L'ocular allergy and dry eye syndrome (DED) are two very common eye diseases that have a significant negative impact on quality of life. Epidemiological studies report a prevalence in the general population of 10%-30% and 5%-50% for ocular allergies and DED, respectively. However, while ocular allergies seem to most commonly affect children and adolescents, the prevalence of DED tends to increase with age. Although both conditions are different clinical entities, they affect the ocular surface and may manifest with similar symptoms.
The coexistence of these two diseases was hypothesised more than 20 years ago and has been confirmed by extensive cross-sectional studies. Several studies have also attempted to investigate the relationship between ocular allergy and DED, suggesting that the former may predispose to the latter. The TFOS DEWS II (Tear Film and Ocular Surface Society), in fact, recently included allergic conjunctivitis among the probable risk factors for DED.
Ocular allergy and dry eye syndrome in adults and children
Ocular allergy is a group of disorders of the surface of the eye, usually classified into two groups:
- common allergic conjunctivitis, including seasonal and perennial forms;
- kerato-conjunctivitis, including spring and atopic forms.
The former are mild to moderate allergic diseases, often associated with rhinitis, while the latter are severe chronic inflammatory diseases of the ocular surface, with a more complex pathogenesis. Ocular itching, swelling and tearing are the most frequent symptoms complained of by patients suffering from all forms of ocular allergy, while photophobia and pain are typical of the more severe forms, due to frequent corneal involvement.
DED, on the other hand, is defined as a multifactorial ocular surface disease characterised by a loss of tear film homeostasis, accompanied by ocular symptoms in which tear film instability, hyperosmolarity, inflammation, ocular surface damage and neurosensory abnormalities all play an aetiological role.
Eye allergies and DED, what correlation?
I recent advances in understanding the pathogenetic mechanisms of DED have made it possible to identify several pathways of interaction between these 2 conditions, providing important elements for considering ocular allergies as a risk factor for DED:
- An increasing number of studies report the association between ocular allergy and tear film instability, even more so in allergic kerato-conjunctivitis;
- ocular allergies also have an effect on the osmolarity of the tear film, mediated by an increase in evaporation;
- Inflammation is a common condition in the pathogenesis of DED and ocular allergies, be it the common forms or kerato-conjunctivitis;
- The damage to the cells of the ocular surface is well known in DED and is due to the presence of dryness and the inflammatory state, which also characterise allergic kerato-conjunctivitis, but not the milder forms of ocular allergies;
- the crucial role of neurosensory abnormalities in DED has recently been highlighted and similar abnormalities have also been observed in allergic kerato-conjunctivitis.
DED and ocular allergies: how to intervene
Dry eye syndrome can be caused by a variety of factors, including the use of topical or systemic medications, contact lens wear and surgical and non-surgical ophthalmic procedures. Several studies have shown that systemic antihistamines are a risk factor for DED, which could represent a further correlation between dry eye syndrome and allergies.
In the case of ocular allergies, treatment involves, first of all, identifying and avoiding the agents that cause the allergic manifestation. In addition, tear substitutes may be used. In particular, hyaluronic acid-based ophthalmic solutions can be used to lubricate and moisturise the ocular surface and help restore comfort, which can also be of great benefit for DED. L'hyaluronic acidIn fact, it is a molecule that has been used for years as an ocular lubricant due to its special characteristics: it has a structure that gives it a special ability to combine with water and excellent viscoelasticity. The property of hyaluronic acid to bind large amounts of water and its ability to mimic the behaviour of mucins help to maintain the stability of the tear film and ensure optimal ocular protection and lubrication. In addition to these special properties, hyaluronic acid also plays an important biological role in tissue repair processes, promoting cell motility, adhesion and proliferation.
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