Sickle cell disease:
- Normal HbA = 2 alpha-globin + 2 beta-globin + central haem molecule.
- Point mutation at the 6th position of chromosome 11 –> replacement of glutamic acid by a valine in beta-globin of Hb –> HbS.
- Autosomal recessive.
- Both genes are sickle cell variant = SS disease.
- When one gene has HbC variant = SC disease (less severe form).
- When one gene is normal –> no disease = SC trait (carrier).
- Associated with beta-thalassemia gene.
- Afro-American / Hispanic – 0.15% sickle cell disease overall.
- Black Americans – 8% SC trait.
- Orbital – orbital bone infarction ; orbital haematoma (need Abx + steroid Rx or orbital decompression) ; lacrimal gland swelling.
- Anterior segment – Paton’s conjunctival sign (corkscrew saccular dilation of conjunctival vessels) ; radial iris neovascularisation (–> NVG) ; hyphaema (EMERGENCY – risk CRAO even with mild IOP rise – need AC washout or paracentesis)
- Retinal changes
- Non-proliferative sickle retinopathy:
- 1) Salmon-patch haemorrhages (result of sudden giving way of occluded vessel)
- 2) Black sunburst (localised choroidal ischaemic damage of RPE –> localised CNVM or subretinal tracking of retinal haemorrhage)
- 3) Peripheral retinal whitening with strong vitreoretinal adhesion – like white without pressure (common).
- 4) Macular iscahmeia – enlarged FAZ.
- 5) Rarely – macular hole, ERM, foveoschisis, CNVM
- Proliferative sickle retinopathy:
- Staging by Goldberg (1971):
- Stage I – peripheral vascular occlusion with silver wiring of arterioles at temporal retina.
- Stage II – AV anastomosis – non-leaking
- Stage III – sea fan neovascularisation (commonly superotemporal)
- Stage IV – Vitreous haemorrhage
- Stage V – Tractional retinal detachment
- Commonly SC disease patient & HbS-beta thalassaemia.
Investigations: Ultrawide field angiography ; OCT macula
- Non-proliferative cases: observe 3-6 months.
- Proliferative cases: observe (1/3 regress with autoinfarction)
- Proliferative cases with bilateral disease, rapid Stage III onwards progression: targeted laser treatment of ischaemic areas.
- Vitreous haemorrhage without RD: Observe.
- Vitreous haemorrhage with RD: PPV + endolaser +/- preop anti-VEGF.
- Scleral buckle – use with caution due to risk of anterior segment ischaemia.
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