We asked for suggestions from our Facebook fans for blog posts and we got some great responses. This is the third of 5 posts on Dr. Beach’s blog to be based on these topics/questions.
Jessica, a CEC Facebook fan, asks: “What is the difference between near/far sighted and whats the difference physically that makes a person one or the other?“
Great question.
Nearsightedness, also called Myopia, is when a person experiences blurred vision for far away distances and clear vision while reading up close.
Farsightedness, also called Hyperopia, is when a person experiences clear vision for far away distances and blurred vision while reading up close. (some exceptions apply to hyperopia though)
I like to think about the visual system like a projector system at the movie theater. In order for your vision to be clear, it needs to be focused directly on the retina which would be equivalent to the screen at the movie theater. If the projector system overfocused, the image would be blurry. If the projector system underfocused it would also be blurry. The focus has to be just right. People who don’t need glasses or contacts have visual systems which accurately focus images on the retina.
People with myopia, or farsightedness, essentially have a vision system that is overfocussed or too strong. The image focus before the retina. Why does this happen? One possible reason is the the cornea on the front surface of the eye is too steep in curvature which makes it too strong. Imagine someone sneaks into the projector room at the m
ovie theater and turns the focussing knob to a much stronger setting. The movie on the screen is now blurry. Another reason for myopia is the eye may be too long. Sounds strange, but the visual system of the eye is designed to focus at a certain distance between the cornea and the retina. Imagine that same movie theater in which the engineers have designed a projector system focussed on a screen with a set distance. But what if someone knocked out the back wall of the movie theater and moved the screen back 10 feet? It would be blurry because now the projector is over-focused for this new longer screen distance.
Hyperopia, or farsightedness, is the exact opposite. The visual system is essentially too weak and focuses images somewhere 
behind the retina instead of directly on the retina. This may happen if the cornea curvature is too flat (too weak) or if the eye is too short. Just to muddy the waters, if someone has a lot of hyperopia their far away vision can also be blurry….we’ll save that one for another blog post!
Jessica, thanks for the great question. The human visual system is essentially physics in motion, which is pretty cool….of course I’m a little biased.
Dr. Beach.
