Currently, due to the advantage of noninvasive, localized, rapid, painless and easily repeatable of impression specimens, the technique is an ideal method of investigating ocular surface disorders when the diagnosis is not clinically obvious or detecting the post-operative change without tissue damage. Using impression cytology for primary diagnosis and follow-up of ocular surface squamous neoplasia, including after therapy with topical mitomycin C has been well-studied. [29]. In addition to the applications described above, pterygium is another disease of interest. Pterygium, a common disease of ocular surface, has high recurrence rate after surgical excision. [30-33] However, the exact etiology and mechanism for recurrence is unknown. A transformation of the phenotypic characteristics of the conjunctival fibroblasts may play an important role. Due to the concern of improvement in treatment, it is important to explore the change of cytomorphology after pterygium operation, to identify the risk factors of developing recurrence, and, furthermore, to clarify the etiology and mechanism. Some ophthalmologists may think this procedure too time-consuming to be a routine examination in outpatient clinics. [34] However, National Taiwan University Hospital (NTUH), as one of the largest tertiary medical centers in Taiwan, is now in charge of a big part of difficult cases of ocular surface. With the need of further precise diagnosis and delicate clinical skills, the investigators are competent for this meaningful program.