This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
A child presented with difficulty in seeing the blackboard at school. His teachers say that he frequently 'squint' his eyes. Most probable cause is: 
Select and explain. 
A. Hypermetropia, B. Myopia, C. Presbyopia, D. Astigmatism
B: Myopia
Answer: B: Myopia 
Explanation: For the myopic or nearsighted individual, objects nearby are in focus; those at a distance are blurred. This is because the plane of focus is anterior to the retina. The onset is typically at about age 8 years and may progress throughout adolescence and young adulthood. A myopic person may squint to produce a pinhole effect, which improves distance vision. Divergent lenses provide clear distance vision. Ref: Braverman R.S. (2012). Chapter 16. Eye. In W.W. Hay, Jr., M.J. Levin, R.R. Deterding, J.J. Ross, J.M. Sondheimer (Eds), CURRENT Diagnosis & Treatment: Pediatrics, 21e.