Silicone Oil Eyes
Ophthalmologists considering IOL implantation in eyes filled with silicone oil encounter 2 major problems. The first is obtaining an accurate AL measurement with the ultrasonic biometer. Recall that this instrument measures the transit time of the ultrasound pulse and, using estimated ultrasound velocities through the various ocular media, calculates the distance. This concept must be taken into consideration when velocities differ from the norm, for example, when silicone oil fills the posterior segment (980 m/s for silicone oil vs 1532 m/s for vitreous). Use of optical biometry to measure AL solves this problem somewhat. It is recommended that retinal surgeons perform an optical or immersion AL measurement before silicone oil placement, but doing so is not common practice. The second problem is that, as the refractive index of silicone oil is greater than that of the vitreous humor, the oil filling the vitreous cavity reduces the optical power of the posterior surface of the IOL in the eye when a biconvex IOL is implanted. This problem must be counteracted by an increase in IOL power of 3–5 D.
Suk KK, Smiddy WE, Shi W. Refractive outcomes after silicone oil removal and intraocular lens implantation. Retina. 2013;33(3):634–641.
Symes RJ. Accurate biometry in silicone oil-filled eyes. Eye (Lond). 2013;27(6):778–779.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.