What is Munson's sign in the context of keratoconus?

Munson's Sign

Munson's sign is the outward bowing or V-shaped protrusion of the lower eyelid that occurs when a patient with severe corneal ectasia looks downward, caused by the protruding cone-shaped cornea pushing against the lid. 1

Clinical Significance

• This is a nonspecific finding seen only in severe, advanced ectasia, indicating significant corneal protrusion and structural compromise 1
• The sign represents a late-stage clinical manifestation of keratoconus and is not present in early or moderate disease 1
• When present, Munson's sign serves as a simple visual identifier of advanced keratoconus in patients who may be otherwise undiagnosed 2

How to Elicit the Sign

• Ask the patient to look downward (downgaze position) while you observe the lower eyelid from the side 1
• The protruding cornea will push the lower lid outward, creating a characteristic V-shaped deformation 3
• This finding is best appreciated with lateral viewing of the patient's profile during downgaze 2

Associated Clinical Context

When Munson's sign is present, expect to find other advanced keratoconus features:

• Severe corneal thinning and protrusion in the area of maximal ectasia 1
• Corneal scarring at Bowman's layer or deeper stroma 1
• Fleischer ring (epithelial iron deposition at the cone base) present in 55.5% of keratoconus cases 4
• Vogt striae (vertical fine folds in mid and deep stroma) 1
• Marked visual impairment that cannot be corrected to 20/20 with spectacles 1
• Scissors reflex on retinoscopy indicating severe irregular astigmatism 1

Clinical Implications

• The presence of Munson's sign indicates the patient is at risk for acute corneal hydrops, a break in Descemet's membrane causing sudden pain and acute vision loss 2
• Patients with this finding typically require advanced management beyond spectacles, including specialty contact lenses or surgical intervention 5, 3
• The sign correlates with significantly higher keratometry values, anterior and posterior elevation, and lower corneal thickness measurements 4

Important Caveats

• Munson's sign is not sensitive for keratoconus detection—its absence does not rule out keratoconus, as most patients with mild to moderate disease will not demonstrate this finding 1
• Early keratoconus detection requires corneal topography and tomography, not clinical signs alone 1, 5
• The sign is nonspecific and can theoretically occur with any severe corneal ectasia, not just keratoconus 1