Final answer:
People with difficulty seeing objects at a distance suffer from myopia or nearsightedness, not hyperopia, presbyopia, or astigmatism. Myopia is due to the lens being too powerful or the eyeball being too long, and is corrected with a diverging lens. Hyperopia and presbyopia have different causes and are corrected differently.
Step-by-step explanation:
People who have difficulty seeing objects at a distance are said to have myopia or nearsightedness. This condition affects about one-third of the population, where nearby objects are seen clearly, but distant objects appear blurry. In myopia, the light from distant objects is focused in front of the retina rather than on it. This can be caused by the lens of the eye being too powerful or the eye length being too long, which leads to a divergence of light rays by the time they reach the retina. Myopia is corrected with a diverging lens, which is designed to move the focal point back onto the retina, allowing for clear distance vision.
Hyperopia, on the other hand, commonly known as farsightedness, is where distant objects are seen clearly, but close objects appear blurry. This condition, affecting about one fourth of people, is due to the eye being too short, causing images to be focused behind the retina. Hyperopia is corrected with a convex lens that converges light rays onto the retina.
Presbyopia differs from myopia and hyperopia as it is related to aging and involves a gradual loss of the eye's ability to focus on close objects. Presbyopia typically occurs between the ages of 40 and 50 and results from the lens becoming less elastic and the weakening of the muscles controlling the lens.
Astigmatism is characterised by an irregular curvature of the cornea or lens, causing distorted and blurred vision at all distances, which is different from the other conditions.