What primarily causes long sightedness?

Long sightedness, also known as hyperopia, primarily occurs when the eyeball is too short. This anatomical characteristic means that light entering the eye is focused behind the retina rather than directly on it. As a result, distant objects can appear clearer while closer objects may appear blurry. This condition can often be corrected with convex lenses, which help to bend the light rays so that they converge properly onto the retina.

In contrast, the other options refer to different conditions or factors that do not primarily cause long sightedness. For example, excessive curvature of the lens or cornea would result in myopia (short sightedness) rather than long sightedness. Corneal distortion can lead to vision problems but again does not directly correspond to the typical cause of hyperopia. Similarly, while excessive eye strain can cause temporary discomfort or worsen pre-existing conditions, it is not a fundamental cause of long sightedness.