What causes hypertropia?

Causes of Hypertropia

Hypertropia results from a diverse range of etiologies, with superior oblique palsy (fourth nerve palsy) and thyroid eye disease being the two most common causes in adults, together accounting for over 50% of cases. 1, 2

Primary Causes in Adults

Most Common Etiologies

• Superior oblique palsy is the single most frequent cause of vertical strabismus in adults, with an annual incidence of 6.3 cases per 100,000 people, occurring more commonly in males 1
• Thyroid eye disease represents the other major cause and comprises the largest group among patients with ocular motility deficits (33% of hypertropia cases) 2

Congenital vs. Acquired Superior Oblique Palsy

• Congenital superior oblique palsy may remain asymptomatic for decades due to effective compensatory head positioning, then decompensate with age-related deterioration 1
• Acquired superior oblique palsy results from head trauma (most common precipitant), trochlear schwannoma, or microvascular ischemia 1
• The distinction matters clinically: hypertropia equal or greater in upgaze than downgaze occurs in 86% of decompensated congenital cases but never in traumatic or tumorous cases 3

Other Neurological Causes

• Skew deviation must be distinguished from superior oblique palsy as it indicates more serious brainstem or cerebellar pathology 1
• Third nerve palsy can produce hypertropia when the inferior rectus is affected 2
• Myasthenia gravis presents with variable, fatigable hypertropia that worsens throughout the day 1, 2

Mechanical and Restrictive Causes

• Orbital fractures cause restrictive hypertropia, most commonly from inferior rectus entrapment in floor fractures 2
• Prior ocular surgery (strabismus surgery, retinal detachment repair, or orbital surgery) can result in iatrogenic hypertropia 2
• Craniofacial abnormalities alter orbital anatomy and extraocular muscle mechanics 1

Sensory and Developmental Causes

• Sensory hypertropia develops secondary to unilateral vision loss from structural ocular pathology (retinal disease, optic nerve disorders, dense cataract) 1
• Infantile strabismus syndromes including dissociated vertical deviation (DVD) present as hypertropia, typically in patients with history of infantile esotropia 1
• Duane syndrome and congenital fibrosis syndromes represent congenital cranial dysinnervation disorders causing restrictive hypertropia 1

Secondary and Consecutive Causes

• Consecutive hypertropia occurs after surgical overcorrection of esotropia or exotropia 1
• Decompensated vertical phorias become manifest with aging, illness, or loss of fusional control 2

Critical Diagnostic Distinctions

Parks-Bielschowsky Three-Step Test

• Positive three-step test (hypertropia greatest in opposite lateral gaze and ipsilateral head tilt) confirms superior oblique palsy 1
• Caveat: Thyroid eye disease can mimic superior oblique palsy with a positive three-step test, requiring orbital imaging for differentiation 1

When to Image

• Neuroimaging is mandatory if additional CNS signs/symptoms are present, if diplopia is acute with poor fusional amplitudes (suggesting trochlear schwannoma), or if skew deviation is suspected 1
• Orbital imaging (MRI or ultrasound) is indicated when thyroid eye disease is suspected; ultrasonography is highly sensitive for detecting thyroid orbitopathy 2
• Neuroimaging is rarely needed for isolated unilateral superior oblique palsy or bilateral cases with known trauma 1

Associated Findings That Guide Diagnosis

• Excyclotorsion (measured by double Maddox rod testing or fundus examination) accompanies superior oblique palsy but is present in only 54% of congenital cases 1
• Compensatory head posture (head tilt away from affected side, chin down) suggests longstanding superior oblique palsy 1
• Latent or manifest latent nystagmus with DVD indicates infantile strabismus syndrome 1
• Forced duction testing reveals lax superior oblique tendon in congenital cases or restriction in thyroid eye disease 1

Common Pitfalls

• Abducens palsy can present with small hypertropia (present in 19-57% of cases depending on measurement method), which does not indicate multiple cranial nerve involvement 4
• Vertical fusional amplitudes are unreliable for distinguishing congenital from acquired superior oblique palsy (increased in only 56% of congenital cases) 3
• Giant cell arteritis must remain in the differential for new-onset vertical diplopia in patients over 50 years 1