Manikya, also known as ruby, and sapphire are gemstones that are forms of the mineral corundum. Corundum is not an oxide but rather a crystalline form of aluminum oxide (Al₂O₃). Both ruby and sapphire are varieties of corundum, with ruby being red due to the presence of chromium impurities, and sapphire coming in various colors, except red (which would be classified as ruby), often due to different trace elements.

Cats (and many other animals) have a layer of cells behind their retinas called the tapetum lucidum. This layer enhances night vision by reflecting light that passes through the retina back into the eyes. When light enters the eye, some of it is absorbed by the retina's cells, allowing the brain to process visual information. However, the tapetum lucidum reflects the remaining light back through the retina, giving the photoreceptor cells a second chance to detect the light. This reflection of light enhances their night vision capabilities and is what causes a cat's eyes to appear to glow in the dark or in low light conditions.