Periorbital hyperpigmentation is characterized by dark circles around the eyes, which are common, often familial, and frequently found in individuals with dark pigmentation or Mediterranean ancestry. Atopic dermatitis patients may also exhibit periorbital pigmentation (allergic shiners) due to lower eyelid venous stasis, and treatment is ineffective.

Studies have recorded an incidence of about 3–5 cases per 1,000 newborn babies.

The lack of nutrients in the diet, or the lack of a balanced diet, can contribute to the discoloration of the area under the eyes. It is believed that iron deficiency can cause dark circles as well. Iron deficiency is the most common type of anemia and this condition is a sign that not enough oxygen is getting to the body tissues.

The skin can also become more pale during pregnancy and menstruation (due to lack of iron), allowing the underlying veins under the eyes to become more visible.

Any medications that cause blood vessels to dilate can cause circles under the eyes to darken. Because the skin under the eyes is very delicate, any increased blood flow shows through the skin.

Port-wine stains were shown to be caused by a somatic activating c.548G→A mutation in the GNAQ gene. An association with RASA1 has also been described.

Congenital heterochromia is usually inherited as an autosomal dominant trait.

This condition can also occur in ruminants suffering from a vitamin B (thiamine) deficiency due to thiamine-related cerebrocortical necrosis (CCN).

In segmental heterochromia, sometimes referred to as sectoral heterochromia, areas of the same iris contains two completely different colors.

Segmental heterochromia is rare in humans; it is estimated that only about 1% of the population have it.

Optic pits occur equally between men and women. They are seen in roughly 1 in 10,000 eyes, and approximately 85% of optic pits are found to be unilateral (i.e. in only one eye of any affected individual). About 70% are found on the temporal side (or lateral one-half) of the optic disc. Another 20% are found centrally, while the remaining pits are located either superiorly (in the upper one-half), inferiorly (in the lower one-half), or nasally (in the medial one-half towards the nose).

Those experiencing amaurosis are usually advised to consult a physician immediately as any form of vision loss, even if temporary, is a symptom that may indicate the presence of a serious ocular or systemic problem.

Anisocoria is a common condition, defined by a difference of 0.4 mm or more between the sizes of the pupils of the eyes.

Anisocoria has various causes:

- Physiological anisocoria: About 20% of normal people have a slight difference in pupil size which is known as physiological anisocoria. In this condition, the difference between pupils is usually less than 1 mm.

- Horner's syndrome

- Mechanical anisocoria: Occasionally previous trauma, eye surgery, or inflammation (uveitis, angle closure glaucoma) can lead to adhesions between the iris and the lens.

- Adie tonic pupil: Tonic pupil is usually an isolated benign entity, presenting in young women. It may be associated with loss of deep tendon reflex (Adie's syndrome). Tonic pupil is characterized by delayed dilation of iris especially after near stimulus, segmental iris constriction, and sensitivity of pupil to a weak solution of pilocarpine.

- Oculomotor nerve palsy: Ischemia, intracranial aneurysm, demyelinating diseases (e.g., multiple sclerosis), head trauma, and brain tumors are the most common causes of oculomotor nerve palsy in adults. In ischemic lesions of the oculomotor nerve, pupillary function is usually spared whereas in compressive lesions the pupil is involved.

- Pharmacological agents with anticholinergic or sympathomimetic properties will cause anisocoria, particularly if instilled in one eye. Some examples of pharmacological agents which may affect the pupils include pilocarpine, cocaine, tropicamide, MDMA, dextromethorphan, and ergolines. Alkaloids present in plants of the genera "Brugmansia" and "Datura", such as scopolamine, may also induce anisocoria.

- Migraines

Despite its name, the "presumed" relationship of POHS to "Histoplasma capsulatum" is controversial. The fungus has rarely been isolated from cases with POHS, the condition has also been found in locations where histoplasmosis is rare, and there appears to be a relationship with tobacco smoking.

Keratoconjunctivitis sicca is relatively common within the United States, especially so in older patients. Specifically, the persons most likely to be affected by dry eyes are those aged 40 or older. 10-20% of adults experience Keratoconjunctivitis sicca. Approximately 1 to 4 million adults (age 65-84) in the USA are effected.

While persons with autoimmune diseases have a high likelihood of having dry eyes, most persons with dry eyes do not have an autoimmune disease. Instances of Sjögren syndrome and keratoconjunctivitis sicca associated with it are present much more commonly in women, with a ratio of 9:1. In addition, milder forms of keratoconjunctivitis sicca also are more common in women. This is partly because hormonal changes, such as those that occur in pregnancy, menstruation, and menopause, can decrease tear production.

In areas of the world where malnutrition is common, vitamin A deficiency is a common cause. This is rare in the United States.

Racial predilections do not exist for this disease.

Reticular pigmented anomaly of the flexures (also known as "dark dot disease", and "Dowling–Degos' disease") is a fibrous anomaly of the flexures or bending parts of the axillae, neck and inframammary/sternal areas. It is an autosomal-dominant pigmentary disorder that may appear in adolescence or adulthood. This condition is due to mutations in structural/desmosomal proteins found within stratified squamous epithelium.

Dark dot disease is associated with "KRT5".

It is suggested that the early hominin evolved in East Africa around 3 million years ago. The dramatic phenotypic change from primate to early hominin is hypothesized to have involved the extreme loss of body hair – except for areas most exposed to UV radiation, such as the head – to allow for more efficient thermoregulation in the early hunter-gatherers. The skin that would have been exposed upon general body hair loss in these early hominins would have most likely been non-pigmented, reflecting the pale skin underlying the hair of our chimpanzee relatives. A positive advantage would have been conferred to early hominids inhabiting the African continent that were capable of producing darker skin – those who first expressed the eumelanin-producing MC1R allele – which protected them from harmful epithelium-damaging ultraviolet rays. Over time, the advantage conferred to those with darker skin may have led to the prevalence of darker skin on the continent. The positive advantage, however, would have had to be strong enough so as to produce a significantly higher reproductive fitness in those who produced more melanin. The cause of a selective pressure strong enough to cause this shift is an area of much debate. Some hypotheses include the existence of significantly lower reproductive fitness in people with less melanin due to lethal skin cancer, lethal kidney disease due to excess vitamin D formation in the skin of people with less melanin, or simply natural selection due to mate preference and sexual selection.

When comparing the prevalence of albinism in Africa to its prevalence in other parts of the world, such as Europe and the United States, the potential evolutionary effects of skin cancer as a selective force due to its effect on these populations may not be insignificant. The prevalence of albinism in some ethnic groups in sub-Saharan Africa is around 1 in 5,000, while in Europe and the US it is 1 in 20,000. It would follow, then, that there would be stronger selective forces acting on albino populations in Africa than on albino populations in Europe and the US. Rates as high as 1 in 1,000 have been reported for some populations in Zimbabwe and other parts of Southern Africa. In two separate studies in Nigeria, people with albinism were found to be of reproductively significant age more often than not. One study found that 89% of people diagnosed with albinism are between 0 and 30 years of age, while the other found that 77% of albinos were under the age of 20.

Albinism affects people of all ethnic backgrounds; its frequency worldwide is estimated to be approximately one in 17,000. Prevalence of the different forms of albinism varies considerably by population, and is highest overall in people of sub-Saharan African descent.

Certain ethnic groups and populations in isolated areas exhibit heightened susceptibility to albinism, presumably due to genetic factors. These include notably the Native American Kuna, Zuni and Hopi nations (respectively of Panama, New Mexico and Arizona); Japan, in which one particular form of albinism is unusually common; and Ukerewe Island, the population of which shows a very high incidence of albinism.

Keratoconjunctivitis sicca is uncommon in cats. Most cases seem to be caused by chronic conjunctivitis, especially secondary to feline herpesvirus. Diagnosis, symptoms, and treatment are similar to those for dogs.

Complications are the exception rather than the rule from simple corneal abrasions. It is important that any foreign body be identified and removed, especially if containing iron as rusting will occur.

Occasionally the healed epithelium may be poorly adherent to the underlying basement membrane in which case it may detach at intervals giving rise to recurrent corneal erosions.

Anisocoria is a condition characterized by an unequal size of the eyes' pupils. Affecting 20% of the population, it can be an entirely harmless condition or a symptom of more serious medical problems.

Any intense exposure to UV light can lead to photokeratitis. Common causes include welders who have failed to use adequate eye protection such as an appropriate welding helmet or welding goggles. This is termed "arc eye", while photokeratitis caused by exposure to sunlight reflected from ice and snow, particularly at elevation, is commonly called "snow blindness". It can also occur due to using tanning beds without proper eyewear. Natural sources include bright sunlight reflected from snow or ice or, less commonly, from sea or sand. Fresh snow reflects about 80% of the UV radiation compared to a dry, sandy beach (15%) or sea foam (25%). This is especially a problem in polar regions and at high altitudes, as with every thousand feet (approximately 305 meters) of elevation (above sea level), the intensity of UV rays increases by four percent.

As Kayser–Fleischer rings do not cause any symptoms, it is common for them to be identified during investigations for other medical conditions. In certain situations, they are actively sought; in that case, the early stages may be detected by slit lamp examination before they become visible to the naked eye.

Livedo racemosa is a cutaneous condition characterized by a skin discoloration appearing as irregular-broken circles.

Presumed ocular histoplasmosis syndrome (POHS) is a syndrome affecting the eye, which is characterized by peripheral atrophic chorioretinal scars, atrophy or scarring adjacent to the optic disc and maculopathy.

The loss of vision in POHS is caused by choroidal neovascularization.

No particular risk factors have been conclusively identified; however, there have been a few reports that demonstrate an autosomal dominant pattern of inheritance in some families. Therefore, a family history of optic pits may be a possible risk factor.

A meta-analysis found evidence that does not support the use of patching.