Summarize this article in one sentence.
Nearsightedness makes it difficult to see objects far away. This is caused by having an eyeball that is too long, or a cornea that is too curved. This affects the way light is reflected on the retina, which causes blurred vision. Farsightedness makes it difficult to see objects that are up close. This is caused by having an eyeball that is too short, or a cornea that is not curved enough. An Astigmatism is when the eye doesn’t focus light properly into the retina. Astigmatism causes objects to appear blurry and stretched out. It is caused by an irregular shaped cornea. This condition typically comes with age (over 40). This condition makes it difficult for the eye to focus on objects clearly. Presbyopia is caused by a loss of flexibility and thickening of the lens inside the eye.

Summary:
Identify nearsightedness. Identify farsightedness. Identify astigmatism. Identify presbyopia.