A device made of transparent matter like glass with bent surfaces, which helps focus ray of lights to create an image at a desired place are called lens.
Lenses is the plural form of lens. People, who are struggling with vision through one eye or both, use a lens or lenses to enhance their eye sight.
Lens allows a human to see everything around him/her clearly. They are also used in cameras and play a huge role in their efficiency.
It is also considered to be a part of human anatomy. This word is also used for safety glasses or sunglasses used by human beings.
Lense is exactly the same as lens and is just a spelling variant, used in different parts of the world. This variation of the word is widely accepted as correct by most language experts.
MS Word rejects this spelling when you type it there. However, it is accepted by many reliable dictionaries. Some people wrongly believe that lense means something else or the spellings are incorrect. This perception is only there because lens is more commonly used.