Astigmatism occurs because the cornea is shaped more like a football than a baseball. This different curvature causes 2 images to appear on the retina and causes blurry vision for any distance. Read article
Color Blindness, or Color Vision Deficiency, is an eye condition where a person is not able to distinguish certain colors or shades of colors to some degree. Read article
Hyperopia is a refractive error where the eyeball is shorter than normal. This causes the image to focus behind the retina rather that on it. Read article
Myopia is a refractive error where the eyeball is longer than normal. This causes the image to focus in front of the retina rather that on it. Read article