WEEK 4: The Child with Blindness Flashcards
What is childhood?
Childhood: from 0 to 15 years old (UNICEF)
What is blindness?
*Corrected visual acuity < 3/60 better eye
or
*Central visual field each eye<10 degrees
Define the following:
*Low vision
*Blindness
*Visual impairment
Low Vision:
*Visual acuity of less than 6/18 but equal to better than 3/60 or corresponding visual field loss to less than 20 degrees in the better eye with the best possible correction
Blindness:
Visual acuity <3/60 or a corresponding visual field loss to less than 10 degrees in the better eye with the best possible correction.
Visual Impairment:
Includes low vision as well blindness.
Define visual acuity and visual field.
Visual acuity refers to the clarity or sharpness of vision. It is a measure of the ability to see fine details and distinguish objects at a given distance.
To put it simply, if you have a visual acuity of 6/18, you will need to be six meters away from an object to see it as clearly as someone with normal vision could see it from 18 meters away.
Visual field is the total area in which objects can be seen while focusing on a central point. If there’s a loss to less than 20 degrees, it means that the person can’t see as much in their peripheral (side) vision as someone with a normal visual field.
Describe the embryology of the eye.
- Formation of the Neural Tube:
Early in embryonic development, a flat sheet of cells called the neural plate forms on the embryonic surface.
This neural plate then folds and fuses to form the neural tube. This process is called neurulation.
- Development of the Forebrain and Optic Vesicles:
The neural tube differentiates into three primary regions: the forebrain, midbrain, and hindbrain.
The forebrain gives rise to the optic vesicles, which are bilateral outgrowths that extend from the forebrain.
- Optic Cup Formation:
The optic vesicles invaginate (fold inward) to form double-walled optic cups.
The inner layer of the optic cup gives rise to the neural retina, which contains the light-sensitive cells (photoreceptors).
The outer layer gives rise to the retinal pigmented epithelium (RPE), which provides nourishment to the photoreceptors.
- Lens Formation:
Meanwhile, the surface ectoderm overlying the optic cup thickens to form the lens placode, a specialized area that will become the lens of the eye.
The lens placode invaginates to form the lens vesicle, which later pinches off to become a separate structure.
- Differentiation of Eye Structures:
The optic cup continues to develop into different layers of the retina, including the ganglion cell layer, inner nuclear layer, and outer nuclear layer.
Different cell types, such as bipolar cells and photoreceptor cells, differentiate within these layers.
- Formation of the Cornea and Sclera:
The cells surrounding the optic cup give rise to the cornea and sclera, the transparent front part and the white outer layer of the eye, respectively. - Vascularization:
Blood vessels begin to grow into the developing eye to supply nutrients. The hyaloid artery, for example, supplies the developing lens and vitreous humor. - Maturation and Further Differentiation:
The eye continues to mature, and various structures within the eye, including the lens, cornea, and retina, undergo further differentiation and specialization.
Epidemiology: The exact number of children blind in the world is not known but it is estimated that the figure is approximately __________.
______________new cases every year. Many of these children die within months after they become blind.
The frequency and causes of blindness vary widely in different parts of the world.
In Africa and parts of Asia, up to ___________children are blind, compared to ____________children in Europe and North America
The exact number of children blind in the world is not known but it is estimated that the figure is approximately 1.4 million.
500,000 new cases every year. Many of these children die within months after they become blind.
The frequency and causes of blindness vary widely in different parts of the world.
In Africa and parts of Asia, up to 15/10,000 children are blind, compared to 3/10,000 children in Europe and North America.
State contributing to blindness that are more common in developing countries.
State the main causes in countries with better standards of living and health care services.
Nutritional factors and infections are more common in developing countries,
whereas hereditary factors, developmental disease and the consequences of prematurity are more frequent causes in countries with better standards of living and health care services.
Survey in Botswana 2011
It is easily correctable with glasses, is the most common cause of bilateral VI, with cataracts a close second.
A nationwide intervention is currently being planned to reduce the burden of avoidable childhood VI in Botswana.
What is that?
Refractive error
A careful history should be taken, preferably from the mother who has had the closest contact with the child. Visual acuity should be assessed, and the findings recorded.
Children over the age of 5 years can usually be tested with what?
Children over the age of 5 years can usually be tested with a Snellen eye chart.
Visual acuity is a measure of the clarity or sharpness of vision.
It quantifies the ability of the eye to discern fine details and is typically assessed using an eye chart.
Visual acuity Testing in preverbal children
- Fixation and following may be assessed using bright attention-grabbing targets (a face is often best.
Comparison between the behavior of the two eyes may reveal a unilateral preference.
Occlusion of one eye, if strongly objected to by the child, indicates poorer acuity.
- Preferential looking tests can be used from early infancy and are based on the fact that infants prefer to look at a pattern rather than a homogeneous stimulus.
The infant is exposed to a stimulus and the examiner observes the eyes for fixation movements, without themselves knowing the stimulus position.
Pictures with a wider outline are seen more easily than high frequency gratings or thin outline pictures, and an assessment of resolution (not recognition) visual acuity is made accordingly.
- Pattern visual evoked potentials (VEP) give a representation of spatial acuity but are more commonly used in the diagnosis of optic neuropathy.
What to check for after the initial exam?
*Do check for red reflex
State the causes of childhood blindness.
1. In Asia and Africa
Over a million children in Asia and Africa are blind and the single commonest avoidable cause:
In Africa, corneal ulceration leading to corneal scarring is often associated with measles infection.
In Asia severe diarrhea may lead to acute vitamin A deficiency causing blindness.
State Other causes of corneal scarring.
Other causes of corneal scarring are:
*Conjunctivitis of the newborn (ophthalmia neonatorum),
*Herpes simplex infection and
*The use of harmful (traditional) eye medicines.
These causes are all preventable or treatable.
Describe the following factors resulting in corneal scarring.
1. Factors from conception:
2. Factors during pregnancy
3. Factors at the time of birth
4. Factors during childhood
- Factors from conception: hereditary
Familial cataract, Retinal dystrophies, Retinoblastoma - Factors during pregnancy
Rubella, Toxoplasmosis - Factors at the time of birth
Retinopathy of prematurity, Newborn conjunctivitis - Factors during childhood
Vitamin A deficiency, Measles, Eye infections, Traditional eye medicines, Injuries
Worldwide, what is the commonest single cause of blindness in children, accounting for an estimated 350,000 new cases each year?
Vitamin A deficiency
What was the first fat-soluble vitamin to be discovered?
Vitamin A was the first fat-soluble vitamin to be discovered .
Early observation by ancient Egyptians recognized that night blindness could be treated with consumption of liver.
Vitamin A deficiency is also very important as it is associated with higher infant and childhood mortality rates, particularly associated with measles.
State the Three forms of Vitamin A and their sources.
Three forms of Vitamin A
-Retinol -the most active form is mostly found in animal source of food and predominant form in human.
- Beta carotenes – the plant source of
- Carotenoids -the largest group contain multiple conjugated double bonds and exist in a free alcohol or in fatty acyl –ester form.
It is estimated that 60% to 80% of children who become blind from vitamin A deficiency die within a few years.
Why?
Because of increased susceptibility to infection and sometimes lack of care.
Vitamin A deficiency can occur for three major reasons. State them.
-reduced intake of foods rich in vitamin A
-vitamins are not absorbed, usually because of diarrhea
- increased need for vitamin A, as occurs during infections, particularly measles.
What is xerophthalmia?
Xerophthalmia is a medical condition related to the eyes, specifically involving severe dryness of the eyes.
It is often associated with a deficiency in vitamin A. Vitamin A is essential for maintaining the health of the eyes, and its deficiency can lead to a range of eye problems, including dryness.
Which children are at risk of developing xerophthalmia?
While vitamin A deficiency can occur at any age, the group at risk of blindness is pre-school age children, from 6 months to 6 years of age.
A typical child at risk of corneal blindness is a child who is one to 3 years old, no longer breast fed, who receives a poor diet and is malnourished, and who has developed measles (or another infection) or is suffering from diarrhea
State the Symptoms and signs of xerophthalmia.
Night blindness (XN):
Vitamin A is needed to replace rhodopsin (visual purple) in the retina at the back of the eye and this is necessary for night vision.
Conjunctival xerosis (XIA): Vitamin A is required for the production of secretions on the surface of the eye. This dry appearance together with xerosis of the corneal epithelium gives the condition its name, xerophthalmia.
Corneal xerosis (X2): The surface of the cornea can have a typical dry appearance.
Bitot’s spots (XIB): A Bitot’s spot has a typical white foamy appearance and is localized on the surface of the conjunctiva. Bitot’s spots may be found in both eyes, most often on the temporal conjunctiva
- It is area of abnormal squamous cell proliferation and keratinization of the conjunctiva
Corneal scarring (XS): The significant end stage of malnutrition causing eye damage, in a child who survives, is corneal scarring.
Describe the Treatment of xerophthalmia according to age.
Children over one year
*Immediately on diagnosis (Day 1): 200,000 IU vitamin A orally
*The following day (Day 2): 200,000 IU vitamin A orally
*Four weeks later (Week 4): 200,000 IU vitamin A orally
If there is vomiting, an intramuscular injection of 100,000 IU of water-soluble vitamin A (not an oil-based preparation) may be used instead of the first oral dose.
Children under one year old or < 8 kg Use half the doses of the regimen given above.
A topical antibiotic eye ointment such as tetracycline 1% or chloramphenicol 1%, 3 times a day, is recommended to reduce the possibility of secondary bacterial infection of the eyes.
How would you treat a woman of reproductive age who is deficient in vitamin A?
Women of reproductive age should not receive large doses of vitamin A which are contra-indicated in pregnancy.
If a woman has night blindness or Bitot’s spot she should have a daily dose of 10,000 IU of vitamin A orally for 2 weeks.
Immediately after the birth of her child a woman may be given 3 doses of vitamin A 200,000 IU, on Day 1, Day 2, and Day 8, to ensure a good supply of vitamin A in her breast milk for the newborn baby.
