Asteroid hyalosis: Description, Causes and Risk Factors
Numerous small spherical bodies (“snowball” opacities) in the corpus vitreum, visible ophthalmoscopically; an age change, usually unilateral, and not affecting vision.
Asteroid hyalosis is a degenerative condition of the eye involving small white opacities in the vitreous humor. It is known to occur in humans, dogs, and chinchillas. Clinically, these opacities are quite refractile, giving the appearance of stars (or asteroids) shining in the night sky — except that ocular asteroids are often quite mobile. Ocular asteroids must be distinguished from the more common typical vitreous floaters, which are usually fibrillar or cellular condensates.
The cause of this disease is unknown, but it has been associated with diabetes mellitus, hypertension, hypercholesterolemia, and in certain animals, tumors of the ciliary body. In dogs, asteroid hyalosis is considered to be an age related change. The asteroid bodies are made up of hydroxylapatite, which in turn consists of calcium and phosphates or phospholipids. While asteroid hyalosis does not usually severely affect vision, the floating opacities can be quite annoying, and may interfere significantly with visualization and testing of the retina.
Asteroidhyalosis has been reported to have astrong positive association in patients with diabetes mellitus.Additionally,systemic arterial hypertension and atherosclerotic vascular disease have beenassociated with asteroid hyalosis.However,a number of reports refute theassociations between asteroid hyalosisand systemic diseases.
In whites the prevalence of asteroid hyalosis is 1-2%, and it is bilateral in about 10% of cases.This prevalence seems to increase with age.
Overall, 547 cases of asteroid hyalosis were reported in 11 case series and population-based reports in the literature as well as 1 series of asteroid hyalosis in enucleated eyes. One study was population based; all other reports originated from eye clinic populations, which may reflect selection bias for diseases that are more prevalent among outpatients in an eye clinic, and cannot be extrapolated to the general population. Statistical methods and patient and control selection criteria used in these studies were difficult to assess and highly variable. Healthy, age-matched controls were used in 1 study, whereas age-matched controls from the same clinic population were used in other studies. Several works did not attempt to compare patients with asteroid hyalosis with controls. Because of small sample sizes, only univariate statistical analyses were used in the case-control studies. Only 1 report collected a large enough sample size to use multivariate statistical analysis. However, that report surveyed a population from Beaver Dam, Wis, that was predominantly restricted to a white northern European background. In addition, asteroid hyalosis was diagnosed retrospectively by inspection of fundus photographs. The photographs were not interpretable in 3.6% of patients, most of whom were older (mean age, 71 years) and more likely to have a history of diabetes mellitus and cardiovascular disease. The authors indicated that asteroid hyalosis was likely to be underestimated because photographs did not include the periphery and the camera focused on the posterior retina rather than on the vitreous.
Asteroid hyalosis Symptoms:
Asteroid hyalosis is a primarily unilateral disorder that typically occurs in patients over 60 and in men twice as often as women. Usually asymptomatic, in severe cases asteroid hyalosis can mildly affect visually acuity. Complaints of floaters are a rarity.Ophthalmoscopically, asteroid hyalosis appears as multiple, discrete, refractile yellow or yellow-white particles suspended in the vitreous. In early stages, there are fewer bodies and they accumulate in the inferior vitreous. Advanced cases can be so dense as to impair your view of the posterior fundus.
Differential diagnosis includes amyloidosis and cholesterolosis bulbi.
Diagnosing asteroid hyalosis is more problematic to the examiner. Asteroid hyalosis changes the optical quality of the vitreous and can cause an incorrect reading from automated technologies such as autorefraction and A-scan ultrasonography. Thus, in addition to compromising ability to visualize fundus details, the presence of asteroid bodies can lead to erroneous axial length measurements, refractions,and intraocular lens power calculations. Also inconsideration of intraocular lens implantation, it has been documented that silicone lenses can calcify when implanted in eyes with asteroid hyalosis, making silicone an unacceptable material choice forthese subjects.
Fortunately,there are options for fundus examinations in cases in which dense asteroid hyalosis obscures ophthalmoscopic views. Fluorescein angiography optically “removes” the asteroid bodies from the vitreous, allowing detailed angiographic evaluation. Additionally, optical coherence tomography (OCT) allows for anatomic visualization and detection of maculopathies, in spiteof dense asteroid hyalosis.
Asteroid hyalosis is a benign condition in itself. Although it progresses, it never leads to severe vision loss, and the mild symptoms occur rarely. The vast majority of cases merely require documentation. More often than not, this disorder poses a greater challenge to the examining physician because it can obscure details of the underlying retina. Consider treatment only in patients who are also being managed for retinal disease (proliferative diabetic retinopathy, retinal tear or detachment). Vitrectomy is typically indicated in these instances.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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