Measurement of axial length of eyes with incomplete filling of silicone oil in the vitreous cavity using x ray computed tomography.

AIMS To establish a reliable method for measuring the axial length of the eye with incomplete filling of silicone oil in the vitreous cavity in order to determine the IOL power before executing combined cataract surgery and silicone oil removal. METHODS 12 eyes of 12 patients undergoing combined cataract extraction and silicone oil removal between October 1998 and June 2000 were entered prospectively into this study. All eyes were examined using an x ray computed tomography (CT) scanner. Each axial length of a silicone oil injected eye was measured on the best CT slice among eyeball cuts, which showed both the insertions of the medial and lateral rectus muscle, the thickest slice of the lens, and the optic nerve. The IOL power for the eyes was determined using the SRK/T formula based on the CT data. The deviation of postoperative refraction from the goal refraction was evaluated for each eye. RESULTS The CT slices demonstrated that the vitreous cavity was not completely filled with the oil in all of the silicone oil injected eyes. The deviation of postoperative refraction from the goal refraction was less than 1 dioptre (D) error in six of 12 eyes (50%), and was less than 2 D error in nine eyes (75%). In the other three eyes having more than 2 D error, the axial length was 27 mm or more. CONCLUSION The CT measurement of axial eye length for determining IOL might be a useful method for evaluating silicone oil injected eyes before combined cataract surgery and silicone oil removal.