observation,
1
,
2
,
3
,
4
old-age sight,
see
presbyopia
optic chiasma,
1
,
2
optic disc,
1
,
2
optic tract,
1
,
2
,
3
optical axes,
see
visual axes
optical illusions,
1
optical media,
1
,
2
opticians,
1
,
2
,
3
,
4
ora serrata,
1
,
2