Myopia (Nearsightedness)

Nearsightedness (myopia) is a common vision condition in which you can see objects near to you clearly, but objects farther away are blurry. It occurs when the shape of your eye causes light rays to bend (refract) incorrectly, focusing images in front of your retina instead of on your retina.

Nearsightedness may develop gradually or rapidly, often worsening during childhood and adolescence
and tends to run in families.

Symptoms may include:

• Blurry vision when looking at distant objects with squinting to see clearly.
• Headaches caused by eyestrain
• Difficulty seeing while driving a vehicle, especially at night (night myopia)

Nearsightedness is often first detected during childhood and is commonly diagnosed between the early school years through the teens. A child with nearsightedness may:

• Persistently squint
• Need to sit closer to the television, movie screen or the front of the classroom
• Seem to be unaware of distant objects
• Blink excessively
• Rub his or her eyes frequently

Causes
Your eye has two parts that focus images:

• The cornea is the clear, dome-shaped front surface of your eye.
• The lens is a clear structure about the size and shape of an M&M’s candy.

In a normally shaped eye, each of these focusing elements has a perfectly smooth curvature, like the surface of a marble. A cornea and lens with such curvature bend (refract) all incoming light to make a sharply focused image directly on the retina, at the back of your eye.

A refractive error
If your cornea or lens isn’t evenly and smoothly curved, light rays aren’t refracted properly, and you have a refractive error.
Nearsightedness usually occurs when your eyeball is longer than normal or your cornea is curved too steeply. Instead of being focused precisely on your retina, light is focused in front of your retina, resulting in a blurry appearance for distant objects.

Risk factors
Certain risk factors may increase the likelihood of developing nearsightedness, such as:

• Genetics. Nearsightedness tends to run in families. If one of your parents is nearsighted, your risk of developing the condition is increased. The risk is even higher if both parents are nearsighted.
• Environmental conditions. Some studies support the idea that a lack of time spent outdoors may increase the chances of developing myopia.

Studies have found that light levels above 1,000 lux are protectant against myopia.

Outdoor light levels ranged between 5556lux under a tree to 18,176 lux in the sun, while indoor levels were only 112 lux to156 lux. Although these levels were weaker than those obtained with tree shade and a hat, the team adds that they were still 11 to 43 times higher than indoors.