Fig. 1. Principle of Raman spectroscopy and molecular energy levels change diagram^[8]. (a) Principle of Raman spectroscopy; (b) changes in molecular energy levels corresponding to different scattering patterns

Fig. 2. Schematic diagram of confocal Raman spectroscopy system

Fig. 3. Tissue structure of cornea

Fig. 4. Raman spectra of human corneas in the culture medium without (upper) and with (lower) dextran^[13]

Fig. 5. Raman spectra of corneas after exposure to sunlight and different methods of decellularization. (a) Raman spectra of the cornea sample exposed to the solar radiation of the mid-summer in Antarctica for two weeks (upper) and the sample protected from the solar radiation (lower) in Antarctica^[18]; (b) schematic representation of the four different methods used for the decellularization of goat cornea^[20]; (c) Raman spectra of decellularized cornea samples, where the amide I (1600‒1700 cm^-1), amide III (1200‒1300 cm^-1), GAG (1000‒1100 cm^-1), and protein backbone (800‒900 cm^-1) regions are zoomed in the insets^[20]

Fig. 6. Applications of Raman spectroscopy in disease diagnosis. (a) SERS detection of ACD gene point mutations^[28]; (b) schematic diagram of Raman spectroscopy for detecting DK^[29]; (c) classification of DK using PCA-KNN model^[29]

Fig. 7. Raman spectroscopy for drug component detection. (a) Relationship between Raman intensity and concentration (mass fraction) of Trusopt in HPLC-grade water^[31]; (b) corneal hydration in the rabbit under in vivo conditions as a function of time^[31]; (c) Raman spectra of corneal scrap, corneal epithelium, and besifloxacin^[32]

Fig. 8. Multimodal imaging of the cornea^[38]. (a) Schematic diagram of multimodal (TSFG, SHG, and CARS) and multi-channel spectral imaging system; (b) multimodal and multi-channel spectral 3D imaging of rat corneal tissue