Thyroid disease induced diplopia.

This report describes a patient who was suffering from incomitant vertical diplopia due to Graves' ophthalmopathy. Previous optical treatment was a diffusing lens for the left eye resulting in monocular vision only. We proceeded to measure the amount of diplopia and prescribed a vertical Fresnel prism to be placed on the left spectacle lens to alleviate his diplopia and resolve his mobility problems. The amount of prism was further reduced by five prism dioptres after extraocular muscle surgery.