eye health

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 has an infectious origin, the causes of corneal inflammation can also be found in traumas of a different nature.

The keratites (especially the infectious ones) represent an optical eye urgency in all respects since, when not treated in time, they can cause serious damage to the eye such as the feared perforation of the cornea.

  • Neglected keratitis can pose a real threat to eyesight.

To understand...

Before proceeding with the treatment, it is necessary to take a step back to briefly analyze the corneal anatomy.

The cornea is a transparent and blood vessel-free membrane that constitutes - along 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 innermost membrane of the eye from which originates a complex neurological process that allows vision).

The thin corneal membrane consists of 5 layers:

  1. Outer 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 corneal anatomy because the severity of symptoms related to possible keratitis depends precisely on the corneal layer affected by the inflammation.

Causes and classification

There are different types of keratitis, distinct both on the basis of the corneal layer involved and on 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 the photo-trauma in general, such as specifically prolonged exposure to UV radiation and the glow of the oxyhydrogen flame. In addition to these causes, also Adenovirus conjunctivitis and recurrent viral infections can 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 often, the cause lies in an infection sustained by Treponema pallidum, the same causative (causal) agent of syphilis. Less often, interstitial keratitis recognizes other causes as infectious agents (bacterial, viral, parasitic) or autoimmune disorders.

INFECTIOUS KERATITIS

Infectious inflammation of the cornea can be caused by:

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

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 inadequate use of contact lenses. Even some autoimmune diseases - such as Sjögren's syndrome - can cause similar corneal damage.

Risk factors

Together with the skin, the ocular surface represents one of the most important natural defenses against external insults, whether they are infectious or traumatic.

Metaphorically speaking, it is as if the corneal epithelium, the tear film and the eyelids were the protagonist players of a game, teammates who work together to defend the eye from infections and injuries of any kind. When, for some reason, this team is weakened, the opponent (eg bacteria, viruses) has the upper hand because the players can no longer support the game (thus being unable to protect the eye effectively).

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

That said, it is easy to understand why the patients who are weakened and those who are severely immunocompromised (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 immune system of the eye can be weakened in several circumstances:

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

Systemic rheumatic diseases, diabetes, collagen pathologies and chronic alcoholism are also undervaluable risk factors for keratitis.

Keratitis: symptoms, treatment and prevention "