Keratitis

Definition of Keratitis

In medicine the term keratitis identifies a generic inflammation of the cornea, the thin membrane that covers the iris and pupil of the eye. Although the most common keratitis have an infectious origin, the causes of corneal inflammation can also be found in traumas of a different nature.
Keratitis (especially infectious ones) represent an "ophthalmological urgency in all respects since, when not treated in time, they can cause serious damage to the eye" such as the fearful perforation of the cornea.

• Neglected keratitis can pose a real threat to vision.

To understand...

Before proceeding with the discussion, it is necessary to take a step back to briefly analyze the anatomy of the cornea.
The cornea is a transparent membrane devoid of blood vessels that constitutes - together with the sclera - the fibrous (external) tunic of the eye. Located in front of the iris, the cornea has a very important function because it transmits images to the retina (the most important membrane). of the eye from which a complex neurological process that allows vision originates).
The thin corneal membrane is made up of 5 layers:

1. Outermost layer: consisting of multilayered epithelium
2. Three underlying layers: composed of connective tissue
3. Last layer: composed of endothelium (epithelial cells in a single layer).

It is important to know the anatomy of the cornea because the severity of the symptoms related to a possible keratitis depends on the corneal layer affected by the inflammation.

Causes and classification

There are different types of keratitis, distinguished both on the basis of the corneal layer involved and the triggering cause:

• Superficial or ulcerative keratitis
• Interstitial keratitis
• Infectious keratitis
• Non-infectious or traumatic keratitis

SURFACE OR ULCERATIVE KERATITIS

It affects the most superficial layers of the cornea. The main culprits are phototraumas in general, such as in particular the prolonged exposure to UV radiation and the glow of the blowtorch. In addition to these causes, conjunctivitis due to Adenovirus and recurrent viral infections can also predispose to the risk of superficial keratitis.

INTERSTIZIAL KERATITIS

This form of keratitis involves the deeper layers of the cornea: it is a serious condition since, when left untreated, it can cause irreversible damage to the eye, including permanent blindness.
Most of the time, the cause lies in an "infection sustained by." Treponema pallidum, the same etiological (causal) agent as syphilis. Less often, interstitial keratitis recognizes other causes such as infectious agents (bacterial, viral, parasitic) or autoimmune disorders.

INFECTIOUS KERATITIS

Infectious inflammation of the cornea can be caused by:

• Bacterial infections, in particular caused by Staphylococcus aureus And Pseudomonas aeruginosa.
• Viral insults: Adenoviruses - which are also the major causative agents of common respiratory diseases and viral conjunctivitis - together with "Herpes simplex and" Herpes zoster, are the viruses most involved in viral infectious keratitis.
• Parasitic attacks: amoeba-borne corneal infection (such as Acanthamoeba) undoubtedly represents the most serious and dangerous form of infectious keratitis, typical of contact lens wearers.
• Fungal (fungal) infections: also some fungi belonging to the genus Fusarium And Candida they can cause serious damage to the cornea.

NON-INFECTIOUS OR TRAUMATIC KERATITIS

It is an "inflammation of the cornea induced by trauma such as surgery, penetration of objects into the eye (eg pens, pencils, etc.) and inappropriate use of contact lenses. Some autoimmune diseases - such as Sjögren's syndrome - can also cause similar damage to the cornea.

Risk factors

Together with the skin, the ocular surface represents one of the most important natural defenses against external insults, whether of an infectious or traumatic nature.
Metaphorically speaking, it is as if the corneal epithelium, the tear film and the eyelids were the protagonists of a match, teammates who work together to defend the eye from infections and injuries of all kinds. When, for some reason, this team is weakened, the opponent (eg bacteria, virus) has the upper hand because the players are no longer able to sustain the game (thus being unable to protect the eye effectively).

The vulnerability of the eye's defense system (or, in this specific case, the cornea) lies precisely in the inability of the tear film, corneal epithelium and eyelids to fight infections and protect the eye from traumatic events.

That said, it is well understood why defied patients and severely immunocompromised subjects (especially AIDS patients) are particularly exposed to the risk of infections, including those affecting the eye such as keratitis, blepharitis (inflammation of the eyelid) and scleritis (inflammation of the sclera).
In addition to the factors listed above, the eye's immune system can be weakened in several circumstances:

• Excessive corneal exposure due to eyelid malocclusions
• Loss of eyelid tone
• Alteration of the qualitative and quantitative production systems of tears
• Maldistribution of the eyelid film
• Indiscriminate use of corticosteroid drugs and topical / systemic antibiotics

Systemic rheumatic diseases, diabetes, collagen diseases and chronic alcoholism are also not underestimated risk factors for keratitis.

Keratitis: symptoms, treatment and prevention "