Final answer:
Your vision is blurry underwater because water alters the refractive index that the eye relies on for clear vision. A face mask restores this change by providing an air layer for proper light refraction. Intraocular lenses after cataract surgery can restore distance vision but may require glasses for reading.
Step-by-step explanation:
Your vision is blurry when you open your eyes while swimming underwater because water changes the effective refractive index of the eye. On land, the eye is optimized to refract light adequately in air, which has a refractive index of approximately 1. However, water has a higher refractive index (about 1.33), so the light bends differently than the eye is designed to accommodate. This results in blurry vision. When wearing a face mask, a layer of air is maintained in front of the eyes, ensuring that the refractive index in front of the eye remains similar to air. Therefore, the light is refracted properly onto the retina, allowing for clear vision underwater.
Regarding vision correction such as replacing a cataract-clouded lens with an intraocular lens, this lens can be chosen to improve distant vision. However, since the lens is fixed in terms of focusing power, the person may still need glasses to read or see things up close if the lens does not accommodate for the full range of vision needed. For nearsightedness correction, the power of the intraocular lens would be less than the power of the removed natural lens to rectify the focal distance.