glasses - dioptre, diamond - ?

CARAT
List of words for the clue glasses - dioptre, diamond - ? from the crossword:
FOOD CALORIE ICE SPOT OVAL CRYSTAL UNIT DIOPTER OPERA SPECS NEIL RIMS SPECTACLES NEZ LENS GOBLETS EYEWEAR DOC BASE
WordClue
GEMdiamond or sapphire
FOODdioptre - glasses, calorie - ?
JEWELdiamond or sapphire
ZOBELdiamond
CALORIEglasses - dioptre, food - ?
DIAMONDdioptre - glasses, carat - ?
DIOPTREdiamond - carat, glasses - ?
GLASSEScarat - diamond, dioptre - ?
GOGGLESsafety glasses
RHINESTONEartificial diamond, strass
SPECTACLESglasses
SPECTACLESglasses
CALORIEglasses - dioptre, food - ?