Biomedical Engineering Reference
In-Depth Information
vision system will still be somewhat different from what that person experienced
with natural sight. With this in mind, a new test must test functions that are
relevant to the patient. In other words, it should not simply measure technical
specifications, but rather reflect the patient's benefit in daily living.
As the development of technical devices for artificial vision is still at the
beginning, the first devices under clinical investigation may provide quite basic
visual impressions like perception of light or movement of light. For a blind
person even the simple ability to gain orientation by being able to localize light
sources like windows or doors can mean a substantial improvement in mobility
and self-determined life. As the development of these devices proceeds, there
is good reason to expect further improvements. Thus, a new test has to cover
a wide scope of visual functions, including very basic visual perceptions (see
Table 5.2).
With a view to ongoing developments, new tests must be designed to provide
a better understanding of the properties of the human-machine interface and
functions of the device. They must provide substantial data about the properties
of the human-machine interface and the technical data needed to allow the
enhancement of the next generation of devices.
A test aimed at characterizing visual abilities provided by AVD should be
suitable for generic use. Different prostheses that are under development so far
use a variety of coupling methods to connect to the biological system. Devices for
epiretinal and subretinal coupling as well as for stimulation of the optic nerve and
cortex are being developed [11-15]. All these approaches have special benefits
and technical or biological and surgical limitations. A new test should not be
tailored to the specific features of one individual prosthesis design, but rather
be suitable for generic use. This will facilitate comparability of the functional
results of different technical approaches in humans.
Implementation of a New Test Battery
The specifications listed above provide the basis for developing a new test
design. However, the demands for a new test may be conflicting to some extent.
For example, a test designed for evaluating visual performance may be highly
objective and reliable, but may not be suitable for assessing how well a device
facilitates everyday activities. Conversely a setup for testing performance in
daily activities may show deficiencies in objectivity and validity, because such
tests by their very nature are subjective and influenced by habituation to the test.
To approach this problem of conflicting requirements a battery of sequential
tests may be advantageous. Individual tests are designed to provide partial infor-
mation focused on one main topic. The synopsis of this battery of tests will
provide sufficient information about the efficacy of an AVD in severely visually
impaired patients as well as information needed for further development.
Figure 5.1 illustrates schematically the concept of a set of tests based on three
different methodological approaches.
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