Blindness By Birth | Group 1

Blindne­ss is the condition of lacking visual perception due to physiological or neurological factors. Various scales have been developed to describe the extent of vision loss and define blindness

Visual acuity (VA) is acuteness or clearness of vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain. Visual acuity is a measure of the spatial resolution of the visual processing system. VA is tested by requiring the person whose vision is being tested to identify characters (like letters and numbers) on a chart from a set distance. Chart characters are represented as black symbols against a white background (for maximum contrast). The distance between the person's eyes and the testing chart is set at a sufficient distance to approximate infinity in the way the lens attempts to focus.

An ophthalmologist is a doctor who specializes in eye problems. Visual impairment and blindness in children pose a special problem for ophthalmologists, as many eye care practitioners are not familiar with performing pediatric eye examinations and measuring visual acuity in infants. Infants are unable to verbalize their complaints, and history from parents and care takers may lack important details. However, the first year of life is also the time when the visual system develops and binocular vision is formed. If a visual deficit at this age is not treated in a timely manner, amblyopia and permanent visual deficit can occur. Hence, early diagnosis and prompt treatment is essential.

The burden of blindness, measured in blind-person years (i.e., the no of years spent as a blind individual), due to childhood blindness is second most common cause of avoidable blindness. Studies worldwide show that many of the causes of blindness in children are either preventable or treatable (ie, avoidable). Even children who have visual loss that cannot be clinically treated can be helped with low vision devices and rehabilitation. Childhood blindness affects the individual, their family, and the community. Blindness also has implications for infants’ development, education, and future social, marital, and economic prospects. Nearly 80% of all sensory input and 75% of early learning comes from vision. Early onset visual loss can have profound consequences on a child’s motor, social, emotional, and psychological development.

Severe Visual Impairment (SVI) and blindness in infants must be detected as early as possible to initiate immediate treatment to prevent deep amblyopia. Although difficult, measurement of visual acuity of an infant is possible. The causes of SVI and blindness may be prenatal, perinatal, and postnatal:

·         Prenatal: Congenital anomalies such as anophthalmos (missing an eye), microphthalmos (small eye), coloboma ( hole in one of the structures of the eye, such as the iris), congenital cataract, infantile glaucoma, and neuro-ophthalmic lesions are causes of impairment present at birth.

·         Ophthalmia neonatorum(conjunctivitis contracted by a newborn), retinopathy of prematurity, and cortical visual impairment are acquired during the perinatal period

·         Postnatal conditions (ie, those acquired after birth) are unusual during infancy. 

While few medical or surgical options are available for congenital anomalies or neuro-ophthalmic disorders, many affected infants can still benefit from low vision aids and rehabilitation. Ideally, surgery for congenital cataracts should occur within the first 4 months of life.

If one is completely blind, one can see nothing. If one is partially blind, one might experience the following symptoms:

·         cloudy vision

·         the inability to see shapes

·         seeing only shadows

·         poor night vision

·         tunnel vision

A child’s visual system begins to develop in the womb, but will not be fully formed until about 2 years of age. By 6 to 8 weeks of age, a baby should be able to fix his or her gaze on an object and follow its movement. By 4 months of age, the child’s eyes should be properly aligned (not turned inward or outward).

A pediatrician will screen the baby for eye problems shortly after birth. At 6 months of age, parents should have an eye doctor or pediatrician check the child again for visual acuity, focus, and eye alignment. The doctor will look at the baby’s eye structures and see whether the baby can follow a light or colorful object with his or her eyes.

The following conditions can cause vision impairment or blindness in infants:

• infections, such as pink eye
• blocked tear ducts
• cataracts
• strabismus (crossed eyes)
• amblyopia (a lazy eye)
• ptosis (a droopy eyelid)
• congenital glaucoma
• retinopathy of prematurity (when the blood vessels that supply the retina are not fully developed in premature babies)
• visual inattention (delayed development of the child’s visual system)

A child should be able to pay attention to visual stimuli by 6 to 8 weeks of age. If he or she child does not react to light shining in his or her eyes or focus on colorful objects by 2 to 3 months of age, or if it is noticed that the child has crossed eyes or any other symptoms of impaired vision, the child’s eyes must be examined right away.

Symptoms of visual impairment in young children include:

• constant eye rubbing
• extreme sensitivity to light
• poor focusing
• chronic eye redness
• chronic tearing of the eyes
• a white instead of a black pupil
• poor visual tracking (following an object with the eyes)
• abnormal eye alignment or movement (after 6 months of age)
  
  

Tests

Orthoptic evaluation of an infant requires patience. Jampolsky’s dictum of “one toy-one look” should be used to examine the infant’s ocular motility in the nine cardinal directions of gaze. An assortment of soft toys, brightly colored objects, and even mobile phones can be used to arouse the child’s interest. The objects should not make noise as the child will be attracted through the auditory and not the visual signals, which would defeat the purpose of the examination.

Visual acuity can be formally assessed using forced preferential looking tests (eg, Cardiff cards), with the child sitting comfortably on a parent’s lap. The test is based on the psychological percept that humans are attracted to novel stimuli. If the child is shown a line drawing at one end of the card sheet and the other end is kept blank, the child will divert its eyes to the drawing rather than the blank area. The line drawings are made progressively finer to estimate higher orders of form vision. Worth’s ivory fall test and small sweets commonly used to decorate cakes, “hundreds and thousands”, can also be used. The child picks up the small sweets if it is able to see them. At first, bilateral vision is tested followed by monocular testing. The mother should be asked to occlude the infant’s eyes one at a time, and report on the infant’s response. If the infant objects to occlusion of one eye, this may indicate the visual acuity of the other eye is poor.

Brain Plasticity

People who have been blind from birth make use of the visual parts of their brain to refine their sensation of sound and touch, according to an international team of researchers led by neuroscientists at Georgetown University Medical Center (GUMC).
Using functional magnetic resonance imaging (fMRI), the researchers found that the blind use specialized "modules" in the visual cortex that process the spatial location of an object when a person localizes it in space. More generally, they believe that the different functional attributes that make up vision, such as analysis of space, patterns, and motion, still exist in the visual cortex of blind individuals. But instead of using those areas to understand what the eyes see, the blind use them to process what they hear and touch because the same components are necessary to process information from those senses.
"That tells us that the visual cortex in the blind takes on these functions and processes sound and tactile information which it doesn't do in the sighted," he says. "The neural cells and fibers are still there and still functioning, processing spatial attributes of stimuli, driven not by sight but by hearing and touch. This plasticity offers a huge resource for the blind."

Dreams

A series of questionnaire and interview studies conducted in the 1970s led to four generalizations about the dreams of the blind:

1. People born blind, and who never experienced visual imagery in waking life, have no visual images in their dreams.

2. People who became blind before the age of five rarely experience visual imagery in their dreams.

3. People who became blind between the ages of five and seven sometimes retain some visual imagery and experience it in their dreams.

4. Most people who became blind after the age of seven continue to experience at least some visual imagery in their dreams, but the clarity and frequency of the imagery is often reduced with time.

Several studies in sleep laboratories, in which blind participants were woken up during REM sleep for the collection of dream reports, reported similar results.

A more recent study analyzed a sample of 372 dreams from 15 blind adults—some born blind, and others who went blind later in life. Again, the study found that people blind since birth or very early childhood experienced no visual imagery, and people blinded later in life did retain some visual imagery from their sighted waking lives and experienced it while dreaming.

Bibliography:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3119278/
http://en.wikipedia.org/wiki/Blindness
http://en.wikipedia.org/wiki/Visual_acuity
http://www.sciencedaily.com/releases/2010/10/101006131203.htm
http://www.healthline.com/health/blindness