[Objective determination of refractive changes in silicon oil filled eyes--effect of head position on refraction]

The refraction of the eye is altered significantly after silicone oil instillation into the vitreous cavity due to its high refractive index. The degree of the refractive change varies during the daily course and depends on the position of the head.

To analyze the degree and time course of the refractive change depending on the head position we performed refractive measurements in 5 aphakic and 5 phakic silicone oil-filled eyes with attached macula by an automatic handrefractometer. This new device was used for 25 measurements at short intervals in each patient at different eye positions (supine position, prone position and primary eye position).

Mean visual acuity in all patients valued 0.14 (+/- 0.05). The highest shift in refraction of +5.95 (+/- 2.63) dpt in spherical equivalents occurred in the aphakic eyes and of +2.45 (+/- 0.71) dpt in the phakic eyes after position change from face up to face down. Three minutes after position change the refraction remained stable in nearly all eyes. Only slight changes in cylinder and corresponding axis were found during the measurements with a mean axial shift of 10.1 (+/- 5.1) degrees.

Immediately after change of the head position especially aphakic eyes demonstrated remarkable refractive shifts. The results of this study explain patients' complaint of visual changes during the daily course after intraocular silicone oil injection. Refractive alterations evoked by silicone oil stabilized a few minutes after change of the head position.