Application of terahertz (THz) radiation in novel non-invasive biomedical technologies has recently received considerable attention. However, experimental data about the safety of exposure to THz radiation for biological objects (including eye structures in vivo) are limited. To our knowledge, the safety of THz reflectometry (frequency range of 0.30-0.40 THz) has not been closely examined in an animal model with subsequent morphological assessment of corneal tissues.PURPOSE:To assess the safety of pulsed THz radiation with various parameters (time, power, and frequency) for the cornea in a rabbit model.MATERIAL AND METHODS:The sample for the current study consisted of 18 Chinchilla rabbits (18 eyes). Corneal imaging and epithelial cell density before and after the exposure were evaluated using confocal laser scanning microscopy (CLSM). The histological study for objective assessment of the cornea state (day 1 and day 14) was performed after experiment termination.RESULTS:Single and multiple exposures of laser radiation at a frequency below 0.1 THz and power density below 30 nW/cm2 do not cause visible structural changes in any layers of the rabbit cornea. The results obtained in the long-term period showed insignificant reversible morphological changes only within the epithelium.CONCLUSION:The described parameters of terahertz and subterahertz radiation can be considered safe for assessing changes in corneal epithelium hydration level using non-invasive methods based on THz reflectometry.

Dry eye syndrome (DES) is a multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film, and accompanied by ocular symptoms, in which tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play etiological roles. The clinical manifestations of DES can be highly variable, so its diagnosing is typically based on a combination of symptoms, signs, and clinical tests. Majority of the techniques involved in the diagnosis of this disease has a large degree of subjectivity. The present article reviews current dry eye diagnostic tests and presents a new tear film stability assessment technique that may potentially become the objective method for establishing DES diagnosis.