Thyroid eye disease is an autoimmune process that causes enlargement and stiffening of some eye muscles. This change can restrict the movement of each eye, cause a misalignment between the two eyes and lead to double vision. Because the eye muscles become bigger, they take up extra room in the eye socket and cause the eyes to bulge out, also called proptosis. When there is proptosis, the eye lids may not be able to completely cover the eye itself and this leads to dry eyes that can be severe. In extreme cases, the eye muscles may become so thick that they press on the optic nerve causing vision loss.
If thyroid eye disease is suspected, a complete eye examination will be performed, including checking the range of movement of each eye, measuring the amount of proptosis, and checking for color vision, in addition to visual field testing and special photographs of the eyes. In addition, a MRI or CT scan of the eyes will be obtained to further assess the size of the eye muscles and the extent of optic nerve compression if present.
CT scan of a patient with thyroid eye disease showing enlarged eye muscles (red arrows) as compared to the more normal sized eye muscles (green arrows).
Double vision can be treated by covering one eye with a patch or covering one glasses lens with opaque tape. Special prism glasses may help treat the double vision by lining up the images that each eye sees. Eye muscle surgery treats double vision by physically realigning the two eyes. Before surgery, the surgeon may want to monitor the condition for approximately 6 months to ensure there are no further changes in the misalignment between the two eyes.
Artificial tears and ointment will be necessary to treat dry eyes from exposure due to lack of poor eyelid coverage.
If there are findings to suggest optic nerve compression and vision loss from the thickened muscles, radiation therapy to shrink the muscles or surgery to make more space in the eye socket may be done. If the vision loss is found and treated early, the visual outcome can be excellent.
Overall, each patient’s course and outcome vary and requires routine evaluations to monitor for changes. Close follow-up with an endocrinologist is important to regulate any changes in the thyroid function. However, because thyroid eye disease is an autoimmune process, the eye symptoms may still fluctuate even if the thyroid levels is normal. Patients are strongly recommended to discontinue smoking if they do, as this has been found to worsen thyroid eye disease.
For more information: view PDF brochure from North American Neuro-Ophthalmology Society (NANOS).