Optic nerve atrophy
Optic nerve degeneration
Optic nerve hypoplasia
Optic neuritis
Onychodystrophy – idiopathic
Osteochondrosis (site unspecified)
Osteogenesis imperfecta
Osteoma (type unspecified)
Osteomyelitis (unspecified)
Osteomyelitis of other aetiology