MGD is a common disease in ophthalmology, which is closely associated with evaporative dry eye.8 A systematic review and meta-analysis showed that the Global prevalence of MGD was 35.9%.22 According to several population-based cross-sectional studies, the prevalence of MGD and DED in Japan was 32.9% and 33.4%, respectively, with a coexistence rate of 12.9%.23 The prevalence of MGD and DED in the United States were 21.2% and 8.1%, respectively.24 The prevalence of MGD and DED among people over 40 years of age in Russia were 52.6% and 35.3%, respectively.25 In addition, with the widespread use of video display terminals in daily work and life, the prevalence of MGD in video display terminals workers is high (74.3%),26 and it plays an important role in the severity of DED.27
Obstructive MGD is characterized by the abnormal gland structure and changes in lipids of meibum.1 Clinically, warm compresses is a routine recommended treatment for MGD.10–12 But so far, the temperature and time required to melt the secretions in the meibomian gland ducts have not been clear.11 Several studies had shown that the melting point of meibomian gland lipids ranged from 30℃ to 45℃,28–31 which partly reflected that the lipids are a highly complex mixture.32 McCulley et al.33 suggested that the lipids with different compositions had different melting points, and MGD could make lipids shift to higher melting points, resulting in stagnant and poor dynamic tear films. In addition, Murakami et al.13 believed that heating a single meibomian gland to a temperature of 40℃ might be the best treatment. It should be pointed out here that 40℃ referred to the temperature of the conjunctiva and meibomian glands, not the temperature on the contact surface of the device or eyelid skin.
The application of warm compresses with or without moisture, has been extensively studied in the treatment of MGD.13–15,34−40 Murakami et al.13 tested 8 forms of contact and non-contact warm compress methods (dry, wet/moist and chemically activated dry heat), and found the efficacy of the compresses with moisture was better than that of the compresses using dry heat, which may be related to the different physical properties of heat transfer. Conversely, Arita et al.40 suggested that the repeated eyelid warming with non-moist devices was more effective than that with warm-moist devices in improving the tear film function. The likely explanation for this discrepancy was that the rapid evaporative cooling of oculur surface after the wet heating treatment limited the efficacy of the heating devices. Based on the mentioned above, compared with dry heat treatment, the heating effect of moist warm compresses on the eyelids is still controversial. In addition, the novel eyelid warming treatments are also used in clinical practice, such as the vectored thermal pulsation system (42.5℃) and Activa mask (42℃).41,42
In this study, our results showed that the disposable eyelid warming masks could be effective and the overall improvement of symptoms could be due to significant improvement of the function of the meibomian glands, which was consistent with the previous studies.15,34,38 Reheating the compresses every 3 minutes to maintain the therapeutic levels of heat was time consuming and tedious in the hot towel group, which might result in poor compliance with treatment. At this time, the efficacy of the treatment was often hampered. In addition, the discrepancies in the ocular surface temperature between two groups might contribute to different outcomes, which might partly explain the poor efficacy of the hot towel group compared with the eye masks group.
Although warm compresses are convenient for patients with diverse economic capability in daily life, the compliance with warm compress therapy is a long-existing problem in MGD treatment.10,11 So far, there are few relevant published literatures. In this trial, referring to the data on the compliance with warm compress therapy for 12 weeks, we believed that it was very difficult to urge patients to keep conducting warm compresses to maintain long-term control of symptoms. Therefore, in order to improve the patient compliance, it is necessary to develop or invent a warm compress device which can maintain long-time efficiency after a single or short-term treatment. The vectored thermal pulsation system seems to provide a good reference for future research.43
It should be noted that we didn't measure the ocular temperature before and after warm compresses in this pilot study. Nevertheless, both two warm compresses raised the ocular temperatures to levels showing potential to provide the symptomatic relief in patients with lower disease severity. Referring to previously published literatures,13,15,39,44 the external eyelid temperature after using the disposable eyelid warming masks for 2–5 minutes ranged from 38.6℃ to 40.3℃, which was lower than that (40.4℃ to 41.4℃) after using the warming towel for 4–6 minutes. However, a randomized, controlled trial demonstrated that the effect of the disposable eyelid warming masks was similar to that of the warm towel, which was inconsistent with our study.45 A possible explanation was that different products, and the severity of symptoms and signs of MGD at baseline might affect the results of the study.45 Moreover, although many studies have demonstrated the efficacy of the disposable eyelid warming masks in treating MGD,13,15,39,44,45 there is a lack of relevant data in China. Therefore, in order to increase the integrity of the global data, we conducted this study, although new information or additional benefit exceed the current methods of heating eye masks is insufficient compared to other similar products previously studied.
Generally, the disposable eyelid warming masks are safe and effective, with mild ocular AEs and no SAES, which is similar to previous reports.45,46 Furthermore, despite positive outcomes, there are some limitations in this prospective clinical trial, including the following aspects: 1) Care should be taken to avoid the thermal damage after warm compresses. Fortunately, the pain response is a safeguard to avoid thermal damage to the eyelid skin. 2) To facilitate the study, we excluded patients with moderate to severe meibomian gland dropout, which might diminish the relevance of this article. 3) Additionally, the thickness of tear lipid layer before and after warm compresses was not investigated. Further studies are warranted to provide more information.