In this paper we propose a method for quantitative assessment of pathological nystagmus by using eye gaze data recorded with an eye tracker (Tobii T60). In detail, we use data acquired while patients perform two tests, the smooth pursuit and the saccadic movement test (implemented on the Tobii T60 using its API), that may indicate altered ophthalmic functions typical of the pathological nystagmus. Afterwards, data is analyzed by using statistical, spectral and chaotic methods in order to provide the physicians with a useful tool for assessing quantitatively the severity (or the presence) of the pathological nystagmus. A pilot study carried out on a set of 15 patients is here reported for a preliminary investigation of the suitability of the proposed eye tracker method.