Episcleritis is a common disease, and its exact prevalence and incidence are unknown. It typically affects young adults, and may be more common in women.

Episcleritis is a benign, self-limiting condition, meaning patients recover without any treatment. Most cases of episcleritis resolve within 7–10 days. The nodular type is more aggressive and takes longer to resolve. Although rare, some cases may progress to scleritis. However, in general, episcleritis does not cause complications in the eye. Smoking tobacco delays the response to treatment in patients with episcleritis.

Scleritis is not a common disease, although the exact prevalence and incidence are unknown. It is somewhat more common in women, and is most common in the fourth to sixth decades of life.

Most of the time, scleritis is not caused by an infectious agent. Histopathological changes are that of a chronic granulomatous disorder, characterized by fibrinoid necrosis, infiltration by polymorphonuclear cells, lymphocytes, plasma cells and macrophages. The granuloma is surrounded by multinucleated epitheloid giant cells and new vessels, some of which may show evidence of vasculitis.

Of the many causes, conjunctivitis is the most common. Others include:

"Usually nonurgent"

- blepharitis - a usually chronic inflammation of the eyelids with scaling, sometimes resolving spontaneously

- subconjunctival hemorrhage - a sometimes dramatic, but usually harmless, bleeding underneath the conjunctiva most often from spontaneous rupture of the small, fragile blood vessels, commonly from a cough or sneeze

- inflamed pterygium - a benign, triangular, horizontal growth of the conjunctiva, arising from the inner side, at the level of contact of the upper and lower eyelids, associated with exposure to sunlight, low humidity and dust. It may be more common in occupations such as farming and welding.

- inflamed pinguecula - a yellow-white deposit close to the junction between the cornea and sclera, on the conjunctiva. It is most prevalent in tropical climates with much UV exposure. Although harmless, it can occasionally become inflamed.

- dry eye syndrome - caused by either decreased tear production or increased tear film evaporation which may lead to irritation and redness

- airborne contaminants or irritants

- tiredness

- drug use including cannabis

"Usually urgent"

- acute angle closure glaucoma - implies injury to the optic nerve with the potential for irreversible vision loss which may be permanent unless treated quickly, as a result of increased pressure within the eyeball. Not all forms of glaucoma are acute, and not all are associated with increased 'intra-ocular' pressure.

- injury

- keratitis - a potentially serious inflammation or injury to the cornea (window), often associated with significant pain, light intolerance, and deterioration in vision. Numerous causes include virus infection. Injury from contact lenses can lead to keratitis.

- iritis - together with the ciliary body and choroid, the iris makes up the uvea, part of the middle, pigmented, structures of the eye. Inflammation of this layer (uveitis) requires urgent control and is estimated to be responsible for 10% of blindness in the United States.

- scleritis - a serious inflammatory condition, often painful, that can result in permanent vision loss, and without an identifiable cause in half of those presenting with it. About 30-40% have an underlying systemic autoimmune condition.

- episcleritis - most often a mild, inflammatory disorder of the 'white' of the eye unassociated with eye complications in contrast to scleritis, and responding to topical medications such as anti-inflammatory drops.

- tick borne illnesses like Rocky Mountain spotted fever - the eye is not primarily involved, but the presence of conjunctivitis, along with fever and rash, may help with the diagnosis in appropriate circumstances.

Causes of photophobia relating directly to the eye itself include:

- Achromatopsia

- Aniridia

- Anticholinergic drugs may cause photophobia by paralyzing the iris sphincter muscle.

- Aphakia (absence of the lens of the eye)

- Blepharitis

- Buphthalmos (abnormally narrow angle between the cornea and iris)

- Cataracts

- Coloboma

- Cone dystrophy

- Congenital abnormalities of the eye

- Viral conjunctivitis ("pink eye")

- Corneal abrasion

- Corneal dystrophy

- Corneal ulcer

- Disruption of the corneal epithelium, such as that caused by a corneal foreign body or keratitis

- Ectopia lentis

- Endophthalmitis

- Eye trauma caused by disease, injury, or infection such as chalazion, episcleritis, glaucoma, keratoconus, or optic nerve hypoplasia

- Hydrophthalmos, or congenital glaucoma

- Iritis

- The drug isotretinoin (Accutane/Roaccutane) has been associated with photophobia

- Optic neuritis

- Pigment dispersion syndrome

- Pupillary dilation (naturally or chemically induced)

- Retinal detachment

- Scarring of the cornea or sclera

- Uveitis

Those with conjunctivitis may report mild irritation or scratchiness, but never extreme pain, which is an indicator of more serious disease such as keratitis, corneal ulceration, iridocyclitis, or acute glaucoma.

Neurological causes for photophobia include:

- Autism spectrum disorders

- Chiari malformation

- Occipital Neuralgia

- Dyslexia

- Encephalitis including Myalgic encephalomyelitis aka Chronic fatigue syndrome

- Meningitis

- Trigeminal disturbance causes central sensitization (hence, multiple other associated hypersensitivities. Causes can be bad bite, infected tooth, etc.

- Subarachnoid haemorrhage

- Tumor of the posterior cranial fossa

Depending on severity, therapies may range from topical or oral anti-inflammatories to irrigation and surgical repair.

DLK is predominantly associated with Lasik, as the creation of a flap creates a potential space for cells to accumulate. Individuals with atopic conditions with pre-existing allergic conjunctivitis, or ocular rosacea, are more prone to developing the condition after surgery. Some authors have reported that moderate to severe eye allergies and chronic allergic conjunctivitis are an absolute contraindication to the LASIK procedure. This is in distinction to findings of earlier studies. Keratitis can also occur after photorefractive keratectomy (PRK), although because it occurs in the setting of infection, it is distinct from the sterile infiltrates of DLK. DLK can also occur following myopic keratomileusis, in which a disc of corneal tissue is removed, shaped and sutured back into place, although this technique is more historical, having been replaced by Lasik and PRK.

Late congenital syphilitic oculopathy is a disease of the eye, a manifestation of late congenital syphilis. It can appear as:

- Interstitial keratitis – this commonly appears between ages 6 and 12. Symptoms include lacrimation and photophobia. Pathological vascularization of the cornea cause it to turn pink or salmon colored. 90% of cases affect both eyes.

- Episcleritis or scleritis – nodules appear in or overlying the sclera (white of eye)

- Iritis or iris papules – vascular infiltration of the iris causes rosy color change and yellow/red nodules.

- Chorioretinitis, papillitis, retinal vasculitis – retinal changes can resemble retinitis pigmentosa.

- Exudative retinal detachment

Congenital syphilis is categorized by the age of the child. Early congenital syphilis occurs in children under 2 years old, and late congenital syphilis in children at or greater than 2 years old. Manifestations of late congenital syphilis are similar to those of secondary syphilis and tertiary syphilis in adults.

Conjunctivitis is part of the triad of reactive arthritis, which is thought to be caused by autoimmune cross-reactivity following certain bacterial infections. Reactive arthritis is highly associated with HLA-B27. Conjunctivitis is associated with the autoimmune disease relapsing polychondritis.

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

DUSN may be caused by a helminthic infection with Toxocara canis, Baylisascaris procyonis, or Ancylostoma caninum. The characteristic lesions are believed to result from a single nematode migrating within the subretinal space. Although previously thought to be endemic in some areas, that belief was likely due to under awareness. DUSN has been diagnosed in patients in many countries and climates including America, Brazil, China and India.

Diffuse unilateral subacute neuroretinitis (DUSN) is a rare condition that occurs in otherwise healthy, often young patients and is due to the presence of a subretinal nematode.

A limbal nodule is any nodular lesion at the limbus (junction of the cornea and sclera) of the eye.

The differential diagnosis for a limbal nodule can include:

- Pinguecula

- Early Pterygium

- Foreign body / foreign body granuloma

- Phlycten, an inflamed nodule of lymphoid tissue

- Episcleritis

- Scleritis

- Granuloma

- Limbal dermoid, a kind of choristoma (NB: in other organs "dermoid" can refer to a teratoma)

- malignant melanoma

The exact cause of IOI is unknown, but infectious and immune-mediated mechanisms have been proposed. Several studies have described cases where onset of orbital pseudotumor was seen simultaneously or several weeks after upper respiratory infections. Another study by Wirostko et al. proposes that organisms resembling Mollicutes cause orbital inflammation by destroying the cytoplasmic organelles of parasitized cells.

Orbital pseudotumor has also been observed in association with Crohn’s disease, systemic lupus erythematosus, rheumatoid arthritis, diabetes mellitus, myasthenia gravis, and ankylosing spondylitis all of which strengthen the basis of IOI being an immune-mediated disease. Response to corticosteroid treatment and immunosuppressive agents also support this idea.

Trauma has also been seen to precede some cases of orbital pseudotumor. However, one study by Mottow-Lippe, Jakobiec, and Smith suggests that the release of circulating antigens caused by local vascular permeability triggers an inflammatory cascade in the affected tissues.

Although these mechanisms have been postulated as possible causes of IOI, their exact nature and relationships to the condition still remain unclear.

IOI or orbital pseudotumor is the second most common cause of exophthalmos following Grave’s orbitopathy and the third most common orbital disorder following thyroid orbitopathy and lymphoproliferative disease accounting for 5–17.6% of orbital disorders, There is no age, sex, or race predilection, but it is most frequently seen in middle-aged individuals. Pediatric cases account for about 17% of all cases of IOI.

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.

Palinopsia (Greek: "palin" for "again" and "opsia" for "seeing") is the persistent recurrence of a visual image after the stimulus has been removed. Palinopsia is not a diagnosis, it is a diverse group of pathological visual symptoms with a wide variety of causes. Visual perseveration is synonymous with palinopsia.

In 2014, Gersztenkorn and Lee comprehensively reviewed all cases of palinopsia in the literature and subdivided it into two clinically relevant groups: illusory palinopsia and hallucinatory palinopsia. Hallucinatory palinopsia, usually due to seizures or posterior cortical lesions, describes afterimages that are formed, long-lasting, and high resolution. Illusory palinopsia, usually due to migraines, head trauma, prescription drugs, or hallucinogen persisting perception disorder (HPPD), describes afterimages that are affected by ambient light and motion and are unformed, indistinct, or low resolution.

Posterior visual pathway cortical lesions (tumor, abscess, hemorrhage, infarction, arteriovenous malformation, cortical dysplasia, aneurysm) and various seizure causes (hyperglycemia, ion channel mutations, Creutzfeldt–Jakob disease, idiopathic seizures, etc.) cause focal cortical hyperactivity or hyperexcitability, resulting in inappropriate, persistent activation of a visual memory circuit.

Illusory palinopsia is a dysfunction of visual perception, resulting from diffuse, persistent alterations in neuronal excitability that affect physiological mechanisms of light or motion perception. Illusory palinopsia is caused by migraines, HPPD, prescription drugs, head trauma, or may be idiopathic. Trazodone, nefazodone, mirtazepine, topiramate, clomiphene, oral contraceptives, and risperidone have been reported to cause illusory palinopsia. A patient frequently has multiple types of illusory palinopsia, which represent dysfunctions in both light and motion perception. Light and motion are processed via different pathways, suggesting diffuse or global excitability alterations.

Neonatal toxic shock-like exanthematous disease is a cutaneous condition characterized by a generalized diffuse macular erythema or morbilliform eruption with confluence.

Diffuse proliferative nephritis (DPN) or glomerulonephritis (DPGN) is a type of glomerulonephritis that is the most serious form of renal lesions in SLE and is also the most common, occurring in 35% to 60% of patients. Most of the glomeruli show endothelial and mesangial proliferation affecting the entire glomerulus, leading to diffuse hypercellularity of the glomeruli, producing in some cases epithelial crescents that fill Bowman's space. When extensive, immune complexes create an overall thickening of the capillary wall, resembling rigid "wire loops" on routine light microscopy. Electron microscopy reveals electron-dense subendothelial immune complexes (between endothelium and basement membrane). Immune complexes can be visualized by staining with fluorescent antibodies directed against immunoglobulins or complement, resulting in a granular fluorescent staining pattern. In due course, glomerular injury gives rise to scarring (glomerulosclerosis). Most of these patients have hematuria with moderate to severe proteinuria, hypertension, and renal insufficiency.

Before modern treatments, the 2-year mortality was over 90% and average survival five months. Death usually resulted from uremia or respiratory failure.

With corticosteroids and cyclophosphamide, 5-year survival is over 80%. Long-term complications are common (86%), mainly chronic kidney failure, hearing loss and deafness.

Today, drug toxicity is managed more carefully and long-term remissions are possible. Some patients are able to lead relatively normal lives and remain in remission for 20+ years after treatment.