1) An eyecup 2) An eyepiece 3) Lens 4) Lens system 5) Lense 6) Monocle 1) Lens 2) Monocle 
• (n.) Eyepiece of a telescope, microscope, etc. • (n.) A glass eyecup. See Eyecup. • (n.) A lens of glass to assist the sight. Eyeglasses are used singly or in pairs. • (n.) The retina.
Eye'glass` noun 1. A lens of glass to assist the sight. Eyeglasses are used singly or in pairs. 2. Eyepiece of a telescope, microscope, etc. 3. The retina. [ Poetic] 4. A glass eyecup. See Eyecup . 
eyeglass, spectacles 1. A glass lens used to correct a defect in visual acuity or to prevent exposure to bright light if the lens is tinted. 2. A transparent refractive device worn to correct reflection errors in the patient's eyes. 3. A device worn to protect the eyes from glare or particles in the air.
glass (def. 5). · a single lens used to aid vision, esp. one worn or carried on the person; monocle. · an eyepiece. · an eyecup.