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.

Parry–Romberg syndrome appears to occur randomly and for unknown reasons. Prevalence is higher in females than males, with a ratio of roughly 3:2. The condition is observed on the left side of the face about as often as on the right side.

The causes of TSPK are currently not yet well known.

However, there seem to be indications that dysfunctioning of the Meibomian gland can cause the condition. Inflammation of the meibomian glands (also known as meibomitis, meibomian gland dysfunction, or posterior blepharitis) causes the glands to be obstructed by thick waxy secretions. Besides leading to dry eyes, the obstructions can be degraded by bacterial lipases, resulting in the formation of free fatty acids, which irritate the eyes and sometimes cause punctate keratopathy.

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.

The fact that some people affected with this disease have circulating antinuclear antibodies in their serum supports the theory that Parry–Romberg syndrome may be an autoimmune disease, specifically a variant of localized scleroderma. Several instances have been reported where more than one member of a family has been affected, prompting speculation of an autosomal dominant inheritance pattern. However, there has also been at least one report of monozygotic twins in which only one of the twins was affected, casting doubt on this theory. Various other theories about the cause and pathogenesis have been suggested, including alterations in the peripheral sympathetic nervous system (perhaps as a result of trauma or infection involving the cervical plexus or the sympathetic trunk), as the literature reported it following sympathectomy, disorders in migration of cranial neural crest cells, or chronic cell-mediated inflammatory process of the blood vessels. It is likely that the disease results from different mechanisms in different people, with all of these factors potentially being involved.

ARN is associated with people who have latent herpes viruses that have been reactivated. The most common causes of the disease have been linked to VSV, HSV-1, HSV-2, and CMV respectively.

ARN cases have been reported in patients who have AIDS, are immunocompromised and in children. The disease is not limited to a specific gender. Most cases have been reported in young adults though children and the elderly can be affected.

Specific genetic markers in Caucasians in the United States have shown elevated risk for disease development (HLA-DQw7 and Bw62, DR4) as well as HLA-Aw33, B44, and DRw6 in the Japanese population.

Thygeson's superficial punctate keratopathy (TSPK; also "Thygeson Superficial Punctate Keratitis") is a disease of the eyes. The causes of TSPK are not currently known, but details of the disease were first published in the Journal of the American Medical Association in 1950 by the renowned American Ophthalmologist, Phillips Thygeson (1903–2002) - after whom it is named.

Achromatopsia (ACHM), also known as total color blindness, is a medical syndrome that exhibits symptoms relating to at least five conditions. The term may refer to acquired conditions such as cerebral achromatopsia, also known as color agnosia, but it typically refers to an autosomal recessive congenital color vision condition, the inability to perceive color and to achieve satisfactory visual acuity at high light levels (typically exterior daylight). The syndrome is also present in an incomplete form which is more properly defined as dyschromatopsia. It is estimated to affect 1 in 40,000 live births worldwide.

There is some discussion as to whether achromats can see color or not. As illustrated in "The Island of the Colorblind" by Oliver Sacks, some achromats cannot see color, only black, white, and shades of grey. With five different genes currently known to cause similar symptoms, it may be that some do see marginal levels of color differentiation due to different gene characteristics. With such small sample sizes and low response rates, it is difficult to accurately diagnose the 'typical achromatic conditions'. If the light level during testing is optimized for them, they may achieve corrected visual acuity of 20/100 to 20/150 at lower light levels, regardless of the absence of color. One common trait is hemeralopia or blindness in full sun. In patients with achromatopsia, the cone system and fibres carrying color information remain intact. This indicates that the mechanism used to construct colors is defective.

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.

Sympathetic ophthalmia is rare, affecting 0.2% to 0.5% of non-surgical eye wounds, and less than 0.01% of surgical penetrating eye wounds. There are no gender or racial differences in incidence of SO.

Norrie disease is a genetic disorder that primarily affects the eye and almost always leads to blindness. In addition to the congenital ocular symptoms, some patients suffer from a progressive hearing loss starting mostly in their 2nd decade of life, and some may have learning difficulties.

Patients with Norrie disease may develop cataracts, leukocoria (a condition where the pupils appear white when light is shone on them), along with other developmental issues in the eye, such as shrinking of the globe and the wasting away of the iris. Around 30 to 50% of them will also have developmental delay/learning difficulties, psychotic-like features, incoordination of movements or behavioral abnormalities. Most patients are born with normal hearing; however, the onset of hearing loss is very common in early adolescence. About 15% of patients are estimated to develop all the features of the disease.

The disease affects almost only male infants, because the disease is inherited X-linked recessive. Only in very rare cases, females have been diagnosed with Norrie disease as well. The exact incidence number is unknown; only a few hundred cases have been reported. It is a very rare disorder that is not associated with any specific ethnic or racial groups.

MDM is most common on the Dalmatian island of Mljet (or "Meleda"), thought to be because of a founder effect. It is of autosomal recessive inheritance. It may be caused by a mutation on the "SLURP1" gene, located on chromosome 8.

Other causes of color blindness include brain or retinal damage caused by shaken baby syndrome, accidents and other trauma which produce swelling of the brain in the occipital lobe, and damage to the retina caused by exposure to ultraviolet light (10–300 nm). Damage often presents itself later on in life.

Color blindness may also present itself in the spectrum of degenerative diseases of the eye, such as age-related macular degeneration, and as part of the retinal damage caused by diabetes. Another factor that may affect color blindness includes a deficiency in Vitamin A.

Some subtle forms of colorblindness may be associated with chronic solvent-induced encephalopathy (CSE), caused by longtime exposure to solvent vapors.

Red–green color blindness can be caused by ethambutol, a drug used in the treatment of tuberculosis.

Norrie disease and other NDP related diseases are diagnosed with the combination of clinical findings and molecular genetic testing. Molecular genetic testing identifies the mutations that cause the disease in about 85% of affected males. Clinical diagnoses rely on ocular findings. Norrie disease is diagnosed when grayish-yellow fibrovascular masses are found behind the eye from birth through three months. Doctors also look for progression of the disease from three months through 8–10 years of age. Some of these progressions include cataracts, iris atrophy, shallowing of anterior chamber, and shrinking of the globe. By this point, people with the condition either have only light perception or no vision at all.

Molecular genetic testing is used for more than an initial diagnosis. It is used to confirm diagnostic testing, for carrier testing females, prenatal diagnosis, and preimplantation genetic diagnosis. There are three types of clinical molecular genetic testing. In approximately 85% of males, mis-sense and splice mutations of the NDP gene and partial or whole gene deletions are detected using sequence analysis. Deletion/duplication analysis can be used to detect the 15% of mutations that are submicroscopic deletions. This is also used when testing for carrier females. The last testing used is linkage analysis, which is used when the first two are unavailable. Linkage analysis is also recommended for those families who have more than one member affected by the disease.

On MRI the retinal dysplasia that occurs with the syndrome can be indistinguishable from persistent hyperplastic primary vitreous, or the dysplasia of trisomy 13 and Walker–Warburg syndrome.

Color blindness is typically inherited. It is most commonly inherited from mutations on the X chromosome but the mapping of the human genome has shown there are many causative mutations—mutations capable of causing color blindness originate from at least 19 different chromosomes and 56 different genes (as shown online at the Online Mendelian Inheritance in Man (OMIM)).

Two of the most common inherited forms of color blindness are protanomaly (and, more rarely, protanopia – the two together often known as "protans") and deuteranomaly (or, more rarely, deuteranopia – the two together often referred to as "deutans").

Both "protans" and "deutans" (of which the deutans are by far the most common) are known as "red–green color-blind" which is present in about 8 percent of human males and 0.6 percent of females of Northern European ancestry.

Some of the inherited diseases known to cause color blindness are:

- cone dystrophy

- cone-rod dystrophy

- achromatopsia (a.k.a. rod monochromatism, stationary cone dystrophy or cone dysfunction syndrome)

- blue cone monochromatism (a.k.a. blue cone monochromacy or X-linked achromatopsia)

- Leber's congenital amaurosis

- retinitis pigmentosa (initially affects rods but can later progress to cones and therefore color blindness).

Inherited color blindness can be congenital (from birth), or it can commence in childhood or adulthood. Depending on the mutation, it can be stationary, that is, remain the same throughout a person's lifetime, or progressive. As progressive phenotypes involve deterioration of the retina and other parts of the eye, certain forms of color blindness can progress to legal blindness, i.e., an acuity of 6/60 (20/200) or worse, and often leave a person with complete blindness.

Color blindness always pertains to the cone photoreceptors in retinas, as the cones are capable of detecting the color frequencies of light.

About 8 percent of males, and 0.6 percent of females, are red-green color blind in some way or another, whether it is one color, a color combination, or another mutation. The reason males are at a greater risk of inheriting an X linked mutation is that males only have one X chromosome (XY, with the Y chromosome carrying altogether different genes than the X chromosome), and females have two (XX); if a woman inherits a normal X chromosome in addition to the one that carries the mutation, she will not display the mutation. Men do not have a second X chromosome to override the chromosome that carries the mutation. If 8% of variants of a given gene are defective, the probability of a single copy being defective is 8%, but the probability that two copies are both defective is 0.08 × 0.08 = 0.0064, or just 0.64%.

Risk factors of progressive and severe thyroid-associated orbitopathy are:

- Age greater than 50 years

- Rapid onset of symptoms under 3 months

- Cigarette smoking

- Diabetes

- Severe or uncontrolled hyperthyroidism

- Presence of pretibial myxedema

- High cholesterol levels (hyperlipidemia)

- Peripheral vascular disease

Uveitis is usually an isolated illness, but can be associated with many other medical conditions.

In anterior uveitis, no associated condition or syndrome is found in approximately one-half of cases. However, anterior uveitis is often one of the syndromes associated with HLA-B27. Presence of this type of HLA allele has a relative risk of evolving this disease by approximately 15%.

The most common form of uveitis is acute anterior uveitis (AAU). It is most commonly associated with HLA-B27, which has important features: HLA-B27 AAU can be associated with ocular inflammation alone or in association with systemic disease. HLA-B27 AAU has characteristic clinical features including male preponderance, unilateral alternating acute onset, a non-granulomatous appearance, and frequent recurrences, whereas HLA-B27 negative AAU has an equivalent male to female onset, bilateral chronic course, and more frequent granulomatous appearance. Rheumatoid arthritis is not uncommon in Asian countries as a significant association of uveitis.

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.

In a study done published by the British Journal of Ophthalmology, the cases of ARN/BARN reported in 2001-2002 in the UK, Varicella Zoster Virus was the most common culprit for the disease and presented mostly in men than in women.

Researchers have also looked at two cases of ARN in patients who have been diagnosed with an immunodeficiency virus. The disease presented itself more so in the outer retina until it progressed far enough to then affect the inner retina. The patients were not so responsive to the antiviral agents given to them through an IV, acyclovir specifically. The cases progressed to retinal detachment. The patients tested positive for the herpes virus. Researchers are now wondering if this type of ARN is specific to those who have the immunodeficiency virus.

Acquired achromatopsia/dyschromatopsia is a condition associated with damage to the diencephalon (primarily the thalamus of the mid brain) or the cerebral cortex (the new brain), specifically the fourth visual association area, V4 which receives information from the parvocellular pathway involved in colour processing.

Thalamic achromatopsia/dyschromatopsia is caused by damage to the thalamus; it is most frequently caused by tumor growth since the thalamus is well protected from external damage.

Cerebral achromatopsia is a form of acquired color blindness that is caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina. It is most frequently caused by physical trauma, hemorrhage or tumor tissue growth.

Distortion of vision refers to straight lines not appearing straight, but instead bent, crooked, or wavy. Usually this is caused by distortion of the retina itself. This distortion can herald a loss of vision in macular degeneration, so anyone with distorted vision should seek medical attention by an ophthalmologist promptly. Other conditions leading to swelling of the retina can cause this distortion, such as macular edema and central serous chorioretinopathy.

An Amsler grid can be supplied by an ophthalmologist so that the vision can be monitored for distortion in people who may be predisposed to this problem.

Tunnel vision implies that the peripheral vision, or side vision, is lost, while the central vision remains. Thus, the vision is like looking through a tunnel, or through a paper towel roll. Some disorders that can cause this include:

Glaucoma - severe glaucoma can result in loss of nearly all of the peripheral vision, with a small island of central vision remaining. Sometimes even this island of vision can be lost as well.

Retinitis pigmentosa - This is usually a hereditary disorder which can be part of numerous syndromes. It is more common in males. The peripheral retina develops pigmentary deposits, and the peripheral vision gradually becomes worse and worse. The central vision can be affected eventually as well. People with this problem may have trouble getting around in the dark. Cataract can be a complication as well. There is no known treatment for this disorder, and supplements of Vitamin A have not been proven to help.

Punctate Inner Choroidopathy - This condition is where vessels gro (( material is missing ))

Stroke - a stroke involving both sides of the visual part of the brain may wipe out nearly all of the peripheral vision. Fortunately, this is a very rare occurrence

Phthisis bulbi is a shrunken, non-functional eye. It may result from severe eye disease, inflammation, injury, or it may represent a complication of eye surgery. Treatment options include insertion of a prosthesis, which may be preceded by enucleation of the eye.

Individuals affected by certain ED syndromes cannot perspire. Their sweat glands may function abnormally or may not have developed at all because of inactive proteins in the sweat glands. Without normal sweat production, the body cannot regulate temperature properly. Therefore, overheating is a common problem, especially during hot weather. Access to cool environments is important.