Idiopathic epiretinal macular membrane is a common vitreo-retinal interface disease, which occurs frequently in old women. In China, series studies have reported that subjects with ERMs were older adults, where female was dominant [1, 6, 7]. Risk factors of ERMs have been investigated in many clinical studies. However, the results were not consistent. In the Hisayama study, Miho et al. found that hypercholesterolemia was significantly associated with ERMs . The Funagata study has shown that HDL cholesterol and fasting plasma glucose were associated with an increased ERM prevalence; however, after adjusting for age and gender, older age and diabetes were the only two risk factors associated with ERM . In another series, Wang and associates found that cardiovascular disease was not associated with ERMs, meanwhile, the prevalence of severe ERMs (preretinal macular fibrosis) was higher in a high cardiovascular risk group than a population-based group. However, the authors did not further analyze the causes of high prevalence of severe ERM in the cardiovascular risk cohort . In the Handan study, the results showed that myopia was associated positively with primary ERM and smoking was an inverse associated factor . In contrast, Ye and colleagues found that besides older age, female and myopia, hyperlipimida were also the risk factors of idiopathic ERM in Jiangning study. However, the authors did not distinguish which compounds were elevated in hyperlipimida . As mentioned above, in our study, hyperlipidemia was significant in the ERMs group. Furthermore, serum triglycerides were higher in ERM group than the control group, which was different from previous reports. Although serum total cholesterol was not statistically different between two groups, it was higher in ERMs group (P = 0.06). In addition, interestingly, we found that BMI was statistically different between two groups, which was different from previous studies [5, 6]. In our study, the subjects were those who needed to be vitrectomied for peeling the ERMs. According to previous definition, the ERMs in this study were categorized as preretinal membrane fibrosis (PMF) and not cellophane macular reflex (CMR). The severity of iERMs might be the reason for the different results in this study compared to previous studies.
Given that patients with hypertension might have hyperlipidemia, subjects were further grouped according to whether with hypertension or not. The results showed that Serum TG was significantly different between two groups with hypertension, although the average age of the control group was older than iERMs group. Certainly, in the two groups without hypertension, Serum TG was still statistically different. Our results have suggested that serum TG might play a role in the mechanism of ERMs. Interestingly, in two groups without hypertension, the serum urea was statistically different. However, we had no adequate explanation for the difference.
Our results suggested that serum TG might be a role for the formation of iERMs. The mechanism is still not well known. The presence of remnants of the cortical vitreous following posterior vitreous separation may determine the clinicopathological feature of this entity . As well we known, hyalocytes are mainly distributed close to the retina in the posterior hyaloid and at the vitreous base , which has characteristics of tissue macrophages . Using immunocytochemistry and transmission electron microscopy, hyalocytes and vitreous collagen have been observed in the cellular complex of premacular membrane. It is suggested that hyalocytes play a key role for the formation of premacular membrane [12, 13]. The correlation between hyalocytes and serum lipids remains incompletely understood. However, in non-alcoholic fatty liver disease, a fibrous liver disease, the accumulation of lipids in hepatic cells is considered a key event in the development of this disease. Hepatic macropahges and Kupffer cells are thought to play a key role in the progression . As macrophages of posterior hyaloid, it is possible that hyalocytes in the condition of high serum lipids should play a role in the development of iERMs.
There are several limitations in this study, and potential bias should be noted. First, Subjects in this study were retrospectively collected from hospitalization, whose eyes needed to be vitrectomized to peel the epiretinal macular membranes. As mentioned above, epiretinal membranes were categorized as PMF. Subjects with CMF were not included, which might result in selection bias. Second, unlike previous epidemiologic studies which included subjects with ERMs in all ages, the age of populations in this study was older, and we did not stratified for age. Third, we did not investigate the association between OCT characteristics and serum lipids.
In conclusion, we describe the elevation of serum lipid in patients with iERMs. Serum TG and BMI are elevated in the iERMs group. It suggests that obese people seem to be prone to iERMs. Hyperlipemia seems to play a role in the formation of iERMs. Further investigations should be to clarify the etiological relationship between serum lipids and iERMs.