What diseases could be diagnosed?

Normally, we consider tears as a fluid that serves to keep the eye moist and transmit feelings. Thus, we can cry when it is very cold, when something gets in our eye or when we are very sad or very happy. They may also be missing if we suffer from dry eye syndrome.

These are some of the circumstances in which tears give us information without the need to analyze them.

However, when we examine them in detail using all the technologies we have at our disposal, such as analyzes of proteins (proteomics) or the fats they have dissolved (lipidomics), they provide us with very important data about the functioning of our body.

They could even help us diagnose diseases early.

Our research group, which works in the visual system, has been researching tears for more than 20 years. Now we know many things about them thanks to the aforementioned techniques.

A valuable source of information

Although the fundamental component of tears is salt water, it contains many other dissolved substances; fundamentally, a fatty layer secreted at the base of the eyelashes by the so-called meibomian glands, which are inside the eyelid and open to the ocular surface.

This component mixes with the aqueous, excreted by the tear glands and, when blinking, is organized in such a way that the fat remains in the superficial area. This prevents the evaporation of the liquid part.

Likewise, the tear is in contact with the ocular surface thanks to molecules called mucins, which anchor the tear to the cornea (the transparent part of the eye). Precisely, the cornea is the most innervated part of the body – that is, where the most nerve endings reach -, so tears have almost direct contact with the nervous system.

And finally, the conjunctiva (white part of the eye) is very vascularized, it has an abundance of blood vessels. Therefore, if substances are released from the vascular system, we can also detect them in the tears, which bathe this part of the visual organ.

In summary, we could say that the tear is in contact with the vascular, nervous and glandular systems. A great source of information, but in a very small volume.

What is a biomarker and what is it for?

Biomarkers are biological molecules found in the blood or other fluids or tissues of the body, and their presence warns whether the body is functioning normally or not. Therefore, they are used to predict diseases.

The sooner we have information about the alteration of a marker, the sooner we can correct or cure what causes it.

We all understand that high blood glucose levels can be indicative of diabetes; those of cholesterol, of cardiovascular diseases; and those of PSA, of prostate problems.

This measurement, very common today, may be carried out in the future using less invasive methods than blood extraction, such as tear analysis.

Currently, one of the goals of biomedical research is to discover new biomarkers and find a way to detect them quickly and reliably.

We must keep in mind that predicting a disease does not depend on the presence or absence of these biological signs, but on the quantity in which they are found, as happens with the levels of glucose, cholesterol, PSA, etc.

Therefore, devices capable of detecting them must also reliably discriminate the quantity in which they occur.

Can we detect diseases through tears?

The answer is yes. More and more predictive biomarkers are being identified in them, with the capacity to determine the amount of that molecule present in the body.

At this time, tear analysis is being developed to provide what is called point of care (immediate diagnosis), devices that allow for simple and rapid analysis of some of these markers.

We have all seen the very rapid development of covid tests. In reality, that type of technology was already available; What was done during the pandemic was to adapt it to the specific marker of the virus envelope that was wanted to be detected.

In the case of tears, it is probably necessary to analyze more than one marker simultaneously and quantify their presence to ensure that we are dealing with true indicators of an illness.

You will also have to be very careful with the way the tear is collected and transferred to the analysis device.

Signs of Parkinson’s, coronary heart disease and breast cancer

Several articles have recently been published on the possibility of early prediction or diagnosis of diseases by analyzing the fluid secreted by the eyes.

Thus, our research group has just published an article where we have detected several candidate molecules to be Parkinson’s biomarkers. The hope is to explore others that allow us to identify more neurodegenerative ailments, such as Alzheimer’s, early.

Furthermore, the identification of a growth factor (G-CSF), from the blood, could help predict coronary artery disease, together with other typical markers of cardiovascular disorders and the combination of parameters such as age, sex or the thickness of the conjunctiva.

And in the oncological section, several recent publications indicate the possibility of analyzing tears to diagnose breast cancer.

An important step in this field has been the design of a type of contact lenses that would be placed over the iris (the colored part of the eye) of the person. They have microscopic wells where the liquid is deposited and which allow the diagnostic test to be carried out directly in the eye.

After being tested in the laboratory with patients’ tears, researchers have identified markers related to breast cancer, although they have not been tested directly in people.

The early diagnosis of diseases through biomarkers could mark the future of biomedicine, and tears can give us the keys to be able to predict ailments in a non-invasive way, but we still need more research.

*Elena Vecino Cordero is a professor of Cellular Biology at the University of the Basque Country. This article originally appeared on The Conversation and is published here under a Creative Commons license.

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