BS EN ISO 10939:1998 download free.Ophthalmic instruments Slit-lamp microscopes.
BS EN ISO 10939, together with ISO 15004, specifies requirements and test methods for slit-lamp microscopes to provide slit illumination and observation under magnification of the eye and its adnexa.
BS EN ISO 10939 is not applicable to microscope accessories, e.g. photographic equipment and lasers.
BS EN ISO 10939 takes precedence over ISO 15004, if differences exist.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of BS EN ISO 10939. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on BS EN ISO 10939 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 7944:1998, Optics and optical instruments — Reference wavelengths.
ISO 15004:1997, Ophthalmic instruments— Fundamental requirements and test methods.
IEC 60601-1:1988, Medical electrical equipment — Part 1: General requirements for safety.
3 Definitions
For the purposes of BS EN ISO 10939, the following definitions apply.
slit-lamp microscope
instrument consisting of a microscope and a swivelling illumination system providing a slit image
3.2
magnification
ratio of the viewing angle of an object when observed through a magnifying system with the image at infinity to that of the object when observed by the naked eye at a reference viewing distance of 250 mm
NOTE 1 The magnification, U, can be calculated using the following equation:
= tanG’ tanG
where
0’ is the angle at which an object is seen through the microscope:
a is the angle at which the same object is seen without any instrument at a viewing distance of 250 mm.
NOTE 2 The magnification of the microscope comprises the magnifications of the complete system.
3.3
high eye point eyepiece
eyepiece in which the exit pupil is of sufficient clearance from the eyepiece to allow spectacles to be worn
4 Requirements
4.1 General
The slit-lamp microscope shall conform to the requirements specified in Iso 15004.
4.2 Optical requirements
The slit-lamp microscope shall conform to the requirements given in Table 1. These requirements are verified as described in 5.1.
4.3 Construction and function
4.3.1 General
The following requirements shall apply:
a) the parallel slit edges shall be smooth and free from any imperfections when observed using the highest magnification;
b) the slit image shall be evenly illuminated:
c) no contrast decrease in the slit image caused by reflections or scattered light shall be observed:
d) the brightness and colour transmission of the left and right optical systems shall be identical;
e) at the highest magnification, the resolving power in the centre of the field shall be at least 1 800 . N line pairs/mm.
Compliance with these requirements is checked by observation.
NOTE 3 For slit-lamp microscopes with non-pulsed radiation, the assumptions used to set the limit value for radiation shorter in wavelength than 400 am are based on considerations of the typical spectral distribution of a 3000 K standard black body source, an illuminating solid angle at the corneal plane of 0,031 sr, a maximum exposure time of 5 mm and the weighting factcrs for LA (see Annex A).
The limit is set to ensure that the fraction of the photochemical hazard dose due to radiation shorter in wavelength than 400 nm is no greater than 1/8 of the total photochemical hazard dose over all wavelengths when that total dose is at the threshold limit for an 8 mm diameter pupil.
Using the American Conference of Governmental Industrial Hygienists (ACGIH) guidelines, that threshold limit is 14 J!(cm2 sr). To convert from photochemical hazard weighted radiance to irradiance. over t.he designated spectral range 305 nm to 400 nm, the conversion factor 0.276 is used. Thus the limit is then found by the formula
114 J/(cm2 sr)l x (0,031 sr) x [0,276/(300s 8)j = 0,05 mW/cm2 However, several of the assumptions used in determining the (1,05 mW/cm2 limit are not valid for slit-lamp microscopes:
i) the pupil of the eye, assumed to have a diameter of 8 mm, is no longer the limiting stop in the system;
ii) the assumed solid angle subtended by the source at the retina of 0,173 9. based on an 8 mm pupil and used to create the ISO 15004 hazard weighting values, is no longer the effective solid angle experienced by the retina under the direct viewing situation of the slit-lamp microscope (the most hazardous condition);
iii) the solid angle of the source in the cornea) plane assumed in the development of the 0,05 mW/cm2 limit of 0,031 sr needs to be replaced by the actual solid angle subtended by the slit lamp exit aperture in the focal plane of the slit-lamp microscope.
Therefore, based on a cut-off of the UV radiation below 370 mm, the limit for radiation between 305 nm and 400 am can be increased to 0.22 mW/cm2.
4.4.3 Variable brightness
For slit-lamp microscopes where provision is made to vary the brightness, the manufacturer shall provide indications of the proportions of the maximum intensity.
4.4.4 Particular information
The manufacturer shall provide the user with a graph showing the relative spectral output of the slit-lamp microscope between 305 nm and 1 100 nrn when the instrument is operating at maximum light intensity and maximum aperture. The spectral output shall be shown for the beam after it exits the illumination system.
The manufacturer shall provide the user with the values for the spectrally-weighted photochemical source radiance, both phakic (LB) and aphakic (LA), measured in the beam exiting from the instrument when operating at maximum intensity and maximum aperture and determined by using the spectral weighting values given in Annex A.
The manufacturer shall provide information on the meaning of LB and LA to the user.
NOTE An example of such information is given in Annex B.
5 Test methods
All tests described in BS EN ISO 10939 are type tests.
5.1 Checking the optical requirements The requirements specified in 4.2 shall be verified by use of measuring devices the measuring errors of which are smaller than 10 % of the smallest value to be determined.
Test results shall be evaluated in accordance with general rules of statistics.
5.2 Checking optical radiation safety for slit-lamp microscopes
5.2.1 Deter,nination of spectral irradiance Spectral irradiance shall be measured with an uncertainty of less than ± 30 % at regular intervals over the effective portion of the spectrum. For aphakic photochemical hazard (LA), the effective portion is 305 nm to 700 nm. For phakic photochemical hazard (L&, the effective portion is 380 nm to 700 nm.
NOTE The intervals for spectral irradiance measurement should be centred on the values given in Annex A with a recommended bandwidth of 5 nm or 10 nm as indicated, The recommended measurement unit is milliwatts per square centimetre per nanometre [mW/(cm2 nm)]. This value should be recorded and, after being multiplied by the bandwidth. recorded as milliwatts per square centimetre (mW/cm2) for that interval (see also Annex B).
5.2.2 Determination of irradiance
Irradiance shall be measured with an uncertainty of less than ± 30 % over the effective portions of the spectrum. For the short wavelength limit, the effective portion of the spectrum is from 305 nm to 400 nm. For the long wavelength limits, the effective portions of the spectrum are from 380 nm to 700 nm and 700 nm to 1100 nm.
NOTE A spectroradiometer can he used to make these measurements.
5.2.3 Determination of beam cross-section
When determining the area of the beam cross-section which is required for several caculations, the measuring method used shall be capable of an accuracy of± 30% (see B.2).
NOTE For irregular cross-sections. it may be appropriate to measure the area by exposing a piece of film and then measuring the area on the negative.
6 Accompanying documents
The slit-lamp microscope shall be accompanied by documents containing instructions for use. In particular this information shall contain:
a) name and address of the manufacturer.