The aim of this study was to understand the pathogenesis of the enophthalmos of Horner's syndrome.

We performed right cervical sympathectomy in 10 Sprague-Dawley rats weighing 200~300 grams at 8 weeks of age. We obtained bilateral extraocular muscle and fat from all 10 rats. These tissues were observed under light and electron microscopy.

After 8 weeks, ptosis and enophthalmos were seen in the right eye in all rats. We found no change bilateral fat, but the right extraocular muscle fibers had smaller diameters than the left. The right intermuscular distance was longer than the left upon light microscopy and the right extraocular muscle contained fewer and smaller mitochondria than the left extraocular muscle upon electron microscopy.

Based on these results, it is believed that enophthalmos resulted from extraocular muscle atrophy that resulted from decreasing metabolism of mitochondria in Horner's syndrome. However, enophthalmos in Horner's syndrome requires more intensive study.