A C T A O P H T H A L M O L O G I C A VOL. 5 7 1 9 7 9
Department of Ophthalmology (Head: Biretta Zetterstriim-Karpe). Huddinge Uniriersity Hocpital, Karolin cka Institutrt, Stockholm
ULTRASONIC MEASUREMENTS OF THE EYE IN THE NEWBORN INFANT BY
SVEN BLOMDAHL
The right eyes of 28 newborn infants have been examined retinoscopically, and the anterior chamber depth, the lens thickness and the length of the vitreous were measured by ultrasound. In 15 of the infants keratometry was performed using the Javal-Schiotz keratometer. The total axial length of the eye was found to be longer the heavier the weight of the baby, whereas the lens thickness showed no correlation to the total axial length or to the weight of the baby. In only 1/3 of the babies was the corneal astigmatism less than 0.5 D. A significant correlation (P < 0.01) was found between the total axial length of the eye and the length of the corneal radius. K q uwd.s: corneal radius infants - axial length.
-
astigmatism
-
lens thickness - ultrasound -
Ultrasound biometry has recently been used for determining the axial length of the eye in the newborn child as well as the depth of the anterior chamber, the lens thickness and the length of the vitreous body (Gernet 1964; Luyckx 1966; Grignolo 8c Rivara 1968; Larsen 1971).A survey of their values is presented in Table I. Previously, the axial length of the eye in the newborn infant had to be measured on cadavers (von Jaeger 1861; von Pflugk 1909; Sorsby 8c Sheridan 1960). The aim of the present study has been to investigate the possible interrelationships between the weight of the newborn baby, the axial length of the eye, the lens thickness, the corneal radius and the refraction. T o this aim the axial depth of the anterior chamber, lens thickness and vitreous length have been measured by ultrasound in newborn babies. Retinoscopy has been performed and in some cases also keratometry, using the Javal-Schiotz keratometer. Received December 4, 1978.
1048
Tnhlp 1. Earlier determinations of the axial values of the eye in infants.
Larsen F M ant. chamber lens vitreous tot.ax.length refraction i n f a n t s examined eyes examined cykloplegic
(mm)
2,39 2,37 3,99 3,93 (mm) (mm) 10,22 10,48 (mm)
-
(0)
-
-
(n) (n)
37 74
43 86
-
-
Gernet
Luyckx
F
M
2,9 3,4
2,9 3,4
-
-
17,2 17,l t2,6 +3,0 15 21 29 41 At r o p i n
F
Grignolo
M
2,5 2,6 3,6 3,7 10,8 10,8 17,7 17,5 +2,2 t2,6 25 27 50 54 Cyklogy l
F t 4I -
17.02 to,52 18 36 Tropamide
Material and Methods Twenty-eight healthy fullterm infants, 14 girls and 14 boys have been examined. Their ages ranged from 1-4 days and their weights from 23 10 to 4790 g. The eyes to be examined were made cykloplegic by 2 drops of 1% cyklopentolate hydrochloride (Cyklogyl@)instilled twice in the conjunctival sac. 45 min later the examination started. After local anesthesia with 0.2% oxibuprocaine chloride (NovesinB) a speculum, not causing any pressure upon the bulb, was inserted to keep the lids apart. The infants were held in an upright position by an assistant. Their heads were put on the chin- and forehead rest of the Javal-Schiotz keratometer. The examiner could easily see the reflexes on the cornea and repeated examinations in different meridians were performed. In 15 babies, everyone quite peaceful, the reflexes could be seen on the central cornea and 3-5 repeated examinations showed unanimous low measuring values. In 13 babies it was impossible to centralize the reflexes on the cornea. With the baby lying down, the horisontal corneal diameter was measured using a caliper. Retinoscopy was performed in two axes, and finally the ultrasonic biometry could take place. This was done with an A-scan apparatus, the Kretztechnik 7200 MA, and with a transducer frequency of 8 MHz. This instrument is equipped with an electronic scale and a built-in quarts oscillator which makes calibration possible previous to each examination. A contactglass similar to that described by Jansson (1963) and Pallin (1969) was used, with an outer opening of 12,5 mm, large enough not to press on the cornea during the examination, as the corneal diameters were all less than 11 mm. The distance between the transducer and the cornea was 15 mm and this part of the contactglass was filled with saline easily refilled (if needed). The baby was lying down during the examination with the head kept steady by an assistant. When the echogram on the screen showed maximal amplitudes from the 1049
reflecting surfaces a Polaroid picture was taken. T h e distance in microseconds could then be converted into millimetres according to the velocities given by Jansson ( 1963) 1532 m/sec in the vitreous and aqueous and 164 1 m/sec in the lens at 97°C. Both eyes were measured by ultrasound in 10 of the infants in order to find out if there were any measurable differences between the right and the left eye.
Results R P t i n a w p . T h e range of the retinoscopic readings was from + 1.0 D to + 5.5 D with an average of + 3.6 D. T h e girls had an average of + 3.9 D and the average of the boys was +3.4 D. Sixteen of the 28 infants showed no astigmatism, nine had an astigmatism with the rule and three infants had an astigmatism with oblique axes. Table I I . T h e retinoscopic findings in two axes, values of the corneal radies in two axes and the corneal power in diopters of the corneas in two axes (calculated from the corneal radius). corneal infant nr
retinosmpy(D1
radius(mm1
corneal power(D1
1
40 t3.0
%.9
19 0 +9.0
2
y
y 7 0 .5
52 0 t48.0
t3
3 4 5
y
y
y
ts.0
q.5
t1.0
7 8
t3.5
T7.25
t3.5
y 7 . 4 6.9 6,7
X
+5.0
y 6 . 6
4.0
10 11
X
y y
13 14
.o
y 7 . 5
t(5.0 46.5 48.5
7.4
45.5 46.5
7.3
4.0
X
4.0
T 7 . 4
X
X
45 5
X
7 y
x
530 +1
7.25 7.0
X
4.0 t3.0
12
445.5
49.0 50.5
45 5
4 . 5 r2.0
9
+6.5 15 5
X
y
t 5 2 . 0
46 5
4.0 t3.0
6
52 0
6.6 6.45
x
51.5 52.5
7.2 7.4
47.0 45.5
X
t5.0
y7.4
*.O
445.5
X X
41 5 4-15.5
500
+W
15
1050
refraction(D)
+6,0..
+SO,.
+4,0
+a0
A
t20,,
r=
+to
-0.13~
0
'
16.0
15.0
I
$20
Ur.0
.
15D female 0
16.0 male A
17,O 1 W total axial length (mm)
Fig. 2. The weight of 28 infants plotted against the total axial length of the eye.
1051
weight(g) 5000, A
A
A A
4000
A A
3000.'
A
A
0
2000,. 3.4 3.5 female 0
3.6
3.7
male A
3.8
3.9
4.0
I~I'IS thickness (mm)
Fig. 3 . The weight of 28 infants plotted against the total axial length of the lens.
lens thickness (mm)
. .. .
.
. . ....
. female
male A
total axial length fmm)
Fig. 4 . The lens thickness plotted against the total axial length of the eye in 28 infants.
1052
A A
A A 0
A
A
0
A A A
0
I
16.0
15.0 female 0
male A
17,O 180 total axial kngth(mn)
Fig. 5. T h e corneal radius plotted against the total axial length of the eye in 15 infants.
T h e highest astigmatism was 4 D, with + 6 D in the horisontal and + 2 D in the vertical meridian. Ultrmound measurements. T he depth of the anterior chamber in the 28 children ranged from 2 , 4 to 2.9 mm. T h e average value was 2.6 mrn. T he central thickness of the cornea was included in these readings. T h e lens thickness values ranged from 3.4 to 3.9 mm with an average of 3.6 mm. T h e axial vitreous length ranged from 8.9 to 11.2 mm with an average of 10.4 mm. T h e total axial length ranged from 15.3 to 17.6 mm with an average of 16.6 mm. T h e mean value of the boys was 16.7 mm, and 16.5 mm of the girls. In the ten babies where both eyes were measured by ultrasound, the difference of the axial lengths never exceeded 0.2 mm. Kpratmetry. In the 15 babies examined with keratometry, the range of the corneal radius was from 6.4 to 7.4 mm with an average of 7.0 mm. In five of the babies there was no astigmatism to be found and five babies had an astigmatism with the rule ranging from 1-4 D. Five babies showed an oblique astigmatism ranging from 1-2 D. Table I1 shows the values of the retinoscopic figures of the corneal curvature and of the corneal power in the same eye. In two of the infants with oblique corneal astigmatism this had not been registered by retinoscopy. Corneal diameter. T h e values of the corneal diameter in the horisontal plane varied from 9.0 to 10.5 mm with an average of 9.8 mm.
Corrplutions. Fig. 1 shows the association between the refraction and the total axial length of the eye. T h e correlation coefficient is -0.132, and there is no significant correlation between the degree of hypermetropia and the axial length of the eye (P> 0.1) in this group. Fig. 2 is a graph of the association between the weight of the baby and the total axial length of the eye. The correlation coefficient is 0.660, a value that differs from zero (P < 0.001) showing that the heavier child has a longer eye. Fig. 3 shows the relation between the weight of the baby and the lens thickness. T h e correlation coefficient for these parameters is 0.072, a value quite close to zero, (P > 0.1) and there is no correlation. Fig. 4 shows the association between the lens thickness and the total axial length of the eye. Again, the correlation coefficient is close to zero (0.029), and these parameters are not significantly correlated (P > 0.1). In Fig. 5 the corneal radius is plotted against the total axial length of the eye in 15 infants. T h e value of the corneal curvature radius is given as the average value of the main meridians. The correlation coefficient of the parameters is 0.690 which significantly differs from zero (P < 0.01). This suggests that the longer the total axial length of the eye, the longer the corneal radius i.e. the flatter the cornea.
Discussion T h e refractive values of new borns found by other investigators mostly lie between + 2 D to + 3 D (Duke-Elder 1969). In the 28 babies of this study, the values vaned from + 1.0 D to +5.5 D and the average value of +3.6 D is somewhat higher than that normally found. Luyckx (1966) and Larsen (197 1) using a contact glass between the eye and the transducer found the anterior chamber to be about 2.4 and 2.6 mm. The central thickness of the cornea was included in these values. Gernet (1964) found a value of 2.9 mm of the anterior chamber (still including the central corneal thickness). This value, however can not be compared to the value found by the former authors because Gernet did not use a contact glass between the transducer and the eye and had to reckon with a pressure on the cornea in his calculations. T h e mean values of the lens thickness recorded from other ultrasonic studies vary from 3.4 mm to 4.0 mm and the values of the vitreous length from 10.2 mm to 10.8 mm (Table I). T h e oculometric mean values of the present study are all in accordance with these figures. T h e average of the total axial length is 16.6 mm, slightly less than the values obtained by Gernet, Luyckx and Grignolo, but close to the average value 16.7 mm from Larsen’s studies.
1054
Luyckx and Gernet found no relationship between the refraction and the axial length of the eye, neither could this be found in the present study. This is rather unique keeping in mind that refraction and axial length are so strongly correlated in all other age-classes. The finding implies that in the smaller eye the refractive power of the cornea and - or the lens must be stronger than in the longer eye. In emmetropic eyes of adults, Sorsby et al. (1957) found a good correlation between the axial length and the corneal power. Fledelius (1976) found a significant correlation between these parameters in children aged about ten years. This study shows a significant correlation between the total axial length of the eye and the corneal power, and the longer the total length of the eye the smaller is the corneal refractive power. Thus the cornea compensates for the high degree of hyperopia which otherwise would be expected. Changes in lens power might also be compensatory, but the present investigation shows no correlation between the lens thickness on one side and refraction or axial lengh on the other. Keratometry performed on stillborn infants in the early 20th century showed a corneal radius of about 7.0 mm (de Vries 1901; von Pflugk 1909). In two living infants Gernet (1964) found a radius of 6.4 mm and 7.7 mm using a Zeiss ophthalmometer. Grignolo & Rivara (1968) measured the corneal curvature in premature newborns, fullterm newborns and children to the age of ten. They used the Java1 ophthalmometer, and when this was not possible, the measurements were carried out by juxtaposition of concave stencils representing arcs of circles with known curvature radies. They found the corneal power to be +54.3 D in fullterm newborns, a value that equivalates with a radius of about 6.3 mm. All considered the mean value 7.0 mm of the corneal radius from the present study seems to be close to the mean value of earlier investigators. There seem to be no measurements of the astigmatism of the cornea carried out in living newborn infants. Marin-Amat (1956) expected most corneas to be spherical. This assumption was made on the fact that in children of the age of three, 50% had corneal astigmatism and at the age of seven 90%had corneal astigmatism. They therefore found it probable that in newborns the astigmatism approximately was zero. The present investigation does not favour this theory, 66%of the fifteen babies having astigmatic corneas. It must be pointed out, however, that the material is limited.
References Duke-Elder S. (1970) Text-hook ofOphthnlmolnp, V, 229, Kimpton. London. Fledelius H. (1976) Prematurity and the eye. Ophthalmic 10-year follow-upof children of low and normal birth weight. Arta ophthnl. (Khh.), Suppl. 128. Gernet H. ( 1964) Achsenlange und Refraktion lebender Augen von Neugeborenen, Alhrerht 71.Gmefet Arch. ophthnl. 166, 530-536.
Sivn Blomdahl
Grignolo A. & Rivara A. (1968) Biometry of the human eye from the sixth month of pregnancy to the tenth year of life (measurements of the axial length, retinoscopy refraction, total refraction, corneal and lens refraction) In: Vanisek J., ed. Diaposticu ultmsonicu in ophthalmologica, I I Symposium Internationale de Diagnostica Ultrasonica in Ophthalmologia, 1968, Universita J. E. PurkynC, Brno, Czechoslovakia (Opuscula Ophthalmologica, Acta Facultatis Medicae Universitatis Brunensis, No. 35.25 1-257. von Jaeger J. (1861) Uber die Eimtellungen de.7 dioptrischen Applrutm im menschlichen Auge, pp. 10- 12. L. W. Siedel u Sohn, Wien und Masson, Paris. Jansson F. (1963) Measurement of intraocular distances by ultrasound and comparison between optical and ultrasonic determinations of the depth of the anterior chamber. Actu ophthal. (Kbh.)41, 25-61. Larsen J . S. (1971) The sagittal growth of the eye. I. Ultrasonic measurement of the depth of the anterior chamber from birth to puberty. Acta ophthal. (Kbh.) 49,239-262. Larsen J. S. (1971) The sagittal growth of the eye. 11. Ultrasonic measurement of the axial diameter of the lens and the anterior segment from birth to puberty. Actu ophthnl. (Kbh.) 49, 427 -440.
Larsen J. S. (1971) The sagittal growth of the eye. 111. Ultrasonic measurement of the posterior segment (axial length of the vitreous) from birth to puberty. Acta ophthal. (Khh.) 49,44 1-453.
Luyckx J. (1966) Mesure des composantes optiques de I'aeil du nouveaune par echographie ultrasonique. Arch. Ophtul. (Paris)26, 159- 170. Marin-Amat M. (1956) Les variations physiologiques de la courbure de la cornie pendant la vie. Leur importance et transcendance dans la &fraction oculaire. Bull. Soc. Belge Ophthal.
I I?, 251 -293. Pallin 0. (1969) The influence of the axial length of the eye on the size of the recorded B-potential in the clinical single flash electroretinogram. Actu ophthul. (Kbh.), Suppl. 101. von Pflugk A. (1909) Die Fixierung der Wirbeltierlinsen insbesondere der Linse des neugeborenen Menschen. Klin. Mbl. Augenhtilk. 47, I , 1 - 14. Sorsby A., Benjamin B., Davey J. B. &TannerJ. M. (1957) Emmetropia and its aberrations. A study in the correlation of the optical components of the eye. Med. Res. Counc. Spec. Ref. Ser. No. 293, London. Sorsby A. & Sheriaan M. (1960) The eye at birth: Measurements of the principal diameters in forty-eight cadavers.j. Anal. (London) 94, 192- 197. de Vries W. M. (1901) Uber das Sauglingsauge. Ned. T. Gmeesk. I . Authori address:
Dr. Sven Blomdahl, Huddinge University Hospital, Department of Ophthalmology, S- 14 1 86 Huddinge, Sweden.
1056
Department of Ophthalmology (Head: Biretta Zetterstriim-Karpe). Huddinge Uniriersity Hocpital, Karolin cka Institutrt, Stockholm
ULTRASONIC MEASUREMENTS OF THE EYE IN THE NEWBORN INFANT BY
SVEN BLOMDAHL
The right eyes of 28 newborn infants have been examined retinoscopically, and the anterior chamber depth, the lens thickness and the length of the vitreous were measured by ultrasound. In 15 of the infants keratometry was performed using the Javal-Schiotz keratometer. The total axial length of the eye was found to be longer the heavier the weight of the baby, whereas the lens thickness showed no correlation to the total axial length or to the weight of the baby. In only 1/3 of the babies was the corneal astigmatism less than 0.5 D. A significant correlation (P < 0.01) was found between the total axial length of the eye and the length of the corneal radius. K q uwd.s: corneal radius infants - axial length.
-
astigmatism
-
lens thickness - ultrasound -
Ultrasound biometry has recently been used for determining the axial length of the eye in the newborn child as well as the depth of the anterior chamber, the lens thickness and the length of the vitreous body (Gernet 1964; Luyckx 1966; Grignolo 8c Rivara 1968; Larsen 1971).A survey of their values is presented in Table I. Previously, the axial length of the eye in the newborn infant had to be measured on cadavers (von Jaeger 1861; von Pflugk 1909; Sorsby 8c Sheridan 1960). The aim of the present study has been to investigate the possible interrelationships between the weight of the newborn baby, the axial length of the eye, the lens thickness, the corneal radius and the refraction. T o this aim the axial depth of the anterior chamber, lens thickness and vitreous length have been measured by ultrasound in newborn babies. Retinoscopy has been performed and in some cases also keratometry, using the Javal-Schiotz keratometer. Received December 4, 1978.
1048
Tnhlp 1. Earlier determinations of the axial values of the eye in infants.
Larsen F M ant. chamber lens vitreous tot.ax.length refraction i n f a n t s examined eyes examined cykloplegic
(mm)
2,39 2,37 3,99 3,93 (mm) (mm) 10,22 10,48 (mm)
-
(0)
-
-
(n) (n)
37 74
43 86
-
-
Gernet
Luyckx
F
M
2,9 3,4
2,9 3,4
-
-
17,2 17,l t2,6 +3,0 15 21 29 41 At r o p i n
F
Grignolo
M
2,5 2,6 3,6 3,7 10,8 10,8 17,7 17,5 +2,2 t2,6 25 27 50 54 Cyklogy l
F t 4I -
17.02 to,52 18 36 Tropamide
Material and Methods Twenty-eight healthy fullterm infants, 14 girls and 14 boys have been examined. Their ages ranged from 1-4 days and their weights from 23 10 to 4790 g. The eyes to be examined were made cykloplegic by 2 drops of 1% cyklopentolate hydrochloride (Cyklogyl@)instilled twice in the conjunctival sac. 45 min later the examination started. After local anesthesia with 0.2% oxibuprocaine chloride (NovesinB) a speculum, not causing any pressure upon the bulb, was inserted to keep the lids apart. The infants were held in an upright position by an assistant. Their heads were put on the chin- and forehead rest of the Javal-Schiotz keratometer. The examiner could easily see the reflexes on the cornea and repeated examinations in different meridians were performed. In 15 babies, everyone quite peaceful, the reflexes could be seen on the central cornea and 3-5 repeated examinations showed unanimous low measuring values. In 13 babies it was impossible to centralize the reflexes on the cornea. With the baby lying down, the horisontal corneal diameter was measured using a caliper. Retinoscopy was performed in two axes, and finally the ultrasonic biometry could take place. This was done with an A-scan apparatus, the Kretztechnik 7200 MA, and with a transducer frequency of 8 MHz. This instrument is equipped with an electronic scale and a built-in quarts oscillator which makes calibration possible previous to each examination. A contactglass similar to that described by Jansson (1963) and Pallin (1969) was used, with an outer opening of 12,5 mm, large enough not to press on the cornea during the examination, as the corneal diameters were all less than 11 mm. The distance between the transducer and the cornea was 15 mm and this part of the contactglass was filled with saline easily refilled (if needed). The baby was lying down during the examination with the head kept steady by an assistant. When the echogram on the screen showed maximal amplitudes from the 1049
reflecting surfaces a Polaroid picture was taken. T h e distance in microseconds could then be converted into millimetres according to the velocities given by Jansson ( 1963) 1532 m/sec in the vitreous and aqueous and 164 1 m/sec in the lens at 97°C. Both eyes were measured by ultrasound in 10 of the infants in order to find out if there were any measurable differences between the right and the left eye.
Results R P t i n a w p . T h e range of the retinoscopic readings was from + 1.0 D to + 5.5 D with an average of + 3.6 D. T h e girls had an average of + 3.9 D and the average of the boys was +3.4 D. Sixteen of the 28 infants showed no astigmatism, nine had an astigmatism with the rule and three infants had an astigmatism with oblique axes. Table I I . T h e retinoscopic findings in two axes, values of the corneal radies in two axes and the corneal power in diopters of the corneas in two axes (calculated from the corneal radius). corneal infant nr
retinosmpy(D1
radius(mm1
corneal power(D1
1
40 t3.0
%.9
19 0 +9.0
2
y
y 7 0 .5
52 0 t48.0
t3
3 4 5
y
y
y
ts.0
q.5
t1.0
7 8
t3.5
T7.25
t3.5
y 7 . 4 6.9 6,7
X
+5.0
y 6 . 6
4.0
10 11
X
y y
13 14
.o
y 7 . 5
t(5.0 46.5 48.5
7.4
45.5 46.5
7.3
4.0
X
4.0
T 7 . 4
X
X
45 5
X
7 y
x
530 +1
7.25 7.0
X
4.0 t3.0
12
445.5
49.0 50.5
45 5
4 . 5 r2.0
9
+6.5 15 5
X
y
t 5 2 . 0
46 5
4.0 t3.0
6
52 0
6.6 6.45
x
51.5 52.5
7.2 7.4
47.0 45.5
X
t5.0
y7.4
*.O
445.5
X X
41 5 4-15.5
500
+W
15
1050
refraction(D)
+6,0..
+SO,.
+4,0
+a0
A
t20,,
r=
+to
-0.13~
0
'
16.0
15.0
I
$20
Ur.0
.
15D female 0
16.0 male A
17,O 1 W total axial length (mm)
Fig. 2. The weight of 28 infants plotted against the total axial length of the eye.
1051
weight(g) 5000, A
A
A A
4000
A A
3000.'
A
A
0
2000,. 3.4 3.5 female 0
3.6
3.7
male A
3.8
3.9
4.0
I~I'IS thickness (mm)
Fig. 3 . The weight of 28 infants plotted against the total axial length of the lens.
lens thickness (mm)
. .. .
.
. . ....
. female
male A
total axial length fmm)
Fig. 4 . The lens thickness plotted against the total axial length of the eye in 28 infants.
1052
A A
A A 0
A
A
0
A A A
0
I
16.0
15.0 female 0
male A
17,O 180 total axial kngth(mn)
Fig. 5. T h e corneal radius plotted against the total axial length of the eye in 15 infants.
T h e highest astigmatism was 4 D, with + 6 D in the horisontal and + 2 D in the vertical meridian. Ultrmound measurements. T he depth of the anterior chamber in the 28 children ranged from 2 , 4 to 2.9 mm. T h e average value was 2.6 mrn. T he central thickness of the cornea was included in these readings. T h e lens thickness values ranged from 3.4 to 3.9 mm with an average of 3.6 mm. T h e axial vitreous length ranged from 8.9 to 11.2 mm with an average of 10.4 mm. T h e total axial length ranged from 15.3 to 17.6 mm with an average of 16.6 mm. T h e mean value of the boys was 16.7 mm, and 16.5 mm of the girls. In the ten babies where both eyes were measured by ultrasound, the difference of the axial lengths never exceeded 0.2 mm. Kpratmetry. In the 15 babies examined with keratometry, the range of the corneal radius was from 6.4 to 7.4 mm with an average of 7.0 mm. In five of the babies there was no astigmatism to be found and five babies had an astigmatism with the rule ranging from 1-4 D. Five babies showed an oblique astigmatism ranging from 1-2 D. Table I1 shows the values of the retinoscopic figures of the corneal curvature and of the corneal power in the same eye. In two of the infants with oblique corneal astigmatism this had not been registered by retinoscopy. Corneal diameter. T h e values of the corneal diameter in the horisontal plane varied from 9.0 to 10.5 mm with an average of 9.8 mm.
Corrplutions. Fig. 1 shows the association between the refraction and the total axial length of the eye. T h e correlation coefficient is -0.132, and there is no significant correlation between the degree of hypermetropia and the axial length of the eye (P> 0.1) in this group. Fig. 2 is a graph of the association between the weight of the baby and the total axial length of the eye. The correlation coefficient is 0.660, a value that differs from zero (P < 0.001) showing that the heavier child has a longer eye. Fig. 3 shows the relation between the weight of the baby and the lens thickness. T h e correlation coefficient for these parameters is 0.072, a value quite close to zero, (P > 0.1) and there is no correlation. Fig. 4 shows the association between the lens thickness and the total axial length of the eye. Again, the correlation coefficient is close to zero (0.029), and these parameters are not significantly correlated (P > 0.1). In Fig. 5 the corneal radius is plotted against the total axial length of the eye in 15 infants. T h e value of the corneal curvature radius is given as the average value of the main meridians. The correlation coefficient of the parameters is 0.690 which significantly differs from zero (P < 0.01). This suggests that the longer the total axial length of the eye, the longer the corneal radius i.e. the flatter the cornea.
Discussion T h e refractive values of new borns found by other investigators mostly lie between + 2 D to + 3 D (Duke-Elder 1969). In the 28 babies of this study, the values vaned from + 1.0 D to +5.5 D and the average value of +3.6 D is somewhat higher than that normally found. Luyckx (1966) and Larsen (197 1) using a contact glass between the eye and the transducer found the anterior chamber to be about 2.4 and 2.6 mm. The central thickness of the cornea was included in these values. Gernet (1964) found a value of 2.9 mm of the anterior chamber (still including the central corneal thickness). This value, however can not be compared to the value found by the former authors because Gernet did not use a contact glass between the transducer and the eye and had to reckon with a pressure on the cornea in his calculations. T h e mean values of the lens thickness recorded from other ultrasonic studies vary from 3.4 mm to 4.0 mm and the values of the vitreous length from 10.2 mm to 10.8 mm (Table I). T h e oculometric mean values of the present study are all in accordance with these figures. T h e average of the total axial length is 16.6 mm, slightly less than the values obtained by Gernet, Luyckx and Grignolo, but close to the average value 16.7 mm from Larsen’s studies.
1054
Luyckx and Gernet found no relationship between the refraction and the axial length of the eye, neither could this be found in the present study. This is rather unique keeping in mind that refraction and axial length are so strongly correlated in all other age-classes. The finding implies that in the smaller eye the refractive power of the cornea and - or the lens must be stronger than in the longer eye. In emmetropic eyes of adults, Sorsby et al. (1957) found a good correlation between the axial length and the corneal power. Fledelius (1976) found a significant correlation between these parameters in children aged about ten years. This study shows a significant correlation between the total axial length of the eye and the corneal power, and the longer the total length of the eye the smaller is the corneal refractive power. Thus the cornea compensates for the high degree of hyperopia which otherwise would be expected. Changes in lens power might also be compensatory, but the present investigation shows no correlation between the lens thickness on one side and refraction or axial lengh on the other. Keratometry performed on stillborn infants in the early 20th century showed a corneal radius of about 7.0 mm (de Vries 1901; von Pflugk 1909). In two living infants Gernet (1964) found a radius of 6.4 mm and 7.7 mm using a Zeiss ophthalmometer. Grignolo & Rivara (1968) measured the corneal curvature in premature newborns, fullterm newborns and children to the age of ten. They used the Java1 ophthalmometer, and when this was not possible, the measurements were carried out by juxtaposition of concave stencils representing arcs of circles with known curvature radies. They found the corneal power to be +54.3 D in fullterm newborns, a value that equivalates with a radius of about 6.3 mm. All considered the mean value 7.0 mm of the corneal radius from the present study seems to be close to the mean value of earlier investigators. There seem to be no measurements of the astigmatism of the cornea carried out in living newborn infants. Marin-Amat (1956) expected most corneas to be spherical. This assumption was made on the fact that in children of the age of three, 50% had corneal astigmatism and at the age of seven 90%had corneal astigmatism. They therefore found it probable that in newborns the astigmatism approximately was zero. The present investigation does not favour this theory, 66%of the fifteen babies having astigmatic corneas. It must be pointed out, however, that the material is limited.
References Duke-Elder S. (1970) Text-hook ofOphthnlmolnp, V, 229, Kimpton. London. Fledelius H. (1976) Prematurity and the eye. Ophthalmic 10-year follow-upof children of low and normal birth weight. Arta ophthnl. (Khh.), Suppl. 128. Gernet H. ( 1964) Achsenlange und Refraktion lebender Augen von Neugeborenen, Alhrerht 71.Gmefet Arch. ophthnl. 166, 530-536.
Sivn Blomdahl
Grignolo A. & Rivara A. (1968) Biometry of the human eye from the sixth month of pregnancy to the tenth year of life (measurements of the axial length, retinoscopy refraction, total refraction, corneal and lens refraction) In: Vanisek J., ed. Diaposticu ultmsonicu in ophthalmologica, I I Symposium Internationale de Diagnostica Ultrasonica in Ophthalmologia, 1968, Universita J. E. PurkynC, Brno, Czechoslovakia (Opuscula Ophthalmologica, Acta Facultatis Medicae Universitatis Brunensis, No. 35.25 1-257. von Jaeger J. (1861) Uber die Eimtellungen de.7 dioptrischen Applrutm im menschlichen Auge, pp. 10- 12. L. W. Siedel u Sohn, Wien und Masson, Paris. Jansson F. (1963) Measurement of intraocular distances by ultrasound and comparison between optical and ultrasonic determinations of the depth of the anterior chamber. Actu ophthal. (Kbh.)41, 25-61. Larsen J . S. (1971) The sagittal growth of the eye. I. Ultrasonic measurement of the depth of the anterior chamber from birth to puberty. Acta ophthal. (Kbh.) 49,239-262. Larsen J. S. (1971) The sagittal growth of the eye. 11. Ultrasonic measurement of the axial diameter of the lens and the anterior segment from birth to puberty. Actu ophthnl. (Kbh.) 49, 427 -440.
Larsen J. S. (1971) The sagittal growth of the eye. 111. Ultrasonic measurement of the posterior segment (axial length of the vitreous) from birth to puberty. Acta ophthal. (Khh.) 49,44 1-453.
Luyckx J. (1966) Mesure des composantes optiques de I'aeil du nouveaune par echographie ultrasonique. Arch. Ophtul. (Paris)26, 159- 170. Marin-Amat M. (1956) Les variations physiologiques de la courbure de la cornie pendant la vie. Leur importance et transcendance dans la &fraction oculaire. Bull. Soc. Belge Ophthal.
I I?, 251 -293. Pallin 0. (1969) The influence of the axial length of the eye on the size of the recorded B-potential in the clinical single flash electroretinogram. Actu ophthul. (Kbh.), Suppl. 101. von Pflugk A. (1909) Die Fixierung der Wirbeltierlinsen insbesondere der Linse des neugeborenen Menschen. Klin. Mbl. Augenhtilk. 47, I , 1 - 14. Sorsby A., Benjamin B., Davey J. B. &TannerJ. M. (1957) Emmetropia and its aberrations. A study in the correlation of the optical components of the eye. Med. Res. Counc. Spec. Ref. Ser. No. 293, London. Sorsby A. & Sheriaan M. (1960) The eye at birth: Measurements of the principal diameters in forty-eight cadavers.j. Anal. (London) 94, 192- 197. de Vries W. M. (1901) Uber das Sauglingsauge. Ned. T. Gmeesk. I . Authori address:
Dr. Sven Blomdahl, Huddinge University Hospital, Department of Ophthalmology, S- 14 1 86 Huddinge, Sweden.
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