Optical assessment of genital changes associated with female sexual arousal: a mini-review.

Background: Optical techniques, including laser Doppler flowmetry (LDF), photoplethysmography (PPG), and near-infrared spectroscopy (NIRS), are emerging as one of the most popular tools for female sexual arousal response (FSAR) assessment. However, to our knowledge, no narrative reviews have focused on the application of these optical techniques in FSAR assessment. Aim: To fill out the existing gap, we review the literature regarding using optical techniques in FSAR assessment in preclinical and clinical studies. Methods: A literature search was performed on the manuscript with terms including "female sexual dysfunction, FSAR, LDF, PPG, NIRS" between 1974 and 2024 using PubMed, Google Scholar, and MEDLINE. Among the articles identified, 18 articles were reviewed after excluding articles with non-relevant topics, duplicate articles, and articles not written in English. Outcomes: This article reviews 11 studies that used LDF/imaging, four studies that used PPG, and three studies that used NIRS, including the employed experimental protocols in each study. Results: Various optical techniques were used in FSAR assessment during electrical stimulation, visual and tactile stimulation, and drug administration. Additional studies, including using non-human primate models, testing the effects of different anesthetics on FSAR in preclinical studies, and performing more clinical studies to develop a standard for human FSAR monitoring using optical techniques that can lead to the use of optical techniques in clinical practices, could be considered. Meanwhile, non-contact systems and other optical techniques like optical coherence tomography, photoacoustic endoscopy, and Raman spectroscopy can be developed for future FSAR studies. Clinical Translation: This article can provide a good overview of the preclinical and clinical investigations of FSAR using LDF, PPG, and NIRS. Understanding the differences between the techniques will allow clinicians to choose an appropriate technique for their FSAR studies. Strengths and Limitations: This review is the first to overview various optical techniques used to evaluate FSAR. A limitation of the review is that there is no clinical study that uses NIRS for FSAR monitoring. Conclusions: LDF/imaging, PPG, and NIRS have been used in various FSAR investigations. Such optical techniques have the potential to be used in future FSAR studies to quantitatively analyze the physiological changes during FSAR.