Asteroid Hyalosis

A degenerative vitreous condition in which small spherical opacities composed of calcium soaps (calcium-phosphate complexes bound to lipid) are suspended within the otherwise normal vitreous gel. They are attached to the collagen framework and move with eye movements but return to their original position.

• Prevalence about 1 percent of people over 50 years (0.5 to 2 percent), rising with age; unilateral in about 75 percent; males are slightly more affected.
• Associations: age, diabetes and hyperlipidaemia (weak and inconsistent), hypertension, hypercalcaemia, and ocular conditions such as retinal vein occlusion; it is generally idiopathic.
• It differs from synchysis scintillans, a condition of cholesterol crystals in liquefied vitreous of previously damaged eyes (trauma, haemorrhage, inflammation, ageing), where golden crystals settle inferiorly when the eye is still and rise when the eye moves.
• The condition is benign and has no inflammation, and does not cause retinal detachment on its own.

• Usually asymptomatic and found incidentally at examination; mild floaters in a minority.
• Slit lamp: numerous small (0.01 to 0.1 mm) yellow-white round refractile bodies scattered throughout a formed vitreous, like stars in a night sky ("stars in the night"), which move with the eye and return to position when the eye stops; often more obvious on dilated examination.
• Visual acuity is normal or minimally reduced; rarely symptoms of glare or reduced contrast.
• The fundus view with indirect ophthalmoscopy may be poor because of light scatter, despite good vision, and the fovea may appear obscured.
• Posterior vitreous detachment is frequent; severe asteroid hyalosis can degrade imaging of the retina.

• Diagnosis is clinical, by slit lamp biomicroscopy with a fundus lens in dilated eyes.
• B-scan ultrasound: multiple high-reflective dots in the vitreous with a clear space between the opacities and the retina; the echoes disappear when the gain is lowered, whereas vitreous haemorrhage and tumour echoes persist.
• Optical coherence tomography is hindered; use enhanced depth imaging and widefield imaging if needed; fluorescein angiography is often obscured.
• Examine the retina carefully for diabetic changes, retinal vein occlusion, retinal tears, and tumours that may be hidden by the opacities, using scleral depression, widefield photography, and ultrasound where required.
• Systemic review: glucose, lipids, blood pressure, calcium if clinically indicated.

• No treatment is required for most patients; reassure that the condition is benign, does not affect long-term vision, and has no association with serious eye disease in most cases.
• Monitor routinely; because retinal examination is harder, screen for diabetic retinopathy and retinal vein occlusion with widefield imaging, ultrasound or enhanced-depth optical coherence tomography as needed, and examine the periphery at intervals (every 1 to 2 years) with scleral depression.
• Floaters causing significant visual disability (rare) can be treated by pars plana vitrectomy after careful counselling about risks (cataract, retinal tear and detachment, endophthalmitis, haemorrhage); neodymium:YAG vitreolysis has limited and variable benefit for large solitary opacities.
• Surgical precautions: asteroid hyalosis can impair visibility during laser photocoagulation (use higher power, indirect laser, or endolaser after vitrectomy) and cataract or retinal surgery (the opacities can cloud intraoperative view and may be removed with vitrectomy); complete posterior vitreous removal and meticulous peripheral examination reduce the risk of missed breaks.
• Advise patients to report flashes, a shower of floaters, or a curtain-like field loss, because posterior vitreous detachment is common in asteroid hyalosis.
• Prognosis is excellent, with vision usually preserved throughout life.