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Common eye problems in students

1. 3.1
   Objective: To describe and identify the common eye problems in students – refractive errors, strabismus and amblyopia 
   

   By completing this chapter, you will learn the following list of topics： Three types of refractive errors – nearsightedness, farsightedness and astigmatism Formation of strabismus and amblyopia

2. 3.2
   Refractive errors
   

   Nearsightedness, farsightedness and astigmatism are the types of refractive errors among school children in Hong Kong. 

   Nearsightedness	Farsightedness	Astigmatism

    

3. 3.3
   Nearsightedness (Myopia)
   Nearsightedness (Myopia) is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it. This causes the image that one sees when looking at a distant object to be out of focus, but in focus when looking at a close object.
   

    

   Nearsightedness (Myopia) Video

    

   	Nearsightedness is the commonest refractive errors, and affecting around 40% of primary school children in Hong Kong.Fan et al, IOVS 2004

    

   Hong Kong has one of the highest prevalence of myopia in the world. Our prevalence was three times that of the United States, more than 10 times that reported from the Middle East, and near twice that in South America. Fan et al, IOVS 2004

    

   Heredity	Reading in Dim Light	Excessive Nearsighted Work

    

   While the exact cause of nearsightedness remains unknown, it is believed that an interaction of heredity and environment may play a role. It tends to run in families. Environmental factors such as reading in dim light or doing excessive amount of nearsighted work may contribute to nearsightedness.

    

   A common sign of nearsightedness is difficulty with the clarity of distant objects like a movie, TV screen or the chalkboard in school. Nearsightedness can be corrected by spectacles with concave lens.

    

4. 3.4
   Farsightedness (Hyperopia)
   

   Farsightedness (Hyperopia) is a condition of the eye where the light that comes in focus behind the retina. This occurs if eyeball is too short or the cornea has too little curvature, so light entering your eye is not focused correctly, causing difficulty focusing on near objects, and in extreme cases causing difficulty to focus on objects at any distance.

    

    

   Farsightedness (Hyperopia) Video

    

   Common signs of farsightedness include difficulty in concentrating and maintaining a clear focus on near objects, eye strain, fatigue and/or headaches after close work, aching or burning eyes, irritability or nervousness after sustained concentration. Farsightedness can be corrected by spectacles with convex lens.

    

    Farsightedness can be corrected by spectacles with convex lens.

    

5. 3.5
   Astigmatism 
   

   Astigmatism is a condition where the light comes into the eye but do not focus on a single point of the retina. It is caused by the irregular shape of the cornea or sometimes the unequal curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, and thus, the vision becomes blurred at any distance.
   Astigmatism is a very common vision condition. Most people have some degree of astigmatism. Slight amounts of astigmatism usually do not affect vision and do not require treatment. However, larger amounts cause distorted or blurred vision, eye discomfort and headaches. Astigmatism can be corrected by spectacles with cylindrical lens.

    

    Astigmatism Video 

    

   3.6 Summary Congratulation! You have completed Chapter 3. You should now be able to distinguish the three types of refractive errors.