Page 48 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
● Careful selection of fluence is required to obtain just the right amount of damage to achieve the desired end result. If you think about it, what we are trying to achieve with laser/IPL energy is a “controlled and selective damage” of target tissues.
● Many clinical studies into laser/IPL treatments will determine a ‘threshold fluence’. This is the fluence required to initiate a response in tissue. To achieve a sufficient amount of damage you will need to exceed this threshold fluence, but the total amount of damage will be directly determined by how much you exceed the threshold.
● Thankfully tissue is quite forgiving and, in most cases, a reasonable range of fluences will prove quite safe during treatment.
 It can be quite difficult to determine the maximum fluence a patient can tolerate during treatment. There is no rule of thumb, but most clinicians will stop increasing the fluence when they see some colour or textural changes on the skin surface.
● As described in the ‘Spot Size’ section some lasers can produce a very small spot size some distance from the end of the spacer (the beam waist). In some cases this might be as small of 0.5 mm (0.05 cm) in diameter.
● The fluence generated at this point will be very high – potentially hazardous for the skin.
 For the avoidance of doubt:
Fluence - this is the laser energy delivered to the skin surface divided by the spot area. It is, essentially, how "concentrated" the energy is at the skin surface. Its units are 'Joules per square centimetre'.
Fluency - is defined as “being able to speak and write quickly or easily in a given language.” It comes from the Latin word fluentem meaning “to flow.”
Loss of Fluence in the Skin
Fluence is ‘lost’ in the skin for three main reasons (what is fluence? - video or here for a pdf): ________________________________________________________________________ 47
Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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