 Eye Institute's Dr Mantell researches Operating Microscope Damage to the Retina
During eye surgery, neither the patient
nor the surgeon thinks much about the operating
microscope, except as a mere accessory to the
procedure. Recently, however, I had the opportunity
to do research on the potential dangers of operating
microscopes for an assignment for my Masters. The
results are worth thinking about for all professionals
working in eye care, as well as for patients considering
any eye surgery.
 Operating microscopes have become an essential tool
in the treatment of ocular disease. It is well
documented, however, that there are risks to the
patient’s eyes from the microscope’s illumination system.
A number of reports have described cases of retinal
damage caused by these microscopes.
The problem is that during surgery, a patient has the
operating microscope positioned directly above his fully
dilated eye, with his retina typically exposed to the
microscope light for relatively long periods of
surgery.
However, to provide a caveat, damage to the cornea
and crystalline lens from operating microscope
illumination is always minimised because most of the
ultraviolet and infrared wavelengths in the illumination
light are filtered. The human eye’s exposure limit for
these structures is actually quite high, but it is still
valuable to think about potential damage. The main concern
is potential damage to the retina.
There are many variables that are difficult to quantify,
and each patient is different, so determining the irradiance
in any particular situation is difficult. It is possible,
though, to create useful ‘worst-case’ values that help us
determine the risk of retinal toxicity. These are:
- The operating microscope illumination is at
maximum setting.
- The pupil is fully dilated.
- There is no movement or interruption of the
illumination by eye movement or other factors.
At Eye Institute we take precautions to protect our
patients. We use a modern microscope, which has appropriate
filters to eliminate harmful ultraviolet radiation. The
microscope has advanced optics and this reduces the need for
high illumination to achieve good visualisation. When
operating we always use the lowest illumination possible and
offset the axis so that the macular is protected. When
possible the pupil is covered to protect the retina. Most
surgeries are very short lasting only 10 to 15 min, this also
limits the risk.
Despite the theoretical risks with the above steps the real
risk is extremely low. Reported cases of retinal toxicity
are now extremely rare.
By Dr Nick Mantell
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