A 45-year-old Caucasian male presented with sudden painless loss of vision in his left eye 2 years after undergoing uneventful cataract surgery. Original refraction was −6.50 D in both eyes. On examination, visual acuity was 0.8 RE and HM LE. There was a dense vitreous haemorrhage. A pars plana vitrectomy was performed and revealed superonasal and inferotemporal rhegmatogenous retinal detachments (RRD). A break was identified in the superior but not in the inferior detachment. The retina flattened under perfluorooctane (PFO). Tamponnade was achieved with 20% SF6 after PFO-air exchange. Postoperative acuity LE was 0.8 at 1 month and the retina remained attached. A large postoral inferotemporal retinal cyst was noted. The wall was uncorrugated and vascularized (Figure 1). A small subretinal PFO residue was noted posterior to the cyst. B-scan ultrasonography confirmed the hypoechogeneity of the lesion (Figure 2). No prophylactic retinopexy was applied and the lesion remained stable over 24 months.

Figure 1
figure 1

Large postoral cyst in the inferotemporal retina. Note smooth vascularized surface. Small subretinal perfluorooctane cyst posterior to the large lesion.

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Figure 2
figure 2

Standard B-scan echography showing the inferior macrocyst as an elevated, hypoechogenic lesion. Note long orbital shadow.

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The differential diagnosis of a large postoral cyst includes pars plana cysts (PPCs) and retinal cysts. PPCs are physiological and can become quite large.1 Less common causes include haemorrhagic retinal macrocysts,2 cysts of chronic RRD,3 subretinal hydatid cysts,4 and retained subretinal perfluorocarbon.5 Known risk factors for perfluorocarbon retention include peroperative retinotomy or retinectomy. In this case no break was identified in the inferotemporal detachment, but PFO could have entered the subretinal space through the superior horsehoe tear and tracked inferiorly postorally.

The postoral cyst did not change in size, shape or pigmentation over 24-month follow-up. As it was not seen peroperatively, it is likely to represent a PFO retention cyst. The echographic characteristics of retained PFO have been described by Hasenfratz et al.5 Delayed display of the echo signal results in a hypoechogenic image due to slower sound conduction in PFO. The lesion presented here is unusually large. On the basis of clinical history and echographic findings, we believe this cyst is likely to contain PFO. It has had no functional effect on vision and no attempt should be made to remove it.