Final answer:
Cataract grading is done during an eye examination to assess the severity of a cataract. 'Trace' refers to a very mild level of cloudiness. Laser light used in retinal repair must be parallel for focused, precise spot-welding of the retina.
Step-by-step explanation:
Cataract grading is typically done during an eye examination to determine the severity of the cataract, which is cloudiness in the lens of the eye. The term "trace" in cataract grading refers to a very slight opacity that is noticed upon close inspection, indicating a very mild cataract. The cloudiness caused by a cataract can lead to the dispersion or diffusion of light as it passes through the lens, affecting vision quality.
When laser light is used to repair a retinal tear, it is important that the rays entering the eye are parallel. This ensures that the light is properly focused, allowing for precise spot-welding of the retina to the back of the eye to effectively repair the tear, and to prevent any further damage to the normal vision of the eye.