Computational Modeling of Electromagnetic and Thermal Effects for a Dual-Unit Retinal Prosthesis: Inductive Telemetry, Temperature Increase, and Current Densities in the Retina - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 292

Figure 15.8. The location of the two receiving-coil positions considered for thermal
simulations. Note that both have been assumed to be tightly wound four-turn coils.

Table 15.1. Maximum temperature increase in various tissues
of the human body due to the power dissipation of the receiving
coil for the wireless telemetry. “Anterior” indicates the results
with the receiving coil implanted in place of the lens, while
“Surrounding” implies that the receiving coil is of ∼ 25mm
diameter and surrounds the eyeball.

Maximum temperature rise C

Tissue

Anterior Surrounding

Retina 0.025 0.358

Skin 0.089 1.433

Fat 0.152 1.222

Muscle 0.409 1.045

Cornea 0.240 0.105

Vitreous Humor 0.415 0.314

the maximum temperature increments caused by the two considered coil config-
urations on some of the tissues, for a given power dissipation 546W. Further
details can be found in [30].

Electrode Array

The effect of the power dissipation of the electrode array can also be quantified.
Figure 15.9a and 15.9b are horizontal and vertical cross sections, respectively,
showing the position on the retina, at the back of the eyeball, of an 8 8 stimulating

electrode array, in a 0.125mm resolution head model. This model was extracted
from the larger, lower resolution (0.25mm) eye model shown in Figure 15.6b.
The current injected in each electrode is biphasic in nature, with a pulse that
for illustrative purposes can be assumed of equal width for the cathodic and
anodic phase. Figure 15.10 shows the power dissipation pattern in each electrode
for two different current waveforms.

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