Ocular tremor

[1] These constant oscillations are called fixational eye movements, and they include ocular microtremor, microsaccades, and drift.

[1][4] It has also been suggested that ocular tremor is a result of the eye being balanced between opposing muscles.

[1] Ocular microtremor is smaller than the other fixational eye movements of microsaccades and drift.

[1][3] The measured frequency and amplitude of ocular tremor have been found to vary.

[1] While non-contact methods of measuring ocular tremor have been found, they are not typically used due to their low resolution.