A computer program including instructions to cause a processing circuitry to execute a method, the method comprising: - acquiring a video sequence from an IR-sensitive camera module, including a plurality of video frames, of an eye of a patient, wherein a first video sequence of the eye of the patient is acquired while the patient is in a supine position, and a second video sequence of the eye of the patient is acquired while the patient is in an upright position; - selecting a parameter being one of a baseline pupil size, a maximum change in size of a pupil and an average velocity of constriction of the pupil; - determining, using the processing circuitry and based on the first video sequence, a first version of the selected parameter; - determining, using the processing circuitry and based on the second video sequence, a second version of the selected parameter; - determining, using the processing circuitry, whether the patient has postural orthostatic tachycardia syndrome (POTS) based on a comparison of the first version and the second version of the selected parameter; the method further comprising: - determining, using the processing circuitry, that the patient has POTS when the patient's maximum pupil diameter measured in the supine position is 2.5% greater than the patient's maximum pupil diameter measured in the upright position; - determining, using the processing circuitry, that the patient has POTS when the patient's minimum pupil diameter measured in the supine position is 6.7% greater than the patient's minimum pupil diameter measured in the upright position; - determining, using the processing circuitry, that the patient has POTS when the patient's first change in size of the pupil measured in the supine position is 8.5% less than the patient's second change in size of the pupil measured in the upright position; or - determining, using the processing circuitry, that the patient has POTS when the patient's first average velocity of constriction of the pupil measured in the supine position is 7.3% less than the patient's second average velocity of constriction of the pupil measured in the upright position. - acquiring a video sequence from an IR-sensitive camera module, including a plurality of video frames, of an eye of a patient, wherein a first video sequence of the eye of the patient is acquired while the patient is in a supine position, and a second video sequence of the eye of the patient is acquired while the patient is in an upright position; - selecting a parameter being one of a baseline pupil size, a maximum change in size of a pupil and an average velocity of constriction of the pupil; - determining, using the processing circuitry and based on the first video sequence, a first version of the selected parameter; - determining, using the processing circuitry and based on the second video sequence, a second version of the selected parameter; - determining, using the processing circuitry, whether the patient has postural orthostatic tachycardia syndrome (POTS) based on a comparison of the first version and the second version of the selected parameter; the method further comprising: - determining, using the processing circuitry, that the patient has POTS when the patient's maximum pupil diameter measured in the supine position is 2.5% greater than the patient's maximum pupil diameter measured in the upright position; - determining, using the processing circuitry, that the patient has POTS when the patient's minimum pupil diameter measured in the supine position is 6.7% greater than the patient's minimum pupil diameter measured in the upright position; - determining, using the processing circuitry, that the patient has POTS when the patient's first change in size of the pupil measured in the supine position is 8.5% less than the patient's second change in size of the pupil measured in the upright position; or - determining, using the processing circuitry, that the patient has POTS when the patient's first average velocity of constriction of the pupil measured in the supine position is 7.3% less than the patient's second average velocity of constriction of the pupil measured in the upright position. - determining, using the processing circuitry, that the patient has POTS when the patient's maximum pupil diameter measured in the supine position is 2.5% greater than the patient's maximum pupil diameter measured in the upright position; - determining, using the processing circuitry, that the patient has POTS when the patient's minimum pupil diameter measured in the supine position is 6.7% greater than the patient's minimum pupil diameter measured in the upright position; - determining, using the processing circuitry, that the patient has POTS when the patient's first change in size of the pupil measured in the supine position is 8.5% less than the patient's second change in size of the pupil measured in the upright position; or - determining, using the processing circuitry, that the patient has POTS when the patient's first average velocity of constriction of the pupil measured in the supine position is 7.3% less than the patient's second average velocity of constriction of the pupil measured in the upright position.