1. Asteroid Hyalosis
Asteroid hyalosis (Benson’s Disease) is an acquired degeneration of the vitreous gel, characterized by the development of small aggregates of calcium salts. The vitreous deposits occur for an unknown reason, and oddly are unilateral in a majority of cases. There is no predilection for gender or ethnicity. Although some reports have associated the condition with diabetes mellitus and elevated blood lipid levels, others have not. Asteroid hyalosis is uncommon (approximately 1/1,000) although more common in late middle age.
Symptoms And Signs
Patients with asteroid hyalosis often report floaters, although the condition is rarely of visual consequence. Asteroid bodies are small yellow/white deposits floating in the vitreous, associated with vitreous fibrils and showing movement with eye movements. There may be a few or they may be exceedingly numerous, obscuring the ophthalmoscopic evaluation of the fundus.
No treatment is necessary for asteroid hyalosis. Patients should be reassured and regularly assessed as per normal management practise.
2. Vitreous Cyst
Intraocular cysts can occur in the anterior chamber, the retrolental space and the vitreous cavity. Some believe a vitreous cyst represents a congenital choristoma whereas others have suggested the cyst could result from the displacement of pars plana pigmented ciliary epithelium following blunt trauma. It is most often unilateral, there are no systemic associations and the condition is rare.
Symptoms and Signs
A vitreous cyst rarely causes vision difficulties, although if the cyst encroaches on the visual axis, the patient may complain of an annoying floater.
Typically, a pigmented cystic mass is seen floating in the vitreous. The cyst may glisten in the beam of the ophthalmoscope and cast a shadow on the fundus. They can vary in size from a fraction of a millimetre to a little over a centimetre. An acute observer may detect an area of depressed sensitivity on visual field testing. B-scan ultrasound should confirm the cystic nature of the lesion.
If the cyst causes unremitting vision problems, it can be aspirated via a pars plana approach or disrupted with argon laser photocystotomy. The latter technique may be simpler, safer and non-invasive. The cyst is unlikely to reform and any residual debris should rapidly settle.
3. Other Vitreous Opacities
(a) Vitreous floaters associated with vitreous liquefaction (synchysis senilis) and shrinkage (vitreous syneresis). See Posterior vitreous detachment.
(b) Blood. See Vitreous hemorrhage.
(c) Synchisis Scintillans (Cholesterolosis bulbi) is a rare entity where cholesterol crystals have been liberated into the vitreous. The crystals are shiny golden brown and freely mobile i.e. not attached to the vitreous fibrils and tend to sink when the eye is stationary. Synchisis Scintillans may occur subsequent to severe ocular disease such as chronic vitreous hemorrhage, long standing retinal detachment, uveitis or trauma.
(d) Tobacco dust (Shaffer’s sign) refers to pigment cells in the anterior vitreous. See Retinal Detachment.
(e) Amyloidosis: A rare systemic condition in which there is abnormal protein deposition in tissues. Ocular involvement may be widespread; the retinal blood vessels may be affected, with breakthrough of fibril deposits into the vitreous.
(f) Neoplasia: See Retinoblastoma, Melanoma – malignant and Lymphoma – primary intraocular.
Asteroid hyalosis showing vitreous refractile bodies of mild (left image) and moderate density (right image).
Slitlamp image of mild asteroid hyalosis (left image) and a vitreous cyst floating in the centre of the pupil (right image).