Colposcope image of the human cervix, showing moderate dysplasia (CIN 2), the presence of abnormal, potentially cancerous tissue. The application of dilute acetic acid to the area has rendered the abnormal tissue white. The cervix is lined by a stratified squamous epithelium with cell division normally confined to the basal epithelial layer. In dysplasia the gradual stratification in cell maturation seen in normal epithelium is disrupted and dysplastic (abnormal) cells may extend throughout a large proportion of the thickness of the epithelium. Colposcopy is used to examine and treat cervical abnormalities after their detection by cytological screening.