Biomedical Engineering Reference
In-Depth Information
Fig. 17.4.
Confocal scanning laser ophthalmoscope under development for image-
guided 2
γ
PDT of age related macular degeneration, showing the optical design
(
top
), the system in use, and a typical high-resolution retinal image (
normal
)
The operator would then define the “target” and the laser beam would be
switched to “treatment mode,” using the high peak-power fs laser. Apart from
the fs light source itself, there are several optics challenges in implementing
2
γ
PDT for AMD, in particular, the following:
- E
cient coupling of the fs laser source into the cslo is complicated by ef-
fects such as pulse dispersion that take place as the laser beam propagates
through the optical elements
- Achieving diffraction-limited focusing at the back of the eye is restricted
by the low numerical aperture of the eye and possibly by scattering (e.g.,
by cataract) and wavefront distortion (e.g., from astigmatism).
To tackle the second problem, adaptive optics approaches will likely be needed
and, in addition, automatic eye tracking will be required to keep the focal spot
at the correct location. Both technologies are under development.
Case B
, so-called two-photon/two-color activation (2
γ
/2
λ
)-PDT, uses two
laser pulses of different wavelength and separated in time. The first pulse
