The disease incidence varies widely depending on the geographical location. The most extensive epidemiological survey on this subject has been carried out by Dharmasena et al. who analysed the number of neonates who developed neonatal conjunctivitis in England from 2000 to 2011. In addition to the incidence of this sight threatening infection they also investigated the time trends of the disease. According to them the incidence of Neonatal conjunctivitis (Ophthalmia Neonatorum) in England was 257 (95% confidence interval: 245 to 269) per 100,000 in 2011.

Prevention of trauma with vegetable / organic matter, particularly in agricultural workers while harvesting can reduce the incidence of fungal keratitis. Wearing of broad protective glasses with side shields is recommended for people at risk for such injuries.

Conjunctivitis may also be caused by allergens such as pollen, perfumes, cosmetics, smoke, dust mites, Balsam of Peru, and eye drops.

The most common causes of acute bacterial conjunctivitis are "Staphylococcus aureus", "Streptococcus pneumoniae", and "Haemophilus influenzae". Though very rare, hyperacute cases are usually caused by "Neisseria gonorrhoeae" or "N. meningitidis". Chronic cases of bacterial conjunctivitis are those lasting longer than 3 weeks, and are typically caused by "Staphylococcus aureus", "Moraxella lacunata", or gram-negative enteric flora.

This disease is quite common in the tropics and with large agrarian population. India has a high number of cases with fungal keratitis, but poor reporting system prevents accurate data collection. Florida in US regularly reports cases of fungal keratitis, with Aspergillus and Fusarium spp. as the most common causes.

Primary infection most commonly manifests as blepharoconjunctivitis i.e. infection of lids and conjunctiva that heals without scarring. Lid vesicles and conjunctivitis are seen in primary infection. Corneal involvement is rarely seen in primary infection.

Chemical irritants such as silver nitrate can cause chemical conjunctivitis, usually lasting 2–4 days. Thus, prophylaxis with a 1% silver nitrate solution is no longer in common use. In most countries neomycin and chloramphenicol eye drops are used instead. However, it is possible for newborns to suffer from neonatal conjunctivitis due to reactions with chemicals in these common eye drops. Additionally, a blocked tear duct may be another non-infectious cause of neonatal conjunctivitis.

Recurrent herpes of the eye is caused by reactivation of the virus in a latently infected sensory ganglion, transport of the virus down the nerve axon to sensory nerve endings, and subsequent infection of ocular surface.

The following classification of herpes simplex keratitis is important for understanding this disease:

The Appaloosa has a higher risk of developing ERU than other breeds; this predisposition has a genetic basis. Appaloosas which develop ERU are more likely than other breeds to have ERU in both eyes, and more likely to become blind in one or both eyes.

Several aetiologies are suggested, and any combination of these may be present in any given case.

- Vitamin deficiency (A, B or C)

- Viral infection

- Bacterial infection

- "Leptospira

- "Streptococcus

- "Brucella

- Parasitic infection

- Strongyle

- "Onchocerca cervicalis"

- Autoimmune disease

The disease has been suggested to be primarily autoimmune in nature, being a delayed hypersensitivity reaction to any of the above agents.

A study in Austria found over the course of the testing, a total of 154 cases of "Acanthamoeba" keratitis. The age of the positive tests ranged from 8 to 82 years old and 58% of the people were female. The data showed that 89% of the infected patients were contact lens wearers and 19% required a corneal transplant.

A study conducted in November of 2017, conveyed a correlation between blepharitis and early onset metabolic syndrome (MetS). To investigate the relationship between blepharitis and MetS, researchers used the Longitudinal Health Insurance Database in Taiwan. Results indicated that hyperlipidaemia and coronary artery disease were significantly correlated with the prior development of blepharitis. Therefore, blepharitis was shown to be significantly related to MetS and can serve as an early indication of the condition.

In another recent study, the presence of Demodex has been unveiled as a common cause of blepharitis. However, the pathogenesis of demodicosis is still unclear. In this study, researchers provide a diagnosis of the disease and propose diagnostic criteria of Demodex blepharitis.

Most household disinfectants will inactivate FHV-1. The virus can survive up to 18 hours in a damp environment, but less in a dry environment and only shortly as an aerosol.

Keratoconjunctivitis is inflammation ("-itis") of the cornea and conjunctiva.

When only the cornea is inflamed, it is called "keratitis"; when only the conjunctiva is inflamed, it is called "conjunctivitis".

There are several potential causes of the inflammation:

- Keratoconjunctivitis sicca is used when the inflammation is due to dryness. ("Sicca" means "dryness" in medical contexts.) It occurs with 20% of rheumatoid arthritis patients.

- The term "Vernal keratoconjunctivitis" (VKC) is used to refer to keratoconjunctivitis occurring in spring, and is usually considered to be due to allergens.

- "Atopic keratoconjunctivitis" is one manifestation of atopy.

- "Epidemic keratoconjunctivitis" is caused by an adenovirus infection.

- "Infectious bovine keratoconjunctivitis" (IBK) is a disease affecting cattle caused by the bacteria "Moraxella bovis".

- "Pink eye in sheep and goat" is another infectious keratoconjunctivitis of veterinary concern, mostly caused by "Chlamydophila pecorum"

- "Superior limbic keratoconjunctivitis" is thought to be caused by mechanical trauma.

- "Keratoconjunctivitis photoelectrica" (arc eye) means inflammation caused by photoelectric UV light. It is a type of ultraviolet keratitis. Such UV exposure can be caused by arc welding without wearing protective eye glass, or by high altitude exposure from sunlight reflected from snow ("snow blindness"). The inflammation will only appear after about 6 to 12 hours. It can be treated by rest, as the inflammation usually heals after 24–48 hours. Proper eye protection should be worn to prevent keratoconjunctivitis photoelectrica.

Some infections may scar the cornea to limit vision. Others may result in perforation of the cornea, (an infection inside the eye), or even loss of the eye. With proper medical attention, infections can usually be successfully treated without long-term visual loss.

There is a vaccine for FHV-1 available (ATCvet code: , plus various combination vaccines), but although it limits or weakens the severity of the disease and may reduce viral shedding, it does not prevent infection with FVR. Studies have shown a duration of immunity of this vaccine to be at least three years. The use of serology to demonstrate circulating antibodies to FHV-1 has been shown to have a positive predictive value for indicating protection from this disease.

The mechanism by which the bacteria causes symptoms of blepharitis is not fully understood and may include direct irritation of bacterial toxins and/or enhanced cell-mediated immunity to S. aureus.

Staphylococcal blepharitis is caused by an infection of the anterior portion of the eyelid by Staphylococcal bacteria. In a study of ocular flora, 46% to 51% of those diagnosed with staphylococcal blepharitis had cultures positive for Staphylococcus aureus in comparison to 8% of normal patients. Staphylococcal blepharitis may start in childhood and continue into adulthood. It is commonly recurrent and it requires special medical care. The prevalence of Staphylococcus aureus in the conjunctival sac and on the lid margin varies among countries, likely due to differences in climate and environment. Seborrheic blepharitis is characterized by less inflammation than Staphylococcal blepharitis; however, it causes more excess oil or greasy scaling. Meibomian Gland Dysfunction is a result of abnormalities of the meibomian glands and altered secretion meibum, which plays an imperative role in lagging the evaporation of tear films and smoothing of the tear film to produce an even optical surface. Posterior blepharitis is an inflammation of the eyelids, secondary to dysfunction of the meibomian glands. Like anterior blepharitis, it is a bilateral chronic condition and may be associated with skin rosacea. There is growing evidence that, in some cases, it is caused by Demodex mites.

Treatment depends on the cause of the keratitis. Infectious keratitis can progress rapidly, and generally requires urgent antibacterial, antifungal, or antiviral therapy to eliminate the pathogen. Antibacterial solutions include levofloxacin, gatifloxacin, moxifloxacin, ofloxacin. It is unclear if steroid eye drops are useful or not.

In addition, contact lens wearers are typically advised to discontinue contact lens wear and replace contaminated contact lenses and contact lens cases. (Contaminated lenses and cases should not be discarded as cultures from these can be used to identify the pathogen).

Aciclovir is the mainstay of treatment for HSV keratitis and steroids should be avoided at all costs in this condition. Application of steroids to a dendritic ulcer caused by HSV will result in rapid and significant worsening of the ulcer to form an 'amoeboid' or 'geographic' ulcer, so named because of the ulcer's map like shape.

Corneal ulcers are a common human eye disease. They are caused by trauma, particularly with vegetable matter, as well as chemical injury, contact lenses and infections. Other eye conditions can cause corneal ulcers, such as entropion, distichiasis, corneal dystrophy, and keratoconjunctivitis sicca (dry eye).

Many micro-organisms cause infective corneal ulcer. Among them are bacteria, fungi, viruses, protozoa, and chlamydia:

- Bacterial keratitis is caused by "Staphylococcus aureus", "Streptococcus viridans", "Escherichia coli", "Enterococci", "Pseudomonas", "Nocardia", "N. Gonorrhoea" and many other bacteria.

- Fungal keratitis causes deep and severe corneal ulcer. It is caused by "Aspergillus" sp., "Fusarium" sp., "Candida" sp., as also "Rhizopus", "Mucor", and other fungi. The typical feature of fungal keratitis is slow onset and gradual progression, where signs are much more than the symptoms. Small satellite lesions around the ulcer are a common feature of fungal keratitis and hypopyon is usually seen.

- Viral keratitis causes corneal ulceration. It is caused most commonly by Herpes simplex, Herpes zoster and Adenoviruses. Also it can be caused by coronaviruses & many other viruses. Herpes virus cause a dendritic ulcer, which can recur and relapse over the lifetime of an individual.

- Protozoa infection like "Acanthamoeba keratitis" is characterized by severe pain and is associated with contact lens users swimming in pools.

- "Chlamydia trachomatis" can also contribute to development of corneal ulcer.

Superficial ulcers involve a loss of part of the epithelium. Deep ulcers extend into or through the stroma and can result in severe scarring and corneal perforation. Descemetoceles occur when the ulcer extends through the stroma. This type of ulcer is especially dangerous and can rapidly result in corneal perforation, if not treated in time.

The location of the ulcer depends somewhat on the cause. Central ulcers are typically caused by trauma, dry eye, or exposure from facial nerve paralysis or exophthalmos. Entropion, severe dry eye and trichiasis (inturning of eyelashes) may cause ulceration of the peripheral cornea. Immune-mediated eye disease can cause ulcers at the border of the cornea and sclera. These include Rheumatoid arthritis, rosacea, systemic sclerosis which lead to a special type of corneal ulcer called Mooren's ulcer. It has a circumferential crater like depression of the cornea, just inside the limbus, usually with an overhanging edge.

According to the American Optometric Association, the following steps can be taken to prevent "Acanthamoeba" keratitis:

- Always wash and dry your hands before handling contact lenses, ordinary water should never come in contact with your lenses.

- Rub and rinse the surface of the contact lens before storing.

- Use only sterile products recommended by your optometrist to clean and disinfect your lenses. Saline solution and rewetting drops are not designed to disinfect lenses.

- Avoid using tap water to wash or store contact lenses.

- Contact lens solution must be discarded upon opening the case, and fresh solution used each time the lens is placed in the case.

- Replace lenses using your doctor’s prescribed schedule.

- Do not sleep in contact lenses unless prescribed by your doctor and never after swimming.

- Never swap lenses with someone else.

- Never put contact lenses in your mouth.

- See your optometrist regularly for contact lens evaluation.

The disease is classified as either gonococcal urethritis, caused by "Neisseria gonorrhoeae", or non-gonococcal urethritis (NGU), most commonly caused by "Chlamydia trachomatis". NGU, sometimes called nonspecific urethritis (NSU), has both infectious and noninfectious causes.

Urethritis is part of triad of Reiter's Syndrome.

Other causes include:

- Adenoviridae

- Uropathogenic "Escherichia coli" (UPEC)

- Herpes simplex

- Cytomegalovirus

- "Mycoplasma genitalium"

- Reactive arthritis

- "Trichomonas vaginalis"

- "Ureaplasma urealyticum"

- "Methicillin-resistant Staphylococcus aureus"

- "Group B streptococcus"

Herpes zoster ophthalmicus (HZO) and also known as ophthalmic zoster is a disease characterised by reactivation of dormant varicella zoster virus residing within the ophthalmic nerve (the first division of the trigeminal nerve). This condition is an important subtype of shingles, representing 15% of all cases.

Herpes zoster ophthalmicus is transmitted via direct contact or droplets. Varicella zoster virus is a DNA virus which produces acidophilic intranuclear inclusion bodies. The virus is neurotrophic in nature.

The frontal nerve is more commonly affected than the nasociliary nerve or lacrimal nerve.

Any potential ocular involvement should be assessed by an ophthalmologist as complications such as episcleritis and uveitis may occur.

Interstitial keratitis (IK) is corneal scarring due to chronic inflammation of the corneal stroma. Interstitial means space between cells i.e. corneal stroma which lies between the epithelium and the endothelium. Keratitis means corneal inflammation.

By far the most common cause of IK is syphilitic disease. However, there are two possible causes of the corneal inflammatory response: an infection and/or an immunological response, such as a hypersensitivity type reaction, or (rarely) Cogan syndrome. Infectious causes include syphilis (commonest), followed by other bacterial infections (TB, Leprosy and Lyme disease) and parasitic infections (Acanthamoeba, Onchocerciasis or river blindness, Leishmaniasis, Trypanosoma cruzi or "Chagas disease", Trypanosoma brucei or "African sleeping sickness" and microsporidia)