On the synoptophore, a patient with a small-angle strabismus can superimpose the slides of a lion and a cage, can fuse a pair of rabbit slides with a fusional amplitude of 12 degrees, and correctly localises a slide presented to each eye in depth. Which grade of binocular vision corresponds to this last ability?
- A Grade 1: simultaneous perception
- B Grade 2: fusion
- C Grade 3: stereopsis ✓
- D Grade 4: harmony of the sensory and motor systems
Correct answer: C. Grade 3: stereopsis
Explanation
Grades of binocular vision on the synoptophore are: Grade 1, simultaneous perception (superimposing dissimilar images such as lion and cage); Grade 2, fusion with measurable fusional amplitude using nearly identical slides such as two rabbits differing in one detail; Grade 3, stereopsis, the perception of depth from horizontally disparate images. The ability to localise in depth is therefore Grade 3. There is no Grade 4 in this classification, which eliminates option D outright.
Reference: Khurana's Comprehensive Ophthalmology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.