Congenital Insensitivity to Pain: A Case Report With Corneal Esthesiometry and In Vivo Confocal Microscopy

PURPOSE To report the findings of a comprehensive eye examination from an individual with congenital insensitivity to pain because of loss-of-function mutations in the SCN9A gene. METHODS Ophthalmologic examination and confocal microscopy were performed on a patient with congenital insensitivity to pain. RESULTS A 39-year-old man with compound heterozygous mutations in the SCN9A gene underwent examination. Cochet-Bonnet esthesiometry readings averaged 38 mm (SD 8 mm) in the right eye and 55 mm (SD 7 mm) in the left eye. Other corneal findings included mild conjunctival lissamine green staining, nonvisually significant corneal scars, mild anterior basement membrane dystrophy, and a tear breakup time of 3 seconds in each eye. In vivo confocal microscopy of the corneal subbasal nerve plexus revealed relatively normal corneal nerve morphology, but a reduction in corneal nerve fiber density. CONCLUSIONS An individual with loss-of-function mutations in SCN9A had reduced corneal nerve fiber density but normal corneal mechanoreception.