Brückner, in 1962, published a paper in German describing a "trans-illumination" test extremely useful in the diagnosis of small angle deviations and amblyopia in young uncooperative children. A bright coaxial light source, such as a direct ophthalmoscope, is used. Both eyes of the patient are simultaneously illuminated from approximately one meter distance. First, the position of the corneal light reflex, (Hirschberg test), along with brightness difference of the fundus reflex as seen in the pupil through the ophthalmoscope, is evaluated. When strabismus is present. the fixing eye has a darker reflex than the deviated eye. The second step evaluates pupil size, pupil reaction, and fixation movement of the eyes on "successive" illumination of one eye at a time. This is useful in detecting amblyopia.