Primary SS ADDE patients between Jan 2019 to Oct 2020 at dry eye clinical center in the First Affiliated Hospital of Chongqing Medical University were included. Gender- and age-matched non-SS ADDE patients seen during the same period of time were set as control group. Primary SS patients all met the criteria reported by the American–European Consensus Group (11). ADDE was diagnosed as having decreased tear production ( ≤ 5 mm/5 min in Schirmer I test) etc. (1). Inclusion criteria also included that both SS and non-SS patients received preservative-free artificial tear (0.1% sodium hyaluronate) treatment for at least 2 months before this study and the dry eye symptoms were not relieved. Exclusion criteria included pregnant or lactating women, acute inflammation or infection of the eye, other ocular surface diseases, history of ocular surface surgery or lid abnormalities. All patients were diagnosed and evaluated by one ocular surface disease specialist (MX).

Polyacrylic acid punctal plugs (Smart Plug, Medennium, US) were inserted into the lower lacrimal duct in both eyes of all the included patients and preservative-free artificial tears (0.1% sodium hyaluronate) were permited to use 4 times a day. Punctal plugs remained in-situ and there had no obvious complications during the follow-up visits. The right eyes of both groups were chosen for the statistical analysis.

All subjects underwent a clinical evaluation at each visit (pre-punctal obstruction, 2 weeks, 2 months, and 6 months after punctal obstruction), which included ocular surface examination, meibomian gland evaluation and measurement of lipid layer thickness (LLT). Before clinical evaluations, patients were required to complete Ocular Surface Disease Index (OSDI) questionnaire and the Standard Patient Evaluation of Eye Dryness (SPEED). Data included age, gender was collected in both groups.

Standard OSDI questionnaire was employed to evaluate the frequency of symptoms over the preceding weeks (12). Total OSDI score equals [(sum of the scores for each question answered) ×100]/[(overall number of questions answered) ×4] and the scores ranged from 0 to 100. The SPEED was used to evaluate frequency and severity of dry eye symptoms especially for the assessment of longer-term symptom changes over 3 months with a score ranging from 0 to 28. It should be noted that the higher the scores of either of the two questionnaires were, the more severe the symptoms were (13).

Ocular surface examination consisted of the measurement of tear meniscus height (TMH), test of non-invasive Keratograph break-up time (NIKBUT), Schirmer test without anesthesia (Schirmer I test, SI T) and corneal fluorescein staining (CFS). Ocular surface examination was performed 2 h after using artificial tears. Since forced eye opening required for the assessment of tear film stability increased TMH possibly due to reflex tear secretion, so TMH should be measured for accuracy before a non-invasive assessment of tear film stability (14).

TMH was measured using a keratograph 5M (Oculus GmbH, Wetzlar, Germany), which is equipped with a modified tear film scanning function. Lower tear film meniscus images were captured and TMH was measured before NIKBUT measurements in each subject.

NIKBUT was evaluated automatically through a Keratograph 5M. We required that the patients to blink first and subsequently open their eyes as long as possible. The time between the last blink and the first sign of distortion of the ring pattern was recorded. The process was repeated three times and the average of the three measurements was recorded as the final BUT.

SI T was performed with the patient's eyes closed for 5 min without anesthesia. The tear strip (30 mm; Jingming Tianjin, China) was folded in the front, positioned in the mid-lateral portion of the lower fornix for 5 min. The length of the wetting strip was recorded using the millimeter scale.

The score of CFS was evaluated through a white light and cobalt blue filter. The cornea was divided into four quadrants (superior nasal, inferior nasal, inferior temporal, and inferior temporal) and each quadrant got 0–3 points according to the degree of staining (15). Corneal staining was graded individually as follows: 0 point (no staining), 1 point (mild staining), 2 points (staining between 1 and 3), and 3 points (severe staining with bulk or strip staining). The total score of each eye was 0~12 points (15).

Meibomian gland evaluation consisted of meibomian gland structure, gland morphology (gland dropout), gland function (meibum expressibility and quality) and lid margin assessment. We also measured lipid layer thickness (LLT) using the LipiView® interferometer (TearScience, Inc., Morrisville, NC) since ocular surface lipids are closely related to meibomian gland function.

The meibography images of the upper and lower eyelids were documented to assess the structure of the meibomian gland after satisfying focus using the LipiView® interferometer. The meibomian gland dropout (meiboscore) was analyzed by using Image J in Keratograph 5M as described previously by Pult and Nichols (16). The meibomian gland dropout rate was divided into four grades: grade 0 (no meibomian gland loss was detected), grade 1 (no more than 33% of meibomian gland loss was detected), grade 2 (33–66% of meibomian gland loss was detected), and grade 3 (>67% of meibomian gland loss was detected) (17). Upper and lower eyelids scores were added to calculate a total meiboscore (0–6) for each eye (18).

Meibomian gland function assessment was conducted in accordance with the recommendations of the International Workshop on Meibomian Gland Dysfunction and TFOS DEWS II (2, 17, 19). For assessing the gland expression, the Meibomian Gland Evaluator (MGE; TearScience, Inc.) was placed in the lower eyelid 2 mm from the root of the eyelash applying constant, gentle pressure for 10–15 s to evaluate meibomian gland secretions by simulating the pressure of a normal blink. And then, the lipid secretion from the meibomian gland orifices was observed through a slit-lamp microscope. Five continuous glands were evaluated, respectively, in the temporal, central, and nasal parts of the lower eyelid, 15 glands in total (20). The meibum expressibility score (MES) was graded by counting the central eight expressed meibomian gland orifices of the lower lid as follows: Grade 0 means all glands are expressible; Grade 1 means 3–4 glands are expressible; Grade 2 means 1–2 glands expressible; Grade 3 means no gland is expressible. The secretion of the meibum quality score (MQS) of each of the 15 glands in the lower eyelid was graded from 0 to 3 as follows: Grade 0, clear; Grade 1, cloudy; Grade 2, cloudy with granular debris; Grade 3, thick like toothpaste or non-expressible glands. The total possible score of both MES and MQS was ranged from 0 to 3 points (2, 17, 19).

Lid margin abnormality score was documented as 0 (absent) or 1 (present) in accordance with the existence of the following four signs: vascular engorgement, plugged meibomian gland orifices, anterior or posterior displacement of the mucocutaneous junction and irregularity of the lid margin. If any of these signs was present, one point was assigned for each item, with a total possible score range of 0–4 points (17).

LipiView® II interferometer was applied to measure LLT of the tear film as described previously: the interferometer converts the specific interference colors into the values of LLT (21). The results of LLT were automatically obtained after the measurement.

Statistical analyses were performed using Graphpad (version 6.01, San Diego, CA, USA). Comparisons of parameters between the two groups were performed using student-t test at baseline and each visit (all parameters are normally distributed). Comparisons of parameters at different visits among the same group were performed with one-way ANOVA. P < 0.05 was considered as significant from the statistic perspective.

Fifty cases were qualified in this study (25 in SS group and 25 in non-SS group). Mean age of the SS patients was 55.41 ± 10.07 and 58.85 ± 15.36 years for non-SS patients. The numbers of males and females were the same in both groups (2 males, 23 females). There was no statistically significant difference of age and dry eye parameters between the two groups (all P > 0.05) before punctal obstruction except SPEED scores and CFS scores.

At the baseline, OSDI score has no difference between the SS group and non-SS group. It was improved at every visit compared with the baseline (all p < 0.01) in both SS patients and non-SS patients. However, the patients in SS group had significantly larger OSID scores than that in the non-SS group at 2 weeks, 2 months, and 6 months after punctal plugs insertion (all p < 0.01).

SPEED scores in SS group were statistically higher compared with the non-SS group (p < 0.05) at the baseline. After the obstruction they were improved in both groups at every visit compared with the baseline (all p < 0.05). There had no statistical difference between the two groups at 2 weeks (P > 0.05) and the SS group had a significantly larger SPEED scores compared with the non-SS group at 2 months and 6 months (both p < 0.01).

The changes of SPEED and OSDI scores in both groups were summarized in Table 1.

The TMH had no difference between the non-SS and SS group at baseline (P > 0.05). After punctal plugs insertion, a significantly larger TMH was found in non-SS group comparing with SS group at 2 weeks, 2 months, and 6 months visit (all p < 0.05). The TMH improved at every visit compared to baseline (all p < 0.01) both in SS group and non-SS group. The highest TMH was noted at 6 months after punctal plugs insertion in both groups (Figure 1A).

At the baseline, there was no statistical difference in NIKBUT between non-SS an SS patients. A statistically longer NIKBUT was found in the non-SS group compared with the SS group at 2 weeks, 2 months, and 6 months after the treatment (P < 0.01, respectively). Compared with the baseline, NIKBUT statistically increased in non-SS patients at every visit (p < 0.01, respectively), while in SS patients it was improved at 2 weeks and 2 months (p < 0.01, respectively) and had no difference at 6 months (P > 0.05) (Figure 1B).

Though initial SI T score had no difference between the two groups (P > 0.05), a significantly larger SI T was found in non-SS group comparing with SS group at 2 weeks, 2 and 6 months visit after the treatment (all p < 0.01). Compared to baseline it improved at every visit both in SS group and non-SS group (all p < 0.01). The highest SI T score was noted at 2 weeks after punctal plugs insertion in both groups (Figure 1C).

Comparing with the non-SS group, the SS group had a significantly larger score in CFS at baseline and every visit (all p < 0.01). After punctal plugs insertion, there was no CFS in non-SS patients during the follow-up. In SS group, the lowest score was found at 2 weeks, and it slowly increased at 6 months (Figure 1D).

(1) Meibomian gland dropout (Meiboscore)

The meiboscores seemed higher in the SS group than in the non-SS group at baseline, 2 weeks, 2 months, and 6 months, but there was no statistically significant difference between the two groups in the mean meiboscores (P > 0.05, respectively). Both in the SS and non-SS dry eye patients, the meiboscores did not change significantly after punctal plugs insertion at 2 weeks, 2, 6 months compared with the baseline (Figure 2A).

(2) Meibum expressibility score (MES)

The MES had no difference between the two groups at baseline (P > 0.05). After punctal plugs insertion, no statistically difference was found in SS group comparing with non-SS group at 2 weeks, 2 months, and 6 months visit (all P > 0.05). Compared with the baseline, the MES was improved in both groups at every visit, but there was no statistical difference at 2 weeks in both groups (P > 0.05, respectively). The meibum expressibility seemed to reached a peak at 2 months in both groups (Figure 2B).

(3) Meibum quality score (MQS)

There was no significant difference in MQS at baseline between the SS and non-SS group (P > 0.05). After the obstruction, the MQS in the SS group looked higher than that in the non-SS group at 2 weeks, 2 months, and 6 months, but no statistical difference was found between the two groups at every visit (P > 0.05, respectively). Compared with the baseline, the MQS was decreased in both groups at every visit, but only at 2 months the difference was statistically significant in both groups (P < 0.01, respectively) (Figure 2C).

(4) Lid margin abnormalities

There was no statistical difference in the scores of lid margin abnormalities at baseline between the two groups (P > 0.05). After the obstruction, the scores of lid margin abnormalities in the non-SS group appeared to be lower than that in the SS group during follow-up, but there had no statistical difference between the two groups at each visit (P > 0.05, respectively). Compared with the baseline, the scores of lid margin abnormalities were significantly improved in non-SS group at 2 and 6 months (P < 0.05, respectively), while SS group showed statistical difference only at 2 months (P < 0.05) (Figure 2D).

(5) LLT

There was no difference in LLT between the two groups at baseline (P > 0.05). At 2 weeks, 2 and 6 months after the obstruction, it was significantly larger in the non-SS group than that in the SS group (all p < 0.05). Compared with baseline, LLT increased in SS group after the treatment, but the difference was statistically significant only at 2 months (p < 0.05). In non-SS patients, LLT reached its highest level at 2 weeks (p < 0.0001) and experienced continuous decrease, although it decreased to some extent at 2 and 6 months, it was still greater than baseline (p < 0.05) (Figure 3).