|Year : 2021 | Volume
| Issue : 3 | Page : 306-310
Clinical profile of silicon oil-induced ocular hypertension: A prospective study
Nishat Sultana Khayoom, Rose Mary George
Department of Glaucoma, Minto Ophthalmic Hospital, Regional Institute of Ophthalmology, Bangalore Medical College and Research Institute, Bengaluru, Karnataka, India
|Date of Submission||01-Dec-2020|
|Date of Decision||14-Mar-2021|
|Date of Acceptance||17-Mar-2021|
|Date of Web Publication||08-Dec-2021|
Dr. Rose Mary George
Paikada House, Vazhakulam, Bengaluru - 686 670, Karnataka
Source of Support: None, Conflict of Interest: None
Background: Silicone oil (SO) is an important adjunct for internal tamponade, especially in eyes with proliferative vitreoretinopathy, diabetic tractional retinal detachments, and traumatic retinal detachments. SO has been associated with complications, such as cataract, keratopathy, and glaucoma. Secondary glaucoma has been reported to occur at any time in the postoperative period with a wide range of intraocular pressures (IOPs) and vision loss. Aim: The aim of this study is to assess the incidence and clinical profile of SO-induced ocular hypertension (SOIOH) at our institution, after pars plana vitrectomy (PPV) and silicone oil tamponade (SOT) in patient requiring the procedure. Materials and Methods: This is a prospective study of patients who attended Minto Ophthalmic Hospital, Regional Institute of Ophthalmology, Bengaluru from November 2017 to October 2020 who were requiring SOT for various vitreoretinal pathology. Preoperative complete ophthalmic evaluation was done, starting from visual acuity recording using Snellen's chart, slit-lamp examination, IOP measurement using Goldmann's applanation tonometry, gonioscopy, and dilated fundus examination. A standard three-port PPV with SO injection was performed. SOIOH was defined as IOP >21 mmHg after a period of 3 weeks postoperative, which required either medical or surgical therapy. Patients who developed SOIOH were compared to those who did not develop SOIOH (SOIOH free group), in terms of age, length of SOT, presence of retained SO in anterior chamber and angle, and IOP outcomes. Results: Among 26 patients who met our inclusion criteria were evaluated. Among them, 19 (73%) were male and 7 (27%) were female. The mean average age of all the patients was 36.88 (standard deviation [SD] 17.53) ranging from 10 years to 63 years. The mean average IOP of all patients preoperatively was 13.77 mm of hg (SD 3.45 mm of hg). It increased postoperatively showing a mean average postoperative IOP of all patients as 26.08 mm of hg (SD 11.2 mm of hg). The mean overall increase in IOP postoperatively was 12.31 mm of hg (P = 0.001). The mean average preoperative IOP was 12.2 mm of hg and mean postoperative IOP was 15.4 mm of hg in the SOIOH free group, with a mean average IOP spike postoperatively was 3.2 mm of hg (P = 0.061). In the SIOH group, the postoperatively average IOP spike was 15.75 mm Hg with values ranging from 14.75 mm hg preoperative to 30.5 mm hg postoperative (P = 0.001). Interpretation and Conclusions: Patients who underwent PPV with SOT should be followed up for longer period and those who have retained SO in anterior chamber or angles should be followed up more frequently as chances of development of SOIOH is more in them as proved by this study.
Keywords: Intraocular pressure, silicone oil-induced ocular hypertension, silicone oil tamponade
|How to cite this article:|
Khayoom NS, George RM. Clinical profile of silicon oil-induced ocular hypertension: A prospective study. Kerala J Ophthalmol 2021;33:306-10
| Introduction|| |
In a wide variety of vitreoretinal procedures, silicone oil (SO) is an important adjunct for internal tamponade, especially in eyes with proliferative vitreoretinopathy, diabetic tractional retinal detachments, and traumatic retinal detachments. SO is a good internal tamponade with unique chemical characteristics such as an effective buoyant force and high surface tension. There are currently two types of SO available to use in vitreoretinal surgery which differ in their viscosity. The 1000cs SO is less viscous and has a lower molecular weight, and the 5000cs SO is more viscous and has a higher molecular weight. SO has been associated with complications, such as cataract, keratopathy, and glaucoma.,,,, Secondary glaucoma has been reported to occur at any time in the postoperative period. This secondary glaucoma can manifest with a wide range of intraocular pressures (IOPs) and vision loss.,, Mechanisms of secondary glaucoma following the silicone oil tamponade (SOT) are, SO causing pupillary block, migration of SO into the anterior chamber with consequent mechanical obstruction to filtration, and emulsified SO causing mechanical obstruction to aqueous outflow.
The purpose of our study was to assess the incidence and clinical profile of silicone oil-induced ocular hypertension (SOIOH) at our institution, after pars plana vitrectomy (PPV) and SOT in patient requiring the procedure due to various vitreoretinal pathologies.
| Materials and Methods|| |
This is a prospective interventional study of patients who attended Minto Ophthalmic Hospital, Regional Institute of Ophthalmology, Bengaluru, from November 2017 to October 2020 who were requiring SOT for various vitreoretinal pathology. Twenty-nine patients were enrolled in the study. Preoperative complete ophthalmic evaluation was done, starting from visual acuity recording using Snellen's chart, slit-lamp examination, IOP measurement using Goldmann's applanation tonometry, gonioscopy, and dilated fundus examination. A standard three-port PPV with SO injection was performed. All had small fluid menisci to ensure the absence of overfill.
SOIOH was defined as IOP >21 mm hg after a period of 3 weeks postoperative, which required either medical or surgical therapy. Patients were analyzed in terms of age and length of SOT and those who developed SOIOH were compared to those who did not develop SOIOH (SOIOH free group), in terms of the presence of retained SO in anterior chamber and angle, and IOP outcomes and development of glaucomatous cupping in the form of increase in the cup to disc ratio during their follow-up visits which was every three monthly.
Exclusion criteria were patients previously diagnosed with glaucoma, ocular hypertension, glaucoma suspects, and those on IOP-lowering agents. Furthermore, patients with SO overfill or IOP spikes on the postoperative days 1–21 were excluded from the study.
The data obtained from the patients were recorded and analyzed. Descriptive analysis of the population's characteristics was carried out. Results of continuous variables are reported as mean and standard deviation (SD). The differences between quantitative variables were analyzed using paired t-test. P < 0.05 was considered as statistically significant for all the comparisons.
Data were analyzed using SPSS 20.0 is an IBM software Version and Microsoft Excel 2013.
The sample size was calculated using single mean-paired t-test
where μ1 = Pretest mean
μ2 = Posttest mean
σ 1 = SD in the pretest
σ 2 = SD in the posttest
Δ = Effect size
α = Significance level
1−β = Power
Taking alpha error as 1.96 and absolute precision at 10%, the minimum sample size using the above formula was 20.
| Results|| |
Among 29 patients enrolled in the study, three subjects were excluded later because of immediate postoperative IOP spikes within 3 weeks. Hence, 26 patients who met our inclusion criteria were evaluated. Among them, 19 (73%) were male and 7 (27%) were female. The mean average age of all the patients was 36.88 (SD 17.53) ranging from 10 years to 63 years. The average length of SOT was 17.5 months (2–36 months).
Of these 26 patients, SOT was done for different reasons such as 7 (30%) cases had proliferative diabetic retinopathy with tractional retinal detachment, 11 (42%) had traumatic retinal detachment, 4 (15%) with rhegmatogenous retinal detachment, and rest of the 4 (15%) patients with aphakic retinal detachment.
The mean average IOP of all patients preoperatively was 13.77 mm of Hg (SD 3.45 mm of Hg). It increased postoperatively showing a mean average postoperative IOP of all patients as 26.08 mm of hg (SD 11.2 mm of hg). The mean overall increase in IOP postoperatively was 12.31 mm of hg (P = 0.001)
Among 26 patients evaluated, 16 who had persistently raised IOP after 3 weeks were included in the SOIOH group and ten patients maintained normal range of IOP and were included in SOIOH free group. The mean average preoperative and postoperative IOPs in both groups are given in [Table 1]. The average rise in IOP in the SOIOH group was 15.75 mm hg (P = 0.001) and in SOIOH free group was 3.2 mm hg (P = 0.061). Comparison between preoperative and postoperative IOP among the patients showed statistically significant (P < 0.001) increase after SOT.
|Table 1: Comparison of intraocular pressure pre- and post-operative in silicone oil-induced ocular hypertension and silicone oil-induced ocular hypertension free group|
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Sixteen patients who had persistently raised IOP were put on medical treatment and followed up frequently of the SOIOH group who were not responding to medical treatment underwent SO removal and three of them underwent filtering surgery.
Three out of 10 (30%) patients in SOIOH free group and 13 out of 16 (81%) patients in SOIOH group had emulsified SO in the anterior chamber, which was statistically significant with P = 0.009 [Figure 1], [Figure 2] and [Table 2], [Table 3] and visible oil in superior angle on gonioscopy. Two out of 10 (20%) patients in SOIOH free group and 10 out of 16 (62.5%) patients in the SOIOH group showed glaucomatous optic disc cupping.
|Figure 1: Emulsified silicone oil deposited on iris and intraocular lens|
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|Figure 2: Emulsified silicone oil in the anterior chamber causing inverse hypopyon|
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|Table 2: Clinical characteristics of patients with SOIOH and SOIOH free group|
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| Discussion|| |
The mechanisms of IOP elevation following SOT are directly attributed to pupillary block caused by SO and emulsified SO in the anterior chamber. Histological studies have shown obstruction of trabecular meshwork by silicone bubbles, pigmented cells, and silicone-laden macrophages.
According to a study by Ichhpujani et al., the reported frequencies with which SOT is associated with postoperative IOP spike can vary widely, ranging from 2% to 50% and another study by Nariani et al. where they used SOT with 1000cs SO after PPV seemed to be associated with the development of SOIOH in 33.3% of patients. Our study showed SOIOH for 61% of patients enrolled in our study. This discrepancy may be related to the underlying disease of the eye, which can alter aqueous outflow and inflow and the resultant IOP represents the balance between the two.
The length of SOT was associated with increased incidence of SOIOH. This suggests that SO should be removed as soon as there is no further need for it. However, even after SO removal the majority of patients with SOIOH had persistence of the disease. This attributes that the pathogenesis of SOIOH includes irreversible damage to the angle structures. And also small silicone bubbles could have persisted in the trabecular meshwork, even after oil removal.
In our study, we found that emulsified SO in the anterior chamber was more common in the SOIOH group (81%) as compared to the other group (30%). This is in accordance with other studies by Valone and McCarthy. and Nariani et al. where they showed increased incidence in ocular hypertension in eyes with retained SO in the anterior chamber. The absence of raised IOP in few eyes with retained SO in the anterior chamber or angles can be due to the pressure-lowering effect of ciliary body detachment by cyclitic membranes or total retinal detachments. Fibrous tissue has been shown to form around silicone vesicles, the retraction of these may lead to these detachments.
We excluded patients with immediate IOP spike to investigate a more homogeneous group of patients who had no spikes of IOP in the first 3 weeks of postoperative days and patients without SO overfill. SO overfill can lead to acute glaucoma with shallowing of the anterior chamber and oil displacement into the anterior chamber.
de Corral et al. have shown that lOP elevation associated with SO injection is independent of systemic conditions such as diabetes mellitus.
In the study by Nariani et al., age and family history of glaucoma had a positive correlation with the development of SOIOH. This is consistent with the tendency of glaucoma to be an age-related disease. In our study, we failed to analyze any correlation of age with the development of SOIOH and any correlation of family history of glaucoma or systemic conditions with SOIOH.
Weinberg et al. reported elevated lOP after PPV alone, without SOT attributing it to neovascularization, hemorrhage, hemolysis, or phacolysis. IOP elevation also may be due to peripheral anterior synechiae and/or inflammation. One of the major drawbacks of our study was the presence of certain confounding factors. Raised IOP could not be attributed completely to SOT alone in all cases. Steroid-induced glaucoma and postoperative inflammatory glaucomas could also have been contributory factors.
lOP elevation is a common occurrence after intravitreal SO injection used in the management of complicated retinal cases. The underlying mechanism is often unclear, and may frequently be multifactorial in nature. Patients should be monitored closely for the development of elevated postoperative lOP, especially if they have a history of elevated preoperative lOP, and they may benefit from aggressive medical and or surgical treatment of glaucoma with SO removal, glaucoma implants, or cyclodestructive procedures to avoid additional optic nerve damage.
Our study was limited by its relatively small number of patients. Moreover, we failed to include visual field and pachymetry testing to define the SOIOH group with more accuracy.
| Conclusions|| |
Ocular hypertension following intravitreal injection of SO is a known complication. So patients who underwent PPV with SOT should be followed up for the longer period and in those who have retained SO in the anterior chamber or angles should be followed up more frequently as chances of development of SOIOH are more in them as proved by this study. The longer the duration of tamponade caused by SO, the more is the incidence of SOIOH. Hence, it is advisable to remove SO as soon as its purpose has been served.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]