There are various ways to examine the optic disc, the techniques and merits of some are described below.
When assessing a disc for glaucoma there are many subtle characteristics which should be examined, and are covered in detail in the Glaucoma Evaluation Tutorial

At the very least, all one should remember for an assessment of the optic disc is “the 3 Cs” - the cup, colour and contour.

The Contour.
The borders of the optic disc should be clear and well defined. If not one becomes concerned that the disc may be swollen such as in the case of papilloedema - disc swelling secondary to raised intracranial pressure. Alternatively, the disc margins may appear blurred due to presence of optic disc drusen.

The Colour.
Typically the optic disc looks like an orange-pink donut with a pale centre. The orange-pink appearance represents healthy, well perfused neuro-retinal tissue. There are many pathological reasons why a disc may lose this orange-pink colour and appear pale ie optic atrophy. These include advanced glaucoma, optic neuritis, arteritic or non-arteritic ischaemic optic neuropathy or a compressive lesion. The causes of an optic neuropathy can be remembered by NIGHT TICS

Neuritis
Ischaemic
Granulomatous
Hereditory
Traumatic
Toxic
Irradiation
Compression