CHAPTER 15

Growth and Development of the Eye

Normal Growth and Development

The human eye undergoes dramatic anatomical and physiologic development throughout infancy and early childhood (Table 15-1). Ophthalmologists caring for children should be familiar with the normal growth and development of the pediatric eye, because departures from the norm may indicate pathology. See also BCSC Section 2, Fundamentals and Principles of Ophthalmology.

Table 15-1

Dimensions of the Eye

Most of the growth of the eye takes place in the first year of life. The change in the axial length of the eye occurs in 3 phases (Fig 15-1). The first phase (birth to age 2 years) is a period of rapid growth. The axial length increases by approximately 4 mm in the first 6 months of life and by an additional 2 mm during the next 6 months. During the second (age 2 to 5 years) and third (age 5 to 13 years) phases, growth slows, with axial length increasing by about 1 mm per phase.

Figure 15-1 Axial length plotted with respect to age. Dots represent mean values for age group indicated; bars represent

standard deviations. (Reproduced with permission from Gordon RA, Donzis PB. Refractive development of the human eye. Arch Ophthalmol. 1985;103(6):785–789. © 1985, American Medical Association.)

Similarly, the cornea grows rapidly during the first year of life (Fig 15-2). Keratometry values change markedly in the first year, starting at approximately 52.00 D at birth, flattening to 46.00 D by age 6 months, and reaching adult measurements of 42.00–44.00 D by age 12 months. The average horizontal diameter of the cornea is 9.5–10.5 mm in newborns and increases to 12.0 mm in adults. Mild corneal clouding may be seen in healthy newborns and is common in premature infants. It resolves as the cornea gradually thins, decreasing from an average central thickness of 691 µm at 30– 32 weeks’ gestation to 564 µm at birth.

Figure 15-2 Keratometry values plotted with respect to age on a logarithmic scale. The negative number represents months of prematurity; dots represent the mean value for the age group indicated; and bars, the standard deviations. (Reproduced with

permission from Gordon RA, Donzis PB. Refractive development of the human eye. Arch Ophthalmol. 1985;103(6):785–789. © 1985, American Medical Association.)

The power of the pediatric lens decreases dramatically over the first several years of life—an important consideration when intraocular lens implantation is being planned for infants and young children after cataract extraction. Figure 15-3 shows the theoretical power of the pediatric lens at a given age, based on intraocular lens power calculations performed with the modified SRK formula, which uses pediatric keratometry and axial length values.

Figure 15-3 Mean values (dots) and standard deviations (bars) for calculated lens power as determined by modified SRK

formula, plotted with respect to age. (Reproduced with permission from Gordon RA, Donzis PB. Refractive development of the human eye. Arch Ophthalmol. 1985;103(6):785–789. © 1985, American Medical Association.)

Kirwan C, O’Keefe M, Fitzsimon S. Central corneal thickness and corneal diameter in premature infants. Acta Ophthalmol Scand. 2005;83(6):751–753.

Refractive State

The refractive state of the eye changes as the eye’s axial length increases and the cornea and lens flatten. In general, eyes are hyperopic at birth, become slightly more hyperopic until age 7 years, and then experience a myopic shift toward plano until the eyes reach their adult dimensions, usually by about age 16 years (Fig 15-4). Changes in refractive error vary widely, but if myopia presents before age 10 years, there is a higher risk of eventual progression to myopia of 6.00 D or more. Astigmatism is common in infants and often regresses.

Figure 15-4 Change in mean refractive error as a function of age. (Modified with permission from Eustis HS, Guthrie ME. Postnatal development. In: Wright KW, Strube YNJ, eds. Pediatric Ophthalmology and Strabismus. 2nd ed. New York: Springer-Verlag; 2003:49.)

The term emmetropization refers to the process in the developing eye in which the refractive power of the anterior segment and the axial length of the eye adjust to reach emmetropia. The reduction in astigmatism that occurs in many infant eyes and the decreasing hyperopia that occurs in eyes after age 6–8 years are examples of emmetropization.

Orbit and Ocular Adnexa

During infancy and childhood, the orbital volume increases and the shape of the orbital opening becomes less circular, resembling a horizontal oval. The lacrimal fossa becomes more superficial, and the angle formed by the axes of the 2 orbits becomes less divergent. The palpebral fissure measures approximately 18 mm horizontally and 8 mm vertically at birth and changes very little during the first year of life. However, from age 1 to 10 years, the palpebral fissure length increases rapidly, causing the round infant eye to acquire its elliptical adult shape.

Histologic studies show that the nasolacrimal duct is not fully canalized in many newborns, but most are asymptomatic.

Cornea, Iris, Pupil, and Anterior Chamber

Average central corneal thickness (CCT) decreases during the first 6–12 months of life (see the section Dimensions of the Eye). It then increases from 553 µm at age 1 year to 573 µm by age 12 years and stabilizes thereafter. CCT is similar in white and Hispanic children but decreased in African American children. Most changes in iris color occur over the first 6–12 months of life, as pigment accumulates in the iris stroma and melanocytes. Compared with the adult pupil, the infant pupil is