This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ocular motility and squint, Subject name: Ophthalmology
Binocular single vision is tested by - 
Select and explain. 
A. Amsler grid, B. Synoptophore, C. Maddox rod, D. Cardboard test
B: Synoptophore
Answer: B: Synoptophore 
Explanation: Synoptophore (major amblyoscope) consists of two tubes, having a right-angled bend, mounted on a base. Each tube contains a light source for illumination of slides and a slide carrier at the outer end, a reflecting mirror at the righth-angled bend and an eyepiece of +6.5 D at the inner end. The two tubes can be moved separately or together by means of knobs around a semicircular scale. Synoptophore tests for sensory functions include: Estimation of grades of binocular vision Detection of normal / abnormal retinal correspondence (ARC) Neutral density filter test.