Depth-resolved dynamics of aceto-whitening in rabbit cornea studied by 1300nm optical coherence tomography

Cervical cancer is the eleventh most common cancer in the UK, especially for women under 35. In developed countries, cervical cancer is diagnosed by performing colposcopy. Contrast is enhanced by spraying dilute acetic acid onto the surface of the tissue. In the past decades, it has been shown that abnormal cervical epithelium turns opaque white upon contact with this weak acid whereas normal epithelium is generally not affected. This mechanism is known as aceto-whitening. However, the exact mechanism of this phenomenon is not fully known. In this study, OCT using near infrared light was used to quantify depth-resolved kinetics of aceto-whitening in a simple squamous epithelium model: rabbit cornea. We have found that both the epithelium and stroma brighten with approximately the same time course, reaching a peak reflectivity at about 50 seconds. The most significant increase in reflectivity was seen in the first 20 seconds upon the application of acid, and was measured to be 11dB. This result is compared with phosphate buffered saline solution, which was shown to exhibit no effect. Lactic acid, an alpha-hydroxy acid, has been reported as a negative control for aceto-whitening. However, our OCT results showed a significant epithelial brightening effect of approximately 8 dB in the first 20 seconds. The key difference with acetic acid is the lack of brightening in the corneal stroma. This could be due to inability to permeate through the basal lamina between corneal epithelium and stroma or lack of interaction with stromal keratocytes.