On the synoptophore, a patient is shown two slides of two cats, one lacking a tail and the other lacking ears, with small control marks present on each slide. Fusion is achieved only when both control marks are seen simultaneously. This corresponds to which grade of binocular vision?
- A Grade I, simultaneous perception
- B Grade II, fusion with sense of depth ✓
- C Grade II, fusion with stereoacuity
- D Grade III, stereopsis
Correct answer: B. Grade II, fusion with sense of depth
Explanation
Synoptophore grades follow the classic classification: grade I is simultaneous perception tested with dissimilar slides such as a bird and a cage, grade II is fusion tested with similar slides having small dissimilar control details such as the two cats, and grade III is stereopsis tested with paired slides that differ only by horizontal disparity. The question describes fusion with control marks, so it is grade II. Note that grade II fusion is not itself stereopsis, which kills option C.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.