The optic disc can be described essentially by cupping and pallor. These are distinct signs; each can progress independently. Cupping has been considered by many as equivalent to the amount of paleness or color contrast estimated by subjective disc examination with a monocular direct ophthalmoscope. In normal eyes, maximum color contrast coincides generally with the degree of cupping. In glaucomatous eyes, increase in cupping occurs. Maximal color contrast no longer coincides with the degree of cupping. This is best seen by examination of the disc with a contact lens and slit lamp. In addition to change in surface contour of the disc, deviation of small vessels defines the extent of cupping. Pallor of the disc is defined by maximum color contrast as well as lack of small vessels.
Schwartz B. Cupping and Pallor of the Optic Disc. Arch Ophthalmol. 1973;89(4):272-277. doi:10.1001/archopht.1973.01000040274002