ISO 8596:2017 pdf download

ISO 8596:2017 pdf download.Ophthalmic optics — Visual acuity testing — Standard and clinical optotypes and their presentation
1 Scope
This document specifies a range of Landolt ring optotypes and describes a method for measuring distance visual acuity under photopic conditions for the purposes of certification or licensing.
This document is neither intended as a standard for clinical measurements nor for the certification of blindness or partial sight.
Other optotypes used for clinical investigations are described in Annex A for information.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3:1973, Preferred numbers — Series of preferred numbers
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1 standard optotype
Landolt ring
Note 1 to entry: The Landolt ring is specified in Table 1 and Figure 1.
3.2 clinical optotype
optotype other than the standard optotype (3.1) used for measuring visual acuity (3.3)
Note 1 to entry: This definition does not exclude the standard optotype from being used for the same purposes as a clinical optotype.
Note 2 to entry: Since clinical optotypes can differ greatly in legibility, it is crucial to refer to the standard optotype whenever the comparability of the results is important. ISO/TR 19498 provides a method for correlation of clinical optotypes to the standard optotype.
3.3 visual acuity
number characterizing the ability of the visual system to recognize optotypes
Note 1 to entry: Currently, three different scaling systems are used to describe the visual acuity of a patient.
These are decimal visual acuity, Snellen fraction, LogMAR acuity. See Table 1.
4.3 Test area and spacing between standard optotypes
The field shall extend at least 0,5° in all directions from the contour of the optotypes to the border of the test field. If more than one standard optotype is used in the same test area, the spacings given in Table 2 shall apply. If more than one acuity grade is used on the test area, the spacing for the largest optotype shall apply. Table 2 applies to both horizontal and vertical spacing. The background to the optotypes shall appear uniformly bright and without any variation of colour or texture which could indicate the orientation of the symbols. If the different orientations are achieved by rotation of the optotypes, this rotary movement shall not be observed by the subject.