In the present study, the effectiveness of IPL for MGD was confirmed, and factors that influence the efficacy of IPL were also explored. After IPL treatment, the TBUT, CFS scores and OSDI had a better performance than before. To take it a step further, we observed a significant association between an effective IPL treatment outcome and a younger age (18–39 years), moderate MGD, higher baseline SIt, and higher baseline OSDI. The severity of MGD attained statistical significance in both our univariate and multivariable logistic regression analyses.
Our results demonstrated that IPL treatment improved TBUT and resulted in reduced CFS scores and OSDI. Postoperative and preoperative data suggested that the beneficial effects of IPL could be sustained for at least three months. This finding indicated that IPL helped stabilize the tear film and improved ocular surface damage and symptoms of MGD[22]. However, there was no significant change in the SIt values after the treatment. The reason might be that MGD is a major cause of evaporative dry eye, whose main manifestation is a significant change in the tear quality rather than the tear amount[17, 23]. The EMAS did not respond ideally to IPL, and this result was similar to previous results reported by Karaca EE et al[24].
Furthermore, we compared the characteristics of the effective and ineffective IPL treatment outcomes. The analysis implied that after three sessions of the IPL treatment, the outcomes were divergent among patients with different age, different severity of MGD, different baseline SIt or different baseline OSDI. As age increased, the occurrence rate of effective IPL decreased. A recent retrospective study showed a similar view and reported that a younger age was associated with greater benefits of IPL[25]. The results might be explained as follows. First, the decrease in the ability to synthesize estrogen in senior patients could affect the quantity and quality of lipid secretion from the MG[11], resulting in tear film instability and ocular surface inflammatory reactions[26]. Second, regarding histology, with increasing age, the acinar basement membrane becomes thicker[26], while the MG density and diameter decrease[27, 28]. In addition, it has been found that older people have fewer acinar cells, which eventually becomes acinar atrophy, solidification and even scarring[29]. Thus, it is possible that elderly MGD patients are more difficult to treat.
In our univariate analysis, higher baseline SIt and baseline OSDI also displayed a higher effective rate of IPL treatment. Thus. the patients with higher amounts of tear and more severe symptoms were more likely to benefit from the IPL treatment. Previous studies have found that IPL significantly improves the thickness of the tear film lipid layer[30]. Patients with high baseline SIT had better secretion function in the main lacrimal gland; thus, it is reasonable to presume that the amount of aqueous layer in patients with high baseline SIt was mainly reduced by evaporation, but the secretion function was less affected. The lipid layer repair by IPL can better protect the aqueous layer to reduce the evaporation of tear, thus achieving a better therapeutic effect. Additionally, IPL regulates the secretion of pro-inflammatory and anti-inflammatory molecules[31]. Their levels were closely related to pain, tear instability, tear production and ocular surface integrity[32]. Through this mechanism, IPL was helpful for patients with high baseline OSDI to repair ocular surface damage[33]. The above research results provided some references for selecting patients and communicating with patients about their prognosis before IPL treatment in the clinic. However, these factors could not be used as prognostic factors independently.
Based on our multivariable logistic regression model, severity of MGD was an independent influencing factor. The effective rate of IPL in the moderate MGD group (65.6%) was the highest among all groups. Moderate MGD was associated with increased odds of effective IPL in our analysis. The results indicated that effective IPL in moderate MGD patients was 22.454 times as high as that in severe MGD patients. Vegunta et al. [10] reported that pronounced gland dropout or atrophy contributed to failed IPL treatment. Similarly, Tang Y et al. [25] proposed that the extent of meibomian gland dropout may be a key factor in the outcome of IPL treatment. Therefore, we inferred that more serious and unrecoverable damage to the physiological structure and function of the MG in patients with severe MGD was a possible reason for this result in our study[34].
An unexpected finding was that there was no significant association between mild MGD and effective IPL when severe MGD was used as the reference group in the multivariable logistic regression analysis. According to published studies, improvements in the OSDI after IPL are negatively correlated with the baseline MG expression, i.e., the higher the baseline MG expression capacity, the smaller the improvement in OSDI[35]. Therefore, we speculated that the MG expression capacity in patients with mild MGD was better than that in those with severe MGD, resulting in smaller improvements in OSDI in patients with mild MGD after IPL. Furthermore, the main efficacy evaluation in this study was based on improvement in OSDI. Consequently, we did not observe any association between mild MGD and effective IPL.
To the best of our knowledge, the optimal candidates for IPL have not been identified. This study represents the first prospective research to perform a statistical analysis of the factors influencing the effectiveness of IPL treatment until now[36]. Nevertheless, the sample size of our study was relatively small. Some factors are difficult to control, such as patients' lifestyle, hormone levels, mood, and environment, which may affect the therapeutic effect of IPL treatment [37, 38]. Large-sample multicenter studies are expected to further confirm these results in the future.
In conclusion, IPL can effectively improve the clinical symptoms and some signs in patients with MGD, and the beneficial effects can be maintained for at least three months. Age, the severity of MGD, and the baseline SIt and OSDI are potential factors that may influence the effectiveness of IPL. The severity of MGD is an independent influencing factor.