The fact that the sensation of<unk>  corresponds with the visual field of the macula means that it can be utilised in training people to look at objects with their macula. People with certain types of strabismus may undergo an adaptation whereupon they look at the object of attention not with their fovea (at the centre of the macula) but with an eccentric region of the retina. This adaptation is known as eccentric fixation. To aid in training a person to look at an object with their fovea rather than their eccentric retinal zone, a training device can be used. One such apparatus utilises a rotating polarised plate backlit with a bright white light. Wearing blue spectacles (to enhance the<unk>  image) and an occluder over the other eye, the user will hopefully notice the<unk>  where their macula correlates with their visual field. The goal of the training is for the user to learn to look at the test object in such a way that the<unk>  overlaps the test object (and the viewer is thus now looking at it with their fovea). The reason for such training is that the healthy fovea is far greater in its resolving power than any other part of the retina. Another diagnostic method that utilises birefringent properties of the retinal tissue is retinal birefringence scanning, that can be used in case of severe amblyopia or when the specialist lacks a cooperation from the patient.
Haidinger's brush
Tao brush
Air ioniser
Cuticura soap
Alger brush
Leech collector
Antimonial cup
Winpepi