Esotropia is a condition in which one or both eyes turn toward the nose at different times due to an inability to work together. This is a type of strabismus or misalignment of the eyes. Esotropia has three main causes. Muscular esotropia involves weakness of the medial and lateral rectus muscles, the muscles on the sides of the eyes. When muscles are weak, they don't hold the eye in the right place, leading to misalignment. This is the most common type of esotropia. Hyperopia, or farsightedness, also causes esotropia. A farsighted person can see objects clearly at a distance but has difficulty seeing objects up close. When a person is very farsighted, looking at objects closely can cause the eyes to roll back. This type of eye misalignment is called accommodative esotropia. The third cause of esotropia is the least common and least studied. This type involves an inability of the brain to use both eyes at once because one eye is weaker or blinded. When one eye is not functioning properly, the brain focuses its efforts on the functioning eye, cutting off the connection to the damaged eye. If this is not corrected, it can lead to permanent blindness. Many people with esotropia have a combination of all three types, but all lead to squinting and impaired vision. Sometimes esotropia is genetic. Scientists have discovered that it can be hereditary and often skips a generation. For example, a grandfather may have it, but his children will not be affected. Later, esotropia will manifest itself in his grandchildren. Scientists continue to research this genetic tendency because they don't know what causes it. When one eye moves toward the nose, diplopia or double vision occurs. A person with overlapping esotropia views middle of paper......onard Press, Dr. "Esotropia". Strabismus.org. Network of Optometrists, 2014. Web. May 17, 2014. .Dorland, W. A. ​​Newman. Dorland's Illustrated Medical Dictionary. 27th ed. Philadelphia: Saunders, 1988. “Eye Disorders” Print. The Merick Handbook of Medical Information. Ed. Robert Berkow, MD Whitehouse Station, New Jersey: Merick Research Laboratories, 1997. 1314-315. Print.Miller, Jonathan. The human body. Library of Congress: Dark Horse Production Limited, 1983. Print. Rutstein, Robert P., OD “Strabismus: Esotropia and Exotropia.” American Optometric Association. American Optometric Association, 2011. Web. May 17, 2014. “Strabismus.” United States National Library of Medicine. ADAM, Inc., September 17, 2012. Web. May 17 2014. .