Final answer:
Cataracts are a clouding of the lens in the eye, causing vision impairment. When a tear in the retina is repaired using laser light, the rays entering the eye must be parallel. The provided information does not allow for accurate estimation of disease percentages.
Step-by-step explanation:
Cataracts are a clouding of the lens in the eye that impairs vision. When light enters the eye, it is dispersed or scattered by the clouded lens, making it difficult to see clearly. This is due to the lens not being able to properly focus the incoming light rays.
When laser light is used to repair a tear in the retina, the rays entering the eye must be parallel because the laser needs to accurately target a specific area on the retina. Parallel rays ensure that the laser light focuses precisely on the intended spot for spot-welding the retina to the back of the eye.
The question about the percentages affected by the disease and the prevalence in the United States cannot be answered as the provided information does not specify the disease being referred to.