Sickle cell and the eye: a Nigerian priority

Nigeria has more people living with sickle cell disease than any other country. Its eye complications are well characterised, they are potentially blinding, and — as with so much in this field — they are silent while they are still easy to treat.

What happens in the retina

Sickled red cells obstruct small vessels. In the retina this occurs first in the far periphery, where the vessels are finest and the blood flow slowest. Areas of retina lose their blood supply.

Deprived tissue then does what deprived retinal tissue does elsewhere: it signals for new vessels to grow. The new vessels are abnormal, fragile, and grow forward into the vitreous gel. They bleed, and the fibrous tissue accompanying them contracts and pulls on the retina.

The sequence — peripheral closure, then proliferation, then haemorrhage, then traction and detachment — defines proliferative sickle retinopathy. Its stages are well described, which is what makes screening effective: the early stages are visible on examination and invisible to the patient.

Which genotype

Counterintuitively, proliferative retinopathy is more common in HbSC disease than in HbSS, even though HbSS is generally the more severe systemic illness. People with HbSC are sometimes told their condition is mild and are not screened. From the eye's point of view that is the wrong conclusion.

HbSS more often produces non-proliferative changes, and both genotypes require screening.

Why it is silent

All of this happens in the peripheral retina, which contributes nothing to the sharp central vision used for reading. A person can have extensive peripheral change with perfect acuity and no symptoms whatsoever.

The first thing they notice is usually a sudden shower of floaters or a dark cloud across the vision — a vitreous haemorrhage from one of the fragile new vessels — or a curtain, which is a detachment. Both are late presentations.

The other eye complications

Hyphaema after trauma is particularly dangerous in sickle cell disease: sickled cells block the eye's drainage more readily, pressure rises sharply, and the optic nerve can be damaged quickly. Any eye injury in someone with sickle cell should be assessed urgently, and the treating clinician must know the diagnosis.

Conjunctival vessel changes, visible as comma-shaped segments on the white of the eye, are a recognised sign.

Central retinal artery occlusion and other vascular events occur, though less commonly.

Screening

Dilated retinal examination, with particular attention to the far periphery, starting in childhood — commonly from around ten years of age — and repeated at intervals determined by what is found. Imaging that captures the peripheral retina is valuable where available.

Treatment of proliferative disease is usually laser to the ischaemic periphery, which removes the stimulus for new vessel growth. Surgery is available for haemorrhage that does not clear and for traction detachment. As everywhere in this field, earlier is better and less.

What to take away

If you or your child has sickle cell disease of any genotype, arrange a dilated eye examination and keep to the review interval you are given, whether or not vision seems fine. Normal vision is the expected finding in the stage that matters.

Seek care the same day for a sudden increase in floaters, a shadow or curtain across the vision, sudden loss of vision, or any eye injury.

Optometrists in the chapter's register can perform this screening and will refer for laser or surgical treatment where it is needed.