Describe posterior vitreous detachment, vitreous haemorrhage and vitreous opacities.

Posterior Vitreous Detachment

• Mechanism — syneresis (liquefaction) creates fluid-filled lacunae, and synchysis aggregates the collagen. Fluid passes through a dehiscence in the posterior hyaloid into the retrohyaloid space and strips the hyaloid forward
• It occurs earlier in myopia (by a decade or more), after cataract surgery, after trauma, after inflammation and in diabetes

Vitreous Haemorrhage and Opacities

• Vitreous haemorrhage presents with sudden painless loss of vision or with floaters and a red haze; the red reflex is diminished or absent, and the fundus view is obscured
• Causes — proliferative diabetic retinopathy, which is the commonest overall; retinal tear or detachment, which is the one that must not be missed; posterior vitreous detachment with an avulsed vessel; retinal vein occlusion; trauma; EALES disease in a young Indian male; neovascular AMD; sickle cell retinopathy; and TERSON syndrome — vitreous haemorrhage accompanying subarachnoid haemorrhage or raised intracranial pressure
• B-scan ultrasound IS mandatory where the fundus cannot be seen, to exclude a retinal detachment, a tear or a mass; and it is repeated at intervals while the haemorrhage persists
• Management — observation with head elevation, which allows the blood to settle inferiorly and clear the visual axis; avoidance of antiplatelet and anticoagulant drugs where clinically permissible; and treatment of the cause once the view allows. vitrectomy for non-clearing haemorrhage (after 2 to 3 months, or sooner in diabetes, in an only eye, or where a detachment is suspected), and immediately where there is a detachment
• Asteroid hyalosis — small refractile calcium soap particles suspended in an otherwise normal gel, giving a striking "stars in the sky" appearance. It is unilateral in 75%, associated with diabetes and age, moves with eye movement and returns to position when the eye stops, and characteristically causes almost NO visual symptoms despite looking dramatic — though it may obscure the examiner’s view of the retina
• Synchysis scintillans (cholesterolosis bulbi) — cholesterol crystals, flat and golden, in an eye with a previous haemorrhage or long-standing damage. It is bilateral more often, occurs in a liquefied vitreous, and settles inferiorly when the eye is still — which is the key distinction from asteroid hyalosis