Unexplained Visual Loss After Silicone Oil Removal

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Article initiated by:

Hashem Abu Serhan

All contributors:

Abdullah Ahmed, Cameron Reinisch, M.D., Christopher Riemann, MD, Anant Pai, Hashem Abu Serhan

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Disease Entity

Disease

Unexplained visual loss after silicone oil removal (UVLASOR) is a sight-threatening complication following vitreoretinal surgery for silicone oil (SO) removal that was first described in 2004. The incidence of this phenomenon varies, with studies reporting rates from 1-10% to as high as 30%.  Banerjee PJ et al reported unexplained vision loss after SO removal in up to 49% of fovea-sparing giant retinal tear retinal detachment.  The exact pathophysiology of this entity remains unclear, with several potential mechanisms having been proposed. Other causes of postoperative visual loss including cataract formation, cystoid macular edema, epiretinal membrane formation, optic atrophy and corneal opacification should be ruled out before making the diagnosis of UVLASOR. In addition, an optical coherence tomography (OCT) evaluation should confirm the absence of structural abnormalities.

Etiology

The etiology of visual loss following removal of oil remains uncertain. Several hypotheses have been proposed including sudden changes in potassium concentration in retro-oil fluid that may lead to macular dysfunction due to photoreceptor apoptosis on oil removal, photo-toxicity at the time of silicone oil removal and fibrogenic growth factor disturbances, transient severe IOP elevation, and changes in oxygen diffusion into the retina with vs without SO.

Risk Factors

Several contributing factors may influence the development of this phenomenon:

• Male Gender: In studies with limited and small sample sizes analyzing the incidence of significant visual acuity loss following silicone oil removal, 85% of the patients who experienced visual acuity loss were male.
• Middle-aged adults: The mean age of affected patients in the study of 421 patients by Moya et al. was 53 years. Newsom et al. reported an average age of 42.8 years in their 7 patient series.
• Duration of silicone oil tamponade: Damage to the inner retinal layers is a common factor in the various proposed mechanisms for unexplained vision loss following SO removal. Two studies with sufficiently large sample sizes identified the duration of SO tamponade as the only statistically significant risk factor associated with unexplained vision loss. Moya et al. reported a mean tamponade duration of 141 days, with a range of 76 to 218 days and an increasing relative risk of unexplained visual loss in patients with macula-on giant retinal tear vs other retinal conditions duration of SO tamponade.

General Pathophysiology

The exact pathophysiology remains uncertain; however, several proposed mechanisms suggest damage to the inner retinal layers, particularly the ganglion cell complex. Both direct and indirect mechanisms of retinal injury may contribute to this phenomenon. Indirect mechanisms could include local changes in concentrations of potassium, Ca++ and Mg++, changes in levels of various cytokines or light photo-toxicity to the posterior pole, effects which all could lead to apoptosis and macular dysfunction. To date, the pathology of eyes with UVLASOR has not been described.

Pathophysiology

Unexplained visual loss after SO removal pathophysiology has not been directly elucidated but it is most likely a multifactorial disease process.

One proposed theory suggests that the bright light from the operating microscope directly induces retinal phototoxicity. The silicone oil as a whole and smaller bubbles comprised to create the whole structure can induce uneven macular illuminations and wildly heterogeneous heightened degree of macular light exposure.

Another theory involves the direct impact of SO on the inner retinal layers. The duration of SO tamponade is a known risk factor for this phenomenon. Thinning of the inner retinal layers and loss of neural retinal cells have both been proposed as potential mechanisms of injury.

Electrophysiological testing including pattern electroretinogram (PERG) and multifocal electroretinogram (mfERG) are potential modalities used to differentiate this phenomenon from other causes. Macular dysfunction is another potential cause of unexplained vision loss, as electrophysiological studies have shown that visual loss predominantly affects the macula, with reduced amplitudes in the pattern electroretinogram. Additionally, this study found that multifocal electroretinogram indicated selective damage to the central part of the macula.

The very reduced volume of distribution of a SO filled eye (<0.5 mL) as compared to a vitreous or BSS filled eye (5mL) may also play a role especially in the setting of sequestered cytokines or other pro-inflammatory agents.

Finally, an additional cause for damage to the inner retinal layers has to do with the high concentration of growth factors in the retro-oil fluid. Fibrogenic growth factors such as basic fibroblast growth factor (bFGF) and inflammatory cytokines like interleukin-6 (IL-6). The increased levels of these growth factors creates a fibrocellular membrane that can alter the retinal layers impacting vision. Unexplained visual loss, OA with cupping and vascular attenuation in the setting of long term  Boston Kpro Type I has been attributed to a chronic uveitic reaction for which immunomodulation therapy has been recommended. Whether this phenomena may inform our understanding of UVLASOR remains to be elucidated.

These potential mechanisms collectively contribute to the complex etiology of unexplained visual acuity loss following SO removal.

Diagnosis

History

Obtaining a thorough history is essential when evaluating patients with unexplained visual loss after SO removal. This should include a detailed ocular history, including the initial reason for SO placement, the specific type of retinal detachment, macular hole or other pathology, duration of tamponade, and any prior ocular surgeries or treatments. Inquiring about systemic conditions that could contribute to visual loss, such as diabetes, hypertension, and autoimmune diseases, is also appropriate.

Signs & Symptoms

UVLASOR patients present with a sudden and significant decrease in visual acuity following the SO removal. Despite this, the fundus examination often appears normal, with no signs of retinal detachment, macular edema, or other obvious pathology, though subtle signs such as ganglion cell layer thinning may be observed on optical coherence tomography (OCT). Toso et al. report that a profound central scotoma extending into the central 10 degrees of visual field, accompanied by a diminished foveal sensitivity can be observable on automated perimetry. The visual impairment manifests as blurred vision, difficulty seeing fine details, or a decrease in overall visual clarity, with severity ranging from mild to severe and often becoming permanent. However, late visual improvement may occur in some patients. The timing of visual loss is usually first day postoperatively. However, Cazabon et al. reported visual loss 1 week following oil removal. It remains unclear whether visual loss with silicone oil in situ represents a distinct phenomenon from visual loss occurring after its removal.Whether optic nerve damage and secondaryOA may play a role in UVLASOR also remains to be elucidated.

Clinical Diagnosis

The diagnosis of unexplained visual loss after SO removal is primarily a clinical one, based on the presence of visual loss after oil removal without any identifiable cause on examination or with diagnostic procedures.

Diagnostic procedures

Several diagnostic procedures can help in evaluating patients with unexplained visual loss after silicone oil removal:

• Optical coherence tomography (OCT): TOptical coherence tomography (OCT): To assess the retinal layers and rule out macular edema, epiretinal membrane, elipsoid zone insufficiency, or other macular abnormalities.
• Intravenous fluorescein angiography (IVFA): To evaluate retinal vascular perfusion and rule out any vascular abnormalities.
• Fundus AutoFluorescence:  To characterized epiretinal pigment deposits. These pigment clumps produced a striking leopard-spot pattern on fundus autofluorescence imaging.
• Electrophysiology: Including pattern electroretinography (PERG) and multifocal electroretinography (mfERG) to assess macular function and differentiate between macular and optic nerve pathology.
• Visual evoked potentials (VEPs): To assess the integrity of the visual pathway from the retina to the visual cortex .
• Automated perimetry: To evaluate the visual field and detect any scotomas or visual field defects.
• Adaptive Optics: This technique can be used to visualize microscopic structures in the retina, including SO that may be present in the retinal tissue after SO removal.

Differential diagnosis

When evaluating a patient with visual loss after SO removal, it is essential to consider other potential treatable causes for visual loss, including:

Diagnosis	Key Features
Posterior ischemic optic neuropathy	Loss of vision, visual field defects, increased inflammatory marker, normal fundus exam
Recurrent retinal detachment	Loss of vision, visual field defects, may see a break in the retina on exam
Cystoid macular edema (CME)	Blurred vision, central scotoma, petaloid late leakage on IVFA, retinal thickening on OCT
Epiretinal membrane (ERM)	Distorted vision, metamorphopsia, may see a membrane on the retinal surface on OCT
Optic neuropathy	Decreased visual acuity, visual field defects, may see optic nerve pallor > cupping on exam
Glaucoma	Visual field defects, optic nerve cupping > pallor on exam
Corneal decompensation	Blurred vision, decreased corneal clarity, may see corneal edema or scarring on exam
Silicone oil adherence to IOLs	Decreased visual acuity, visual distortion, glare, micropsia

Management

The management of unexplained visual acuity loss following SO removal in vitreoretinal surgery is multifaceted and primarily supportive, given the unclear pathophysiology.

General treatment

• Observation: In some cases, visual acuity may spontaneously improve over time. Close monitoring with regular follow-up examinations is recommended.
• Earlier silicone oil removal: Studies suggest that prolonged SO tamponade may be associated with a higher risk of complications, including UVLASOR visual loss. Therefore, early removal of SO may be considered in reducing the risk of UVLASOR. However, there is no consensus on the optimal timing for SO removal.
• Patient education: Patients should be informed about the potential for visual loss after SO removal and the lack of proven treatments. It is important to emphasize that unexplained visual loss is a rare complication and that most patients do not experience this problem.

Medical therapy

• Corticosteroids: Although the treatment of visual loss after SO removal is supportive, there is limited evidence suggesting that intensive steroid treatment (both oral and periocular) may be beneficial in some cases. One study reported significant improvement in visual acuity after a four-week course of oral prednisone and three periocular triamcinolone injections over nine weeks. However, further studies are needed to confirm the efficacy of steroid treatment. Whether other immunomodulatory therapies – such as intraocular methotrexate -- also is not known.

Surgery

There is generally no role for surgery in the primary treatment of visual loss after SO removal. However, surgery may be necessary to address other complications that may arise after SO removal, such as recurrent retinal detachment, the removal of SO droplets that are causing visual disturbances, epiretinal membrane peeling or other complications.

Prognosis

The prognosis for unexplained visual loss after SO removal is variable. Some patients may experience spontaneous improvement in visual acuity, while others may have persistent visual impairment. Factors that may influence the prognosis include the severity of initial visual loss, the presence of any underlying retinal or optic nerve damage, and the overall health of the patient. Studies have shown a correlation between the duration of silicone oil tamponade and the final visual acuity, with longer tamponade durations potentially leading to worse visual outcomes.