Table 1 Exclusion criteria

-Ocular disease in either eye

 a. Ocular surface disease

  Corneal fluorescein staining grade ≥3

  Tear film break up time <5 s

  Schirmer I (without anesthetic) test <5 mm

 b. Best corrected visual acuity < 20/30

 c. Intraocular pressure > 21 mmHg

 d. Optical coherence tomography proven retinal nerve fiber defect

 e. Significant cataract (lens opacities classification system III: ≥NO3/NC3, ≥C3 or ≥ P3)

 f. Significant entropion or ectropion

 g. Significant tear drainage problem proved with fluorescein dye dilution test

-Soft or Hard contact lens use 3 or more days a week

-History of oral intake of health supplement designed to improve asthenopia within 4 weeks before participating this study

-Regular use of any lubricant eye drops

-Pregnant woman

-Systemic disease

 a. Uncontrolled hypertension (systolic/diastolic blood pressure > 140/90 mmHg)

 b. Uncontrolled diabetes mellitus (fasting blood glucose level > 180 mg/dL)

 c. Rheumatoid arthritis

 d. Malignant disease

 e. Active hepatitis (type B and C)

 f. Acute or chronic infectious disease

 g. Renal disease