**Answer:**

(a) The old person is suffering from a condition called presbyopia.

(b) Two causes for the development of presbyopia are:

1. Age-related changes in the eye: As a person gets older, the lens of the eye becomes less flexible and loses its ability to change shape easily. This reduces the eye's ability to focus on nearby objects.

2. Loss of elasticity of the ciliary muscles: The ciliary muscles, which control the shape of the lens, gradually lose their elasticity with age. This makes it difficult for the eye to adjust the focal length required for clear vision of nearby objects.

(c) The old person would require bifocal or multifocal lenses to see clearly both nearby and distant objects. Bifocal lenses have two distinct areas - the upper part for distance vision and the lower part for near vision. Multifocal lenses, such as progressive lenses, have a gradual transition of lens power from distance to near vision. These lenses allow the person to have clear vision at different distances without the need to switch between different pairs of glasses.

The reason for requiring bifocal or multifocal lenses is that presbyopia affects the ability to focus on nearby objects, while still allowing clear vision for distant objects. The added lens power in the lower part of bifocal or multifocal lenses compensates for the loss of accommodation (ability to focus on nearby objects) caused by presbyopia.

(d) The eye defect of an old person, presbyopia, differs from near-sightedness (myopia) and far-sightedness (hyperopia) in the following ways:

1. Cause: Presbyopia is primarily caused by age-related changes in the eye, specifically the loss of flexibility in the lens and the decrease in elasticity of the ciliary muscles. On the other hand, near-sightedness is caused by a longer-than-normal eyeball or a more curved cornea, resulting in light being focused in front of the retina instead of directly on it. Far-sightedness, on the other hand, is caused by a shorter-than-normal eyeball or a flatter cornea, causing light to focus behind the retina instead of directly on it.

2. Focusing ability: Presbyopia affects the ability to focus on nearby objects, while far-sightedness affects the ability to focus on both nearby and distant objects. Near-sightedness, on the other hand, affects the ability to focus on distant objects, while nearby objects may still be clear.

3. Corrective measures: Presbyopia is corrected using bifocal or multifocal lenses, as mentioned earlier. Near-sightedness is corrected using concave lenses, which diverge light before it enters the eye, allowing the image to focus properly on the retina. Far-sightedness is corrected using convex lenses, which converge light before it enters the eye, helping to focus the image properly on the retina.

In summary, presbyopia is an age-related loss of accommodation that affects the ability to focus on nearby objects, while near-sightedness and far-sightedness are refractive errors caused by the shape of the eyeball or cornea, affecting the ability to focus on distant objects and both distant and nearby objects, respectively.

1 he is suffering from presbyopia.2 causes old age and non proper functioning of ciliary muscles3 bifocal lens would be use4 it has both myopia and hypermetropia