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Updated: Oct 28, 2025

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How Much Superior Rectus Underaction is Considered Normal?

Bethany Shaw1, Charlotte Codina2, Sonia Toor2

  • 1Northern Lincolnshire and Goole NHS Foundation Trust, GB.

The British and Irish Orthoptic Journal
|July 19, 2021
PubMed
Summary
This summary is machine-generated.

Most young adults exhibit mild superior rectus weakness. Ocular movement testing shows a mean weakness of -0.70 units, while synoptophore measurements indicate -0.48 degrees. Values exceeding these may warrant further clinical evaluation.

Keywords:
Ocular movementsSuperior rectusSynoptophore

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Area of Science:

  • Ophthalmology
  • Neuro-ophthalmology
  • Strabismus

Background:

  • Superior rectus muscle weakness is common in certain eye positions.
  • Normative data for superior rectus underaction in healthy young adults is lacking.
  • Establishing these parameters is crucial for accurate clinical assessment.

Purpose of the Study:

  • To determine the normal range of superior rectus muscle underaction in healthy young adults.
  • To collect normative data using ocular movement testing and synoptophore measurements.
  • To define expected parameters for superior rectus underaction in this demographic.

Main Methods:

  • Recruited 29 healthy young adults (mean age 20.30 years).
  • Assessed superior rectus underaction and inferior oblique overaction via ocular movement testing.
  • Measured subjective horizontal, vertical, and torsional deviations using a synoptophore.

Main Results:

  • 79.31% showed superior rectus underaction on ocular movement testing (mean -0.69 units).
  • 62.07% exhibited superior rectus underaction on synoptophore testing (mean -0.48 degrees).
  • Identified mean values and ranges for superior rectus underaction in laevo and dextro elevation.

Conclusions:

  • The majority of healthy young adults demonstrate some degree of superior rectus underaction.
  • Mean expected superior rectus underaction is -0.70 units (ocular movement testing) and -0.48 degrees (synoptophore).
  • Underaction exceeding -1 unit (ocular movement testing) or -1 degree (synoptophore) warrants careful clinical evaluation.