concave contact lens?

[Eway]

"Contact lenses are very thin, concave transparent disks that fit onto the cornea to correct a visual defect."

Does this "concave" mean concave and convex at the same time?
Because... as far as I know, there are convex contact lens as well as concave ones...

[MikeNewYork]

Originally Posted by Eway

"Contact lenses are very thin, concave transparent disks that fit onto the cornea to correct a visual defect."

Does this "concave" mean concave and convex at the same time?
Because... as far as I know, there are convex contact lens as well as concave ones...

Things that are concave are also convex, depending upon the perspective. Concave refers to a shape that is like the interior wall of a sphere. Convex refers to a shape like the exterior wall of a sphere. Obviously, it is the same wall.

From the standpoint of the eye, whose surface is convex, only a concave object will fit. If you turn it around, it will fall out.

[Eway]

So this is all and only about shape?
I got confused because concave contact lenses are for myopia while convex contact lenses are for hypermetropia and this sentence I quoted seems to be saying that all contact lenses are concave...

[MikeNewYork]

Originally Posted by Eway

So this is all and only about shape?
I got confused because concave contact lenses are for myopia while convex contact lenses are for hypermetropia and this sentence I quoted seems to be saying that all contact lenses are concave...

I'm not an expert, but I think the words concave and convex when used for correction refer to the focus point of the lens. The definition you read refers to the shape of the lens which conforms to the shape of the cornea.