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Safety Measures
Exposure time to light
Page 20
Duration of exposure to light
According to some publications, the phakic and aphakic eye should not be ex-
posed to the light source longer than a few minutes. In all surgical cases, the
retinal exposure time to light depends on the type and duration of the proce-
dure and possible case complications. It is therefore recommended in oph-
thalmic surgery to keep the light intensity as low as possible, or to use a device
which prevents the light from entering through the patient's pupil. It is also
recommended to make sure that the patient's eye is not additionally exposed
to the light of surrounding light sources. This problem has been solved by
ZEISS by the use of a retinal protection device that can be swung into the mi-
croscope's illumination beam path and a blue barrier filter (retina protection
filter).
The microscope light source - like any bright light source - may present a
hazard to the patient's eye both in the form of immediately visible thermal
damage to the retina as well as phototoxic chemical reactions which may lead
to photoretinitis. The factors which play an important role in determining the
phototoxic risk are:
– Lamp brightness.
– Spectral distribution of the light (UV and blue are more dangerous than
longer wavelengths).
– Duration of direct exposure.
– Pupil size.
– Clarity of ocular media (infants and young children, for example, may be
at a higher risk).
– Phakic status of the eye (aphakic and pseudo-aphakic eyes without UV
and blue filtering IOLs are at a higher risk).
– Previous exposure to bright light such as retinal photography, especially
within the last 24 hrs.
During cataract procedures, factors such as lenticular material, instruments
such as the phaco handpiece, and movement of the eye provide interruption
of the exposure and would be expected to significantly lengthen the time be-
fore photoretinitis might be expected to occur.
7)
A prospective study
of the effects of microscope illumination during surgery
did not reveal any phototoxic retinal injuries for procedure times of up to 30
minutes if the calculated maximum recommended exposure time was 150
seconds. However, it was also found that at the same brightness setting, pho-
totoxic retinal injury could be expected after approximately 100 min.
S7 / OPMI VISU 160
Version 6.0
G-30-1528-en
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