Blepharitis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sara Mehrsefat, M.D. [2]
Overview
Blepharitis is caused by an overgrowth of the bacteria that is normally found on the skin. It is usually due to seborrheic dermatitis or a bacterial infection. Both may occur at the same time. Allergies and lice that affects the eyelashes may also cause blepharitis, although these causes are less common. People who have blepharitis have too much oil being produced by the glands near the eyelid. This allows bacteria normally found on the skin to overgrow.
Pathophysiology
Anterior blepharitis
The exact pathogenesis of anterior blepharitis is unknown, but suspected to be multifactorial. In most blepharitis cases, the eyelids are colonized with bacteria, usually Staphylococcus aureus, Corynebacteria, or Staphylococcus epidermidis. Bacterial lipase changes meibomian gland secretions, increasing cholesterol concentration and creating an environment that promotes bacterial growth and proliferation. Bacterial toxins, mattering, and enzymes can also create inflammation. Allergic response to bacterial antigens, mostly staphylococcal antigens, may also cause blepharitis.
Posterior blepharitis
Posterior blepharitis is often associated with skin condition, such as rosacea. Rosacea is associated with plugging and hypertrophy of the sebaceous glands. Since the meibomian glands are modified sebaceous glands. Meibomian gland dysfunction is characterized by functional abnormalities of themeibomian glands and altered secretion of meibum. The altered meibomian gland secretions result in an impaired lipid layer of the tear film and instability of the tear film. The abnormal secretions also have a direct toxic effect on the ocular surface. Additionally, the altered lipid composition provides an environment that promotes bacterial growth. Demodex folliculorum small parasitic mites that live in hair follicles, sebaceous glands, and meibomian glands may caused or contributed to chronic blepharitis. This theory is still controversial. Demodex infestation has been implicated in rosacea.
Associated Conditions
Blepharitis often is associated with systemic diseases, such as:
Blepharitis also is associated with ocular diseases, such as:
Gross Pathology
On gross pathology, lid margin swelling, misdirection of lashes, loss of lashes, oily or greasy deposits on lid margins, crusting of anterior lid margin, lid margin hyperaemia, and conjunctival hyperaemia are characteristic findings of blepharitis.
Microscopic Pathology
On microscopic histopathological analysis, hyperkeratinization of the meibomian gland ductal epithelium, superficial stromal infiltrate, and neovascularization and dilation of existing blood vessels (chronic blepharitis) are characteristic findings of blepharitis. On microscopic evaluation, Demodex mites may reveal on epilated eyelashes of patient with chronic blepharitis.
Images
The following are gross images associated with blepharitis.
![Blepharitis [1]](/index.php/File:193px-Blepharitis.JPG)
![Infant with blepharitis [2]](/index.php/File:218px-Infant_with_blepharitis_on_the_right_side.jpg)
