Course:KIN366/ConceptLibrary/Visual System

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Visual System
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KIN 366
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Instructor: Dr. Shannon S.D. Bredin
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The visual system is a component of the central nervous system that allows organisms to view the world around them (Alimohammadi, & Doroudi, 2010). Visual input is received from visible light in the environment, and transformed into a three-dimensional interpretation by the brain (Alimohammadi, & Doroudi, 2010). The visual system is an essential sense as more than half of the sensory receptors of the human body are contained within the eye (Alimohammadi, & Doroudi, 2010). While the physical components of the visual system are present at birth, growth and activity in the subsequent years of infancy and childhood are crucial to the development and fine-tuning of the system, and contribute to other important functions such as balance and posture (Australasian College of Behavioural Optometrists, 2014).

Components of the Visual System

The visual system is comprised of multiple constituents. Visual images are received by the eyes, put into focus, and sent to the brain for further instruction (Graven & Brown, 2008). The vital parts of the visual system include:

Eye

The eye is the organ of vision.

Cornea

The cornea is a transparent cover on the front of the eye with focusing abilities (Graven & Brown, 2008).

Lens

The lens is a structure that refracts incoming light onto the retina. It changes its shape accordingly to allow the eye to focus on objects at various distances (Graven & Brown, 2008).

Iris

The iris is a circular ring that controls the amount of light that enters the eye by constricting its inner area, known as the pupil (Graven & Brown, 2008).

Retina

The retina contains light receptors which create an image of the visual world (Graven & Brown, 2008). The event of light striking the retina produces chemical and electrical potentials that trigger nerve impulses to the brain (Graven & Brown, 2008).

Optic Nerve & Tract

Together, these continuous structures relay visual information from the retina to the brain (Graven & Brown, 2008).

Lateral Geniculate Nucleus

The lateral geniculate nucleus is the primary relay center for visual information received from the retina; it is contained within the brain (Graven & Brown, 2008).

Optic Radiations

Collections of nerve fibers in the lateral geniculate nucleus which carry visual information to the primary visual cortex (Graven & Brown, 2008).

Primary Visual Cortex

The primary visual cortex is the part of the brain that processes visual information (Graven & Brown, 2008).

Superior Colliculus

The superior colliculus controls the reflex of turning the head and eyes toward a visual stimulus (Graven & Brown, 2008).

Role in Balance and Postural Control

Appropriate control of maintaining the body’s upright posture depends on the proper integration of proprioceptive, vestibular and visual sensory information (Gaerlan, 2010; Redfern, Yardley & Bronstein, 2001; Steindl, Kunz, Schrott-Fischer & Scholtz, 2007). Of these three systems, the visual system provides the primary source of sensory input for maintaining postural balance (Gaerlan, 2010). Furthermore, research has shown that as a child grows and his visual system becomes further developed, postural regulation and efficacy will improve as well (Gaerlan, 2010). The visual system is responsible for stabilizing posture during low frequency movements, such as when an infant is learning to walk (Redfern et al., 2001; Steindl et al., 2007). Multiple studies have found that vision is the dominant sensory system used for maintaining standing stability in children who have recently begun walking independently (Redfern et al., 2001; Steindl et al., 2007). Conflicts in obtaining proper postural control can arise if sensory cues from one of the three sensory systems (visual, proprioceptive, or vestibular) do not match the others (Redfern et al., 2001). For example, if the visual input fails to be consistent with the input from the vestibular system this will lead to postural swaying and loss of balance (Redfern et al., 2001).

Loss of Vestibular Function

If vestibular function is limited or lost, the visual system will be heavily relied upon in order to maintain upright posture. This implies that if a person in this condition were to close their eyes, they would experience significant postural sway, and possibly a complete loss of balance (Redfern et al., 2001).

Loss of Proprioceptive Function

If proprioceptive function is limited or lost, visual input becomes vital for both maintaining upright posture and also carrying out desired movements (Redfern et al., 2001).

Stages of Development

The visual system is the most dynamic sense in the human body (Australasian College of Behaviour Optometrists, 2014; Alimohammadi & Doroudi, 2010; Graven & Browne, 2008). Because visual input impacts the movement of skeletal muscles, it is instrumental in allowing the individual systems of the body to coordinate and function together (Australasian College of Behaviour Optometrists, 2014).When a baby is born, the organs of the visual system are physically present, but it is not until after the birth that the vital growth and development of the system occurs (Australasian College of Behaviour Optometrists, 2014; American Optometric Association, 2014). Appropriate development of the visual system requires light, movement and a fluctuating physical environment (Australasian College of Behaviour Optometrists, 2014).

Important Milestones in Early Childhood

The following time frames outline typical behaviours that are expected to be observed from the time of birth, to early childhood:

Birth to 3 months
  • At birth, a baby should exhibit close-range vision, approximately 8-10 inches away from their face (American Optometric Association, 2014; Australasian College of Behaviour Optometrists, 2014)
  • By 3 months, coordination between both eyes will begin to develop and the baby should start to visually track and reach for moving objects (American Optometric Association, 2014)
5 to 12 months
  • The infant will begin to watch and track more distant objects (Australasian College of Behaviour Optometrists, 2014).
  • At 5 months, depth perception should begin to form; this will give the infant a three-dimensional view of the environment (American Optometric Association, 2014).
  • By 8 months, the infant may crawl toward objects in the visual field (Australasian College of Behaviour Optometrists, 2014; American Optometric Association, 2014).
  • By 12 months, the child may try to walk toward visually stimulating objects (American Optometric Association, 2014).
1 to 2 years
  • Hand-eye coordination should be well developed, and the child should be able to throw small objects with precision (American Optometric Association, 2014).
  • The child likes to watch the movement of wheels and other moving objects (Australasian College of Behaviour Optometrists, 2014).
  • The child can watch his own hand scribble on paper and is becoming more dextrous (Australasian College of Behaviour Optometrists, 2014).
2 to 4 years
  • The child can visually explore while walking and climbing (Australasian College of Behaviour Optometrists, 2014).
  • The child can watch and imitate the increasingly complex movements of others (Australasian College of Behaviour Optometrists, 2014).
  • The child can draw simple shapes on paper (Australasian College of Behaviour Optometrists, 2014).
4 to 5 years
  • The child has increased dexterity and can draw simple pictures (Australasian College of Behaviour Optometrists, 2014).
  • The child can place small objects into small openings (Australasian College of Behaviour Optometrists, 2014).
  • The child has an increasing interest in exploring new objects and places both visually and physically (Australasian College of Behaviour Optometrists, 2014).

Signs of Visual System Discrepancies in Children

Most babies are born with healthy eyes and develop visual capabilities without difficulty (American Optometric Association, 2014). However, once children reach toddlerhood, minor vision problems are more likely to occur. Problems may include needing to sit very close to a screen, squinting, head tilting, light sensitivity, and troubles with hand-eye coordination when playing with moving toys or throwing and kicking objects (American Optometric Association, 2014). Once children go to school, visual problems can easily affect their academic and social progress, and unfortunately these issues often go undetected (American Optometric Association, 2014). Signs to look for include headaches, avoidance of and difficulty reading, eye discomfort or fatigue, and poor performance in sports (American Optometric Association, 2014). Visual problems can become increasingly worse throughout childhood and adolescence, due to increased amounts of time spent reading and studying books with small print (American Optometric Association, 2014). For this reason, regular appointments with an eye doctor are recommended, and corrective eyeglasses may become necessary (American Optometric Association, 2014).

Tips for Parents and Practitioners

Parents

Parents play a vital role in making sure that their child’s visual system is developing properly. This can be done by looking for signs of eye or vision problems, seeking appropriate professional eye care, and engaging in age-appropriate activities that promote movement (American Optometric Association, 2014). Here are some age appropriate tips that parents can use to facilitate proper visual system development:

Birth to 4 months
  • Change the position of the baby’s crib as well as the position of the baby within the crib to promote eye tracking (American Optometric Association, 2014).
  • Use a nightlight or a lamp in the baby’s room to stimulate visual activity (American Optometric Association, 2014).
5 to 8 months
  • Hang interactive mobiles above the child’s crib to encourage reaching, grabbing, pulling and kicking (American Optometric Association, 2014).
  • Allow the child ample time and space to explore and move around on a carpeted floor (American Optometric Association, 2014).
  • Provide the child with wooden blocks to improve fine motor skills (American Optometric Association, 2014).
9 to 12 months
  • Engage in hide and seek or peek-a-boo games (American Optometric Association, 2014).
  • Encourage the child to crawl and creep around the physical environment (American Optometric Association, 2014).
1 to 2 years
  • Roll balls back and forth to develop the child’s tracking abilities (American Optometric Association, 2014).
  • Provide the child with various sized balls and blocks to develop fine motor skills (American Optometric Association, 2014).
2 and up
  • Practice tossing a ball back and forth; this activity can eventually develop into a game of catch (American Optometric Association, 2014).
  • Provide the child with outdoor playtime, and encourage bike riding, swinging, and rolling activities (American Optometric Association, 2014).
  • Encourage your child to physically interact with other children (American Optometric Association, 2014).

Educational Providers

Educational providers at the preschool level should encourage children to engage in physical activity involving other children. Additionally, there are a variety of other classroom activities such as puzzles, memory activities and visual tracking games that can assist in a child’s visual development (Eye Can Learn, 2014).

Physical Education Providers

Physical education activities for school-age children should incorporate moving equipment such as bicycles, jump ropes and pogo sticks (American Optometric Association, 2014). Additionally, target-oriented games using different size and shape balls, and plastic discs are extremely beneficial in developing hand-eye coordination and muscular strength (American Optometric Association, 2014). Older children and adolescents benefit from multi-skill games that require visual tracking and passing while moving at varying speeds, such as basketball or hockey. Additionally, activities involving the manipulation of equipment, such as a tennis racket or a field hockey stick prove to be beneficial for development as well (American Optometric Association, 2014).

Interesting Facts

  1. Individuals with anxiety disorders have been known to have increased sensitivity to vision in their postural control systems; in other words, many people with anxiety disorders suffer from motion sickness (Jacob, Redfern & Furman, 1995).
  2. Vision problems often lead to behavioural issues and difficulty focusing. For this reason, many school-age children are falsely diagnosed with behavioural disorders such as Attention Deficit Disorder (ADD) (American Optometric Association, 2014).
  3. Colour blindness is the reduced ability to see or distinguish between different colours (Gaerlan, 2010). Men are more affected by this condition than women, and it can be an acquired disorder as well as inherited genetically (Gaerlan, 2010).

References

Alimohammadi, M., & Doroudi, M. (2010). M & M Essential Anatomy. Dubuque, IA: Kendall Hunt Publishing Co.

American Optometric Association. (2014). Infant Vision: Birth to 24 Months of Age. Retrieved from http://www.aoa.org/patients-and-public/good-vision-throughout-life/childrens-vision/infant-vision-birth-to-24-months-of-age#2

Australasian College of Behavioural Optometrists. (2014). Visual Development. Retrieved from http://www.acbo.org.au/news-views/for-patients/92#ja-content

Eye Can Learn. (2014). Eye Can Learn: Eye Exercises for Better Visual Health. Retrieved from http://www.eyecanlearn.com/#Resources

Gaerlan, M.G. (2010). The role of visual, vestibular, and somatosensory system in postural balance (Master’s thesis). Retrieved from http://digitalscholarship.unlv.edu/

Graven, S.N., & Browne, J.V. (2008). Visual development in the human fetus, infant, and young child. Newborn & Infant Nursing Reviews, 8, 194-201. doi:10.1053/j.nainr.2008.10.011

Jacob, R. G., Redfern, M.S., & Furman, J.M. (1995). Optic flow-induced sway in anxiety disorders associated with space and motion discomfort. Journal of Anxiety Disorders, 9, 411-425. doi:10.1016/0887-6185(95)00021-F

Redfern, M.S., Yardley, L., & Bronstein, A.M. (2001). Visual influences on balance. Journal of Anxiety Disorders, 15, 81-84. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/11388359

Steindl, R., Kunz, K., Schrott-Fischer, A., & Scholtz, A.W. (2007). Effect of age and sex on maturation of sensory systems and balance control. Developmental Medicine & Child Neurology, 48, 377-482. doi: 10.1111/j.1469-8749.2006.tb01299.x