Neonatal Ophthalmology

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Chapter 15

Neonatal Ophthalmology

Normal Visual Development

Term newborns can often fixate on a target. The ability to track an object, however, does not generally develop until approximately 2 months after birth. Visual acuity, measured with visual evoked potentials, has been estimated around 20/400 at birth. Color vision and contrast sensitivity have only rudimentary function in the newborn. Best-corrected visual acuity gradually improves during early childhood as the brain and retina mature.

The central retina is still actively developing throughout the 20th and 30th weeks of gestation. Myelination of the optic nerves and radiations continues during this time as well. Infants have fused eyelids until 25 weeks’ gestational age (GA), and the lids can remain fused in some cases until 30 weeks’ GA. The effects of these changes on the development of visual function are still being studied. It is unknown whether earlier exposure to visual stimuli has a positive or negative effect on eventual visual development. However, premature infants may demonstrate delayed visual milestones in early infancy.

The pupillary light reflex should be observable after 31 weeks’ gestational age. A blink reflex to light can often be observed a few days after birth. 123

Basic Ocular Examination

The lids should be examined for any abnormalities, including malformation, swelling, or discharge. Pupils should be examined for signs of irregular shape. The cornea, lens, and retina should be assessed with the red reflex test.

The red reflex test was well described in a policy statement by the American Academy of Pediatrics in 2008, part of which is included here. The test uses the transmission of light from an ophthalmoscope through all the normally transparent parts of a subject’s eye, including the cornea, aqueous humor, lens, and vitreous. The light reflects off the retina and optic nerve, is transmitted back through the optical media and through the aperture of the ophthalmoscope, and is imaged in the eye of the examiner. Any factor that impedes or blocks this optical pathway will result in an abnormality of the red reflex.

The test is performed by holding an ophthalmoscope close to the examiner’s eye with power set at “0” and projecting the light simultaneously onto both eyes of the infant from a distance of approximately 18 inches away in a darkened room. Abnormalities include a diminished reflex, white reflex, or asymmetric reflexes.

Before discharge from the neonatal nursery, all children should have an examination of the red reflex of the eyes performed by a pediatrician or neonatologist. The test is important for the early detection of vision disorders and systemic diseases with eye manifestations. All infants with an abnormal or absent reflex should be referred immediately to an ophthalmologist.

In general, no. An adequate examination can usually be performed through the undilated pupil. There has been some question as to whether pupil-dilated red reflex examinations improve identification of conditions such as retinoblastoma and congenital cataract, but this has not been definitively established.

Leukocoria means “white pupil.” Differential diagnosis includes retinoblastoma, retinal detachment, cataract, retinopathy of prematurity (ROP), coloboma, primary persistent hyperplastic vitreous, congenital infection, and vitreous hemorrhage. Prompt ophthalmologic consultation is important in cases of suspected leukocoria.

Sclerocornea, Peters anomaly, forceps trauma, congenital glaucoma, congenital hereditary endothelial dystrophy, mucopolysaccaridoses, and corneal dermoids can result in a white or clouded appearance to the cornea and cause an abnormal red reflex. Prompt ophthalmologic consultation is important in cases of corneal clouding.

In a term baby tears are produced with crying beginning between month 1 and month 3 of life. Excessive tearing in the early stages of life most often represents congenital nasolacrimal duct obstruction, which is common and spontaneously resolves in approximately 90% of cases within the first year. However, excessive tearing associated with other abnormalities, such as blepharospasm and photophobia (in congenital glaucoma), or periocular erythema and edema (in dacryocystitis), warrants urgent evaluation.

Strabismus refers to misalignment of the eyes. Intermittent strabismus is often observed in the newborn and tends to resolve. Strabismus that persists beyond the first few months of life should be referred to an ophthalmologist for further evaluation. 45

ROP

ROP stands for retinopathy of prematurity. ROP is a vascular disease affecting the developing retina that is a leading cause of childhood blindness in the United States and throughout the world.

Retinal vascular development begins during the second trimester of pregnancy, and full maturation typically occurs during or after the third trimester of pregnancy. In premature babies much of this development is taking place ex utero. The abnormal retinal development seen in ROP is in response to the artificial environment experienced by the neonate after birth.

In the first phase of pathogenesis, hyperoxia leads to cessation of the normal vascular development of the peripheral retina. In the second phase increased metabolic demand causes relative hypoxia to the peripheral retina, which leads to increased production of pro-angiogenic growth factors such as vascular endothelial growth factor (VEGF) in the eye. This in turn stimulates abnormal proliferative vascular development. The proliferation can cause traction on the retina and bleeding inside the eye, which leads to vision loss ( Fig.15-1).

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Figure 15-1 Schematic representation of IGF-1/VEGF control of blood vessel development in ROP. A, In utero, VEGF is found at the growing front of vessels. IGF-1 is sufficient to allow vessel growth. B, With premature birth, IGF-1 is not maintained at in utero levels, and vascular growth ceases despite the presence of VEGF at the growing front of vessels. Both endothelial cell survival (AKT) and proliferation (MAPK) pathways are compromised. With low IGF-1 and cessation of vessel growth, a demarcation line forms at the vascular front. High oxygen exposure (as occurs in animal models and in some premature infants) may also suppress VEGF, further contributing to inhibition of vessel growth. C, As the premature infant matures, the developing but nonvascularized retina becomes hypoxic. VEGF increases in retina and vitreous. With maturation, the IGF-1 level slowly increases. D, When the IGF-1 level reaches a threshold at 34 weeks’ gestation, with high VEGF levels in the vitreous, endothelial cell survival and proliferation driven by VEGF may proceed. Neovascularization ensues at the demarcation line, growing into the vitreous. If VEGF vitreal levels fall, normal retinal vessel growth can proceed. With normal vascular growth and blood flow, oxygen suppresses VEGF expression, so it will no longer be overproduced. If hypoxia (and elevated levels of VEGF) persists, further neovascularization and fibrosis leading to retinal detachment can occur. (Smith LEH. Pathogenesis of retinopathy of prematurity. Semin Neonatol 2003;8:469–73.)

The “first epidemic” of ROP occurred in the 1950s and involved premature babies exposed to high levels of oxygen after birth. In most developed countries the danger of high levels of oxygen to the neonatal eye is a well-known risk factor. Survival rates of extremely-low-birth-weight (ELBW) infants have increased as neonatal and oxygen management has improved in developed countries, and these ELBW infants are at high risk for ROP (“second epidemic”). In developing countries, where neonatal intensive care is still developing and infants are often exposed to high levels of supplemental oxygen, larger and more mature babies are once again getting ROP. This has been termed a potential “third epidemic” of ROP.

Risk factors for ROP include degree of prematurity; low birth weight; slow weight gain after birth; and general health factors, such as anemia; intraventricular hemorrhage; and acidosis. There may be a genetic predisposition to ROP, and advanced maternal age may also be an independent risk factor.

The frequency of ROP in the United States has been found to be approximately 65% in infants with birth weight below 1251 g. In most cases the disease is mild and spontaneously regresses. A small percentage of these infants will progress to disease requiring treatment, usually between 36 and 40 weeks postmenstrual age.

Infants with a birth weight of ≤1500 g or gestational age of 30 weeks or less (as defined by the attending neonatologist), and selected infants with a birth weight between 1500 and 2000 g or gestational age of >30 weeks with an unstable clinical course, should have retinal screening examinations. This examination is to take place either at 31 weeks’ GA or 4 weeks after birth, whichever is later.

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