Correlation between exophthalmos and compressive optic neuropathy in patients with severe thyroid related orbitopathy

Abstract

Abstract: : Purpose:Thyroid related orbitopathy (TRO) is the most common orbital pathology occurring in the general population. Approximately 40% of patients with Graves' disease have or will develop signs of TRO. Compressive optic neuropathy (CON) is the most common cause of irreversible visual loss secondary to TRO. The prevalence of optic neuropathy with visual loss in patients with thyroid related orbitopathy is fortunately less than 5%. Most cases of optic neuropathy are felt to be due to compression of the optic nerve by the enlarged extraocular muscles at the orbital apex. Exophthalmos is a common manifestation of enlarged extraocular muscles.The purpose of this study is to determine the relationship between the degree of exophthalmos and the presence of compressive optic neuropathy in TRO. It is postulated that the presence of severe proptosis may serve as an auto–decompression factor in patients with TRO and serve as a protective mechanism against development of compressive optic neuropathy. Methods: A retrospective review of 200 randomly selected charts of patients with TRO was performed. The charts were reviewed for CON and exophthalmometry readings by Hertel exophthalmometer. Patients were separated in to two groups: Group 1 – patients with CON, Group 2 – Patients with exophthalmometry readings > 2 std deviations from the mean of our patient population Results: Group 1 consisted of 5 patients (7 eyes). Average exophthalmometry readings in this group was 20.14mm. Group 2 consised of 12 patients (24 eyes). Average exophthalmometry in this group was 26.16mm. No patients in Group 2 manifested CON. Conclusions: Higher exophthalmometry readings did not correlate with higher incidence of CON. No patient with CON had an exophthalmometry reading >23mm. The 14 eyes with the highest degree of exophthalmos exhibited no signs of CON. These findings suggests that development of exophthalmos may actually prevent CON by relieving soft tissue crowding of the orbital apex when tissue is allowed to reposition in an anterior direction.

Keywords: clinical (human) or epidemiologic studies: risk factor assessment • neuro–ophthalmology: optic nerve • autoimmune disease