Final answer:
A fluid-filled eye would require a weaker lens than an air-filled eye to have identical focusing power, due to the difference in the refractive index between the fluid and air.
Step-by-step explanation:
A fluid-filled eye would generally require a weaker lens to have the same focusing power as an air-filled eye. This is because the fluid in the eye typically has a higher index of refraction than air, which changes the way light is bent as it passes through the lens. According to the lens maker's equation, the focal length of a lens depends on the index of refraction of the medium it is in. With a higher index of refraction in the fluid-filled eye compared to the air-filled eye, the lens would need to be less powerful to focus light appropriately onto the retina.
Furthermore, the relaxed, normal-vision eye focuses parallel rays of light onto the retina by adjusting its focal length and power. For close vision, the eye increases its power through accommodation, and for distant vision, it decreases its power. Thus, for a person with an intraocular lens, which cannot change its power, the prescribed lens must be of the correct power to provide good distant vision, and the person may need glasses for reading or other close work.