A 4-year-old girl with a history of infantile esotropia shows upward drift of the right eye whenever it is covered. When a progressively darker density filter is placed before the left (fixing) eye, the right eye elevates even more prominently. This response is known as:

• A Hering law response of inferior oblique overaction
• B Bielschowsky head tilt test of superior oblique palsy
• C Bielschowsky phenomenon of dissociated vertical deviation ✓
• D Sherrington law response of superior rectus contracture

Explanation

Dissociated vertical deviation is defined by slow upward drift of an occluded eye with no comparable downward movement of the fellow eye. The Bielschowsky phenomenon refers to the increase in elevation of the covered eye as the density of the filter before the fixing eye rises, reflecting dissociation rather than true paresis. The Bielschowsky head tilt test is a different sign used in cyclovertical palsies, and it does not vary with filter density.

Reference: Khurana Comprehensive Ophthalmology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.