Many people of East Asian descent are prone to developing angle closure glaucoma due to shallower anterior chamber depths, with the majority of cases of glaucoma in this population consisting of some form of angle closure. Higher rates of glaucoma have also been reported for Inuit populations, compared to white populations, in Canada and Greenland.

No clear evidence indicates vitamin deficiencies cause glaucoma in humans. It follows, then, that oral vitamin supplementation is not a recommended treatment for glaucoma. Caffeine increases intraocular pressure in those with glaucoma, but does not appear to affect normal individuals.

Age-related macular degeneration accounts for more than 54% of all vision loss in the white population in the USA. An estimated 8 million Americans are affected with early age-related macular degeneration, of whom over 1 million will develop advanced age-related macular degeneration within the next 5 years. In the UK, age-related macular degeneration is the cause of blindness in almost 42% of those who go blind aged 65–74 years, almost two-thirds of those aged 75–84 years, and almost three-quarters of those aged 85 years or older.

Macular degeneration is more likely to be found in Caucasians than in people of African descent.

CNV causes may be congenital in nature, such as with Aniridia, or acquired. Frequently, inflammatory, infectious, degenerative, traumatic and iatrogenic (from contact lenses) diseases are responsible for acquired CNV.

Some major associated, acquired inflammatory conditions include graft rejection following keratoplasty, graft or host diseases of the new tissue, atopic conjunctivitis, rosacea, ocular pemphigoid, Lyell's syndrome, and Steven's Johnson syndrome.

Infections responsible for CNV range from bacterial (chlamydia, syphilis, pseduomonas), Viral (herpes simplex and herpes zoster viruses), Fungal (candida, asperigillus, fusarium), and parasistic (onchocerca volvolus).

Degenerative diseases such as pterygiums, and terrien's marginal degeneration may be responsible.

Traumas frequently seen with CNV include ulceration, alkali burns, and stem cell deficiency.

One of the most common causes of corneal neovascularization is iastrogenic pathology from contact lens wear. This is especially true of lenses made with older hydrogel materials such as HEMA (2-hydroxyethyl methacrylate) for both daily and extended wear. Such older hydrogel materials have a relatively low oxygen transmissibility so the cornea becomes starved of oxygen leading to the ingress of blood capillaries into the clear cornea to satisfy that oxygen demand. Older estimates have 128,000 to 470,000 cases of lens-induced CNV each year, but this may be decreasing due to the increasing popularity of daily disposable lenses.

The risk for CNV is elevated in certain instances for patients following penetrating keratoplasty without active inflammation or epithelial defects. CNV is more likely to occur in those with active blepharitis, those who receive sutured knots in their host stromas, and those with a large recipient area.

is a program launched by the International Agency for the Prevention of Blindness (IAPB) and is supported by the WHO in 1999 that has made controlling blindness in children a high priority.

Of these, cataract is responsible for >65%, or more than 22 million cases of blindness, and glaucoma is responsible for 6 million cases.

Cataracts: is the congenital and pediatric pathology that describes the greying or opacity of the crystalline lens, which is most commonly caused by intrauterine infections, metabolic disorders, and genetically transmitted syndromes. Cataracts are the leading cause of child and adult blindness that doubles in prevalence with every ten years after the age of 40. Consequently, today cataracts are more common among adults than in children. That is, people face higher chances of developing cataracts as they age. Nonetheless, cataracts tend to have a greater financial and emotional toll upon children as they must undergo expensive diagnosis, long term rehabilitation, and visual assistance. Also, according to the Saudi Journal for Health Sciences, sometimes patients experience irreversible amblyopia after pediatric cataract surgery because the cataracts prevented the normal maturation of vision prior to operation. Despite the great progress in treatment, cataracts remain a global problem in both economically developed and developing countries. At present, with the variant outcomes as well as the unequal access to cataract surgery, the best way to reduce the risk of developing cataracts is to avoid smoking and extensive exposure to sun light (i.e. UV-B rays).

The number of children who suffer from blindness worldwide is approximately 1.4 million. 75% of the world’s blind children live in Africa and Asia. A 2014 review indicated that an estimated of 238,500 children with bilateral blindness (rate 1.2/1,000) in the Eastern Mediterranean region.

Studies indicate drusen associated with AMD are similar in molecular composition to Beta-Amyloid (βA) plaques and deposits in other age-related diseases such as Alzheimer's disease and atherosclerosis. This suggests that similar pathways may be involved in the etiologies of AMD and other age-related diseases.

The most common causes of visual impairment globally in 2010 were:

1. Refractive error (42%)

2. cataract (33%)

3. glaucoma (2%)

4. age related macular degeneration (1%)

5. corneal opacification (1%)

6. diabetic retinopathy (1%)

7. childhood blindness

8. trachoma (1%)

9. undetermined (18%)

The most common causes of blindness in 2010 were:

1. cataracts (51%)

2. glaucoma (8%)

3. age related macular degeneration (5%)

4. corneal opacification (4%)

5. childhood blindness (4%)

6. refractive errors (3%)

7. trachoma (3%)

8. diabetic retinopathy (1%)

9. undetermined (21%)

About 90% of people who are visually impaired live in the developing world. Age-related macular degeneration, glaucoma, and diabetic retinopathy are the leading causes of blindness in the developed world.

Among working age adults who are newly blind in England and Wales the most common causes in 2010 were:

1. Hereditary retinal disorders (20.2%)

2. Diabetic retinopathy (14.4%)

3. Optic atrophy (14.1%)

4. Glaucoma (5.9%)

5. Congenital abnormalities (5.1%)

6. Disorders of the visual cortex (4.1%)

7. Cerebrovascular disease (3.2%)

8. Degeneration of the macula and posterior pole (3.0%)

9. Myopia (2.8%)

10. Corneal disorders (2.6%)

11. Malignant neoplasms of the brain and nervous system (1.5%)

12. Retinal detachment (1.4%)

All people with "diabetes mellitus" are at riskthose with Type I diabetes and those with Type II diabetes. The longer a person has diabetes, the higher their risk of developing some ocular problem. Between 40 and 45 percent of Americans diagnosed with diabetes have some stage of diabetic retinopathy. After 20 years of diabetes, nearly all patients with Type I diabetes and >60% of patients with Type II diabetes have some degree of retinopathy; however, these statistics were published in 2002 using data from four years earlier, limiting the usefulness of the research. The subjects would have been diagnosed with diabetes in the late 1970s, before modern fast acting insulin and home glucose testing.

Prior studies had also assumed a clear glycemic threshold between people at high and low risk of diabetic retinopathy.

However, it has been shown that the widely accepted WHO and American Diabetes Association diagnostic cutoff for diabetes of a fasting plasma glucose ≥ 7.0 mmol/l (126 mg/dl) does not accurately identify diabetic retinopathy among patients. The cohort study included a multi-ethnic, cross-sectional adult population sample in the US, as well as two cross-sectional adult populations in Australia. For the US-based component of the study, the sensitivity was 34.7% and specificity was 86.6%. For patients at similar risk to those in this study (15.8% had diabetic retinopathy), this leads to a positive predictive value of 32.7% and negative predictive value of 87.6%.

Published rates vary between trials, the proposed explanation being differences in study methods and reporting of prevalence rather than incidence values.

During pregnancy, diabetic retinopathy may also be a problem for women with diabetes.

It is recommended that all pregnant women with diabetes have dilated eye examinations each trimester to protect their vision.

People with Down's syndrome, who have extra chromosome 21 material, almost never acquire diabetic retinopathy. This protection appears to be due to the elevated levels of endostatin, an anti-angiogenic protein, derived from collagen XVIII. The collagen XVIII gene is located on chromosome 21.

Scientists are studying different populations and relationships to try to learn more about the disease. They have found associations with different groups but it is not yet clear what the underlying factors are and how they affect different peoples around the world.

- Glaucoma patients. While PEX and glaucoma are believed to be related, there are cases of persons with PEX without glaucoma, and persons with glaucoma without PEX. Generally, a person with PEX is considered as having a risk of developing glaucoma, and vice versa. One study suggested that the PEX was present in 12% of glaucoma patients. Another found that PEX was present in 6% of an "open-angle glaucoma" group. Pseudoexfoliation syndrome is considered to be the most common of identifiable causes of glaucoma. If PEX is diagnosed without glaucoma, there is a high risk of a patient subsequently developing glaucoma.

- Country and region. Prevalence of PEX varies by geography. In Europe, differing levels of PEX were found; 5% in England, 6% in Norway, 4% in Germany, 1% in Greece, and 6% in France. One contrary report suggested that levels of PEX were higher among Greek people. One study of a county in Minnesota found that the prevalence of PEX was 25.9 cases per 100,000 people. It is reportedly high in northern European countries such as Norway, Sweden and Finland, as well as among the Sami people of northern Europe, and high among Arabic populations, but relatively rare among African Americans and Eskimos. In southern Africa, prevalence was found to be 19% of patients in a glaucoma clinic attending to persons of the Bantu tribes.

- Race. It varies considerably according to race.

- Gender. It affects women more than men. One report was that women were three times more likely than men to develop PEX.

- Age. Older persons are more likely to develop PEX. And persons younger than 50 are highly unlikely to have PEX. A study in Norway found that the prevalence of PEX of persons aged 50–59 was 0.4% while it was 7.9% for persons aged 80–89 years. If a person is going to develop PEX, the average age in which this will happen is between 69 and 75 years, according to the Norwegian study. A second corroborating report suggested that it happens primarily to people 70 and older. While older people are more likely to develop PEX, it is not seen as a "normal" part of aging.

- Other diseases. Sometimes PEX is associated with the development of medical problems other than merely glaucoma. There are conflicting reports about whether PEX is associated with problems of the heart or brain; one study suggested no correlations while other studies found statistical links with Alzheimer's disease, senile dementia, cerebral atrophy, chronic cerebral ischemia, stroke, transient ischemic attacks, heart disease, and hearing loss.

Rubeosis iridis, also called neovascularization of the iris (NVI), is a medical condition of the iris of the eye in which new abnormal blood vessels (formed by neovascularization) are found on the surface of the iris.

CNV can occur rapidly in individuals with defects in Bruch's membrane, the innermost layer of the choroid. It is also associated with excessive amounts of Vascular endothelial growth factor (VEGF). As well as in wet macular degeneration, CNV can also occur frequently with the rare genetic disease pseudoxanthoma elasticum and rarely with the more common optic disc drusen. CNV has also been associated with extreme myopia or malignant myopic degeneration, where in choroidal neovascularization occurs primarily in the presence of cracks within the retinal (specifically) macular tissue known as lacquer cracks.

It is usually associated with disease processes in the retina, which involve the retina becoming starved of oxygen (ischaemic). The ischemic retina releases a variety of factors, the most important of which is VEGF. These factors stimulate the formation of new blood vessels (angiogenesis). Unfortunately, these new vessels do not have the same characteristics as the blood vessels originally formed in the eye. In addition, new blood vessels can form in areas that do not have them. Specifically, new blood vessels can be observed on the iris. In addition to the blood vessels in the iris, they can grow into the angle of the eye. These blood vessels eventually go through a process called fibrosis which closes the normal physiologic anatomy of the angle. The closing of the angle prevents fluid from leaving the eye resulting in an increase in intraocular pressure. This is called neovascular glaucoma.

There are many causes of blurred vision:

- Use of atropine or other anticholinergics

- Presbyopia—Difficulty focusing on objects that are close. Common in the elderly. (Accommodation tends to decrease with age.)

- Cataracts—Cloudiness over the eye's lens, causing poor night-time vision, halos around lights, and sensitivity to glare. Daytime vision is eventually affected. Common in the elderly.

- Glaucoma—Increased pressure in the eye, causing poor night vision, blind spots, and loss of vision to either side. A major cause of blindness. Glaucoma can happen gradually or suddenly—if sudden, it is a medical emergency.

- Diabetes—Poorly controlled blood sugar can lead to temporary swelling of the lens of the eye, resulting in blurred vision. While it resolves if blood sugar control is reestablished, it is believed repeated occurrences promote the formation of cataracts (which are not temporary).

- Diabetic retinopathy—This complication of diabetes can lead to bleeding into the retina. Another common cause of blindness.

- Hypervitaminosis A—Excess consumption of vitamin A can cause blurred vision.

- Macular degeneration—Loss of central vision, blurred vision (especially while reading), distorted vision (like seeing wavy lines), and colors appearing faded. The most common cause of blindness in people over age 60.

- Eye infection, inflammation, or injury.

- Sjögren's syndrome, a chronic autoimmune inflammatory disease that destroys moisture producing glands, including lacrimal (tear)

- Floaters—Tiny particles drifting across the eye. Although often brief and harmless, they may be a sign of retinal detachment.

- Retinal detachment—Symptoms include floaters, flashes of light across your visual field, or a sensation of a shade or curtain hanging on one side of your visual field.

- Optic neuritis—Inflammation of the optic nerve from infection or multiple sclerosis. You may have pain when you move your eye or touch it through the eyelid.

- Stroke or transient ischemic attack

- Brain tumor

- Toxocara—A parasitic roundworm that can cause blurred vision

- Bleeding into the eye

- Temporal arteritis—Inflammation of an artery in the brain that supplies blood to the optic nerve.

- Migraine headaches—Spots of light, halos, or zigzag patterns are common symptoms prior to the start of the headache. A retinal migraine is when you have only visual symptoms without a headache.

- Myopia—Blurred vision may be a systemic sign of local anaesthetic toxicity

- Reduced blinking—Lid closure that occurs too infrequently often leads to irregularities of the tear film due to prolonged evaporation, thus resulting in disruptions in visual perception.

- Carbon monoxide poisoning—Reduced oxygen delivery can effect many areas of the body including vision. Other symptoms caused by CO include vertigo, hallucination and sensitivity to light.

Choroidal neovascularization (CNV) is the creation of new blood vessels in the choroid layer of the eye. Choroidal neovascularization is a common cause of neovascular degenerative maculopathy (i.e. 'wet' macular degeneration) commonly exacerbated by extreme myopia, malignant myopic degeneration, or age-related developments.

The pressure within the eye is maintained by the balance between the fluid that enters the eye through the ciliary body and the fluid that exits the eye through the trabecular meshwork.

Ocular hypertension is the presence of elevated fluid pressure inside the eye (intraocular pressure), usually with no optic nerve damage or visual field loss.

For most individuals, the normal range of introcular pressure is between 10 mmHg and 21 mmHg. Elevated intraocular pressure is an important risk factor for glaucoma. The Ocular Hypertension Treatment Study, a large, multicentered, randomized clinical trial, determined that topical ocular hypotensive medication delays or prevents the onset of Primary Open-Angle Glaucoma. Accordingly, most individuals with consistently elevated intraocular pressures of greater than 21mmHg, particularly if they have other risk factors, are treated in an effort to prevent vision loss from glaucoma.

Optic disc drusen are found clinically in about 1% of the population but this increases to 3.4% in individuals with a family history of ODD. About two thirds to three quarters of clinical cases are bilateral. A necropsy study of 737 cases showed a 2.4% incidence with 2 out of 15 (13%) bilateral, perhaps indicating the insidious nature of many cases. An autosomal dominant inheritance pattern with incomplete penetrance and associated inherited dysplasia of the optic disc and its blood supply is suspected. Males and females are affected at equal rates. Caucasians are the most susceptible ethnic group. Certain conditions have been associated with disc drusen such as retinitis pigmentosa, angioid streaks, Usher syndrome, Noonan syndrome and Alagille syndrome. Optic disc drusen are not related to Bruch membrane drusen of the retina which have been associated with age-related macular degeneration.

The cause of pseudoexfoliation glaucoma is generally unknown.

PEX is generally believed to be a systemic disorder, possibly of the basement membrane of the eye. Researchers have noticed deposits of PEX material in various parts of the body, including in the skin, heart, lungs, liver, kidneys, and elsewhere. Nevertheless, what is puzzling is that PEX tends to happen in only one eye first, which scientists call "unilaterality", and in some cases, gradually afflicts the other eye, which is termed "bilaterality". According to this reasoning, if PEX were a systemic disorder, then both eyes should be affected at the same time, but they are not. There are contrasting reports about the extent and speed with which PEX moves from one eye to both eyes. According to one report, PEX develops in the second eye in 40% of cases. A contrasting report was that PEX can be found in both eyes in almost all situations if an electron microscope is used to examine the second eye, or if a biopsy of the conjunctiva was done, but that the extent of PEX is the second eye was much less than the first one. A different report suggested that two thirds of PEX patients had flakes in only one eye. In one long term study, patients with PEX in only one eye were studied, and it was found that over time, 13% progressed to having both eyes afflicted by PEX. Scientists believe that elevated levels of plasma homocysteine are a risk factor for cardiovascular disease, and two studies have found higher levels of plasma homocysteine in PEX patients, or elevated homocysteine concentrations in tear fluids produced by the eye.

There is speculation that PEX may be caused by oxidative damage and the presence of "free radicals", although the exact nature of how this might happen is still under study. Studies of PEX patients have found a decrease in the concentrations of ascorbic acid, increase in concentrations of malondialdehyde, and an increase in concentrations of 8-iso-prostaglandinF2a.

There is speculation that genetics may play a role in PEX. A predisposition to develop PEX later in life may be an inherited characteristic, according to one account. One report suggested the genetic component was "strong". One study performed in Iceland and Sweden has associated PEX with polymorphisms in gene LOXL1. A report suggested that a specific gene named LOXL1 which was a member of the family of enzymes which play a role in the linking of collagen and elastin inside cells. LOXL1 was responsible for "all the heritability" of PEX, according to one source. Two distinct mutations in which a single nucleotide was changed, or called a "single nucleotide polymorphism" or SNP, was discovered in Scandinavian populations and confirmed in other populations, and may be involved with the onset of PEX.

Researchers are investigating whether factors such as exposure to ultraviolet light, living in northern latitudes, or altitude influence the onset of PEX. One report suggested that climate was not a factor related to PEX. Another report suggested a possible link to sunlight as well as a possible autoimmune response, or possibly a virus.

According to recent research not a single theory is able to explain the cause fully. However current plausible theories include infection with "Toxoplasma gondii", Herpes simplex virus, Rubella, neurogenic causes, and autoimmune pathology.

In the United States, the incidence of primary congenital glaucoma is about one in 10,000 live births. Worldwide, the incidence ranges from a low of 1:22,000 in Northern Ireland to a high of 1:2,500 in Saudi Arabia and 1:1,250 in Romania. In about two-thirds of cases, it is bilateral. The distribution between males and females varies with geography. In North America and Europe it is more common in boys, whereas in Japan it is more common in girls.

- Congenital glaucoma

- Incidence: one in every 10000-15000 live births.

- Bilateral in up to 80% of cases.

- Most cases are sporadic (90%). However, in the remaining 10% there appears to be a strong familial component.

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.

Corneal neovascularization (CNV) is the in-growth of new blood vessels from the pericorneal plexus into avascular corneal tissue as a result of oxygen deprivation. Maintaining avascularity of the corneal stroma is an important aspect of corneal pathophysiology as it is required for corneal transparency and optimal vision. A decrease in corneal transparency causes visual acuity deterioration. Corneal tissue is avascular in nature and the presence of vascularization, which can be deep or superficial, is always pathologically related.

Corneal neovascularization is a sight-threatening condition that can be caused by inflammation related to infection, chemical injury, autoimmune conditions, post-corneal transplantation, and traumatic conditions among other ocular pathologies. Common causes of CNV within the cornea include trachoma, corneal ulcers, phylctenular keratoconjunctivitis, rosacea keratitis, interstitial keratitis, sclerosing keratitis, chemical burns, and wearing contact lenses for over-extended periods of time. Superficial presentations of CNV are usually associated with contact lens wear, while deep presentations may be caused by chronic inflammatory and anterior segment ocular diseases.

Corneal neovascularization is becoming increasingly common worldwide with an estimated incidence rate of 1.4 million cases per year, according to a 1998 study by the Massachusetts Eye and Ear Infirmary. The same study found that the tissue from twenty percent of corneas examined during corneal transplantations had some degree of neovascularization, negatively impacting the prognosis for individuals undergoing keratoplasty procedures.

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