70375-EN Rev B
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Procedural Recommendations
I
MPORTANT ELEMENTS OF EVERY LASER PHOTOCOAGULATION PROCEDURE
Ophthalmic laser photocoagulation has a decades-long history of successfully providing durable clinical
outcomes that are both meaningful and beneficial to the patient. It is important, however, to consider the
various hardware controls and adjustments, their interactions with one another, and each patient’s needs to
achieve the best possible clinical results. These considerations include:
•
Spot Size
Spot size at target is dependent on many parameters, including physician’s selection of laser spot size
and choice of laser delivery lens, patient’s refractive power, and proper focus of the aiming laser on the
target.
•
Laser Power
If uncertain of tissue response, start with lower power settings and increase the power until satisfactory
clinical results are achieved.
•
Power, Spot Size, and Power Density
Power density is the ratio of laser power to the area of the spot size. Tissue response to laser light of a
given wavelength is strongly determined by power density. To increase power density, increase the
laser power or decrease the spot size. Because power density varies with the square of spot size, this
parameter is an especially sensitive factor.
•
Red Aiming and Treatment Laser Beams
In single-spot mode, always ensure that the aiming beam is in sharp focus on the intended target prior
to and during laser delivery. Out-of-focus spots can have less consistent power density at the target and
may not produce clinically satisfactory results.
In multi-spot mode, always ensure that the target grid is in sharp focus prior to laser delivery. An out-
of-focus target grid may not produce clinically satisfactory results.
•
Exposure Duration, Heat Flow, and Spacing Between Spots
When absorbed by ocular chromophores such as melanin and hemoglobin, laser energy is converted
into kinetic energy (heat). This heat flows from hotter tissue to cooler tissues nearby. This conduction of
heat in all directions away from directly irradiated tissue begins with the initiation of the laser exposure
and continues throughout the exposure, and even after its end, until thermal equilibrium is regained.
Therefore, longer exposure durations are associated with greater conduction distances, while shorter
exposures have smaller conduction distances. Thus, it may be clinically beneficial to space adjacent
laser spots more closely when using short CW-pulse durations,
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and even more closely when using
MicroPulse mode.
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•
MicroPulse Mode and Thermal Confinement
MicroPulse mode is a method of laser delivery that helps to confine thermal effects to specifically
targeted tissues by reducing heat conduction during the laser treatment. This is achieved by
automatically delivering laser energy as a train of brief pulses, instead of as a single, uninterrupted
exposure of much longer duration as used during CW-Pulse laser delivery. In contrast to “constant
energy” laser systems, shortening the exposure time in MicroPulse mode does not increase peak power.
MicroPulse mode can be thought as a CW-Pulse that has been chopped into a number of shorter pieces
by introducing brief periods of off-time.
The off-time between each sequential MicroPulse application
allows tissue to cool, reducing collateral thermal effects to the nearby tissue. MicroPulse mode can
result in lighter and smaller laser lesions.
