Chapter 3 Physical and Refractive

This chapter is taken Characteristics from: Isenberg, S. (d.). of the Eye at (1989). The eye in infancy. Chicago: Birth and Year Book Medical Publishers. During Infancy

Sherwin J. lsenberg, M.D.

THE to impaired orbital growth. Infants requiring Introduction enucleation for conditions such as retinoblas- Ophthalmologists and pediatricians toma, trauma to the globe, severe glaucoma, should be concerned about development of or congenital structural defects including mi- the orbit for two reasons. The first is the cos- crophthalmos and anophthalmia may require metic effect of a malformed orbit on the ap- pearance of the child. The second and more early prosthesis placement, often within the important reason is the effect of a malformed first few weeks of life. In the rapidly devel- orbit on the state of the eye and brain. An oping infantile eye, a replacement of pros- orbit that is too shallow can cause eversion of thesis may be needed as often as every 2 the , proptosis, and exposure of the weeks' especially if expansion of the orbit is and cornea as well as exotropia desired. Socket development has been re- (see Chapter 24). Maldevelopment of the orbit ported to be stimulated by the presence of a can affect the optic canal, which may decrease globe,' and the early loss of a globe, produced vision through effects on the optic nerve (see experimentally in sheep, has been shown to Chapters 12 and 21). Over 30 congenital mal- formation syndromes that involve the orbit result in a 35% decrease in mature orbital and/or produce microphthalmos have been size* Thus, using correctly sized conformers described.' in the developing neonate may ensure ade- Reciprocally, the state and size of the eye can affect the development and growth of the quate conjunctival growth.3 orbit. There are data in the literature relating Orbital Growth the perinatal removal or absence of the eye Between 6 months ofgestational age and 18 months following birth, the bony orbit undergoes rapid changes in size and shaped 32 General Considerations of the Newborn Eye

Whitnall described the orbital margin to be weight, horizontal and vertical diameters of circular at birth and to remain so until pu- the orbital margin, horizontal and vertical di- berty.5 Then as the face grows, the vertical ameters of the conjunctival fornix, and pal- diameter of the orbit increases dramatically. pebral fissure width for the group of infants Compared with the adult orbit, the orbit at are shown in Table 3-1. The relationship between conjunctival birth has a large flat roof, an increased con- fornix dimensions, body weight, and gesta- tribution of the greater wing of the sphenoid tional age for each infant are indicated in Fig- bone to the lateral wall, and an anteriorly ures 3-1 and 3-2. Statistically significant facing caused by an accentuated correlation coefficients were calculated for lacrimal crest. The transverse orbital axis of both conjunctival fornix horizontal and ver- the neonate is more horizontal than is the tical diameters in relation to weight, as indi- downward sloping axis of the adult. cated with P values in Figure 3-1. Horizontal However, the palpebral fissures, as op- and vertical diameters of the conjunctival for- posed to the rapid growth of the orbit, slowly nixes were similarly significantly correlated with gestational age (see Fig 3-2). increase in size from early in gestation to term. Figure 3-3 illustrates the relationship be- Sivan and colleagues' as well as Mehes7 found tween orbital margin and weight. Statistically the palpebral fissure length to increase 5 mm significant correlation coefficients were found in the last 10 to 14 weeks of gestation. Simi- for the infants' body weight in relation to either larly, Jones and associates found a 4-mm in- orbital margin horizontal or vertical diameter crease in the last 8 weeks of gestation." Hymes (P values are given). Figure 3-4 similarly de- found a similar infantile growth but also doc- picts the statistically significant correlation be- umented a continuous, although slower in- tween each of these parameters and gestational crease until puberty.g Palpebral fissure length age. The relation between palpebral fissure appears to be greater in black than in Hispanic width, body weight, and gestational age is given infants." in Figures 3-5 and 3-6; correlation coeffi- With regard to the development of the cients were statistically significant for these conjunctival fomixes, there is nearly no in- parameters. Statistically significant linear formation in the literature. However, it has regression equations (P < .05) allowing pre- been stated that "the folds of the fornices (in diction of conjunctival fornix, orbital mar- man) are not obvious until the last month of gin, and palpebral fissure dimensions from gestation."" weight or gestational age were calculated laenberg et al. prospectively measured the (Table 3-2). conjunctival fomix and orbital margin dimen- A comparison of individual ocular param- sions of 55 term and premature neonates eters with each other revealed statistically sig- within a week of birth." The means, standard deviations, and ranges for gestational age, body 36 General Considerations of the Newborn Eye TABLE 3-2. Linear Regression Equations for Neonatal Conjunctival Fornix, Orbital Margin, and Palpebral Fissure Dimensions in Relation to Weight and Gestational Age

Gestational Age (wk) Weight (am)

nificant correlation coefficients for the center of the skull in neonates and 45 degrees conjunctival fornix in relation to orbital mar- in adults. In a Belgian population, the distance gin and palpebral fissure only in the horizon- between the eyes was found to be about 21 tal plane (r = .500, P = .0004; and r = .561, mm at birth and, in preterm infants, follow P = ,0001, respectively). A comparison of the the regression curve 0.47 times weeks ofges- orbital margin horizontal diameter to palpe- tational age plus 3-3." This equation should bral fissure width revealed a statistically sig- be considered prior to diagnosing certain nificant correlation coefficient r = .471, P = craniofacial syndromes with hypertelorism or .001). Significant correlation coefficients were hypotelorism. found between orbital margin horizontal and vertical diameters (r = .3149, P = .02) and between conjunctival fornix horizontal and DIMENSIONS AND GROWTH OF THE vertical diameters (r = .331, = .013). EYE AND ITS STRUCTURES The overall proportions of the conjunc- The Eye: Physical Development tival fornix in the premature and term neonate Of all human organs, the eye is one of the (horizontal diameter:vertical diameter ratio, most fully developed at birth. While many 18/15 mm = 1.2) vary greatly from those es- changes will occur with maturity, the absolute tablished previously for the adult (25/29 mm dimensions of the eye are closer to adult size = 0.9)." Conjunctival fornix dimensions cor- than are nearly any other organ of the body. relate closely and in a linear fashion with the In the prenatal period, the eye grows fast- weight and gestational age of the infant. The est between the 8th and 14th week. Overall, growth of the conjunctival fornix also parallels growth of the eye parallels growth of the em- the growth of the palpebral fissure width but bryo until the 30th week, after which it slows only partially correlates with orbital margin down. The sagittal diameter increases from 12 dimensions. There appears to be a different mm at 6 months' gestational age to 17 mm at growth pattern in the palpebral fissure and 8 months' gestational age (Fig 3-7). Postna- conjunctival fornixes from that of the orbit. tally, the eye grows fastest in the first year of Similar findings were reported by Hymes who life (about 3.8 mm in sagittal diameter) and concluded that the palpebral fissure followed then at a progressively slower rate until pu- slow, general body growth in contrast to the berty (Table 3-3). Swan and Wilkins found rapid postnatal changes observed in the eye." that half the expected total increase over one's The axis of the newborn orbit is oriented entire lifetime in ocular diameter, volume, and more laterally than that in the adult. The or- surface area occurs by 6 months of age.'4 bital axis is angulated 115 degrees from the Physical and Refractive Characteristics of the Ey6 at Birth and During Infancy

TABLE 3-3. Physical Ocular Characteristics in Preterm and Term Infants Pooled From the Literature* Sagittal Corneal Refractive Error Age Length (mm) Diameter (mm) (D)

•Data from Adams RJ, Maurer D, Davis M: Newboms' discrimination of chromatic from achromatic stimuli. J Exp Child Psychol 1986; 41:267. Banks MS: The devel- opment of visual accommodation during early infancy. Child Dev 1980: 51:646. Cook RC, Glassock RE: Refractive and ocular findings In the newborn. Am J Ophthal- mot 1951; 34:1407, Gwiazda J, Scheiman M, Mohindra I, et al: Astigmatism inchildren: Changes in axis and amount from birth to six years. Invest Ophthalmol Vis Scl 1984; 25:88. Harayama K. Amemlya T, Nishimura H: Development of the eyeball during fetal life. J Pedlatr Ophthalmol Strabismus 1981; 18:37. Jeanty P. Dramalx-Wilmet M, Van Gansbeke D, et al: Fetal ocular biometry. Radiology 1982: 143:513. Larsen JS: The sagittal growth of the eye, IV. Ultrasonic measurement of the axial length of the eye from birth to puberty. Acta Ophtholmol 1971: 49:873. Swan KC. Wilkins JH: Extraocuiar muscle surgery in early infancy—Anatomical factors. J Pediatr Ophthat- l St bi 1984 21 44 Th F H ld R F LL O th l ti ti

FIG 3-7. Relative size of sectioned eyes of a normal premature infant compared with an adult. (Courtesy of Dr. Robert Foos.) 38 General Considerations of the Newborn Eye

Early studies of the sagittal diameter of ers feel the parameters should be 12.5 and the eye gave variable results due to the inclu- 10.0, respectively). The gestational age of the sion of preterm infants with term infants. In infant must be taken into consideration before 23 term infants, Sorsby and Sheridan found declaring the corneal diameter as being ab- the sagittal diameter to be 17.9 mm." Most normally small. In preterm neonates, Sorsby studies give a figure of about 18.0 mm for this and Sheridan found the corneal diameter to range from 7.5 to 9.2 mm without directly parameter. At birth, the transverse diameter relating the diameter to gestational age. Mu- of the globe is slightly greater than the sagittal sarella and Morin examined 37 infants with a (mean, 18.3 mm) and the vertical diameter mean postconceptual age of 34 ± 2 weeks slightly less (17.3 mm). Males average about and found the corneal diameters to average 0.2 mm more in each diameter. In premature about 8.2 ± 0.5 mm.20 They found corneal infants, the sagittal and transverse diameters diameter to correlate best with weight and are nearly identical, while the vertical diam- approximate regression relationship to be eters are uniformly shorter. However, Hara- corneal diameter = 0.0014 x weight + 6.3 yama and colleagues reported in a Japanese where the corneal diameter is expressed in millimeters and weight in grams. study that the sagittal diameter was shorter The corneal curvature is much steeper in than the transverse or vertical diameters dur- infants than in adults. Donzis and colleagues ing fetal life. 16 They also showed that the ver- found the corneal curvature to be about 60 tical meridian circumference was shorter than Diopters in a 28-week gestational age infant." the transverse or meridian circumferences At term, the mean curvature was about 51 D. during fetal life. When studied by ultrason- By following a population of premature in- ography the sagittal diameter appears shorter fants, they found a reduction of about 8 D in than that measured directly in the pathology comeal curvature in the last 3 months of ges- laboratory. Using ultrasonography, both tation. Thus. using donor corneas from infants for keratOplasty may cause a significant my- Larsen" and Blomdahl" found the mean sag- opic shift due to the steep curvature, espe- ittal ocular diameter of term newborns to be cially in the more premature neonate." about 16.6 mm (range, 15.3 to 17.6). The in neonates has four times the The weight of the newborn eye varies from pliability of adult sclera.23 Therefore, the in- 2.3 to 3.4 gm, and the volume is between 2.20 fant eye has a greater tendency to collapse and 3.25 cc.'" The scleral surface area is about during intraocular surgery than does the adult 828 sq mm. eye. The thickness of the sclera in infants is only 0.45 mm, while in adults it is 1.09 mm. The Anterior Segment Based on scleral stretching experiments, in- The corneal diameter in infants is an im- fantile sclera was found to be about half as portant clinical parameter. Diagnoses such as strong as adult sclera. infantile glaucoma or microphthalmos often The are much closer depend on or are influenced by measure- to the back of the eye at birth than at any time ments of corneal diameter. In 15 term infants, later in life.'4 Because most of the growth of Blomdahl found the comeal diameter to range the sclera is in the posterior portion of the from 9.0 to 10,5 mm with a mean of 9.8 mm." eye, the distance of the extraocular muscles At birth, the vertical cornea] diameter exceeds from the posterior pole of the eye increases the horizontal (10.5 vs. 9.9 mm) according to much more with growth than does the dis- Sorsby and Sheridan." Newborn females have tance from the anterior pole. At birth, the lat- a corneal diameter 0.3 mm greater than do eral rectus muscle insertion lies just about males. The definition ofmacrocomea and mi- over the equator, while the insertion of the crocomea should be 2 SD away from the mean, lies only I or 2 mm in which would be approximately greater than 11.0 and less than 9.0 mm in term infants (oth-