Dry Eyes – One of the most common eye diseases
The dry eye syndrome is one of the most common diseases in ophthalmology. It is currently estimated that about one in every six adults in Germany is affected. The result is an unstable tear film that potentially damages the ocular surface and is accompanied by inflammation. If left untreated, dry eyes cause symptoms like burning, itching and a foreign body sensation. Paradoxically, watery eyes can also occur. In addition, dry eyes can lead to considerable visual impairment as well as a reduced quality of life.
In dry eye patients the tear film is affected. The healthy tear film consists of three layers: a mucus-containing layer (mucin layer) that rests directly on the cornea, an aqueous phase lying on top of it and an outermost lipid (oil) layer.
The tear film’s functions are:
- Nourishing the cornea
- Lubricating and protecting the ocular surface from infection
- Maintaining a smooth refracting surface, thus ensuring optimal vision
- Formation of a lubricating layer to ensure a frictionless blink
The functions of the lipid layer are:
- Counteracting a premature evaporation of the underlying aqueous phase, thereby preventing dry eyes.
- Stabilisation of the aqueous phase of the tear film.
However, the lipid layer is dependent on the blink of the eye as well as the meibomian glands. The meibom glands are located within the upper and lower eyelid and their pores open onto the respective lid margin. These glands produce the oily secretion that makes up the lipid layer, and deposit it as small droplets on the upper and lower eyelid margin. During the blink of the eye, i.e. when the upper and lower eyelids meet, these droplets fuse to form a lipid film. When the eyes are reopened, the lipid film is evenly distributed on the tear film. Thus each blink of the eye serves the renewal of the lipid layer.
The causes of dry eyes are manifold
Dry eyes are caused by various factors. These include diseases (e.g. diabetes mellitus), eye surgery and chemotherapy. Furthermore, a hormonal imbalance plays a role, especially in pregnant or menopausal women and those on oral contraceptives (“the pill”). Drugs as well as our lifestyle (intensive screen activity, low humidity, air conditioning, smoking etc.) can also cause dry eyes.
Women with laptop: sebra – stock.adobe.com
Air conditioner: naypong – stock.adobe.com
Forms of dry eyes
In the classification of dry eyes, a distinction is made between two forms of dry eyes
- Hyposecretory form. This is due to a lack of volume caused by a reduced production of the aqueous phase.
- Hyperevaporative form also known as evaporative dry eyes. This form causes a premature evaporation of the tear film due to a lipid layer disorder.
Both forms lead to a reduction of the tear film and can coexist. Subjective dry eye complaints may be indicative in determining which form of dry eyes is present (Table1).
1 based on Kunert K. S. et. al. Trockenes Auge, Kaden Verlag, 2016: 53
Symptoms associated with the various forms of dry eyes1
(increased evaporation due to a lipid layer disorder)
|Irritated eye lid margin|
|Paradoxically watery eyes|
|Contact lens incompatibility|
|Problems during screen-based activity|
(reduced production of the aqueous phase)
|Foreign body sensation|
|Increased glare sensitivity|
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