Visual Impairment

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As discussed in Chapter 10, retinopathy of prematurity (ROP) is a common complication of prematurity that increases with decreasing gestational age and birth weight. As a group, pre-term children have a higher risk of impaired visual acuity than full-term children (Table 11-4). Myopia (i.e., nearsightedness) is one of the most common visual sequelae, and its incidence increases with the severity of ROP and with decreasing gestational age. Myopia occurs in 20 to 22 percent of children born with birth weights of less than 1,251 or 1,751 grams, and 4.6 percent have a high degree of myopia (i.e., >5 diopters) (O'Connor et al., 2002; Quinn et al., 1998).

TABLE 11-4 Sensory Impairments in Children Born Preterm

Percentage with Severe Impairment_

Study

Year of Birth

No. of Subjects

Age (yr)

Gestational Age (wk)

Body Weight (g)

Visual

Hearing

Vohr et al., 2005

1997-1998

910

1.8

22-26

1

1.80

512

27-38

10.40

Hintz et al., 2005

1993-1996

341

1.8

<25

2.3

4.3

1996-1999

436

1.1

2.6

Wood et al., 2000

1995

26

2.5

</23

8

4

90

24

4

5

Wood et al., 2000

1995

167

2.5

25

1

1

Marlow et al., 2005

1995

241

6

<26

2

3

Wilson-Costello et al., 2005

1990-1998

682

1.8

<750

1

10

750-999

1

6

Wilson-Costello et al., 2005

1990-1998

1.8

<1,000

1

7

Mercier et al., 2005

1998-2001

2446

2

<1,000

2.1

1.2

Hack et al., 2005"

1992-1995

200

8

<1,000

0

2

Hack et al., 2000

1992-1995

221

1.8

<1,000

1

9

Hansen and Greisen, 2004

1994-1995

183

5

<1,000

3.30

3

1,000-1,500

2

0

Doyle et al., 2005

1991-1992

8

<1,000

1.10

1.50

" Two percent of the subjects required hearing aids and 14 percent had hearing impairments.

" Two percent of the subjects required hearing aids and 14 percent had hearing impairments.

Other visual problems include hyperopia and astigmatism (in 12 and 29 percent of children born at less than 29 weeks of gestation, respectively) (Hard et al., 2000). The need for glasses was higher in 7-year-olds born at gestational ages of less than 32 weeks than in controls born full term (13 and 4 percent, respectively) (Cooke et al., 2004). At 10 to 14 years of age, visual impairment was more common in children born with birth weights of less than 750 grams than in children born with birth weights of between 750 and 1,499 grams and children born with normal birth weights (31, 13, and 11 percent, respectively), as was the need for glasses (47, 24, and 27 percent, respectively) (Hack et al., 2000). In a British study of children born at less than 26 weeks of gestation, 24 percent of preterm 6-year-olds wore glasses, whereas 4 percent of controls with full-term gestations did so (Marlow et al., 2005).

Strabismus (i.e., ocular misalignment, or crossed eyes) is also a frequent complication of prematurity. Strabismus has been reported in 3 percent of children born full term; 14 to 19 percent of children born with birth weights less than 1,500 grams, birth weights less than 1,750 grams, and gestational ages less than 29 and 32 weeks; and 24 percent of children born at gestational ages less than 26 weeks (Bremer et al., 1998; Hard et al., 2000; Marlow et al., 2005, O'Connor et al., 2002). The risk of strabismus increases with intraventricular hemorrhage, periventricular leukomalacia, and the severity of ROP (Bremer et al., 1998; Hard et al., 2000; Hardy et al., 1997; Marlow et al., 2005; O'Connor et al., 2002; O'Keefe et al., 2001). Treatments for strabismus include correction with glasses or surgery, or both. Repka and colleagues (1998) reported that 10 percent of children with severe ROP underwent surgery for strabismus.

The sequelae of strabismus include amblyopia (i.e., suppression of the visual input to the cortex) and a loss of binocular vision. Amblyopia has been found to occur in 1 to 4 percent of the general population, 2.5 percent of preterm infants without ROP, 12 percent of children with ROP, and 20 percent of children with severe ROP (Cats and Tan, 1989; Repka et al., 1998). The rate of the absence of stereopsis was higher in 7-year-olds born at less than 32 weeks of gestation than in controls born at full term (16.5 and 3.8 percent, respectively) (Cooke et al., 2004). Optic nerve atrophy and cortical visual impairment can also influence visual acuity in preterm children (Repka, 2002).

Although late or severe ophthalmic findings, including cataracts, angle closure glaucoma, and retinal detachment, are uncommon in children born preterm, they can interfere with function and quality of life in children, adolescents, and adults who were born preterm (Kaiser et al., 2001; Machemer, 1993; Repka, 2002). Cataracts have been associated with untreated ROP and severe ROP (Kaiser et al., 2001; Repka et al., 1998). Glaucoma presents as an acute illness because of the severely increased pressure within the eye globe. The abnormal neovascular tissue of ROP can progressively and silently fold, exert traction, and tear or even detach the retina, causing a loss of vision (Kaiser et al., 2001; Machemer, 1993). Although most retinal tears or detachments occur in those with severe ROP, some children born preterm had mild or no ROP but a high degree of myopia (Kaiser et al., 2001). Surgical treatments, which include placement of a flexible band (i.e., a scleral buckle) around the eye to reduce tractional forces and vitrectomy (i.e., replacement of the vitreous fluid of the eye with sterile fluid), can restore visual function to some individuals. Severe detachment results in poor vision, with only light perception or, if the detachment is complete, no vision.

Ophthalmic morbidities are common in survivors of preterm birth, and early detection carries the best prognosis. Half of children with birth weights less than 1,751 grams had ophthalmic morbidities when they were evaluated at ages 10 to 12 years, whereas 20 percent of full-term controls had ophthalmic morbidities (O'Connnor et al., 2002). Although ophthalmic mor bidities were more likely in individuals with severe ROP, they were more common in survivors of preterm birth who had no or only very mild ROP than in controls born full term. Whether these ophthalmic problems contribute to the higher rate of visual perceptual deficits in the survivors of preterm birth (42 percent of 5- to 9-year-old children born at gestational ages less than 29 weeks compared with 14 percent of controls born full term) is not well understood (Hard et al., 2000, see section on Cognition). For some of these children, even if their visual system is intact, dysfunction of visual processing in the occipital cortex impairs their ability to perceive and understand visual patterns (drawings of figures, letters on a page).

Although the causes of ROP, ophthalmic morbidities, and visual perceptual deficits are, for the most part, unknown, identification of these morbidities allows their correction or amelioration, thereby improving functional outcomes. There is not yet adequate recognition of the need for regular ophthalmologic follow-up during the life span of survivors of preterm birth and assessment of their visual perceptual abilities when they are of preschool and school age (Hard et al., 2000; Kaiser et al., 2001; Repka, 2002).

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