BS EN ISO 10938:2016 pdf download – Ophthalmic optics — Chart displays for visual acuity measurement — Printed, projected and electronic
4.1.3 Contrast of optotypes Optotypes shall be specified by the background luminance in cd/m 2 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.
4.1.4 Quality of presentation 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.
NOTE Anti-aliasing may add or subtract from the width of the detail and may change the calibration. Optotypes presented in displays for which the design prevents viewing at 1/3 the normal distance shall be observed with a magnification of 3× in order to verify the quality of presentation.
4.1.5 Resolution For optically projected charts, the minimum resolved spatial frequency on the screen shall be at least 2 cycles per minute of arc measured from the minimum test distance specified by the manufacturer. For electronically generated charts, the pixel size shall be sufficiently small that there is no performance difference between the electronically displayed optotype and an optotype that meets the requirements of 4.1.4. Ideally, the pixel size should be not larger than 0,25 min of arc measured from the minimum test distance specified by the manufacturer
4.2? Requirements? specific? to? optically? projected? displays
4.2.1 Focus range
For projector charts, the minimum focus range shall be 2,9 m to 6,1 m.
4.2.2 Projector screens
If the projector requires the use of specific screens, the specification of such screens shall be provided by the manufacturer.
4.3? Requirements? specific? to? printed? charts
The test distance for which the optotypes are designed to be used shall be specified.
4.4 Range of compliance
The manufacturer shall specify the range of test distances and visual acuity grades over which the chart complies with this International Standard and if optotype is graduated logarithmically or not.
It is recommended to include a minimum range of 0,1 to 1,25 decimal visual acuity.
4.5 Conformity to ISO 15004-1 Chart displays for acuity measurement that are active ophthalmic instruments, as defined by ISO 15004-1, shall conform to the requirements of ISO 15004-1.
5 Test methods
5.1 Type tests All tests described in this International Standard are type tests. 5.2 Conformity The conformity with the requirements in this International Standard shall be verified using measuring devices for which the measuring error is less than 10 % of the smallest value to be determined.
The resolution requirements for optical projectors can be tested by using a Ronchi ruling having a spatial frequency (lines/millimetre) that is four times the spatial frequency of a grating having an element size of the 1,0 decimal acuity optotype. The grating is placed in the plane of the optotype in the optical projector or generated on the electronic screen. The image is viewed from a distance less than 1/4 of the specified test distance by an observer with a decimal visual acuity of at least 1,0 to determine if the detail can be resolved. Test results shall be evaluated using generally accepted rules of statistics.BS EN ISO 10938 pdf download.