Dr. Jayesh Khandelwal, K18737, Dr. Navneet Mehrotra,
Dr. Rakesh Juneja, Dr. Manish Nagpal
Introduction:
Silicone oil (SO) (polydimethylsiloxane) is a linear synthetic polymercomposed of repetitive SieO units and meets all the requirementsfor intraocular use and can be considered as the ideal material forintraocular tamponade.[1]In the currentera, the use of silicone oil as a surgical tamponade has become astandard technique in the treatment of retinal detachments,especially in proliferative vitreoretinopathy and tractional retinaldetachments, severe cases of diabetic retinopathy, endophthalmitis,viral retinitis, and ocular trauma.[2]The safety and efficacyof silicone oil in ophthalmic surgery has been demonstratedin many studies during the last decades [3, 4]. A potentialtoxicity of silicone oil to the human retina has been denied [5, 6]. Recently, unexpected andunexplained central vision loss has been described in patientswho underwent vitrectomy with silicone oil tamponade[7-10]. There are reports of decreased visual function perceived by the patients in silicone oil filled eyes without significant decrease in best corrected visual acuity or any structural changes on retina. This can be attributed to the functional damage of SO on the retina. There is insufficient data in the literature on the functional changes on the macula in silicone oil filled eyes. This is overcome by the use of newer non-invasive microperimetry (MP3; Nidek, Gamagory, Japan) which measures local retinal sensitivity for functional assessment of the retina. [11] It is a subjective, quantitative, non-invasive diagnostic exam aimed at assessing retinal functionality and puts it in strict correlation with retinal morphology. [12]MP3, otherwise known as fundus-driven perimetry, has evolved into a robust tool to evaluate the retinal function in recent years. [13]In particular, MP3 with real-time fundus imaging along with eye-tracking technology and a quicker acquisition time is considered to have an advantage over the conventional perimetry. [14]Hence the aim of our study was to evaluate the functional changes on macula, pre and post silicone oil removal (SOR) using microperimetry (MP3) in patients operated for macula-off rhegmatogenous retinal detachments (RRD).
Study design and patient enrolment:
This was a single-center, prospective, cross-sectional, interventional study. Institutional Review Board after studying protocol provided approval for the study. All cases provided informed consent to be enrolled in the study. Data was collected from patients diagnosed as macula-off RRD treated with vitrectomy and SO tamponade. Outcome measures were retinal sensitivity on MP3 and BCVA. All patients underwent a pre and post silicone oil removal MP3 evaluation
Eligibility criteria and data collection:
Data was collected under the following headings: demographic details, history of presenting illness, eye laterality, history of associated systemic co-morbidities, clinical examination details including visual acuity at presentation and follow- up with multimodal imaging features, treatment details, complications (if any) and treatment given for that complication. Inclusion criteria were: (1) Age 18-65 years (2) BCVA >6/60 (3) silicone oil filled patients operated for macula off rhegmatogenous retinal detachments with normal macula (4) follow-up of 3 months.
Exclusion criteria include eyes with re-retinal detachment, cataract, glaucoma, SO bubbles post SOR, epiretinal membrane and re-retinal detachment.
Investigations:
All cases underwent full opthalmological examination including BCVA, intraocular pressure, indirect ophthalmoscopy, fundus photograph, optical coherence tomography, MP3 pre-SOR and 1 month post-SOR.
Treatment Regime:
All patients underwent silicone oil removal operated for macula-off rhegmatogenous retinal detachments (RRD). All patients were followed at 1, 4 and 12 weeks (from baseline).
Study Parameters:
Patients who met inclusion criteria were enrolled in the study. All cases underwent complete eye examination. The examination protocol included best-corrected visual acuity (BCVA) with the help of Snellen’s Chart, and converted to logMAR (logarithm of the minimum angle of resolution), dilated fundoscopic examination, color fundus images (Topcon 50 Dx, Medical Systems Inc, Oakland, NJ, USA), spectral domain-optical coherence tomography (SD-OCT) (Spectralis, Heidelberg Engineering Inc, Heidelberg, Germany). Microperimetry (MP3; Nidek, Gamagory, Japan).All patients were operated by same surgeon and parameters with normal IOP and attached retina during follow-up period.
Data Analysis:
MP3 with real-time fundus imaging along with eye-tracking technology and a quicker acquisition time used to measure retinal sensitivity on the macula.The 12-megapixel fundus camera in the MP3 acquires high resolution images of retinal pathology and allows easy image acquisition. The MP3 measures local retinal sensitivity in the dynamic range of 0-34 dB for functional assessment of the retina. [15] MP3 has a software by which it calculates and compensates for the refractive error of the patients.The standardized stimulus grid consists of a 37-stimuli grid overlying the central 12°; Goldmann III stimulus with a duration of 200 ms; 4–2 threshold strategy; red circle fixation target for MP3. A single central foveal response and four concentric rings of retinal loci at 1°, 2˚, 4° and 6° from the centre point. [16]Recordings are considered reliable when false positive responses remained under 25%.
Results:
Forty two eyes of 42 patients were studied. Out of these, 20 eyes met our inclusion criteria and were enrolled in the study for further analysis. The mean age at presentation was 44.5 years. The gender distribution comprised, 14 eyes of male and 6 eyes of females. All subjects included in the study were Asian Indians. (Table 1)
Figure 1 shows pre and post SOR fundus photography with exact location of retinal sensitivity on the macula superimposed on each other by MP3. Figure 2 shows the difference between pre and post SOR by colour coding on MP3 software. Retinal sensitivity increased in all 20 eyes after SOR. Mean foveal sensitivity (FS) on MP3 increased by 79.36 decibels post SOR in all 20 patients (100%) which was statistically significant (p<0.005) (figure 3). BCVA post SOR remained unchanged in 18 (90%) and improved in 2 (10%) patients (figure 4).
In all study patients, slit lamp examination did not show any pathological finding at initial presentation or at follow-up visits. The postoperative healing process was uneventful in all cases. Intraocular pressure was normal at all times in all patients. Optic media were clear at all times (phakic or pseudophakic). The macula remained attached during the entire follow-up period.
Discussion:
Silicone oils are very useful surgical tools because they are able to simplify the surgical management of many vitreoretinal diseases. With the modern vitrectomy systems and the possibility to use such different tamponades, the prognosis of several diseases has improved.
Silicone oil is one of the best-known intraocular tamponadesand it is widely used and considered to be safe. Previous data suggests that there are unexplained cases of visionloss under silicone oil tamponade and that the number ofthese cases might be underestimated.In one of our previous studies we described small hyper-reflective spherical bodies in sub-silicone oil-fovealdepression (SSO-FD) space using SD-OCT and we concluded that these small hyper-reflective spherical bodies in the SSO-FD space weremost likely emulsified silicone oil globules and correlated with significant visual improvement with theirclearance after silicone oil removal.[17] The fact that a reduction of inner layer thickness is mainly seen in the inner parafoveal ring might be due to the fact that the by far largest amount of ganglion cells is found in the inner 5° parafoveal ring. [18]Phototoxicity may have a role, as oil transmits light more in the blue spectrum than aqueous. [19] The fat soluble macular pigments, lutein and zeaxanthin, are thought to protect the macula from photooxidative damage. Silicone oil has previously been reported to dissolve fat soluble elements from the retina.[20] On reviewing the literature there are reports of decreased retinal sensitivity after SO tamponade compared to gas tamponade [21] but there are no studies on retinal sensitivity pre and post silicone oil removal by microperimetry.
The underlying pathophysiologicalmechanisms remain unclear.We hypothesizethat SO tamponade has a potential detrimental effect on inner layers of retina which causes decrease in retinal sensitivity and visual impairment. During the process ofsilicone oil removal, these changes were reversiblein our cases and patient felt symptomatically better. Wenoted mean retinal sensitivity improvement of 79.36 decibels post SOR in all 20 patients (100%) which washighly significant at both 95% and 99% confidence intervals of thedifference remained stable. We also noted visualimprovement after SOR in 2 (10%) of eyes, however it remained stable in 18 (90%) patients. The limitations of this study were the small sample size andshort follow-up. This might have limited the power in detectingother predictors and may have led to insufficiency of the statisticalanalysis.A long-term follow-up of more than 1 year can be recommended, since vision may recover over such a time period after oil removal. A time dependency of silicone oil removal concerning visual outcome remains unclear.
Conclusion:
SO is best known intraocular tamponade and is widely used and considered to be safe. There are many unexplained reports of visual function loss under SO tamponade that are underestimated. SO may affect retinal sensitivity although VA may or may not change. Presence of silicone oil in the eye possibly decreases the sensitivity of the macular area and removal of oil improves the quality of vision.MP3 has an important role in early detection of visual loss even before decline in BCVA. Hence MP3 is an important qualitative indicator of visual function. High-definition OCT monitoring might be a helpful tool to detect early and progressive changes in inner retinal layer thickness under SO tamponade.Timely removal of SO can prevent its toxic effect on retina. Further research is warranted to elucidate the possible effect of SO on structural and functional changes on retina
References:
1. Kreiner CF. Chemical and physical aspects of clinically applied silicones. DevOphthalmol. 1987;14:11-19
2. Gallemore R, McCuen B. Silicone Oil in Vitreoretinal Surgery. Retina. St Louis:Mosby; 2212-2234
3. Gonvers M (1985) Temporary silicone oil tamponade in the managementof retinal detachment with proliferative vitreoretinopathy.Am J Ophthalmol 100(2):239–245
4. Federman JL, Schubert HD (1988) Complications associated withthe use of silicone oil in 150 eyes after retina-vitreous surgery.Ophthalmology 95(7):870–876
5. Inoue M, Iriyama A, Kadonosono K, Tamaki Y, Yanagi Y (2009)Effects of perfluorocarbon liquids and silicone oil on human retinalpigment epithelial cells and retinal ganglion cells. Retina 29(5):677–681
6. Lucke KH, Foerster MH, Laqua H (1987) Long-term results ofvitrectomy and silicone oil in 500 cases of complicated retinal detachments.Am J Ophthalmol 104(6):624–633
7. Christensen UC, la Cour M (2012) Visual loss after use of intraocularsilicone oil associated with thinning of inner retinal layers. ActaOphthalmol 90(8):733–737
8. Rani PK, Raman R, Bhende P, Sharma T (2005) Visual loss may bedue to silicone oil tamponade effect rather than silicone oil removal.Br J Ophthalmol 89(12):1667
9. Williams PD, Fuller CG, Scott IU, Fuller DG, Flynn HW (2008)Vision loss associated with the use and removal of intraocular siliconeoil. ClinOphthalmol 2(4):955–959
10. Moya R, Chandra A, Banerjee PJ, Tsouris D, Ahmad N, CharterisDG (2015) The incidence of unexplained visual loss followingremoval of silicone oil. Eye 29(11):1477–1482
11.Microperimeter MP-3. Retina & Glaucoma. NIDEK CO. Accessed 16 Aug 16
12. Steinberg JS, Saßmannshausen M, Pfau M, Fleckenstein M, Finger RP, Holz FG, Schmitz- Valckenberg S. Evaluation of Two Systems for Fundus-Controlled Scotopic and Mesopic Perimetry in Eye with Age-Related Macular Degeneration. Transl Vis Sci Technol. 2017 Jul 13;6(4):7.
13. Acton JH, Greenstein VC. Fundus-driven perimetry (microperimetry) compared to conventional static automated perimetry: similarities, differences, and clinical applications. Can J Ophthalmol 2013;48:358–63.
14. Balasubramanian S, Uji A, Lei J, Velaga S, Nittala M, Sadda S. Interdevice comparison of retinal sensitivity assessments in a healthy population: the CenterVue MAIA and the Nidek MP-3 microperimeters. Br J Ophthalmol. 2018 Jan;102(1):109-113.
15. Sulzbacher F, Roberts P, Munk MR, Kaider A, Kroh ME, Sacu S, Schmidt-Erfurth U; Vienna Eye Study Center. Relationship of retinal morphology and retinal sensitivity in the treatment of neovascular age-related macular degeneration using aflibercept. Invest Ophthalmol Vis Sci. 2014 Dec 11;56(2):1158-67.
16. Microperimeter MP-3. Retina & Glaucoma. NIDEK CO. Accessed 16 Aug 16
17. Nagpal M, Bhatt KJ, Jain P, Taleb EA, Goswami S, Verma A. Correlation ofspectral domain optical coherence tomography findings in sub-silicone oil foveal depression space and visual outcome in eyes undergoing silicone oil removal. Taiwan J Ophthalmol. 2016 Jan-Mar;6(1):21-25.
18. Oppel O (1967) Studies on the distribution and number of retinal ganglion cells in the human. Graefes Arch ClinExpOphthalmol 172(1):1–22
19. Azzolini C, Docchio F, Brancato R, et al. Interactions between light and vitreous fluid substitutes. Arch Ophthalmol 1992;110:1468–71.
20. Refojo MF, Leong FL, Chung H, et al. Extraction of retinol and cholesterol by intraocular silicone oils. Ophthalmology 1998;95:614–18
21. Scheerlinck LM, Schellekens PA, Liem AT, Steijns D, van Leeuwen R. Retinal sensitivity following intraocular silicone oil and gas tamponade forrhegmatogenous retinal detachment. ActaOphthalmol. 2018 Mar 2. doi:10.1111/aos.13685.
Table 1
| PARAMETERS | n (%) |
| No. of patients | 20 |
| No. of eyes | 20 |
| Male | 14 (70) |
| Female | 6 (30) |
| Age (mean) | 43.7 |
| Age (range) | 18-65 |
Leave a Comment