Final answer:
CRT lenses approved for overnight use are designed for overnight orthokeratology and can finely control the shape of the cornea. Television CRTs can generate X-rays at high accelerating potentials. In eye health, spectacle lenses or surgery may be needed in cases like cataract removal or to repair retinal tears, and a face mask corrects the refractive index disparity underwater.
Step-by-step explanation:
When discussing CRT lenses and their approval for overnight wear, one should consider whether they are specifically designed and approved for overnight orthokeratology. These lenses are used to reshape the cornea temporarily to reduce refractive errors such as myopia. The thickness and design of the lens suggest that the cornea's shape can be fine-tuned to provide normal distant vision, which is effective for more than 90% of patients. This capability allows a high degree of control over the corrective effect, ensuring patient safety and efficacy during overnight wear.
As for television tubes, which are a type of cathode ray tube (CRT), they operate with a high accelerating potential of around 30-kV to electron beams towards a screen coated with phosphors. At these energies, there is potential for X-ray generation, as the high-speed electrons can produce X-rays upon collision with the materials inside the TV. This X-ray production, although incidental and typically at low levels, is indeed expected due to the physics involved in the operation of CRTs.
Regarding the questions on the physics of the eye, if the lens of a person's eye is removed due to cataract, a spectacle lens of about 16 D might be prescribed to compensate for the loss of the eye's natural lens. For laser eye surgery, the rays must be parallel to focus precisely on the retina, avoiding further damage. Blurry vision under water occurs due to the different refractive index of water compared to air, and a face mask provides a clear vision by creating an air space in front of the eyes.