Your eyes see objects as light. Your cornea focuses light rays onto a layer that lines the back of your eye (the retina). If your eyes are normal, this process produces a focused image on your retina. This makes objects look clear.

Your cornea and your retina are too far apart if you’re nearsighted. Sometimes your cornea or your lens has an abnormal shape. This makes light rays from distant objects focus in front of your retina. These objects then look blurry.

Your cornea and your retina are too close together if you’re farsighted. Sometimes your cornea or your lens has an abnormal shape. This makes light rays from close objects focus behind your retina. These objects then look blurry.

Sometimes the curve of your cornea is uneven or the lens inside your eye is curved abnormally. Then light rays can’t focus evenly onto your retina. This is called an astigmatism. It makes both close and distant objects look blurry.