Straylight of Explanted Silicone Oil Samples to Predict Emulsification

While silicone oil tamponades have been majorly improved on during the last decades1Hammer M. Schickhardt S.K. Munro D. et al.THE NOVEL USE OF HIGH-FLOW POLYIMIDE CANNULAS TO IMPROVE SILICONE OIL INJECTABILITY IN VITREORETINAL SURGERY.Retina. 2022; 42: 1170-1175Crossref Scopus (4) Google Scholar, one disadvantage of silicone oil endotamponades is their tendency to emulsify.2Hammer M. Schickhardt S. Munro D.J. et al.Physicochemical Properties of Explanted Silicone Oil After Use as an Intraocular Tamponade.Trans Vis Sci Tech. 2022; 11: 3Crossref Scopus (7) Google Scholar In a recent study by Al-Dwairi and colleagues, other parameters, such as the contact angle, chemical bonding, and light transmittance, were identified as altered after using silicone oil as an endotamponade in five samples of five patients.3Al-Dwairi R. Ahmad A.A. Aleshawi A. et al.Optical and Physical Properties of Silicone Oil Extracted from the Vitreous of Patients Who Underwent Vitrectomy for Retinal Detachment.Journal of Ocular Pharmacology and Therapeutics. 2022; 38: 717-727Crossref Scopus (3) Google Scholar Forward light scattering is another parameter likely to be altered by the water-in-oil droplets: one which can be measured time-efficiently in clinical practice. This approach could prove interesting to detect early emulsification in the eye. Thus, we investigated straylight of Siluron 5000 (Fluoron GmbH, Ulm, Germany) after use as an intraocular tamponade and correlated the results with clinical data. Silicone oil from 37 eyes of 37 patients was used. Only silicone oil was aspirated in a first syringe to minimize interference with the balanced salt solution infusion. This study was conducted in accordance with Good Clinical Practice guidelines and the Declaration of Helsinki. As all tested samples were included in the Apple-Laboratory explant-register no informed consent was necessary. IRB approval was granted by the Heidelberg University ethics-committee (DRKS00007837). To measure straylight, we used a methodology adapted by Łabuz et al. for in vitro evaluation of forward light scattering by using a custom-mount on the C-Quant (Oculus GmbH, Wetzlar, Germany) device4Łabuz G. Vargas-Martín F. van den Berg T.J.T.P. López-Gil N. Method for in vitro assessment of straylight from intraocular lenses.Biomed Opt Express. 2015; 6: 4457Crossref PubMed Scopus (0) Google Scholar (Figure 1a). Patients' information was screened for factors associated with silicone oil emulsification. Stata 17BE and Prism 8 were used for statistical analysis. T-test or Mann-Whitney tests were conducted as appropriate. Silicone oil removal was uneventful in all cases. Explanted samples showed a significantly higher straylight compared to unused control oils (p<0.001). Interestingly, the straylight of silicone oil samples was not normally distributed, only a subset of around one third of samples showed a greater increase in straylight. (Figure 1 B/C) The duration of the tamponade was not significantly correlated with straylight (r2=0.08, p=0.09). The samples explanted from 9 patients that received the oil tamponade for a tractive detachment due to PVR or for giant retinal tears, a severe subtype of a rhegmatogenous retinal detachment, showed a significantly greater straylight compared to oil removed from patients that were treated for uncomplicated rhegmatogenous retinal detachments (p<0.01, 28 cases, Figure 1 D). We further evaluated retinotomies as a possible factor to increase silicone oil straylight: No significant correlation was seen (p=0.72). Seven patients received an anterior-chamber-washout after silicone oil removal because of visible oil droplets. These oil samples showed significantly higher straylight values (p<0.001, Figure E). Endolaser was used in most cases at the time of the initial vitrectomy and not associated with higher straylight values (p=0.29). Similarly, in 3 cases, buckling surgery performed during oil insertion or in an earlier surgery was not associated with increased straylight values (p=0.48). Acute intraocular inflammation, a known risk factor for silicone oil emulsification, was only present in one of the 37 cases. This case had remarkably increased level of straylight of 20.8 deg2Hammer M. Schickhardt S. Munro D.J. et al.Physicochemical Properties of Explanted Silicone Oil After Use as an Intraocular Tamponade.Trans Vis Sci Tech. 2022; 11: 3Crossref Scopus (7) Google Scholar/sr. Our series included only one case with PEX. It showed a significantly higher straylight value compared to baseline 7.5 deg2Hammer M. Schickhardt S. Munro D.J. et al.Physicochemical Properties of Explanted Silicone Oil After Use as an Intraocular Tamponade.Trans Vis Sci Tech. 2022; 11: 3Crossref Scopus (7) Google Scholar/sr. Straylight was not increased in 3 samples extracted from diabetic patients (p=0.61) compared to other explanted samples. We consider that our results recommend that intraocular straylight may be a marker for early emulsification prior to it being detectable by slit lamp examination. The 25% of oil samples with the greatest straylight caused similar straylight to a crystalline lens of a 70-year-old patient of around 10 deg.2Hammer M. Schickhardt S. Munro D.J. et al.Physicochemical Properties of Explanted Silicone Oil After Use as an Intraocular Tamponade.Trans Vis Sci Tech. 2022; 11: 3Crossref Scopus (7) Google Scholar/sr5Son H.-S. Łabuz G. Khoramnia R. et al.Visualization of Forward Light Scatter in Opacified Intraocular Lenses and Straylight Assessment.Diagnostics. 2021; 11: 1512Crossref Scopus (5) Google Scholar Given the retinal comorbidities warranting the use of silicone oil, such straylight values may significantly worsen the already cautious visual prognosis. Previous studies suggested that early silicone oil emulsification generates silicone oil droplets with a diameter of around 1μm6Chan Y.K. Czanner G. Shum H.C. et al.Towards better characterization and quantification of emulsification of silicone oil in vitro.Acta Ophthalmol. 2017; 95: e385-e392Crossref Scopus (12) Google Scholar, a size which cannot be detected non-invasively with current diagnostic instruments. Visible emulsification indicates that the process has already substantially progressed, and possible complications may have already occurred. Optimally, a non-invasive way to detect early emulsification could enhance the decision-making on when to remove silicone oil to prevent further complications such as intraocular pressure spikes or glaucoma. Based on this laboratory data, a clinical study on the dynamics of straylight in patients with silicone oil endotamponade could further illuminate implications of measuring straylight and improving visual outcomes of patients with silicone oil endotamponade. Data on risk factors for emulsification is inconsistent. We found that proliferative vitreoretinopathy and giant retinal tears as indication for surgery lead to higher straylight values at silicone oil removal. Giant retinal tears and PVR are characterized by an ocular inflammation and a possible blood retinal barrier breakdown, known to lower the interfacial tension between silicone oil and the aqueous.7Nepita I. Repetto R. Pralits J.O. et al.The Role of Endogenous Proteins on the Emulsification of Silicone Oils Used in Vitreoretinal Surgery.BioMed Research International. 2020; 2020: 1-8Crossref Scopus (5) Google Scholar This could lead to earlier and more severe emulsification, presenting in higher straylight values of explanted samples. In line, the only case in which strong intraocular inflammation was present at silicone oil removal, majorly increased straylight values were observed. The tamponade duration was previously established as a risk factor for silicone oil emulsification. In this study, no correlation was apparent. However, the cases underwent timely silicone oil removal most likely influence this association. This study has inherent limitations. These are the results from a laboratory study of explanted oil samples, and it remains unclear if the increase in straylight can be quantified in patients during silicone oil endotamponade. The purpose of this study, however, was to evaluate straylight as a possibly statistical proxy for ongoing silicone oil emulsification. Additionally, we are only able to evaluate the straylight of the explanted silicone oil and not the aqueous humor as it is constantly diluted by the infusion of balanced salt solution. While most explanted silicone oil samples induced a low amount of straylight, individual samples induced straylight like a mild to medium lenticular opacification, especially cases with visible anterior chamber silicone oil droplets. This laboratory study suggests that straylight in the silicone oil filled eye could be a non-invasive parameter to estimate intraocular silicone oil emulsification. The results of this laboratory study should be translated into a clinical study using the C-Quant device next.