Cat's eye is a small optical instrument installed on the door of a house. Because the light it refracts looks like the light emitted by Persian cat's eyes in the distance at night, it is nicknamed cat's eye. Generally, the focal length of the cat's eye is relatively long, while the focal length of the objective lens is relatively short, so an enlarged image can be obtained by looking at the cat's eye from the outside, but this image is not clear, and only a rough outline can be seen for the indoor situation.
If you look at the cat's eye from the inside, you can see the outdoor scene. If the cat's eye is installed backwards, or if the cat's eye is defective, you may see the room from the outside. Therefore, whether the cat's eye can see the interior of the room depends on many factors, including the quality, location and installation method of the cat's eye.