euthyscope

eu·thy·scope

(yū'thi-skōp),
A modified ophthalmoscope, now seldom used, with which the site of excentric fixation may be dazzled by a bright light while the true fovea is simultaneously shielded by an opaque disk; used in pleoptics.
[G. euthys, straight, + skopeō, to view]

Visuscope 

A modified ophthalmoscope containing a small graticule target for the measurement of eccentric fixation. The examiner projects a shadow of the target on the patient's retina. The patient is asked to look at the centre of the target. The position of the foveal reflex relative to the centre of the graticule target indicates whether the patient has eccentric fixation and in which direction and by how much. A modified version is the Euthyscope, in which the graticule target consists of black spots rather than a star and concentric circles as in the Visuscope. The Euthyscope is used more for eccentric fixation therapy. See pleoptics.