Asteroid Hyalosis

Asteroid hyalosis is a degenerative eye disease characterized by the appearance of asteroid bodies in the vitreous humor of the eye. Visual impairment due to asteroid hyalosis is usually minimal.

The disease is related to the following processes:  degenerative and has an incidence of about  9 / 100.000.

Presentation

AH is more commonly diagnosed in patients aged 60 years and older. Both men and women may be affected. Although most patients show unilateral AH, bilateral findings do not rule out this degenerative condition. Patients usually do not present with visual impairments and only in severe cases of AH visual acuity may slightly be affected [21].

Patients may report cognitive phenomena that correspond to the Pulfrich effect. Asteroid bodies may reflect light and may alter stimulation of retinal photoreceptors and signal transduction to the cortex in terms of time. Fractions of seconds are sufficient to create the impression that one eye is seeing an object shortly before or after the other one does.

Ophthalmoscopic examination reveals the presence of several- round to oval, opaque but highly refractile particles in the vitreous humor . The number of these so-called asteroid bodies augments over the course of the disease. Initially, asteroid bodies concentrate in the anterior portions of the vitreous humor. They are generally of white-yellowish or yellowish color. If eye movement provokes movement of the vitreous body, asteroid bodies seem to change their position. Because they are suspended in the vitreous humor rather than floating freely, they return to their initial position if the eye is moved accordingly.

While asteroid bodies may not interfere with the patient's vision, they often impede a thorough examination of the ocular fundus that may be required for other reasons. Fluorescein angiography may be helpful in such cases.

Asteroid bodies may alter readouts of autorefraction and A-scan ultrasonography and may also be noted in optical coherence tomography imaging.

Workup

AH is rarely associated with visual impairment but should be distinguished from several differential diagnoses, e.g. floaters, amyloidosis and synchysis scintillans. Floaters are of fibrillar or cellular nature. Amyloidosis is a rare condition characterized by the appearance of amyloid fibrils in the vitreous humor but also in other ocular structures and adnexa. Contrary to AH patients, individuals suffering from amyloidosis will show additional symptoms. As for synchysis scintillans, precipitates consist of cholesterol and are not attached to the vitreous stroma. They move much more freely than asteroid bodies in AH patients and sink to the bottom if eye movement is ceased [17] [22].

Ophthalmologists should also know that asteroid bodies may interfere with certain diagnostic and therapeutic measures that may be required for other reasons.

With regards to the interference with diagnostic and therapeutic measures, the presence of asteroid bodies should be taken into account when evaluating the results of autorefraction measurements, A-scan ultrasonography or optical coherence tomography images. Refraction, intraocular lens power, and axis length may not be measured correctly. Moreover, silicone lenses should not be implanted in eyes affected by AH because they might calcify. Another material needs to be chosen.

Due to the fact that AH has been associated with diabetes mellitus, hypertension, hypercholesterolemia and atherosclerosis, patients diagnosed with AH should be examined for these systemic conditions.

Treatment

AH does not usually require treatment, unless in the advanced state of the disease. The mineral deposits inside the vitreous humor most often do not impair vision but interfere with ophthalmologic examinations of the ocular fundus. With regards to this issue, alternative diagnostic measures should be considered to carry out the intended exam.

In rare cases, AH may decrease visual acuity. Such patients as may benefit from a vitrectomy [18]. This same procedure should also be undertaken if the above-mentioned alternative diagnostics do not suffice to depict the ocular fundus and a thorough examination is still necessary, e.g. in patients suffering from retinal tears or detachment or diabetic retinopathy. Of note, vitreous humor does not regenerate after vitrectomy. It will rather be replaced by an aqueous substance.

Prognosis

Prognosis of this condition is good. AH is generally not associated with visual impairment. If such is the case in severe AH, vitrectomy may serve as a remedy.

Etiology

The causes of AH are not yet understood. The disease may also be detected in other mammals, particularly in dogs. In this species, AH has been related to neoplasms of the ciliary body. This link could, however, not yet be confirmed in men.

While some scientists defend the hypothesis that pathologic systemic conditions may trigger AH, this theory is not uniformly accepted. In this context, the risk for AH may be increased in patients suffering from diabetes mellitus, hypertension, hypercholesterolemia or atherosclerosis.

An inverse relation to posterior vitreous detachment has been found in a large, retrospective study.

To a certain degree, old age seems to be another factor that predisposes for AH.

Epidemiology

AH is a rather common disease of the eye and prevalence has been estimated to range between 1 and 2% in Caucasians. It has been proposed that AH prevalence increases with age and indeed, the vast majority of AH patients are older than 60 years. Due to the fact that AH is a degenerative eye disease, this hypothesis is rather unsurprising. Researchers who examined nearly 5000 individuals in the United States reported a more than 10-fold increase in prevalence between patients who had an average age of 50 years and those who were 80 years old. Here, observed prevalence was 0.2% and 2.9%, respectively [4]. An Australian study reported an even lower prevalence in people aged 50 years [5]. These values could be confirmed in a third, retrospective study conducted in the United States. More than 10,000 autopsy reports were analyzed and an overall AH prevalence of 2% was determined [6]. Of note, this large sample was found to be representative of the population of the United States.

With regards to gender distribution, there does not seem to be any consensus. Different studies reported men to be affected more frequently than women or vice versa. The occurrence of the disease is mostly unilateral.

Sex distribution
Age distribution

Pathophysiology

The asteroid bodies consist of hydroxyapatite, a calcium phosphate mineral. Because little is known about the causes of hydroxyapatite precipitates in the vitreous humor, conclusive information regarding the pathogenesis of AH is not available.

There is a considerable number of studies associating AH with diabetes mellitus [7] [8] [9] [10] [11] [12] [13] [14] [15] [16], hypertension [14] [17] and hypercholesterolemia [7] [15] [16]. Also, increased serum calcium levels have been proposed as a possible trigger of AH [18] [19].

The main argument against systemic causes of AH is the fact that these should trigger bilateral AH, but approximately 90% of all patients present with unilateral AH. In order to explain this apparent contradiction, unilateral and bilateral percentages have been determined for the diabetic subpopulation of AH patients. However, only non-significant trends towards a higher share of bilateral cases could be detected [11]. Indeed, one of the above mentioned, large studies regarding AH found less than 3% of diabetic AH patients to present bilateral AH [4].

Nevertheless, diabetic retinopathy may serve as a possible explanation for an increased prevalence of AH among diabetics. AH may develop secondary to diabetic retinopathy [8] [10] [20].

Prevention

No preventive measures can be recommended. If theories regarding an association between systemic diseases and AH can be verified, prevention of such conditions may also help to prevent AH.

Summary

Asteroid hyalosis (AH) is a degenerative disease affecting the vitreous humor of the eye.

The vitreous body of the eye consists of the vitreous stroma, a delicate net of fibers that confers a certain stability to the vitreous body, and the vitreous humor, a physiologically transparent filling substance. The main function of the vitreous body is to maintain the form of the eye. The vitreous humor itself is composed of water and glycosaminoglycans like hyaluronic acid [1].

Degenerative alterations of the vitreous humor are partially triggered by reactive oxidative species and result in glycosaminoglycan breakdown and liquefaction of the vitreous body [2] [3]. It is not yet known if similar processes trigger the appearance of asteroid bodies in the vitreous humor, i.e. if they provoke AH.

AH does usually affect one eye, not both. In patients suffering from AH, small, light opacities can be observed in ophthalmologic examinations. Because they reflect the incoming light, they appear like bright stars in front of the dark ocular fundus, the "sky". This phenomenon accounts for the name of the disease. AH does not generally interfere with vision and thus, treatment is required only in severe cases. If necessary, a vitrectomy is the method of choice to remove asteroid bodies.

The etiology of AH is not completely understood. Evidence has been provided to support the hypothesis that diabetes mellitus, hypertension, hypercholesterolemia, and atherosclerosis predispose for this condition. However, not many studies could confirm these findings.

Patient Information

Asteroid hyalosis (AH) is a degenerative disease of the eye. Hallmark of this condition is multiple, small, round to oval bodies, which are called asteroid bodies, inside the vitreous humor. In order to understand the function of the latter, one has to know that the vitreous humor is the main component of the vitreous body. The vitreous body, in turn, occupies a very large part of the orbit and maintains the form of the eye. While cornea, iris, pupil and lens are located in front of the vitreous body, the retina is behind it. That means incoming light has to pass through the vitreous body and therefore through the vitreous humor to reach retinal photoreceptors. That's why the vitreous humor is transparent.

Somewhat surprisingly, though, AH is most certainly not associated with visual impairment. Only in rare, severe cases of AH may visual acuity be slightly reduced.

Causes

Even though AH is a very common condition, little is known about the causes of AH. The above-mentioned asteroid bodies consist of calcium phosphate minerals and it has been speculated that certain systemic diseases, e.g. diabetes mellitus, hypertension, hypercholesterolemia, and atherosclerosis predispose for AH. Diabetes mellitus, for instance, may evoke diabetic retinopathy and thereby trigger AH. However, such hypotheses have not yet been confirmed. The fact that AH frequently affects one eye only argues against a systemic cause.

Age seems to be an important factor in AH development. The majority of AH patients are aged 60 years and older.

Symptoms

Usually, asteroid bodies do not cause any symptoms.

Diagnosis

The image of the eye of an AH patient resembles a sky full of stars. The aforementioned asteroid bodies are of yellowish color and reflect the light shown into the eye during an ophthalmologic examination. Thus, light spots appear in front of the dark ocular fundus. This phenomenon gave the disease its name.

Because AH patients are unable to see the asteroid bodies in their own eyes and because they usually don't cause any visual problems, AH is frequently an incidental finding. Asteroid bodies may impede the ophthalmologist to evaluate the patient's retina and certain measurements may be altered by the presence of these bodies.

A thorough examination of the eye will allow for the ophthalmologist to distinguish AH from differential diagnoses such as floaters, amyloidosis and synchysis scintillans.

Of note, due to the possible relation between AH and diabetes mellitus, hypertension, hypercholesterolemia or atherosclerosis, clinical examinations should be carried out for theses causes too.

Treatment

Because AH does usually not cause any symptoms, no treatment is required. In those rare cases where AH does cause visual impairment, a surgical procedure called vitrectomy may be conducted. Here, the vitreous humor and its multiple calcium phosphate deposits will be removed. Although the vitreous humor itself does not regenerate, the interior of the eye will be filled up with a similar substance that doesn't interfere with vision.

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References

  1. Bishop PN. Structural macromolecules and supramolecular organisation of the vitreous gel. Prog Retin Eye Res. 2000; 19(3):323-344.
  2. Ueno N. Changes in vitreous structure caused by oxygen free radicals. Nippon Ganka Gakkai Zasshi. 1995; 99(12):1342-1360.
  3. Takahashi K, Arai K, Hayashi S, Tanaka Y. Degree of degraded proteoglycan in human vitreous and the influence of peroxidation. Nippon Ganka Gakkai Zasshi. 2006; 110(3):171-179.
  4. Moss SE, Klein R, Klein BE. Asteroid hyalosis in a population: the Beaver Dam eye study. Am J Ophthalmol. 2001; 132(1):70-75.
  5. Mitchell P, Wang MY, Wang JJ. Asteroid hyalosis in an older population: the Blue Mountains Eye Study. Ophthalmic Epidemiol. 2003; 10(5):331-335.
  6. Fawzi AA, Vo B, Kriwanek R, et al. Asteroid hyalosis in an autopsy population: The University of California at Los Angeles (UCLA) experience. Arch Ophthalmol. 2005; 123(4):486-490.
  7. Smith JL. Asteroid hyalitis: incidence of diabetes mellitus and hypercholesteremia. J Am Med Assoc. 1958; 168(7):891-893.
  8. Wasano T, Hirokawa H, Tagawa H, Trempe CL, Buzney SM. Asteroid hyalosis: posterior vitreous detachment and diabetic retinopathy. Ann Ophthalmol. 1987; 19(7):255-258.
  9. Luxenberg M, Sime D. Relationship of asteroid hyalosis to diabetes mellitus and plasma lipid levels. Am J Ophthalmol. 1969; 67(3):406-413.
  10. Jones WL, Twamley CR. Documented acquired asteroid hyalosis in a case of early diagnosed diabetes mellitus. Optometry. 2001; 72(5):315-321.
  11. Akram A, Niazi MK, Ishaq M, Azad N. Frequency of diabetics in asteroid hyalosis patients. J Ayub Med Coll Abbottabad. 2003; 15(3):10-11.
  12. Topilow HW, Kenyon KR, Takahashi M, Freeman HM, Tolentino FI, Hanninen LA. Asteroid hyalosis. Biomicroscopy, ultrastructure, and composition. Arch Ophthalmol. 1982; 100(6):964-968.
  13. Stanley JA, Martin DG. Asteroid hyalosis and the blood glucose. N C Med J. 1970; 31(5):183-185.
  14. Bergren RL, Brown GC, Duker JS. Prevalence and association of asteroid hyalosis with systemic diseases. Am J Ophthalmol. 1991; 111(3):289-293.
  15. Bard LA. Asteroid Hyalitis: Relationship to Diabetes and Hypercholesterolemia. Am J Ophthalmol. 1964; 58:239-242.
  16. Hatfield RE, Gastineau CF, Rucker CW. Asteroid bodies in the vitreous: relationship to diabetes and hypercholesterolemia. Proc Staff Meet Mayo Clin. 1962; 37:513-514.
  17. Yazar Z, Hanioglu S, Karakoc G, Gursel E. Asteroid hyalosis. Eur J Ophthalmol. 2001; 11(1):57-61.
  18. Jervey ED, Anderson WB, Jr. Asteroid Hyalitis: a Study of Serum Calcium Levels in Affected Patients. South Med J. 1965; 58:191-194.
  19. Lamba PA, Shukla KN. Vascular factors in asteroid hyalopathy. Clinical and biochemical observations. Can J Ophthalmol. 1971; 6(1):46-51.
  20. Dogru M, Inoue M, Nakamura M, Yamamoto M. Modifying factors related to asymmetric diabetic retinopathy. Eye (Lond). 1998; 12 ( Pt 6):929-933.
  21. Feist RM, Morris RE, Witherspoon CD, Blair NP, Ticho BH, White MF. Vitrectomy in asteroid hyalosis. Retina. 1990; 10(3):173-177.
  22. Renaldo DP. Pars plana vitrectomy for asteroid hyalosis. Retina. 1981; 1(3):252-254.

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