Biomedical Engineering Reference
In-Depth Information
Tabl e 1 Analysis of the accommodation and vergence curves from the Fig. 13
Accomodation
Vergence
Latency: 507 ms
Latency: 501 ms
Duration initial segment: 489 ms
Duration initial segment: 82 ms
Velocity of initial segment: 36.9 ı /s
Velocity of initial segment: 4.84 D/s
Time constant of initial segment: 225 ms
Time constant of initial segment: 49 ms
Peak velocity in initial segment: 306 ı /s
Peak velocity in initial segment: 29.7 D/s
Number of fragments in initial segment: 2
Number of fragments in initial segment: 2
1. fragment - contribution: 64%
1. fragment - contribution: 67%
1. fragment - velocity: 6.46 D/s
1. fragment - velocity: 38.3 ı /s
2. fragment - contribution: 28%
2. fragment - contribution: 20%
2. fragment - velocity: 3.07 D/s
2. fragment - velocity: 33.1 D/s
Proportion of theoretical dynamic range: 93%
Proportion of theoretical dynamic range: 88%
Saccadic trajectory: 88%
Saccadic contribution: 67%
above) with weighting window is used for finding maximum changes in acceleration
profile of the signals. The two maximum values of this difference divide three main
segments in signal (latent, initial and post-initial) in accordance with theoretical
hypothesis Fig. 5 b. Numerical parameters describing initial segment: latency,
duration, percentage contribution to whole reaction, velocity, peak velocity and time
constant (time when signal reach 60% of the maximum of the initial segment).
The determination of fragments in initial and post-initial segments is performed
by searching zero crosses of the first and the second generalized difference of the
signal. Then is computed percetage contribution and mean velocity of fragments in
initial segment. In post-initial segment the parameter of instability (represents ratio
of reverse reaction in this segment) is calculated. If any fragment of the vergence
reaction reaches peak velocity higher than 20 ı /s then saccadic parameters of the
reaction are computed. They are: saccadic trajectory and saccadic contribution.
Saccadic trajectory is defined as sum of all absolute contributions to total vergence
reaction added by saccadic fragments. Saccadic contribution is defined as sum of all
contributions to total vergence reaction added by saccadic fragments. The examples
of the curve analysis from Fig. 13 give Table 1 .
1.4
Ir.M.A. - Infrared Measurement of Accommodation
(3D stimulation)
The Ir.M.A. (Infrared Measurement of Accommodation) measuring system is
the second generation system for accommodation - vergence synkinesis analysis
(Fig. 14 )[ 29 , 30 ].
Measuring methods result from experiences with the E.M.AN. measuring sys-
tem. For determining relative vergence, the Hirschbeg's test is also used. The
relative refractive power of the eye lens is measured by the eccentric photorefraction
 
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