Neuroradiologg
Neuroradiology (1984) 26:419-420
© Springer-Verlag 1984
Originals Ocular volume measured by CT scans F. J. Hahn and Wei-Kom Chu University of Nebraska Medical Center, Department of Radiology, Omaha, Nebraska
Summary. Newer CT scans have greatly enhanced oculometric research and made it possible to measure ocular dimensions. With these measurements, ocular volume can be more accurately estimated to understand its relationship with age and sex. One hundred CT orbit scans with presumed normal eyes were used for the data base. The mean values and normal variations of ocular volumes at various ages in both sexes are presented. Rapid growth of the eyeball was noted during the first 24 months of age. It reached its peak between the ages of 18 and 30 years of age, after which there was a reduction. Results may be of help in recognizing eye abnormalities such as microophthalmus and macrophthalmia. Key words: CT - eye - ocular volume
The volume of an eyeball is subject to change during the entire span of life. Intraocular volumes (OV) have recently been calculated from profile photographs of the enucleated eyeball [1]. Standard reference of ocular volumes calculated from CT scans heretofore has been unavailable to us. Special techniques of later-generation CT scans have made it possible to record measurement of ocular dimensions with relative accuracy. Using the mean values of two linear dimensions (axial and coronal lengths), ocular volumes were calculated. The authors present a statistical base for the normal range of OV at various ages and in both sexes. It is hoped that this will help in the early detection of certain eye abnormalities such as microphthalmus and macrophthalmia.
All scans were considered to be of normal eyes with no observable intraocular disease. Ages ranged from 3-days-old to 99 years. 41 scans were female and 59 were males. All scans were performed using a GE 8800 Scanner with the JC software package. Scanning time was 9.6seconds and display a 320 x 320 matrix. Head scans were viewed with a window center at 35, width 100 and orbit scans at centre 65, width 300. Both images of the eyeball were magnified 2.5 times. The slice chosen for ocular measurement was that showing the largest axial plane of the eyeball (which usually shows the maximum size of the lens). Ocular dimensions were obtained with the cursor (Fig. 1). The AP diameter of the eyeball was taken as the distance from the anterior corneal surface to the posterior wall of the choroid, and it includes the anterior chamber depth, lens thickness, and vitreous length: the coronal diameter was taken as the maximum transverse width. These two dimensions was used to calculate the total volume of the globe.
Materials and methods The study consisted of 100CT scans; 36 scans from orbit study and 64 scans obtained from CT head scans which also show a good image of the eyeballs.
Fig. 1. The midocular slice of the CT orbit or head scan, which shows the maximum size of the eyeball with illustrations of the ocular dimensions (maximum anterior-posterior and lateral diameters of the outer margins of the globe)
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growth period. The difference in measurements remain relatively constant throughout the entire age span and the relative rate of growth of OV is the same in both sexes.
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Discussion 0
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6 9 12 15 18 21 24 Month
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Fig. 2. Growth patterns of the ocular size as measured by the CT ocular volume from birth to adults (200 eyeballs)
Table 1. Ocular volumes Age (Years)
Samples (Eyes)
Total (cm 3)
Male (cm 3)
Female (cm 3)
0- 1 1- 2 2- 5 5-13 13-18 18-30 30-50 50-65 65-99
42 18 28 44 20 8 26 30 12
4.24_ 1.16 5.96+0.78 6.41+1.13 6.90+1.12 8.47+1.60 9.80 + 1.36 9.26+0.88 9.13 + 1.13 8.86 _ 0.73
5.01+1.13 3.89+ 1,18 6.61+0.07 5.53+0,79 6.79___1.20 6.14+0,95 7.05+1.09 6.69+1.21 8.89+1.08 8.19+1.90 9.69 + 1.66 10.13 a 8.81+0.70 9.79+0.70 9.41 +_1.16 8.41 _+0.75 8.90 + 0.61 8.82 + 0.86
a Only one patient in this age group
Even though the eyeball is slightly ellipsoidal, it is assumed to be spherical for volume estimation: the error introduced is likely to be small [1]. The average interobserver error was 1.9%. The average absolute percentage difference between measurements of the same scan by the same person was slightly less than 1.9% (range, 1-3%).
Results
Results of OV at various age groups are shown in Figure 2. Curve shown was smoothed by least square method. The growth of OV is significantly influenced by increasing age. Early ages are shown in months up to 24. The curve shows rapid growth, almost doubling volume, from 3 cm 3 at birth to approximately 6 cm 3 at 24 months of age in both sexes. Another 3 cm 3 increment is noted from two years of age to 18-30 years of age, when its peak of 9-10 cm 3 is reached. OV then seems to decrease by approximately 1 cm 3 up to the age of 99 years in both sexes. A conspicuous sex difference in OV at various ages is shown in Table 1. Values in males were 0.5 cm 3 larger than in females during the entire
Results show a significant correlation between OV and age. Significant rapid increases from birth to two years of age and significant reductions at older ages were found in this study. Priestly Smith (1890) found that in old people the cornea is smaller than in normal young people and suggestet that this might indicate that elderly people have a smaller volume of the eyeball [2]. Our results support this finding. It is suggested that such a reduction in the whole eye with increasing age would contribute to the shallowness of the eye anterior chamber in old age and in angle-closure glaucoma [3]. A slight variation of measurement technique, not used in this paper would be to reduce the mean of ocular dimensions by twice the mean thickness of the sclera of all eyes (2 x 0.22 cm). In conclusion, age and sex showed a conspicuous influence upon OV. The mean values and normal variations of OV and their growth patterns at different ages would be of help in recognizing the early signs of microphthalmus and macrophthalmia, and also in identifying axial myopia in cases of unilateral proptosis [4].
Acknowledgement. Paul
Y. Hahn for assistance in preparing this
manuscript.
References 1. Perkins ES (1981) Ocular volume and ocular rigidity. Exp Eye Res 33:141-145 2. Smith Priestly (1890) On the size of the cornea in relation to age, sex, refraction and primary glaucoma. Trans Ophthalmol Soc U K 10:68-78 3. Leighton DA, Tomlinson A (1972) Changes in axial length and other dimensions of the eyeball with increasing age. Acta Ophthalmol 50:816-826 4. Osher RH, Shields Schatz NJ (1978) Axial myopia: a neglected cause of proptosis. Arch Neurol 35:237-241 Received: 4 December 1983 F.J. Hahn, M.D. Associate Professor Department of Radiology University of Nebraska Medical Center 42nd and Dewey Avenue Omaha, Nebraska 68105 USA