BS EN ISO 10938:2016 pdf free

BS EN ISO 10938:2016 pdf free.Ophthalmic optics一Chart displays for visual acuity measurement一Printed, projected and electronic
Each size of a set of optotypes shall be specified in terms of the size of critical detail common to that set of optotypes. For example, for the Landolt ring, the critical detail is the gap. The permissible deviation is 5 %.
NOTE 1 If letters or figures are used for visual acuity measurement, then it should be acknowledged that these normally show large differences in legibility, even if the size and width of stroke are identical. The impact of this variability can be reduced by choosing letters or figures that are comparable to one another. Comparability can be established for each letter or figure by showing that its effective resolution is equivalent to that of the standard optotype in a direct comparative test.
NOTE 2 See ISO/TR 19498 for description of a method for the correlation of optotypes.
Optotypes shall be specified by the background luminance in cd/m2 and by the luminance of the optotype as a percentage of the background luminance. The luminance of the optotype shall be not more than 15 % of the luminance of the background upon which the optotype is located. Optypes in a series shall not differ noticeably in contrast.
Optotypes as presented shall appear with sharply defined contours to an observer with a binocular visual acuity of 1,0 to 1,25 at an observation distance of 1/3 of the distance at which the optotypes are designed to be used. Similar optotypes in a size series shall not differ noticeably in shape or edge sharpness.
For electronic displays, if anti-aliasing (i.e. modifying the brightness of pixels at the borders of optotypes) is used to smooth the naturally occurring jagged edge formed by pixels at curved edges,it shall not cause a change in the perceived size of the optotype outside of the 5 % variability in optotype size allowed by ISO 8596. Furthermore, there shall be no performance difference between the electronically displayed optotype and a printed display of standard optotypes that meets the requirements of ISO 8596.BS EN ISO 10938 pdf free.