add torsion algorithm

[simonarvin]

Torsional vector algorithm

Fig

Several neuro-ocular pathologies produce torsional eye movement patterns, such as torsional nystagmus and midbrain lesions. Here's a suggestion to compute the torsional vector of the eye (see Fig):

A - B: detect pupil.
C: Expand pupil fit model (via scalar x radii).
D: Extract iris nuances using regular pupil model (B) subtracted from the expanded model (C).

One way to calculate the torsional vector using the iridal nuances is to extract the mean brightness of iridal subsegments segmented radially by increments of x degrees, where x is the size of each segment. The pattern of brightness across subsegments reveals phase shifting of the 'wavy' appearance of the iris, ie torsion is quantised.

Best,
Simon