Ocular drifts[edit]
Ocular drift is the fixational eye movement characterized by a smoother, slower, roaming motion of the eye when fixed on an object. The exact movement of ocular drift is often compared to Brownian motion, which is the random motion of a particle suspended in fluid as a result of its collision with the atoms and molecules that comprise that fluid. The movement can also be compared to a random walk, characterized by random and often erratic changes in direction.[13] Ocular drifts occur incessantly during intersaccadic fixation. Although the frequency of ocular drifts is usually lower than the frequency of ocular microtremors (from 20 to 40 Hz compared to from 40 to 100 Hz), it is problematic to distinguish occular drifts and occular microtremors in the range from 30 to 40 Hz.[14] Resolution of intersaccadic eye movements is technically challenging .[4]
Mechanism[edit]
The motion of ocular drift is related to the processing and encoding of space and time. It is also related to acquiring minute visual details of objects that are stationary, in order for these details to be further processed.[15] Recent results have shown that ocular drift reformats the input signal to the retina equalizing (whitening) spatial power at non-zero temporal frequencies across a broad spatial frequency range.[16]
Ocular microtremors[edit]
Ocular microtremors (OMTs) are small, quick, and synchronized oscillations of the eyes occurring at frequencies in a range of 40 to 100 Hz, although they typically occur at around 90 Hz in the average healthy individual. They are characterized by their high frequency and minuscule amplitude of just a few arcseconds. Although the function of ocular microtremors is debatable and not fully known, they seem to play a role in processing of high spatial frequencies, which allows for perception of fine detail.[16][17][18] Recent studies show that ocular microtremors have become a promising tool for determining the level of consciousness in an individual, as well as the progression of some degenerative diseases including Parkinson's disease[19] and multiple sclerosis.[20]