# Emerging Optical Techniques for the Diagnosis of Onychomycosis
## 4 Conclusions  
Onychomycosis is not just a cosmetic nuisance but a disorder with a reservoir of pathogenic fungi that can give rise to significant health problems. The standard clinical diagnostic algorithm of onychomycosis involves clinical suspicion and a positive laboratory test. Since the clinical presentation is not always conclusive, additional spectroscopic and imaging techniques are needed to aid the on-site diagnostic accuracy in a rapid and non-invasive manner. Proper diagnosis of onychomycosis is important for a rational treatment. The standard therapeutic approach involves the administration of systemic antifungal agents over a long period; for toenails, it typically exceeds 3 months. Thus, the confirmation of diagnosis, i.e., the definite identification of the fungal cause, is essential to protect patients from redundant and costly treatments. RS, OCT, and CLSM are well established modalities for the evaluation of skin diseases, and are currently also emerging as approaches to the study of nail infections. The chemical composition and the structural aspects of healthy and onychomycotic snails can be rapidly assessed using these methods. RS can be easily integrated into the clinical setting for real-time evaluation of onychomycosis. In particular, when RS is coupled with statistical methods, it can achieve flawless classification between healthy and onychomycotic snails, although the detailed discrimination of the different pathogens at species- or strain-level with the currently available instrumentation seems unlikely. OCT can identify morphological nail alterations indicative of onychomycosis, distinguish areas of infected nail and identify the depth of pathogen's invasion. However, it does not allow the differentiation between hyphae/spores and other nail creases and lacks specificity. CLSM takes advantage of its higher resolution, which allows for the detection of cellular and architectural abnormalities of the nail, can quantify the fungi load and has superior specificity compared to KOH preparation. As yet, species differentiation and vitality cannot be assessed with CLSM while it remains an expensive instrumentation. It is worth noting that the integration of different currently available techniques, with their different pros and cons, in a so-called multi-modality imaging approach, is anticipated to significantly improve our diagnostic capabilities in assessing onychomycosis by (i) rapidly identifying the fungal agent, (ii) monitoring treatment response, and (iii) evaluating therapeutic protocols.  
Conceptualization, C.P., G.G., and N.K.; methodology, G.G., I.D.B., A.V., and N.K.; investigation, C.P., E.G., M.Z.V., and N.K.; validation, all authors; writing--original draft preparation, N.K; writing--review and editing, all authors; supervision, N.K. All authors read and agreed to the published version of the manuscript.  
This research received no external funding.  
We thank Stavros Niarchos Foundation for the generous donation of the OCT device. E.G. would like to acknowledge the financial support provided by Catedras CONACYT (project 528). The authors declare no conflict of interest.