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Early Intervention Training Center for Infants and Toddlers With Visual Impairments Module: Visual Conditions and Functional Vision: Early Intervention Issues Session 2: Visual Capacity Major Points A. Introduction to vision Vision provides continuous and holistic information that is not available through any other sense. Vision facilitates attachment between infant and caregivers and development of social, communication, cognitive, and motor skills. Of all of our receptors or senses, vision is the only one that provides holistic simultaneous information that also allows or enables us to integrate information from all of our other sensory systems (Hyvärinen, 2000). Vision enables infants to learn about people, objects, and events in their world, encourages play behaviors, promotes visual imitation of skills and activities of other family members, and facilitates social development and self-help activities, including eating and bathing. Only vision and hearing enable young children to experience people, objects, and events at a distance. Vision alone provides continuous, simultaneous, and holistic information about the world beyond arm’s length (Hyvärinen, 2000). Vision also plays a critical role in attention. For individuals with intact vision, visual cues rather than sound, tactile, or olfactory cues typically determine our attentive focus. Visual attention is closely tied to cognitive development and has been the subject of intense study by developmental and cognitive psychologists (Atkinson, 2000; Johnson, 1991; Ruff & Rothbart, 1996). Vision motivates us to stay awake, alert, and attentive to people, objects, and events that are critical to our happiness and well-being. Vision allows infants to imitate the actions and behaviors of important people in their lives and allows them to learn about appropriate behavior within natural contexts. Vision drives early nonverbal communication (Glass, 2002; Warren & Hatton, 2003). Infants’ ability to see their caregivers’ faces and respond to smiles facilitates bonding, attachment, and reciprocal interactions. Later, vision is used to establish joint attention to key objects in the environment. According to Fazzi and Klein (2002), gestures or nonverbal language comprise half of all communication between individuals, with verbal communication comprising the other half. Vision allows infants to access incidental events or clues from the environment; which provide anticipatory cues that prepare their nervous systems for responding through motor actions such as eating, grooming, and playing (Fazzi & Klein, 2002). Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 1 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments Visual-motor skills, or eye-hand coordination, along with cognitive (or thinking) abilities, enable infants to continually discover new things about the world around them. A critical stage in visual and motor development occurs at around 4-6 months, when infants begin to reach and grasp (Glass, 2002; Hyvärinen, 2000). They can then manipulate objects, and because of the ability to focus on objects at varying distances, infants notice near and distant objects. The development of purposeful movement allows infants to actually move to enticing people and objects in their environment. Physical control of the visual environment provides infants with the opportunity to pair active touch and movement with visual experiences so that they can explore their world and examine it deliberately (Hyvärinen, 2000). According to Hyvärinen (2000), infants acquire the following concepts and cognitive skills as they manipulate objects: size constancy: objects retain their size even though they appear smaller at a distance; shape constancy: objects remain the same shape even though their shapes might appear to alter when viewed at different angles; depth cues: nearer objects overlap with those at a distance, light and shadow effects; and figure-ground relationships: single figures can be visually selected from backgrounds, and elements of a scene can exist at different distances from the eye. Because there are critical or sensitive periods of experience dependent development in the visual system during the first few years of life (Bruer & Greenough, 2001; Horton, 2001; Tychsen, 2001), impairments to the visual system during this early period, even if corrected, can permanently influence a child’s visual learning (Erin, Fazzi, Gordon, Isenberg, & Paysse, 2002; Tavernier, 1993). Key visual structures and the early development of vision in typically developing children will be discussed in the following section. B. Visual development In typically developing children, visual development proceeds in a predictable pattern. Sasha was born full-term without complications. Sylvia and Daniel, first-time parents, were amazed at how quickly their newborn daughter seemed to visually appreciate her world. As a newborn, she turned her head to look at light sources; developed eye contact with family members within 6 to 8 weeks after birth; tracked the family dog, Buster; and looked at the toys on her mobile. Sasha looked at her hands when she was 3 months of age. Before long, Sasha was swiping at her mobile toys, shifting her gaze back and forth to look at toys falling and rolling away, and shifting her gaze from the right to the left side to choose which one of two toys that she wanted. Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 2 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments Daniel was very surprised when Sasha, at 6 months of age, appeared to notice him from a distance of more than 6 feet without him making a sound to catch her attention. A month later, Sasha noticed small breadcrumbs and showed interest in pictures. She looked through windows and recognized familiar people that did not necessarily live in the household. Sylvia and Daniel noticed that as Sasha’s ability to sit and hold her head up when on her stomach become steadier, her visual attention and skills also appeared to improve. Understanding the progression of visual development is important for several reasons. First, it enables us to construct an accurate picture of the visual capabilities of typical infants at various ages and provides an indication of the visual world in which the infant lives. According to Hyvärinen (2000, p. 800), “the clinical evaluation of children with different visual problems uses the visual function of an infant with normal sight as the baseline reference.” Therefore, it is reasonable to expect that ECVCs who are knowledgeable about typical vision development will be able to assess functional vision in children with visual impairments and to recommend appropriate strategies to enhance visual function. In addition, knowledge of the normal course of visual development helps professionals to identify infants with atypical development that might reflect visual or neurological impairments. Research on the development of vision in animals and in humans with cataracts or other early visual deprivation suggests that there are critical or sensitive periods of development of the visual system (Bruer & Greenough, 2001; Horton, 2001; Hyvärinen, 2000; Tychsen, 2001). Consequently, if children are deprived of visual input early in life, they may not be able to achieve full visual potential because they lack early visual experiences and stimulation that are needed for the refinement of eye-brain connections that drive visual function. Thus, the visual system depends on early experiences and stimulation for normal development and is an experience-expectant system according to Greenough (Bruer & Greenough, 2001). Early detection of defects may prevent or facilitate the treatment of some visual disorders such as amblyopia and strabismus. For example, studies show that infants whose congenital cataracts were removed prior to 8 weeks of age can achieve normal visual development as measured by preferential looking techniques (Gelbert, Hoyt, Jastrebski, & Marg, 1982; Rogers, Tishler, Tsou, Hertle, & Fellows, 1981). Prenatal development During the prenatal period, the visual system usually develops in an orderly manner (Chandna & Noonan, 2000). On the twenty-first day of gestation, there is evidence of the first signs of the developing eye (Cook, Sulik, & Wright, 2003). At 6 weeks’ gestation, the optic nerve, called the optic stalk, begins to develop, and the upper and lower eyelid buds grow together and elongate to cover the developing eye. Shortly before and after this time, the oculomotor muscles develop. At 10 weeks’ gestation, the upper and lower lids are fused together, but they gradually separate by 6 months’ gestation. At the same time, the vitreous and retinal areas develop. By the seventh month, the inner layer of the retina develops to form the central macular depression or primitive fovea. The foveal cones, Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 3 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments however, will continue to change after birth. Rods outnumber the cones in density in the mid-peripheral area before birth, and the parafoveal area shows mature rod photoreceptors at birth, making them the principal photoreceptors in the far periphery. Postnatal development The visual system of the newborn is immature but functional at birth (Hyvärinen, 2000). When a full-term baby is born, the eye is 75 to 80% of the size of an adult eye (Eustis & Guthrie, 2003). The cornea is typically flat, causing the infant to be hyperopic or farsighted. Within the first year, the cornea changes in size, shape, and appearance. It becomes enlarged, thinner, and more transparent (Eustis & Guthrie, 2003). According to Eustis and Guthrie (2003), optic nerve myelinization (i.e., the growth of sheath-like material that serves as an electrical insulator) starts at 7 months’ gestation and is complete 1 month after birth. However, the myelin layer is thin and will continue to develop throughout childhood. The macula (i.e., the structure of eye that provides a sharp, clear central vision that allows a person to see color and detail) is the least-developed ocular structure at birth. Ophthalmologic exams show a seemingly mature macula at 42 weeks’ gestational age, although it is not functionally mature until later in childhood (Eustis & Guthrie, 2003). The density of retinal receptor cells called cones (used to detect details and discriminate colors) located in the fovea (the area of the macula responsible for the sharpest vision) is only one-third that of adults, and the cone length is one-tenth that of adults. The peripheral retina is related to motion detection. The macula provides the “what” information while the periphery provides the “where” information in vision. In addition, color changes occur in the iris during the first 6 months of an infant’s life for children with blue, green, or gray eyes (Eustis & Guthrie, 2003). Please see Handout A for a summary of early ocular development. Development of visual abilities and behaviors Young children’s vision and visual systems mature in the months following birth (Eustis & Guthrie, 2003; Hyvärinen, 2000). Both Teller (1997) and Dobson (1993) noted that infants within the first 6 to 12 months demonstrate improved visual awareness, acuity, and fixation, better control of eye movements, improved visual scanning, and integration of information from vision and motor skills. Although children are born with the ability to orient to objects and faces and detect movement, these skills mature over the first 6 months of life as the cortical brain cells experience an increase in responsiveness (Chandna & Noonan, 2000). Glass (2002) noted that newborn infants attend to form, object, and face; are sensitive to bright light; and are more visually responsive under low illumination. Although newborns may not initially have a steady gaze, they are capable of focusing on people and objects quite close to their face. As previously stated, infants are generally farsighted at birth, and become less farsighted during the toddler and preschool years. Before 2 months of age, infants' eyes have the ability to focus on distant objects as well as close objects; but they do not focus very accurately (Hyvärinen, 2000). Infant eye Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 4 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments movements are unsteady during the first few months; sometimes they will focus too close (in front of the object) and sometimes too far (Hyvärinen, 2000). The ability to focus accurately becomes more coordinated by the third month. Eye contact with parents occurs at approximately 6 weeks (Erin & Paul, 1996; Hyvärinen, 2000) and usually no later than 8 weeks. Convergence develops between 3 and 6 months and enables both eyes to work together to view objects near or far. Convergence is driven by the infant’s ability to accommodate. Accommodation occurs when ciliary muscles contract to increase the lens curvature to focus images on the retina. Any accommodation will result in some convergence. Additionally, as the medial rectus muscles contract to keep the eyes aligned and on-target, they converge as the pupils constrict to increase the depth of focus (Wright, 2003a). Binocular vision develops by 3 to 4 months of age (Johnson, 1997; Shea, Fox, Aslin, & Dumais, 1980). At this age, most infants use both eyes together to receive a threedimensional image or stereopsis. Shortly thereafter, at 4 to 5 months of age, infants refine their reach and grasp behaviors. Physical control of the visual environment provides infants with opportunities to pair active touch with visual experiences, as previously indicated. Hall and Bailey (1989) studied the sequence of visual development of typical infants and young children and described visual behaviors observed during the first 2 years. Handout B provides an adapted version that may be useful in assisting families in identifying whether the young child exhibits a variety of visual behaviors within natural environments. For a detailed description of the development of visual function in infants, refer to Developmental Guidelines for Infants With Visual Impairment by Lueck, Chen, and Kekelis (1997). Although infants’ ability to see detail at birth is not fully developed, it improves rapidly during the first year (Hyvärinen, 2000). Newborn visual acuity, or ability to discriminate detail, has been estimated to range from 20/400 to 20/600 depending upon the type of assessment used (Eustis & Gutherie, 2003). The visual evoked potential (VEP) or visual evoked response (VER) electronically measures electrical activity in the visual cortex (occipital cortex) that results from the retinas’ response to stimulation. This information is obtained from electrodes attached to the infant’s scalp during exposure to visual stimuli. The VEP or VER is used to identify objects in the visual nerve pathway from the retina to the brain. No motor response is required; however, VEPs cannot assess the children cognitively process visual input. Forced-choice preferential-looking tasks such as the Teller Acuity Cards (Vistech Consultants, 1990) require a motor response of looking at cards with increasingly small gratings. Eustis and Guthrie (2003, pp. 50-51) provide the following estimates of visual acuities during the preschool years. Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 5 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments Development of Visual Acuity in Young Children Newborn 3 months Forced-choice preferential 20/600 20/120 looking Visual evoked 20/400 potentials Eustis and Guthrie, 2003, pp. 50-51. 6 to 7 months 12 months 3 to 5 years 20/60 20/20 20/20 Preferential looking experiments with 1- to 5-day-old infants using the colors red, green, yellow, and blue suggested that newborns can see red, yellow, and green but not blue (Adler, n.d.). In these experiments, the infant was presented with a gray card with two blocks of rectangular color on one side, and no color on the other. Teller (1997) theorized that if infants see color, they will look at the color first and not at the gray area. According to Teller (1997), the saturation or brightness of the colors has an impact on the infant’s ability to detect color—the brighter the color in the warm-color spectrum, the more easily it is detected by infants. For infants, the macula is more sensitive to higher wavelengths of color in the red/orange/yellow color spectrum (Teller, 1997). According to Adler (n.d.), adult like color perception develops as early as 2 to 4 months of age depending on the saturation of the color. The infant’s response to contrast sensitivity may be a useful indicator of ability to use vision within activities of daily living. Contrast sensitivity, or seeing subtle shades of gray, is underdeveloped at birth, but by 2.5 to 3 months of age, infants can see shades of gray almost as well as adults, provided that the pattern size is large (Atchley, 1999). Overall contrast sensitivity in infants increases as the efficiency and density of the cones at the fovea improve (Chandna & Noonan, 2000). In a detailed review of research on measured visual field extent, Mohan and Dobson (2000) discussed issues related to the development of visual field and the challenges inherent in measuring it. Variations in the assessment used (type of measure, size and luminance of stimulus, etc.) may impact measurement results. In addition, the nasal and upper visual fields may mature faster than the temporal and lower visual fields. Mohan and Dobson noted that there is no doubt as to whether the visual field extent of infants and toddlers is considerably different from that of adults. Nonetheless, measurement confounds make it difficult to determine at what age visual fields reach adult like levels. The large range in ages for adult like visual fields in very young children reported by different researchers in the Mohan and Dobson review is notable, and this suggests that we currently do not know when the entire visual field reaches an adult like status. A description of visual behaviors depicting visual abilities drawn from developmental psychology (Atkinson, 2000; Mohan & Dobson, 2000; Ruff & Rothbart, 1996) and pediatric Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 6 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments ophthalmology (Eustis & Guthrie, 2003; Hyvärinen, 2000; Wright, 2003c) follows and is also included as Handout C, “Development of Visual Behaviors and Skills” (Fox, 2003). Table 2. Chronology of Visual Behaviors Chronological Age At birth Visual Behaviors 2 months attend to different aspects of objects and events track moving objects in a jerky manner that lags behind objects’ movement appear to look through, not at, objects of interest have short periods of visual alertness have preference for moving targets and human faces scan faces with fixation concentrated at the edges have uncoordinated eye movements have difficulty disengaging from visual targets exhibit selective attention from first day of life are aware of sources of light and will turn their heads and eyes toward diffused light attend based on intensity of stimulus—contour, size, and brightness attend longer to patterns rather than blank fields of color prefer patterns and objects that have large features, high contrast, and borders prefer patterns of curved, rather than straight, lines need a period of familiarity and some degree of habituation before shifting gaze attend to attributes such as pattern and form change looking during developmental transition track more smoothly are awake and looking around for longer periods of time are more likely to focus on faces or bull’s-eyes regardless of size or brightness of other alternatives look at caretakers’ faces some of the time and other times fail to establish eye contact, often looking at the hairline or edge of the face have glassy or partly closed eyes during face-to-face interactions scan objects for internal and external contours and larger distribution of scanning space Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 7 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments Chronological Age 3 months Visual Behaviors 4 months 5 months 6 to 7 months 7 to 10 months 9 months reduce obligatory looking behaviors—infants are able to disengage focus on visual target change patterns of looking between 3 to 9 months, recognize repeated events through looking gain greater control of eye movements due to increased cortical development are more likely to make eye contact see better due to maturation of the visual system expand visual field and are therefore more responsive to shape and events develop strong visual preferences for novel objects at novel locations at 3 to 6 months increase amount of time looking at objects acquire greater control over shift of gaze, making attention more flexible shift fixation across midline develop binocular vision begin to reach, grasp, and manipulate objects that engage their visual attention reach adult levels of visual acuity and binocularity with VEP attend to small objects make eye contact with adults at several feet develop eye-hand coordination with small objects coordinate visual joint attention with objects and adults more effectively at 12 months experience a major transition point in development decrease time spent looking because they learn and habituate faster are proficient in visual exploration of novel objects shift visual attention from primary caregiver to objects start looking toward their mother’s faces at a distance—social referencing begin using caregivers as a visual point of reference in ambiguous situations begin to imitate actions of others with a delay Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 8 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments Chronological Age 12 months 18 months Toddler 24 months Birth to 10 years Visual Behaviors attend more to novel objects and events sustain attention for the purpose of exploring and learning increase looking during play with an array of toys change in selectivity as new skills and knowledge emerge comprehend language sufficiently for it to direct visual attention are skilled in following glances and gestures of others have experiences in cognition and play that influence visual attention base visual attention on what others attend to develop sustained attention in naturalistic settings that increases as they learn to play with toys or watch TV attend to complex visual displays such as looking at TV refine looking behaviors as cognitive skills increase have focused visual attention that doubles in length of time experience rapid improvement in visual field development in the first year and then slower maturation the first 10 years (Eustis & Guthrie, 2003) continue to mature until adult like visual field is attained—precise age of attainment is uncertain (Mohan & Dobson, 2000) Variations in visual maturation among children of similar chronological ages In order to understand the differences in visual maturation among children of similar chronological age, it is first important to know that infant visual development and maturation occur rapidly during the first year of life as discussed earlier in this session. The infant’s visual development, however, can be interrupted or modified by internal (e.g., sickness) or external (e.g., lack of opportunity to use vision) factors in the environment. Infants may have reflexes and skills that do not appear to be within the typical range during the first year. Visual abilities may appear to be advanced or delayed, yet still fall within the typical range of development. The vignette below illustrates how two typically developing infants differ in their rate of visual and visual motor development due to individual differences. Sylvia and Letty, best friends since junior high, each married and had their first child within 2 weeks of each other. Sylvia’s son, Raul, and Letty’s son, Kenny, were born at full term with no complications. Kenny looked at his mom’s and dad’s faces almost immediately when he came home from the hospital. He was very visually interested in his environment from the moment he became a member of the family. He seemed to notice shiny, bright reflections from glass tabletops in the living room of the house. He swiped, reached for, and grasped bright toys Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 9 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments as early as 3 months and was touching his mom’s and dad’s faces at the same time. At about 5.5 months, he sat independently and reached for everything around him. He appeared to notice events, objects, and people at distances beyond 6 feet at about that same time. Kenny was interested in looking at bright pictures in books and ate small-sized snack food from his highchair tray. Raul demonstrated many of the same behaviors, but as Sylvia and Letty compared notes, Raul’s timeline for demonstrating visual and visual motor behaviors occurred about 2 months later than Kenny’s demonstration of those skills. There was no medical explanation for the differences, though they were both considered to be developmentally typical. At 18 months, both boys were demonstrating similar developmentally appropriate skills in the visual and visual motor areas of development. C. Atypical visual development Visual impairment can result from prematurity or atypical development of particular ocular structures that may limit visual capacity and result in atypical visual development. The following table can also be found as Handout D. Table 3. Congenital Structural Abnormalities That May Alter Visual Development Name Optic nerve hypoplasia Source Elston (2000) Atypical development of the optic nerve Microphthalmia/ anophthalmia Hertle, Schaffer, & Foster (2002) Anophthalmia, absence of the eye, and microphthalmia, a very small and typically malformed eye, represent structural abnormalities of the globe Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH Comments Occurs in the first or early second trimester May be associated with young maternal age, fetal alcohol syndrome, possible maternal diabetes mellitus Children at increased risk of endocrine disturbances Visual acuity may range from light perception to normal acuity May result from insult at number of developmental stages or from acute exposure to toxins during early development Could be due to failure or late closure of optic fissure Microphthalmia may result in decreased visual acuity, photophobia, fluctuating visual abilities Anophthalmia results in total blindness of affected eye S2 Major Points Page 10 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments Name Coloboma Failure of parts of the ocular system to develop due to abnormal fusion of optic fissure Congenital cataract Source Cook, Sulick, & Wright (2003) Wright (2003b) Clouding or opacity of the lens that produces indistinct image on retina Developmental abnormality of the anterior segment Hertle, Schaffer, & Foster (2002) Defective development of structures near the front of the eye—between cornea and vitreous Comments Defect occurs at 4 to 5 weeks’ gestation Can affect iris, choroid, retina, and optic nerve When optic nerve or retina is involved, vision is affected Isolated iris colobomas may not affect visual acuity Decreased visual acuity, photophobia, field loss often results from colobomas, depending on areas that failed to develop May result from genetic/hereditary conditions, maternal infection, systemic diseases Treatment within the first few weeks of life results in near normal visual development Defects in these structures may result in poor vision due to obstruction of light as it passes through the cornea, pupil, or lens Defects in trabeculum (involved in circulation/drainage of fluid in the eyes) can result in primary glaucoma that can cause vision loss due to damage of the optic nerve Defects of iris (aniridia, coloboma) affect pupil size and can cause blurred image, poor focusing, and sensitivity to glare Prematurity and visual development Glass (2002) and Creger (1989) provided descriptions of the fetal eye of premature infants during the third trimester. Their descriptions of ocular structures are summarized in the following table and in Handout E. This information may be helpful to ECVCs who work with infants and toddlers with retinopathy of prematurity (ROP) or cortical visual impairment (CVI), two visual conditions associated with prematurity. Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 11 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments Table 4. Development of Fetal Eye Structure 24 to 28 Weeks Eyelid Lids are fused early in development, and now reopen. Pupil The tunica vasculosa lentis begins to atrophy, and at 27 weeks, pupillary light response can be observed. Lens By 27 to 28 weeks, the lens is covered with vessels in the anterior capsule. The second layer of the 4layer nucleus is developing. Media The media is cloudy. The hyaloid system begins to regress. 30 to 34 Weeks Eyelids are less translucent. Retina Retina is complete except for the foveal region. Visual cortex All retinal layers are present by 22 weeks. Rods (about 130 million), important for low light and peripheral vision, and cones (about 6.5 to 7 million), important for detail, central vision, daylight, and color, develop by 25 weeks, and differentiation begins. Vascularization is just beginning. Rapid growth and differentiation of nerve cells and dendrites occur. At 28 to 32 weeks, the optic nerve begins to develop. At 14 to 22 weeks, the optic chiasm is evident. Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH 36 Weeks The second layer is complete, and the third begins to form. Vessels of the anterior capsule are completely atrophied by 34 weeks. The media clears. The hyaloid has almost disappeared. Marked development of dendritic spines and synapses occurs. The media is less dense than in adults. Some remnants of the hyaloid may still be present. The number of cones in the fovea increases. The temporal region is almost fully vascularized. The visual cortex structure appears similar to that of a fullterm infant. The nerve, chiasm, and optic tract all myelinate over the next 2 years. S2 Major Points Page 12 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments Glass (2002) and Creger (1989) also described visual function in premature infants. Although each infant is unique, these descriptions provide ECVCs with information that may help them understand the range of visual behaviors observed in premature infants. Table 5. Functional Visual Response of the Preterm Infant Functional Visual Response of the Preterm Infant 24 to 28 Weeks Immature visual function is present once the anatomic pathway to the visual cortex is complete. A visual evoked response is obtainable in bright light. Lids tighten In bright light. The infant is very nearsighted. 30 to 34 Weeks Pupillary reflex is present. 36 Weeks VEP response is like that of a newborn. Bright light causes lid closure. Vertical and horizontal tracking to soft light occur. There is visual attention to highcontrast forms under low illumination conditions. The infant prefers to look at patterns. There is no refractive error. Premature infants tend to be more myopic at birth, especially when retinopathy of prematurity is present (Eustis & Guthrie, 2003). Premature infants also have a smaller pupillary aperture and, therefore, may or may not demonstrate a light response depending upon the degree of prematurity (Eustis & Guthrie, 2003). In a child born pre-term with medical complications or with a documented eye disease, visual skills may emerge at a slower rate or in a different order. The rate of development may be affected by the premature infant’s physiological or autonomic responses, motor development, state control, attention, and self-regulation (Creger, 1989). Charity was born at 24 weeks’ gestation and spent time in the neonatal intensive care unit (NICU). She appeared to be overwhelmed by environmental stimuli, including the toys that her family brought for her, and by being handled by the nursing staff. She was not able to participate in the reciprocal interactions that infants usually engage in with their caregivers, and thus was showing few if any visual gaze responses to familiar caregivers. At 34 weeks, Charity began to recover from her own agitation when left alone. Her parents were then encouraged to assume many of the caregiving responsibilities. Charity was released from the hospital a few days after her original due date and went home with her parents. At about this time, her parents noted that her visual gaze and hand-to-mouth behaviors were becoming more frequent, though they sometimes did not occur, depending upon Charity’s state of alertness. Charity also visually responded to pastel-colored toys by localizing and fixating on them more frequently than to the bright-colored toys that her sister and brother had enjoyed at the same age. Again, Charity’s visual responses Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 13 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments appeared to depend on her waking state, environmental factors, and attributes of the toys and caregivers. D. Physiology, environment, and visual development Corn (1983, 1989) proposed a model of visual functioning with three essential components for individuals with low vision, as shown in Handout F. These three components include visual abilities, stored and available individuality, and environmental cues. ECVCs who understand these physiological and environmental components and how they interact with each other are better able to facilitate visual functioning in young children with visual impairments (Erin, Fazzi, Gordon, Isenberg, & Paysse, 2002). Visual abilities include visual acuity—nearpoint, midpoint, distance; visual field—central, peripheral, hemifields; movement of eyes—alignment, stability, and coordination of eyes (vertical, horizontal, diagonal, crossing midline, and ability to use both eyes together); brain functions (cortical and subcortical)—physiological control of eyes and processing/interpretation; and light and color perception—color, tolerance, light/dark adaptation. Stored and available individuality includes cognition—intelligence, problem solving, communication, concept development, memory, and experience; sensory integration—hearing, touch, taste, and smell; perception—part/whole, figure/ground, closure, and sequence; physical abilities—motor development, muscle tone, stamina, endurance, reaction time, and general health; and psychological make-up—emotional regulation and stability, motivation, attention, self-esteem, identity, and sociability. Environmental cues may help young children with visual impairments use their functional vision more effectively. Environmental cues include color, contrast, time, space/distance, and illumination. When caregivers increase or decrease the intensity of each cue, children may be better able to see a favorite toy that is not within arm’s reach. By encouraging the child to move closer to the toy, space/distance is modified, and the child is more likely to see the toy. The Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 14 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments following two examples demonstrate environmental cue alterations to support the child’s ability to use vision within natural environments. Takoda is accustomed to taking his bath in the kitchen sink. Stephanie, his mother, uses the sink because it provides Takoda a sense of security that he did not have in the regular bathtub. She noticed that when she adjusted the space (decreased size of tub), Takoda did not cry or appear scared in the water during bath time. Takoda is attracted to the color red, and his Winnie the Pooh shampoo bottle is bright red (color/intensity). Stephanie allows Takoda to look at the red washcloth coming toward his face before washing him by adjusting the amount of time she gives him to look at the cloth (time). Sierra, a toddler with albinism, is sensitive to outdoor light. When asked to find her brother’s bike in the backyard (familiar setting), Sierra was within a foot of it and walked past it as she faced the bright sun. Her mother asked her to turn around and walk back toward her to look for the bike. When the sun was at Sierra’s back instead of in her eyes (illumination/glare reduction), she immediately noticed the bike after she turned around. Although the bike was orange and had black tape wrapped around the handlebars, providing high contrast, the glare and degree of illumination initially interfered with Sierra’s ability to find the bike. In addition to the components described above (Corn, DePriest, & Erin, 2000), infants’ visual development and functional use of vision are also impacted by biological factors such as regulation of biobehavioral states and temperament. Simeonsson and colleagues (1988) noted that the behavioral states of infants may range from sleep to active alert to highly distressed and agitated. As infants’ central nervous systems develop and more control of physiological states is possible, they may become more visually attentive and able to use vision effectively. As noted by Lueck, Chen, and Kekelis (1997), infant temperament influences the early development of children. Temperament is biologically based but is amenable to environmental influences via the goodness of fit between the child, the family, and the environment. Temperament dimensions include activity level; willingness to approach new objects, people, and events; adaptability; persistence/attention span; distractibility; rhythmicity; mood; intensity; and sensory threshold. Children who are attentive and approachable may be more likely to elicit experiences that will enhance visual function. When the temperament of a child is suited to the home environment, there will be a goodness of fit between child and family (Thomas & Chess, 1977). Carrie is a fearless 12-month-old with septo-optic dysplasia and low vision who is happy most of the time and loves interacting with her father and sister and exploring her environment. When introduced to new people or new toys, Carrie is a bit hesitant, but after a short period of time, she will initiate interactions with others and tactually and visually explore new toys. If Carrie’s parents completed a temperament questionnaire, we might Visual Conditions Module 06/04/04 EIVI-FPG Child Development Institute UNC-CH S2 Major Points Page 15 of 19 Early Intervention Training Center for Infants and Toddlers With Visual Impairments find that they rated her as being highly approachable, adaptable, and attentive. These temperament characteristics are conducive to learning and make care giving relatively easy. Tommy, on the other hand, has the same diagnosis and is the same age, but is fussy and very active, has little persistence, strongly resists new experiences, foods, and toys, and is not very adaptable. These temperament characteristics make care giving for Tommy much more challenging, and, therefore, may result in fewer opportunities for using his vision in a variety of settings and activities. With an understanding of the physiological, temperamental, and environmental factors that might influence young children’s visual capacity and visual function, early interventionists and families will be better equipped to plan and implement strategies that will facilitate the child’s optimal use of vision. References for Major Points Adler, S. (n.d.). Perceptual development. Retrieved April 24, 2003 from York University, Department of Psychology Web site: http://www.psych.yorku.ca/adler/courses/2110/lectures/lecture_5.htm Atchley, P. (1999). Contrast sensitivity (p. 3). 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