The study was approved by the Institutional Review Board of Seoul National University Hospital (IRB No. 1402–058-557) on February 25, 2014 and performed in accordance with the tenets of the Declaration of Helsinki. The patients with short TFBUT-type DE were prospectively enrolled with informed consent in Seoul National University Hospital from March 14, 2014 to December 19, 2014 and followed-up for 4 weeks. The diagnosis of short TFBUT-type DE was made based upon the presence of DE symptoms, TFBUT value ≤5 s, corneoconjunctival staining score ≤ 2 (on a scale of 0 to 4), and Schirmer I test value > 5 mm/5 min. Patients with systemic immune-mediated diseases such as secondary Sjögren’s syndrome or graft-versus-host disease were excluded. Also, patients who were on topical medication(s) for treatment of ocular diseases other than DED such as glaucoma or allergic conjunctivitis were excluded.
Treatment and examination
The subjective DE symptoms, TFBUT, corneoconjunctival staining scores, and Schirmer I values were examined before and after 4 weeks of instillation of diquafosol tetrasodium 3% ophthalmic solution (Diquas®, Santen Pharmaceutical Co., Ltd., Osaka, Japan) six times per day. Other topical medications than Diquas® were discontinued during the study period. Demographic factors including age and gender were compared between patients who showed improvement in each DE parameter after treatment and those who did not show any change. Systemic or ocular side effects were recorded.
The criteria for subjective DE symptom scoring are as follows: 0 (no symptom), 1 (mild symptoms of ocular dryness, occasional and not interfering with daily life), 2 (moderate symptoms, occasional or chronic, but not interfering with daily life), 3 (severe frequent or constant, but not interfering with daily life), and 4 (severe, constant and disabling). The corneoconjunctival staining score was assessed by fluorescein staining as follows: 0 (no staining), 1 (mild conjunctival and corneal staining), 2 (moderate conjunctival and corneal staining), 3 (moderate to severe conjunctival staining and marked central corneal staining), and 4 (severe conjunctival staining and severe, diffuse corneal punctate erosions).
TFBUT measurements were performed as previously recommended . In brief, after instillation of a small quantity of 1% fluorescein dye into the inferior conjunctival sac, patients were instructed to blink several times to ensure mixing of the dye with the tear. Under a cobalt blue filter and slit lamp biomicroscope, the interval between the last complete blink and appearance of the first corneal black spot in the stained tear film was measured . The measurements were made three times for each eye by the same doctor, and the mean value of the three measurements was calculated.
The Schirmer I test was done by putting the Schirmer paper strip at the junction of the middle and lateral thirds of the lower eyelid of patients without anesthesia. Patients were then instructed to close their eyes for 5 min, and the wetting length of the strip was recorded in mm.
The primary outcome was the mean change from baseline in TFBUT at 4 weeks after treatment and the secondary outcome measures were the changes in the subjective DE symptom scores and Schirmer I test results.
The power analysis was performed to justify the number of patients using G*Power 126.96.36.199. A sample size of 80 patients was determined to provide the study with 80% statistical power to detect 30% mean difference in TFBUT between control and treatment groups under the assumption that data would be missing in 15% of patients.
The GraphPad Prism® (GraphPad Software, Inc., La Jolla, CA) was used for statistical analysis. The change between pre and post-treatment values in each patient was assessed for significant difference by two-tailed paired t test. The comparisons of demographic factors between patients who showed improvement in each DE parameter after treatment and those who did not were made by two-tailed t test. Statistical significance was defined as p value < 0.05.