INFECTIVE CONJUCTIVITIS
inflammation of the conjunctiva caused by microorganisms is the commonest variety.
This is in spite of the fact that the conjunctiva has been provided with natural
protective mechanisms in the form of :
* Low temperature due to exposure to air,
* Physical protection by lids,
* Flushing action of tears,
* Antibacterial activity of lysozymes
* Humoral protection by the tear immunoglobulins.
BACTERIAL CONJUNCTIVITIS
There has occurred a relative decrease in the incidence of bacterial conjunctivitis in general and those caused by gonococcus and corynebacterium diphtheriae in particular.
However, in developing countries it still continues to be the commonest type of conjunctivitis. It can occur as sporadic cases and as epidemics.
Outbreaks of bacterial conjunctivitis epidemics are quite frequent during monsoon season.
Etiology
A. Predisposing factors
especially epidemic forms, are flies, poor hygienic conditions, hot dry climate, poor sanitation and dirty habits.
These factors help the infection to establish, as the disease is highly contagious.
B. Causative organisms.
Range of organisms in the following approximate order of frequency :
1. Staphylococcus aureus is the most common cause of bacterial conjunctivitis and blepharoconjunctivitis.
2. Staphylococcus epidermidis is an innocuous flora of lid and conjunctiva. It can also produce blepharoconjunctivitis.
3. Streptococcus pneumoniae (pneumococcus) produces acute conjunctivitis usually associated with petechial subconjunctival haemorrhages. The disease has a self-limiting course of 9-10 days.
4. Streptococcus pyogenes (haemolyticus) is virulent and usually produces pseudomembranous conjunctivitis.
5. Haemophilus influenzae (aegyptius, Koch- Weeks bacillus). It classically causes epidemics of mucopurulent conjunctivitis, known as ‘red-eye’ especially in semitropical countries.
7. Pseudomonas pyocyanea is a virulent organism. It readily invades the cornea.
8. Neisseria gonorrhoeae typically produces acute purulent conjunctivitis in adults and ophthalmia neonatorum in new born. It is capable of invading intact corneal epithelium.
9. Neisseria meningitidis (meningococcus) may produce mucopurulent conjunctivitis.
10. Corynebacterium diphtheriae causes acute membranous conjunctivitis. Such infections are rare now-a-days.
C. Mode of infection.
Conjunctiva may get infected from three sources,
1. exogenous, local
2. surrounding structures
3.endogenous,
1. Exogenous infections
(i) directly through close contact, as air-borne infections or as water-borne infections;
(ii) through vector transmission (e.g., flies)
(iii) through material transfer such as infected fingers of doctors, nurses, common towels, handkerchiefs, and infected tonometers.
2. Local spread
may occur from neighbouring structures such as infected lacrimal sac, lids, and nasopharynx.
In addition to these, a change in the character of relatively innocuous organisms present in the conjunctival sac itself may cause infections.
3. Endogenous infections
may occur very rarely through blood e.g., gonococcal and meningococcal infections.
Pathology
Pathological changes of bacterial conjunctivitis consist of :
1. Vascular response.
It is characterised by congestion and increased permeability of the conjunctival vessels associated with proliferation of capillaries.
2. Cellular response.
It is in the form of exudation of polymorphonuclear cells and other inflammatory cells into the substantia propria of conjunctiva as well as in the conjunctival sac.
3. Conjunctival tissue repsonse.
Conjunctiva becomes oedematous. The superficial epithelial cells degenerate, become loose and even desquamate.
There occurs proliferation of basal layers of conjunctival epithelium and increase in the number of mucin secreting goblet cells.
4. Conjunctival discharge.
It consists of tears, mucus, inflammatory cells, desquamated epithelial cells, fibrin and bacteria.
If the inflammation is very severe, diapedesis of red blood cells may occur and discharge may become blood stained.
Severity of pathological changes varies depending upon the severity of inflammation and the causative organism.
The changes are thus more marked in purulent conjunctivitis than mucopurulent conjunctivitis.
OPTOMETRY-SHARP VISION
Optometrist