The<unk>  (often notated<unk>  is a measurement used in ophthalmology and optometry to assess the progression of glaucoma. The optic<unk>  is the anatomical location of the eye's "blind spot", the area where the optic nerve and blood vessels enter the retina. The optic<unk>  can be flat or it can have a certain amount of normal<unk> ping. But glaucoma, which is in most cases associated with an increase in intraocular pressure, often produces additional pathological<unk> ping of the optic<unk> . The pink rim of<unk>  contains nerve fibers. The white<unk>  is a pit with no nerve fibers. As glaucoma advances, the<unk>  enlarges until it occupies most of the<unk>  area. The<unk>  compares the diameter of the "cup" portion of the optic<unk>  with the total diameter of the optic<unk> . A good analogy to better understand the<unk>  is the<unk>  of a donut hole to a donut. The hole represents the<unk>  and the surrounding area the<unk> . If the<unk>  fills 1/10 of the<unk> , the<unk>  will be 0.1. If it fills 7/10 of the<unk> , the<unk>  is 0.7. The normal<unk>  is less than 0.5. A large<unk>  may imply glaucoma or other pathology. However,<unk> ping by itself is not indicative of glaucoma. Rather, it is an increase in<unk> ping as the patient ages that is an indicator for glaucoma. Deep but stable<unk> ping can occur due to hereditary factors without glaucoma.
Cup-to-disc ratio
Tear break-up time
Southwick angle
Ventricular-brain ratio
Thyromental distance
Pupillary distance
Fixation disparity
Supplementary eye field