The impact of DES on QoL was rather underestimated because it tended not to be a common cause of permanent visual morbidity compared with other ocular diseases, such as cataract, glaucoma and age-related macular degeneration. Consequently, the proportion to seek medical treatment is fairly low in Chinese elderly population, especially those with mild and moderate DES. However, the higher incidence of DES in old people, ever-increasing demands of modern life style such as computer use and air conditioner, and prolonged life expectancy in recent year all highlighted the consequence of DES for vision-related QoL in the general population.
It was the first time to report that the composite score of the participants with DES decreased significantly compared with those without DES or with suspected DES, indicating that DES can produce a significantly negative impact on the overall vision-related QoL in a non-clinic-based population who didn’t seek medical care. Moreover, the current study revealed that the subscale score for ocular pain decreased significantly in the general population with DES or dry eye symptom, which was in agreement with previous studies focusing on outpatients diagnosed with DES. It has been reported that the subscale score for ocular pain ranged from 62.5 to 87.5 in patients with DES, indicating that DES can cause more ocular pain or discomfort [8
]. It has been considered that the adverse impact on QoL caused by DES, at least partially, resulted from ocular pain, especially in patients with severe dry eye such as in Sjogren’s syndrome [16
]. Meanwhile, the application of artificial tears or other treatment may improve the signs, symptoms, and QoL associated with DES [17
Apart from the decreased scores for ocular pain, lower scores for mental health were also found in the participants with DES, indicating that the disorder caused adverse impact not only on physical health, but also on psychological health. Only a few published studies reported the psychological status of DES subjects, showing that DES subjects were more anxious and depressed compared with those without DES [18
]. On one hand, it is well known that pain or disabilities caused by chronic disease can induce anxiety and depression [21
]. On the other hand, psychosomatic aspects, which include depression, stress, and anxiety, could affect subjective ocular symptoms and pain perception [22
], forming a vicious cycle. The fact [18
] that subjects with severe dry eye, such as Sjogren’s syndrome, experienced increased clinical anxiety or depression supported the hypothesis that more severe DES symptoms could cause more adverse disturbance on mental health and function.
It’s notable that the symptomatic participants also reported lower scores for ocular pain and mental health, even though they didn’t have any definite signs of DES. Meanwhile, asymptomatic subjects with dry eye signs reported similar VFQ-25 scores as compared with normal controls. It highlighted that the symptoms of DES deviated from signs, and DES symptoms rather than signs had an overwhelming impact on VFQ scores, just as shown by the multiple regression analysis. The unpleasant symptoms of dry eye, such as burning or stinging, ocular grittiness, foreign body sensation, blurred vision, and photophobia, and unsatisfying outcome of palliative treatments could contribute to an impaired QoL. Previous studies revealed the lack of concordance between patient-reported symptoms of DES and clinical parameters (TBUT, ST, and FSS) [23
], as well as the absence of correlation between the objective ocular surface examination findings and the VFQ-25 or SF-8 scores [4
], which were in agreement with our study. Symptoms, being the most common motivation for seeking eye care, should therefore be a critical outcome measure when assessing treatment effect and improvement of QoL.
Ocular Surface Disease Index (OSDI) [24
], a 12-item questionnaire, is a disease-specific measure that explores the vision-related function, ocular symptoms, and environmental triggers related with DES. In contrast, NEI VFQ-25 is a vision-specific (but not disease-specific) method to measure QoL. In addition to an overall composite score ranging from 0 to 100 (lower scores indicating greater impairment), the measure yields general numerous subscales, including general vision, ocular pain, near vision, distance vision, social functioning, mental health, role functioning, dependency, driving, color vision, and peripheral vision [25
]. It has been shown that the NEI-VFQ scores were moderately to strongly correlated with scores on the disease-specific OSDI in patients with Sjogren’s syndrome, suggesting the measures were similar in their ability to assess impact of dry eye on vision-targeted QoL [16
]. However, the emphasis of these two measures was different to a certain extent. The OSDI is targeted to assess how much the symptoms of dry eye affect the patients’ current status (i.e., in the past week), while the NEI-VFQ may be more suited for capturing the overall impact of a chronic ocular disease on QoL, especially giving consideration to physical health and psychological health simultaneously [14
In the present study, the diagnosis of DES was done mainly based on both the presence of dry eye symptoms and clinical assessment, which included decreased TBUT, reduced values of Schirmer test and positive corneal staining, according to the criteria of 2007 Dry Eye Work Shop [1
]. However, more recently published studies document that an increased tear osmolarity is the hallmark of dry eye disease [26
]. It has been demonstrated that tear film osmolarity is the single best marker of disease severity across normal, mild/moderate, and severe categories, while other tests, such as Schirmer test without anesthesia, TBUT, corneal staining, meibomian dysfunction assessment, conjunctival staining, and dry eye symptom questionnaire, were found to be informative in the more severe forms of disease [26
]. With the consideration that DES severity of the majority subjects in the community population was mild or moderate, tear film osmolarity should have been a better diagnostic tool for differentiating DES and normal controls, as well as for evaluating disease severity. Unfortunately, the device for the clinical testing of tear osmolarity, named as TearLab Osmolarity System [28
], had not been available in China when the research was performed. It is urgently required to apply tear osmolarity in further studies involving DES.
Another limitation of the current study is that the status of meibomian glands had not been examined. Therefore, the dry eye symptoms resulting from meibomian gland dysfunction (MGD) cannot be discriminated from those caused by deficient aqueous tear secretion. It has been reported that no correlation has been found between Schirmer result and meibomian gland anomalies [5
]. Thus, it’s possible that some symptomatic subjects who have no DES signs can be classified as DES if the assessment of the meibomian glands is carefully performed. However, due to the fact that no significant differences had been found in VFQ score between the participants with DES and those only with DES symptoms, the bias caused by misclassification could be largely neglected. The impact of MGD on vision-related QoL and the differences of QoL between subjects with MGD and other subtypes of DES merit further investigation.