Feasibility of using experimental high viscosity silicone oils: a pilot study

The novel use of high-flow polyimide cannulas to improve silicone oil injectability in vitreoretinal surgery

PURPOSE

The injection of high-viscosity silicone oil lengthens injection time. New polyimide-cannulas offer a greater inner diameter than conventional metal-cannulas at the same gauge. We compared the injection time for polyimide- and metal-cannulas at 23G for a variety of silicone oils including a 12500 mPas prototype oil.

METHODS

In this laboratory study, injection time was measured three times per cannula and per oil. Warming the oil before injection to up to 42°C was also evaluated. Finally, we tested the feasibility of polyimide-cannulas in vitrectomized porcine eyes.

RESULTS

The 23G-polyimide-cannula majorly decreased injection times. The time to inject 5ml of Siluron Xtra and Siluron 5000 decreased by 6:02 (76.9%) minutes (483 s vs 121 s) and 12:01 (74.7%) minutes (973 s vs 252 s), respectively. While the 23G-metal cannula failed to inject 12500 mPas oil, 5ml were injected in 10:21 minutes using the polyimide-cannula. Pre-warming Siluron 5000 to 42°C lowered the injection time by 9.0% and 12.1% when using the metal or polyimide-cannula, respectively.

CONCLUSION

Polyimide-cannulas allow a clinically relevant decrease in injection time. They may not only shorten surgery time but could ease the use of next-generation ultra-high-viscosity silicone oils. Pre-warming silicone oil leads to decreased injection times.

Change in refraction, corneal power and axial length of the eye secondary to silicone oil tamponade injection after pars plana vitrectomy

Background: Refractive and ocular biometric changes after silicone oil tamponade (SOT) in phakic eyes have been studied thoroughly; however, similar studies amongst Sudanese patients with vitreoretinal conditions were not carried out.Aim: This study aimed to assess post-operative changes in refraction, corneal power and axial length after pars plana vitrectomy (PPV) with SOT in phakic patients.Setting: The study was conducted at Sudan Eye Center, Khartoum, Sudan.Methods: A cross-sectional retrospective hospital-based study was performed at Sudan Eye Center. The study included all phakic patients who underwent PPV with SOT for a variety of vitreoretinal conditions from October 2018 to January 2019. Clinical investigations included uncorrected visual acuity (VA), best-corrected VA, refraction, corneal power and axial length pre- and post-surgery. Differences in these parameters were assessed using a paired sample t-test with a significance level of 0.05.Results: Medical records of 59 consecutive patients (59 eyes, 41 men and 18 women) with ages ranging from 22 years to 75 years were studied. The findings revealed a statistically significant hypermetropic change (pre: –0.17 ± 2.44 dioptre [D] and post: +4.43 ± 2.04 D) with a p-value of 0.001. In terms of axial length, there was a significant increase (pre: 23.61 ± 1.17 mm and post: 23.82 ± 1.27 mm; p  0.001). However, no significant change was found in corneal power (pre: –43.60 ± 1.96 D and post: 43.63 ± 2.03 D; p = 0.45).Conclusion: A hypermetropic shift in refraction, longer axial length and non-considerable increase in corneal power were observed amongst Sudanese phakic patients after PPV with instillation of silicone oil.

Study of wetting of the animal retinas by Water and organic liquids and its Implications for ophthalmology

Interfacial properties of the animal retinas are reported. Wetting of the retina-retinal pigment epithelium-choroid-sclera tissues of cow, sheep, and pig eyes by water, silicone and castor oil was explored experimentally. Both water and silicone oils demonstrated complete wetting of the retina, regardless of the viscosity of the silicone oil, whereas the castor oil demonstrated a partial wetting regime. Similar wetting regimes were observed for sheep, cow and pig retinas. The intact surface of animal retina was found to be both hydrophilic and oleophilic. Wetting experiments with double sandwich oil/water layers were performed. Water demonstrated stronger affinity to the retina than silicone and castor oils, and eventually replaced the oils at the liquid/retina interface. We conclude that aqueous solutions continuously secreted in the living eye may displace silicone oil from the retinal surface and contribute to retinal re-detachment. Study of dynamics of wetting of the animal retina by water and organic oils is reported. The exponent describing the dynamics of spreading of the castor oil is lower than that predicted by the Tanner law. Castor oil may provide more effective tamponade than silicone oil.