**4. Conclusions**

*Ocular Surface Diseases - Some Current Date on Tear Film Problem and Keratoconic Diagnosis*

In the last decade, numerous authors have highlighted the importance of hyperosmolarity of the tear film in the pathophysiology of dry eye. Lemp et al. [19] and collaborators also grant a significant diagnostic role. Liv et al. [20] relate the instability of the tear film with the increase in osmolarity and give it a fundamental role in the cascade of pathological events that on the ocular surface is capable of

The importance of hyperosmolarity is such that authors such as Hirata et al. [21] suggest that the increased osmolarity of the tear film induces functional and

In 2010, Mesmer et al. [22] determined that hyperosmolarity is an important

More recently, the final report of the pathophysiology subcommittee of the TFOS DEWS II [23] concluded that the core mechanism of dry eye is evaporationinduced tear hyperosmolarity that produces a vicious circle (**Figure 1**). When osmolarity rises it causes damage on the ocular surface both directly and by initiat-

This subcommittee concluded: "tear hyperosmolarity is considered to be the trigger for a cascade of signaling events within surface epithelial cells, which leads to the release of inflammatory mediators and proteases. Such mediators, together with the tear hyperosmolarity itself, are understood to cause goblet cell and epithelial cell loss and damage to the epithelial glycocalyx. Inflammatory mediators from activated Tcells, recruited to the ocular surface, reinforce damage. The net result is the characteristic punctate epitheliopathy of DED and a tear film instability which leads at some point to early tear film breakup. This breakup exacerbates and amplifies tear hyperosmolarity and completes the vicious circle events that lead to ocular

*The vicious circle of dry eye disease. Image obtained from TFOS DEWS II 2017 pathophysiology subcommittee.*

structural lesions of the corneal nerves and neurotoxicity.

factor in the pathophysiology of dry eye.

**3. Other investigations**

generating.

ing inflammation.

surface damage."

**40**

**Figure 1.**

Undoubtedly, dry eye is nowadays one of the problems most commonly diagnosed by ophthalmologists. The dry eye is a complex multifactor illness of the tear film and of the ocular surface (cornea, conjunctiva, palpebral anexus, glands and nerves) characterized by symptoms of discomfort, vision alterations, and instability of the pre-corneal tear film that may bring about potential damage on the ocular surface. Instability of the film will produce increasing of osmolarity of the tear film, which will trigger epithelium osmotic lesions and inflammation. As these changes take place on the ocular surface, neurophysiologic mechanisms of homeostasis will be altered, which will complicate the process even further, with the cropping up of vicious physiopathologic circuits.

The knowledge of its physiopathologic triggering and its early diagnosis will allow a better management of this pathology. In this sense, evaluation of osmolarity of the tear film in these patients, even if it does not give us an etiologic diagnosis of the disease, does give us an efficient tool to diagnose and evaluate the disease, as its values are directly proportional to the severity of the clinical picture of the dry eye, and is always present in these patients.
