Table 1. Comparison of other tracking and targeted stimulus/beam delivery methods.

Method	Tracking method	Tracking accuracy	Latency	Stabilization accuracy	Comments
AOSLO	Retinal image tracking	<0.1 arcmin	3 msec	0.15 arcmin	Gaze contingent stimulus projection. The stimulus is corrected with adaptive optics and can be as compact as a single cone.
Optical lever	Direct optical coupling	0.05 arcmin [39]	0 (optical)	0.38 arcminutes [40]	Stimulus is very precise but contact lens slippage will cause uncontrollable and unmonitorable shifts in stimulus position
Dual Purkinje (dPi) Eye Tracker with optical deflector [41]	Purkinje reflexes from cornea and lens	~1 arcminute [42]	6 msec	~1 arc minute (error is dominated by tracking accuracy)
EyeRisTM* [43]	dPi**	~1arcmin (dPi)	5-10 msec	~1 arcmin (tracking limited) [44]	Gaze contingent display.
MP1(Nidek, Japan)	Retinal image feature tracking	4.9 arcmin [45]	2.4 msec	Not reported	Gaze contingent display for single stimulus presentations (clinical visual threshhold measurements)
Physical Sciences Inc [46].	Retinal feature tracking	3 arcmin	<1 msec	3 minutes (tracking limited)	Used to optically stabilize a scanning raster on the retina to facilitate line scanning ophthalmoscope imaging.
Heidelberg Spectralis OCT (Heidleberg, Germany)	Retinal image feature tracking	Not reported	Not reported	Not reported	Used to stabilize the OCT b-scan at a fixed retinal location to facilitate scan averaging.

* This technique falls into a broad class of eye trackers coupled with gaze contingent displays. The EyeRIS system here has the best reported performance of any of the systems we found.

** Any tracking method can be used for this type of system but results from a dPi system are reported since they provide the best results.