Biomedical Engineering Reference
In-Depth Information
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Fig. 13
Graph of the courses of accommodation and vergence
For accommodation analysis we use coefficient by second root
a
1
that represents
slope of the curve.
Last step involves calibration of both curves to corresponding units (dioptre and
degrees of movement). This calibration depends on geometrical position of both
monitors and patient. For calibration of accommodation we use distances of the
fixation monitors that represents relative defocus and start dioptric power that is
computed as average of first 25 values of the
a1
(before accommodation starts,
fixation on the first monitor).
Calibration of convergence is angle transformation between view axis of the eye
and camera and it is individual for each eye. Range of convergence is given by
position of the fixation monitors. Start angel is computed as average of first 25
values of relative distance between PI and COL (before convergence starts - fixation
on the first monitor). Results of analysis are graphs of accommodation and vergence
in dependence of time (Fig.
13
). Thin horizontal lines represent the theoretical start-
and end-point of the reactions (see below). The two thick vertical lines divide curves
to three segments (the first line corresponds to latency period; the second line divides
initial and post-initial segments of responses). The thin vertical lines determinate
fragments in segments mentioned below.
First step of the signal analysis is to eliminate noise oscillations by averaging
convolution with two-sided one neighbour window. Generalized difference (see
