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L. Ai, O. Gallo, D.E. Alexander, J.M. Miller; 3–D Video Oculography in Monkey . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2499.
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© ARVO (1962-2015); The Authors (2016-present)
Eye coils are the standard way to monitor eye position in monkeys. However, when it is crucial to avoid implanting in the orbit, video oculography (VOG) is a possible replacement. In humans, VOG systems may monitor 2–D eye movements by tracking the pupil area. Some also track torsion by detecting either the radial pattern of iris crypts or additional scleral markers. Problems arise in VOG monkey use. In the dark, parts of the dilated pupil tend to be obscured by eyelids in eccentric gaze. Also, in torsion tracking, the monkey's smooth iris doesn't provide detectable pattern, and the exposed sclera is too limited to be employed in the sclera marker tracking.
To extend the 2–D tracking range in darkness, and implement torsion tracking in monkey using VOG.
In a trained rhesus macaque, we used pilocarpine to control the pupil size in 2–D tracking of a Chronos Vision VOG. In torsion tracking, we tested three marking methods, Radial Keratopigmentation (RKP), Transchamber Suturing (TCS) with Chronos iris tracking, and Spot Keratopigmentation (SKP) with marker tracking. 2–D Tracking
Pupil size, refraction, and the effective time of pilocarpine were measured with different percentages of pilocarpine (0.10%, 0.20%, 0.40%, 0.80%).
RKP: We made radial incisions deep to one third of the corneal thickness, then, introduced white titanium dioxide paste in the incision.
SKP: Black pigment paste was embedded in two 0.5–0.8 mm2 interlamellar incisions at 4, 8 o'clock in peripheral cornea.
TCS: A black suture will be passed through the anterior chamber immediately in front of the iris, with its cauterized ends covered by 2 previously prepared split–thickness scleral flaps.
Results and Discussion: :
0.2% or higher provides appropriate pupil size (< 2mm), pilocarpine greater than 0.4% causes refractive error ( ∼ –1D with 0.8% ). We chose 0.2% pilocarpine for an effective pupil size lasting about 3 hrs. RKP
The white radial lines contrast well with the brown iris and produce a strong signal. Torsion values were much larger than expected from Listing's law. The problem appears to be that the Chronos assumes the RKP in the iris plane, rather then on the cornea.
We marked the cornea with two black spots (black to avoid confusion with light source reflection on the cornea). Unfortunately, shadows of the black spots on the iris were confused with the spots themselves, and tracking was lost.
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