Visual loss after silicone oil removal

We read with interest the paper by Cazabon et al¹ on the important emerging problem of sudden visual loss after removal of silicone oil. We have seen a similar pattern of visual loss in our own patients, typically in the macula on detachments associated with giant retinal tears. We have identified 12 cases in two units (St Thomas’s, London, and Sunderland Eye Infirmary), but five of these clearly had onset of visual loss before oil removal (onset between 1 month and 5 months after oil insertion).² Results of investigations were very similar to those reported by Cazabon et al. In four of five pattern ERG was suggestive of macular dysfunction. The timing of onset of visual loss obviously alters the potential aetiology, which as stated is unknown.

In their paper, information on acuity for cases 2 and 3, between 1 week after oil insertion and oil removal is not provided. Did these cases have visual loss preceding oil removal? Developing cataract can obviously hinder interpretation of acuity measurements. In our cases the symptoms described did not fit with cataract (scotoma, red desaturation) and persisted if any cataract was removed.

We have seen a further case since this report, a 46 year old woman with a giant retinal tear and macula-on retinal detachment affecting the right eye. Acuity reduced during the period of tamponade from 6/6 at 2 weeks after oil insertion to 6/36+1, which did not recover after oil removal. She reported a central negative scotoma. Electrophysiology suggested macular dysfunction.

We have speculated that phototoxicity may have a role, as oil transmits light more in the blue spectrum than aqueous.³ The fat soluble macular pigments, lutein and zeaxanthin, are thought to protect the macula from photo-oxidative damage. Silicone oil has previously been reported to dissolve fat soluble elements from the retina.⁴

We measured the macular pigment optical density (MPOD) in this case using a modified confocal scanning laser ophthalmoscope and two wavelength autofluorescence technique 3 weeks after oil removal. The results showed a substantially reduced MPOD in the eye that had silicone oil compared to the fellow eye. Although the peak MPOD, at the foveal centre of both eyes was similar (0.47 right versus 0.52 left), the MPOD at ½ degree, 1 degree, and 2 degrees eccentricity from the foveal centre was markedly lower in the eye that had silicone oil (0.12, 0.06, 0.02 respectively versus 0.40, 0.22, 0.07).

Although MPOD varies greatly between individuals, there is usually high interocular symmetry in normal eyes.⁵ Further work is required to determine whether or not this relates to the visual loss and whether therapeutic supplementation may reduce the risk of visual loss.