Possible limits of calibrating reading charts with the Landolt ring: a microscopic study

Table 1 Differences in percent from the calculated nominal values

Parameters	C-Test	Landolt-C RADNER charts	Landolt-C ETDRS format	Landolt-C custom made
0.1 logMAR
Height	1.90	1.52	− 0.14	1.24
Opening	− 18.49	− 16.44	− 10.27	− 8.22
Line thickness	14.38	9.59	6.16	2.74
0.0 logMAR
Height	− 0.52	0.34	0.00	0.00
Opening	− 21.55	− 15.52	− 19.83	− 3.45
Line thickness	18.97	11.21	11.21	2.59
− 0.1 logMAR
Height	2.16	1.08	0.00	0.00
Opening	− 14.13	− 11.97	− 17.29	− 11.96
Line thickness	23.91	14.13	19.57	3.26
− 0.2 logMAR
Height	15.23^a	3.27	1.36	− 1.63
Opening	− 8.22^a	− 17.81	− 17.81	− 1.47
Line thickness	36.99^a	24.66	24.66	5.48
− 0.3 logMAR
Height	–	–	− 0.44	− 1.71
Opening	–	–	− 22.41	− 10.44
Line thickness	–	–	24.14	3.45

^aThe original visual acuity grade of the C-Test is − 0.15 logMAR, which causes a bigger difference in the calculated nominal values for − 0.2 logMAR

ISSN: 2326-0254