Biomedical Engineering Reference
In-Depth Information
Influence of POWER DISSIPATION of implant on tissue heating
3.00
Insulation of the chip
2.75
Vitreous cavity
2.50
Retina
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
0
10
20 30
Power dissipation in the chip (mW)
40
50
60
Figure 17.7
Variation of the temperature as a function of the power dissipated by the retinal implant chip.
4
4
0.5 mm and it was placed in the center of the eyeball. Power density was again kept
uniform throughout the chip. The computation was performed for 26 min of simulated physical
time.
Figure 17.7 graphically compares the temperature increase observed on the insulation, in the
vitreous cavity and on the retina for both cases. From the thermal elevation results, it is observed
that increasing the power dissipation by a factor of 4 does not necessarily lead to a rise in the
temperature by the same factor. In the majority of tissues, a temperature rise by a factor of around
3.5 to 5 is observed for a four times increase in the power dissipation in the implant.
This preliminary investigation provided a qualitative and quantitative estimate of the thermal
influence of such an implanted prosthetic system in the eye. Also, in the actual system, the various
parametric variations can be optimized to yield the least harmful configuration from the point of
view of thermal damage to the tissues of the eye of head. Several efforts are currently underway to
accurately quantify the contribution of each aspect of such a prosthetic configuration to the eventual
thermal and electromagnetic influence on the human tissues.
17.6
FUTURE IMPLICATIONS
A retinal prosthesis will form several interfaces with the eye including thermal, electrical, and
mechanical. All of these interfaces must be considered simultaneously during the design of a safe
and effective retinal prosthesis. For example, it may be possible to reduce the thermal concerns by
using a larger electrode that consumes less power. However, such an electrode may stimulate a
large area of the retina and not allow fine resolution vision. Many other optimization problems are
presented by such a complex interaction. Therefore, future designs may well need to use automated
optimization algorithms to yield the most effective device.
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