen T., Bramsen T. & Poulsen E. H. (1976) Central corneal thickness

Ehlers N., Hansen H. E., Lowes M., Merllekasr K. & Skov P. E. (1976) Eye findings in

Kruse Hansen F. (1971) A clinical study of the normal human central corneal thickness.

ness. Acta ophthal. (Kbh.) 53, 652-659.

in newborns and children. Acta ophthal. (Kblz.) 54, 285-290.

recipients of renal allografts, in preparation.

Actn ofihtlial. (Kbh.) 49, 82-89.

Aiithor's address: Niels Ehlers, Department of Ophthalmology, Arhus Kommunehospital, University of Aarhus, DK-8000 Arhus C, Denmark.

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