[Standardisation of optotypes].

Optotypes are signs of different sizes, systematically placed on the visual acuity chart. The human eye has a spatial resolution of 1' of arc (Snellen). Optotypes in the basic row on all charts subtend 5' of arc and their detail 1' of arc, from the testing distance. The disadvantage of all classical charts is the irregular progresssion of optotype sizes in adjacent rows. This was solved by logMAR (Bailey-Lovie) chart in 1976. The chart was made with optotype sizes in steps with a constant ratio 1:1.2589 (geometric progression). This chart has become the standard for visual acuity testing worldwide. It has been recommended by the following bodies: International Council of Ophthalmology (ICO), 1984 and 2002; World Health Organisation (WHO), 2003; International Organisation for Standardisation (ISO) 1996, and Croatian Standard Institute homologised the ISO standard as nHRN EN ISO 8596:1996. For normative, medical and practical reasons it is advised that all school medicine, occupational health and ophthalmology departments adopt the logMAR charts system.