Biomedical Engineering Reference
In-Depth Information
Fig. 7
Videometric part - pivot holder (
a
) and detail of eccentric diaphragm (
b
)
Fig. 8
Scheme of the image analysis
procedure a vertically variable brightness profile arises in the pupil image and its
gradient corresponding to the immediate accommodation state of the eye (recorded
image shown in Fig.
8
).
The source of the measuring light beam is made up of four luminescent diodes
stacked on one another (Fig.
7
a). The wavelength is chosen from the invisible part of
the light spectrum (
œ D
850 nm), so there is no physiological miosis of the pupil and
the patient's attention is not distracted. At the same time, the measuring light source
is used for creating Purkinje images. Both measured artefacts are thus created by
one wavelength and gained from one image.
A standardised stepped change in the distance of a fixed image stimulates a
change in the accommodation and vergence of the eye apparatus. This is displayed to
the patient on two fixation monitors. The distant monitor is 3.17 m from the patient's
