In a recent post on rosacea-support, drawing on information posted by Geoffrey Nase, comes a discussion of some light therapy terminology:

Beyond the selection of a wavelength or filter, the ability of laser or light device to work efficiently to destroy vessels also has a lot to do with the duration of the exposure, measured in millisecond pulses, or ms for short. The optimum pulse duration varies depending on the blood vessel size.

When the photoderm first came out over 5 years ago, nobody really knew what the best parameters were. There are many to manipulate it: filter, fluence (measured in joules), number of pulses, delay between pulses, and pulse durations. Now the parameters are better known.

A `double pass’ refers to a doctor treating the full face with one filter (e.g. 560 shallow filter), and then redoing the entire face with a different filter (e.g. 590 or 640 filter for deeper blood vessels).

A `double pulse’ means that the laser treats the same area with two quick pulses of light, so that the blood inside the blood vessel wall heats up enough to destroy the blood vessel (photocoagulation). You can change the number of pulses to lengthen the heating period to make it more uniform, and to ensure that the blood vessels are destroyed.