One Eye Getting Smaller: Not Ophthalmoplegia
A noticeable size difference between eyes, with one eye appearing smaller, is not a sign of ophthalmoplegia. Ophthalmoplegia specifically refers to paralysis or weakness of the extraocular muscles that control eye movement, not changes in eye size 1.
What Ophthalmoplegia Actually Presents As
Ophthalmoplegia manifests with specific symptoms that are distinct from eye size changes:
- Double vision (diplopia) is the hallmark symptom, occurring because the eyes cannot move together properly 1
- Impaired eye movements in specific directions, depending on which cranial nerves (III, IV, or VI) or muscles are affected 1
- Disconjugate gaze where the eyes do not align when looking in certain directions 1
- Compensatory head positioning to avoid diplopia in some cases 1
Ophthalmoplegia does not cause one eye to become physically smaller 2, 3.
What Actually Causes One Eye to Appear Smaller
When one eye appears smaller than the other, consider these actual causes:
Eyelid-Related Causes
- Ptosis (drooping eyelid) makes the eye appear smaller by covering part of it 4
- Enophthalmos (posterior displacement of the globe into the orbit) creates the appearance of a smaller eye
- Horner's syndrome causes ptosis and miosis (small pupil) on the affected side
Orbital and Globe Causes
- Orbital trauma can cause enophthalmos from orbital floor fractures
- Thyroid eye disease can cause asymmetric proptosis, making the unaffected eye appear relatively smaller
- Phthisis bulbi (shrinkage of the eyeball itself) from severe ocular disease or trauma
Critical Red Flags Requiring Urgent Evaluation
Seek immediate medical attention if the smaller-appearing eye is accompanied by:
- Sudden onset of double vision - suggests cranial nerve palsy, stroke, or aneurysm 5
- Severe headache - may indicate giant cell arteritis, aneurysm, or increased intracranial pressure 5
- Pupil abnormalities with drooping eyelid - third nerve palsy with pupil involvement suggests aneurysm until proven otherwise 5
- Weakness, numbness, or difficulty speaking - suggests brainstem stroke or multiple sclerosis 5
- Progressive worsening over days to weeks - warrants neuroimaging to exclude compressive lesions 1
Recommended Evaluation Approach
Start with a comprehensive ophthalmologic examination focusing on:
- Measurement of palpebral fissure height to quantify the size difference objectively
- Assessment of eyelid position and function to identify ptosis 4
- Pupil examination to detect anisocoria (unequal pupils) suggesting Horner's syndrome
- Exophthalmometry to measure any difference in globe position
- Ocular motility testing - if eye movements are normal and there is no diplopia, ophthalmoplegia is excluded 3, 6
Imaging Considerations
MRI of the orbits and brain with contrast is the preferred initial imaging if a structural cause is suspected, as it provides superior visualization of orbital soft tissues, extraocular muscles, and neurologic pathways compared to CT 1.
Common Pitfall to Avoid
Do not confuse ptosis with ophthalmoplegia. While ptosis can occur alongside ophthalmoplegia in third nerve palsy, ptosis alone (making an eye appear smaller) without impaired eye movements or diplopia is not ophthalmoplegia 4. The key distinguishing feature is whether eye movements are affected 2, 3.