In our population-based study on adult Chinese in Beijing, the prevalence of AH was 0.9% per eye or 1.5% per subject. AH was associated with elder age (P=0.014, OR 1.057), thicker lens (P=0.032, OR 3.887), higher refractive error (P=0.017, OR 1.396). AH was not associated with the systemic parameters of blood pressure, glucose, diabetes, cholesterol, triglycerides.
Previous studies of the prevalence of AH were in autopsy series and clinical populations.8 However, the best source for prevalence estimates in a general population is population-based studies. To our knowledge, this is the first large population-based study reporting on the prevalence of AH in Asian populations. Our prevalence (1.5%, 95% CI: 1.1 to 1.9%) results are consistent with previous studies of AH.9 In the Beaver Dam Eye Study10 of 4,952 patients, AH was present in 1.2% (95% CI: 0.9 to 1.5%) of the total population. The Australian Blue Mountains Eye Study11 of 3,654 patients confirmed a similar 1.0% (95% CI:0.7 to 1.3%) prevalence of AH. In the autopsy series of 10,801 eyes studied at UCLA12, AH had a prevalence of 1.96%.
Our data show that AH was associated with elder age (P=0.014). Prevalence increased significantly with age from 0.7% in the 50-59 year age group to 2.7% in the 80-93 year age group. Several clinical-based studies10,12,13 concluded that the occurrence of AH was significantly associated with elder age. In the Beaver Dam Eye Study10, the prevalence of AH increasing from 0% of persons aged less than 55 years to 2.1% of persons aged 75 years or older. In the Australian Blue Mountains Eye Study11, the prevalence of AH also increased with age from 0.2% in subjects 43-54 years, to 2.9% in subjects 75-86 years. These findings confirm our results. Komatsu and coworkers14 used samples of AH obtained in vitreous surgery and observed with light and electron microscopes and processed by the focused ion-beam method. They thus concluded that AH was produced not only by changing of ionic tension in the vitreous fluid but also by changes of vitreous matrix in the aging process and diseases.
Our data also show that AH was associated with higher refractive error (P=0.017). Bergren3 and coworkers performed a cross-sectional study of 12,205 patients and reported patients with AH were more hyperopic than control subjects. One explanation is that the complete posterior vitreoretinal interface may be important for the formation of asteroid zona pellucida15. Therefore, the older the age, the more likely the individuals who maintain posterior vitreous attachment are to develop AH. This may explain why AH is associated with higher refractive error, because PVD is more common in myopia and occurs at an earlier age16. However, we did not find the association between AH and PVD(P=0.417) in our study, which may due to the lack of statistics on complete or partial PVD. Another possibility is that, the presence of AH may arrest the process of vitreous collapse or contraction and has a protective effect on vitreous liquefaction17, which prevents PVD.
In our population-based study, AH also correlated to the thicker lens (P=0.032). As there is no relevant report so far, the associations between AH and lens thickness have remained unclear. One of the reasons may be that the lens thickness was associated with higher age and hyperopic refractive error18. Previous studies19 have proved that the age-related increase in lens thickness was due to the continuous production of new lens fibers in the equatorial region of the lens. Besides, the higher refractive power necessary in hyperopic eyes lead to greater lens thickness 19. From a geometric point of view, the thicker lens partially protrudes forward into the anterior chamber and partially bulged backward into the vitreous cavity, which may affect the dynamics of aqueous humor circulation20 and thus cause changes in the composition of vitreous extracellular matrix.
In our study, AH was not associated with systemic parameters of body height (P=0.566), weight (P=0.380), diastolic blood pressure (P=0.342), systolic blood pressure (P=0.780), serum concentrations of low-density lipoproteins(P=0.832), high-density lipoproteins (P=0.407), cholesterol (P=0.567), creatine(P=0.576),triglycerides (P=0.899), glucose (P=0.129), hypertension (P=0.366), hyperlipidemia (P=0.174), diabetes mellitus (P=0.780), self-reported diagnosis of cerebral infarction or haemorrhage (P=1.000), and of coronary heart disease (P=0.264), frequency of reported snoring (P=0.939), smoking (P=0.298), drinking(P=0.647). AH has purportedly been associated with several systemic diseases, including diabetes5, hypercholesterolemia5, hypertension3, hypercalcemia21 and gout13. Many of these studies have been case series, case-control studies, or performed in clinic populations and may reveal a selection bias for diseases that are more prevalent in patients presenting for ophthalmic and vitreoretinal evaluations. Thus, these findings cannot readily be extrapolated to the general population. Besides, the prevalence of bilateral AH was 18.9% in our study. The fact that AH mainly occurs unilaterally3,10−12 does not support an association with systemic parameters.
The findings in our study may have clinical importance, since AH may prevent PVD and have a protective effect17 on vitreomacular traction. Besides, AH generally only has a minor impact on vision and thus may be a useful model for better understanding the interaction between incident light and intravitreal structures. Further studies may assess whether the results of our study help in understanding the pathogenesis of these disorders by showing the correlations of AH and other ocular and general parameters.
This is the first population-based investigation searching for the prevalence and associations between ocular and systemic parameters and AH in the Asian population. Despite the advantages of this population-based study, potential limitations of our study should be mentioned. First, a major concern regarding any prevalence study is non-participation. The Beijing Eye Study 2011 had a reasonable response rate of 78.8%, although differences between participants and non-participants can lead to a selection bias. Second, the presence of AH was determined either from the presence of typical ABs seen at the slit-lamp or on retinal examination or from the stereo fundus images of a limited number of fields. ABs may present only in peripheral areas and not be detected. Thus, we are probably underestimating the prevalence of AH. Another limitation is the cross-sectional design of the study. This prevents us from knowing the antecedent-consequent relationship between the risk factors and the endpoint.
In conclusion, in adult Chinese in Beijing, the prevalence of AH was 0.9% for eyes or 1.5% for subjects. While it was associated with elder age, thicker lens and higher refractive error.