three-step test
The three-step test is a clinical test that identifies the single weak muscle behind a vertical strabismus. It measures the vertical deviation in primary position, in right and left gaze, and with the head tilted to each shoulder.1,3
The first step narrows the eight vertical muscles to four, the second narrows those to two, and the head tilt picks the one. A superior oblique palsy is by far the commonest positive result.
The test is designed for a single, recent paresis. It gives misleading answers when more than one muscle is involved, if the deviation is restrictive or long-standing, or after eye muscle surgery.1
More detail
The first step asks which eye is higher in primary position, and that answer leaves the two depressors of the higher eye and the two elevators of the lower eye. The second step asks whether the deviation is greater in right or left gaze, and that answer leaves the two muscles with the greatest vertical action there. The third step is the Bielschowsky head tilt test. Tilting the head toward one shoulder makes that eye intort with its two superior muscles.1,2 If the superior oblique is weak the superior rectus acts alone and lifts the eye, so the deviation grows on tilt toward the weak side.1,2 The superior oblique pattern follows a marching cadence: right superior oblique is right, left, right (right eye higher, worse in left gaze, worse on right tilt) and left superior oblique is left, right, left.3 Two mnemonics summarize a fourth nerve palsy, worse on opposite gaze and better on opposite tilt.1
Sources (10)
- Kanski, Clinical Ophthalmology (2024), ch. 19, Parks three-step test
- Pickwell's Binocular Vision Anomalies, ch. 17, Incomitant Deviations
- Scheiman and Wick, Clinical Management of Binocular Vision, ch. 14
- American Academy of Ophthalmology. 2020. Pediatric Ophthalmology/Strabismus: Basic and Clinical Science Course. San Francisco: American Academy of Ophthalmology.
- Ansons, A.M. and Davis, H. eds. 2014. Diagnosis and management of ocular motility disorders. 4th ed. Oxford: Wiley-Blackwell.
- Kushner, B.J. 1989. Errors in the three-step test in the diagnosis of vertical strabismus. Ophthalmology, 96(1), pp.127-132.
- Noorden, G.K. and Campos, E.C. 2002. Binocular vision and ocular motility: theory and management of strabismus. 6th ed. St. Louis: Mosby.
- Rutstein, R. and Daum, K. 1997. Anomalies of Binocular Vision: Diagnosis & Management. St. Louis: Mosby.
- Rowe, F.J. 2012. Clinical orthoptics. 3rd ed. Oxford: Wiley-Blackwell.
- Von Noorden, G.K. and Campos, E.C. 2002. Binocular vision and ocular motility: theory and management of strabismus. 6th ed. St. Louis: Mosby.
Reviewed October 2026