Fig. 7. Graphic representation of the molecular structure of the most commonly used silicone oil, dimethylsiloxane. The linear chain coils into a helix, composed of 6 (Si-O) units per turn. For a molecular weight of 28,000 (1,000 centistokes), the helix will have 63 turns in average. Interdigitation of the helices is known to occur for helices with more than 100 turns (5,000 centistokes). The siloxane chain termination is not represented. Inset. Siloxane helix. (From Parel J-M: Silicone oils: Physicochemical properties. In Ryan SJ \[ed\]: Retina, vol 3, pp 261–277. St. Louis, CV Mosby, 1989.)