Table 1 The disc damage likelihood scale.

New DDLS stage	Narrowest width of rim (rim/disc ratio)
	For small disc <1.50 mm	For average size disc 1.50–2.00 mm	For large disc >2.00 mm	Old DDLS stage
1	0.5 or more	0.4 or more	0.3 or more	0a
2	0.4 to 0.49	0.3 to 0.39	0.2 to 0.29	0b
3	0.3 to 0.39	0.2 to 0.29	0.1 to 0.19	1
4	0.2 to 0.29	0.1 to 0.19	less than 0.1	2
5	0.1 to 0.19	less than 0.1	0 for less than 45°	3
6	less than 0.1	0 for less than 45°	0 for 46° to 90°	4
7	0 for less than 45°	0 for 46° to 90°	0 for 91° to 180°	5
8	0 for 46° to 90°	0 for 91° to 180°	0 for 181° to 270°	6
9	0 for 91° to 180°	0 for 181° to 270°	0 for more than 270°	7a
10	0 for more than 180°	0 for more than 270°		7b

The DDLS is based on the radial width of the neuroretinal rim measured at its thinnest point. The unit of measurement is the rim/disc ratio—that is, the radial width of the rim compared to the diameter of the disc in the same axis. When there is no rim remaining the rim/disc ratio is 0. The circumferential extent of rim absence (0 rim/disc ratio) is measured in degrees. Caution must be taken to differentiate the actual absence of rim from sloping of the rim as, for example, can occur temporally in some patients with myopia. A sloping rim is not an absent rim. Because rim width is a function of disc size, disc size must be evaluated before attributing a DDLS stage. This is done with a 60D–90D lens with appropriate corrective factors. The Volk 66D lens minimally underestimates the disc size. Corrective factors for other lenses are: Volk 60D×0.88, 78D×1.2, 90D×1.33. Nikon 60D×1.03, 90D×1.63.⁸