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.

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

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.

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.

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.

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

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

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.

"Xanthelasmata" can be removed with a trichloroacetic acid peel, surgery, lasers or cryotherapy. Removal may cause scarring and pigment changes, but it is an uncommon side-effect of treatment.

Some specific reactive lymphadenopathies with a predominantly follicular pattern:

- Rheumatoid arthritis

- Sjogren syndrome

- IgG4-related disease (IgG4-related lymphadenopathy)

- Kimura disease

- Toxoplasmosis

- Syphilis

- Castleman disease

- HIV-associated lymphadenopathy

- Progressive transformation of germinal centers (PTGC)

EN is associated with a wide variety of conditions, including:

- Idiopathic

In about 30–50% of cases, the cause of EN is unknown.

- Infection

- Streptococcal infection which, in children, is by far the most common precipitant,

- Primary infection of Tuberculosis

- "Mycoplasma pneumoniae"

- "Histoplasma capsulatum"

- "Yersinia"

- Epstein-Barr virus

- "Coccidioides immitis" (Valley fever)

- Cat scratch disease

- Autoimmune disorders, including

- Inflammatory bowel disease (IBD)

- Behçet's disease

- Sarcoidosis

- Pregnancy

- Medications, including

- Sulfonamides

- Penicillins

- Oral contraceptives

- Bromides

- Hepatitis B vaccination

- Cancer, including

- Non-Hodgkins lymphoma (NHL)

- Carcinoid tumours

- Pancreatic cancer

EN may also be due to excessive antibody production in lepromatous leprosy leading to deposition of immune complexes.

There is an association with the HLA-B27 histocompatibility antigen, which is present in 65% of patients with erythema nodosum.

A useful mnemonic for causes is SORE SHINS (Streptococci, OCP, Rickettsia, Eponymous (Behçet), Sulfonamides, Hansen's Disease (Leprosy), IBD, NHL, Sarcoidosis.

Xanthelasma is a sharply demarcated yellowish deposit of fat underneath the skin, usually on or around the eyelids. While they are neither harmful nor painful, these minor growths may be disfiguring and can be removed.

A "xanthelasma" may instead be referred to as a "xanthoma" when becoming larger and nodular, assuming tumorous proportions. Still, "xanthelasma" is often classified simply as a subtype of "xanthoma".

Erythema nodosum is the most common form of panniculitis. It is most common in the ages of 20–30, and affects women 3–6 times more than men.

About 15 percent of patients with inflammatory bowel disease develop erythema nodosum.

Weber–Christian disease, also known as relapsing febrile nodular nonsuppurative panniculitis, is a cutaneous condition characterized by recurrent subcutaneous nodules that heal with depression of the overlying skin.

It is type of panniculitis.

It is a rare disease seen in females 30–60 years of age. It is a recurring inflammation of fatty layers of tissue present beneath the skin. Clinical course is characterised by exacerbations and remissions. Lesions are bilaterally symmetrical and are usually seen in the lower legs.

Follicular hyperplasia (or "reactive follicular hyperplasia" or "lymphoid nodular hyperplasia") is a type of lymphoid hyperplasia. It is caused by a stimulation of the B cell compartment. It is caused by an abnormal proliferation of secondary follicles and occurs principally in the cortex without broaching the lymph node capsule. The follicles are cytologically polymorphous, are often polarized, and vary in size and shape. Follicular hyperplasia is distinguished from follicular lymphoma in its polyclonality and lack of bcl-2 protein expression, whereas follicular lymphoma is monoclonal, and does express bcl-2).

Nontoxic nodular goiter is an enlarged thyroid without hyperthyroidism. It is often present for years before toxic nodular goiter occurs. In the United States it is the most common cause of a large thyroid affecting between 3 and 5% of the population.

Chondrodermatitis nodularis chronica helicis (also known as "Chondrodermatitis nodularis helicis") is a small, nodular, tender, chronic inflammatory lesion occurring on the helix of the ear, occurring most often in men.

Colloid nodules, also known as adenomatous nodules or colloid nodular goiter are benign, noncancerous enlargement of thyroid tissue. Although they may grow large, and there may be more than one, they are not malignant and they will not spread beyond the thyroid gland. Colloid nodules are the most common kind of thyroid nodule.

Inflammatory myofibroblastic tumour is a lesional pattern of inflammatory pseudotumour, as plasma cell granuloma. It is abbreviated IMT.

Until recently, nodular fasciitis have been considered a reactive process of uncertain cause. However, recent findings indicate that nodular fasciitis is a self-limited clonal neoplastic process (see below). Clinically, nodular fasciitis presents as a subcutaneous "growth" over a period of 3–6 weeks that eventually regresses. The lesion usually reaches a size of 2–3 cm. Larger lesions are unusual. Local recurrence has been described after simple surgical excision but it is rare.

PTGC is treated by excisional biopsy and follow-up. It may occasionally recur and in a small proportion of patients has been reported to subsequently develop Hodgkin lymphoma (usually nodular lymphocyte predominant Hodgkin lymphoma).