The meibomian gland (MG) is a modified sebaceous gland located in the upper and lower eyelids. The grades of MG loss (i.e. meiboscore) is calculated as the ratio between the area of the MGs and the eyelids, and this calculation is based on the two-dimensional digital infrared images.In the current formula, the area of the eyelid is the denominator. However, because the eyelids need to be flipped over for the examination and evaluation, and there may be interobserver variability in the measurement of the area of the eyelids. Aging and involutional eyelid disorders, such as ptosis, ectropion, and entropion, may lead to laxity or deformation of eyelids, and impact the shape and area of eyelid area consequently.These factors could cause inaccuracy in current evaluation method, and impact the grading and evaluation of treatment efficacy of MGD, especially in self-controlled studies, such as in clinical trials.

In this study, the investigators propose to use a modified calculation formula for the grading of MGs. The investigators could measure the white to white (WTW) distance of cornea, and then calculate the area of cornea (i.e. corneal base area) accordingly.Unlike the eyelid, the WTW distance does not change significantly during aging or between sexes.Thus, the investigators hypothesize that using the corneal base area as the new denominator in the formula for the grading of MG loss is a better way comparing with the conventional method.

Inclusion Criteria:

• people aged 18 to 80

Exclusion Criteria:

• Exclusion criteria included contact lens wearer, history of eye surgeries, systemic health conditions affecting ocular health and those who were unable to cooperate with examinations.

Outpatient population