Corneal topography in thyroid orbitopathy after orbital irradiation

The orbital tonus changes in thyroid orbitopathy, so it may be expected that corneal topographic results also change. Orbital irradiation may reduce the orbital tonus, and thus, it may affect the topographic changes. Corneal topographic results were examined before and after orbital irradiation in patients with thyroid orbitopathy to determine whether there was a difference.

Twenty eyes of 10 patients with thyroid orbitopathy were included in this study. Corneal topography was performed with Topographic Modeling System 2 (Tomey). The refractive power of the corneal curvature was measured at the center of the corneal apex and in each of the eight quadrants, 1.5 mm and 3 mm from the corneal apex, on the corneal topographer. A total dose of 20 Gy was given in 10 fractions over 2 weeks to the orbital structures sparing the lens, and corneal topography was performed 6 weeks and 8 months later. The measures of the refractive power of the cornea were taken again. Repeated-measures analysis of variance was used to evaluate the differences between the measures.

There were no statistically significant differences in refractive power of the cornea in the topographic maps obtained before the radiotherapy and the two follow-up examinations after the radiotherapy.

Thyroid orbitopathy is an orbital disease and may affect corneal topographic results. Orbital irradiation reduces or eliminates pathogenic orbital lymphocyte infiltration, thereby reducing orbital and extraocular muscle edema in patients with thyroid orbitopathy. In the current study group, corneal topographic changes were observed minimally as a result of the orbital irradiation, but they were not statistically significant.