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.

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

According to the US National Institute for Occupational Safety and Health, computer vision syndrome affects about 90% of the people who spend three hours or more a day at a computer.

Another study in Malaysia was conducted on 795 university students aged between 18 and 25. The students experienced headaches along with eyestrain, with 89.9% of the students surveyed feeling any type of symptom of CVS. Americans spend an average of 8 hours a day in front of a screen, whether that be a television screen, phone/tablet, or a computer screen. This has increased the prevalence of individuals affected by computer vision syndrome.

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.

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%.

Entoptic images have a physical basis in the image cast upon the retina. Hence, they are different from optical illusions, which are perceptual effects that arise from interpretations of the image by the brain. Because entoptic images are caused by phenomena within the observer's own eye, they share one feature with optical illusions and hallucinations: the observer cannot share a direct and specific view of the phenomenon with others.

Helmholtz comments on phenomena which could be seen easily by some observers, but could not be seen at all by others. This variance is not surprising because the specific aspects of the eye that produce these images are unique to each individual. Because of the variation between individuals, and the inability for two observers to share a nearly identical stimulus, these phenomena are unlike most visual sensations. They are also unlike most optical illusions which are produced by viewing a common stimulus. Yet, there is enough commonality between the main entoptic phenomena that their physical origin is now well understood.

There is no good evidence for any preventive actions, since it appears this is a natural response to aging changes in the vitreous. Posterior vitreous detachment (PVD) has been estimated to occur in over 75 per cent of the population over age 65, that PVD is essentially a harmless condition (although with some disturbing symptoms), and that it does not normally threaten sight. However, since epiretinal membrane appears to be a protective response to PVD, where inflammation, exudative fluid, and scar tissue is formed, it is possible that NSAIDs may reduce the inflammation response. Usually there are flashing light experiences and the emergence of floaters in the eye that herald changes in the vitreous before the epiretinal membrane forms g

Dry eye is a major symptom that is targeted in the therapy of CVS. The use of over-the-counter artificial-tear solutions can reduce the effects of dry eye in CVS.

Asthenopic symptoms in the eye are responsible for much of the severity in CVS. Proper rest to the eye and its muscles is recommended to relieve the associated eye strain. Various catch-phrases have been used to spread awareness about giving rest to the eyes while working on computers. A routinely recommended approach is to consciously blink the eyes every now and then (this helps replenish the tear film) and to look out the window to a distant object or to the sky—doing so provides rest to the ciliary muscles. One of the catch phrases is the "20 20 20 rule": every 20 mins, focus the eyes on an object 20 feet (6 meters) away for 20 seconds. This basically gives a convenient distance and timeframe for a person to follow the advice from the optometrist and ophthalmologist. Otherwise, the patient is advised to close his/her eyes (which has a similar effect) for 20 seconds, at least every half-hour.

Decreased focusing capability is mitigated by wearing a small plus-powered (+1.00 to +1.50) over-the-counter pair of eyeglasses. Wearing these eyeglasses helps such patients regain their ability to focus on near objects. People who are engaged in other occupations—such as tailors engaged in embroidery—can experience similar symptoms and can be helped by these glasses.

A Pacific University research study of 36 participants found significant differences in irritation or burning of the eyes, tearing, or watery eyes, dry eyes, and tired eyes, that were each improved by filtering lenses versus placebo lenses, but in a follow-up study in 2008, the same team was not able to reproduce the results of the first study.

Competing research has shown blue light-filtering lenses decrease specific aspects of light emissions. Theoretical reductions in phototoxicity were 10.6% to 23.6%. Additionally, melatonin suppression was reduced by 5.8% to 15.0% and scotpic sensitivity by 2.4% to 9.6%. Over 70% of the participants in this testing were unable to detect these changes. The expansion of technology has led to more individuals utilizing computers and televisions which increase the overall exposure to blue light. This has opened up opportunities for companies such as Gunnar Optiks and Razer Inc. to create glasses focused on reducing the exposure to blue light.

Entoptic phenomena (from Greek ἐντός "within" and ὀπτικός "visual") are visual effects whose source is within the eye itself. (Occasionally, these are called entopic phenomena, which is probably a typographical mistake.)

In Helmholtz's words; "Under suitable conditions light falling on the eye may render visible certain objects within the eye itself. These perceptions are called "entoptical"."

Seeing rainbows around lights, especially at night, usually indicates swelling of the cornea. This may occur from a variety of causes which are discussed under Corneal Edema. Cataract can sometimes cause this also.

Colour vision is perceived mainly by the macula, which is the central vision portion of the retina. Thus any disorder affecting the macula may cause a disturbance in color vision. However, about 8% of males and 0.5% of females have some version of "colour blindness" from birth. Usually this is a genetically inherited trait, and is of the "red-green confusion" variety. The reds, browns, olives, and gold may be confused. Purple may be confused with blue, and pastel pinks, oranges, yellows, and greens look similar. Usually both eyes are affected equally.

There are many obscure macular retinal disorders that can lead to a loss of colour vision, and many of these syndromes are inherited as well. There may also be a problem with a generalized loss of vision with these problems as well. Other retinal problems can lead to a temporary disturbance of colour vision, such as Central serous chorioretinopathy, Macular Edema of different causes, and Macular Degeneration.

Certain types of cataract can gradually affect the colour vision, but this is usually not noticed until one cataract is removed. The cataract seems to filter out the colour blue, and everything seems more blue after cataract extraction. Optic nerve disorders such as Optic Neuritis can greatly affect colour vision, with colours seeming washed out during or after an episode.

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.

This ocular pathology was first described by Iwanoff in 1865, and it has been shown to occur in about 7% of the population. It can occur more frequently in the older population with postmortem studies showing it in 2% of those aged 50 years and 20% in those aged 75 years.

Heterochromia has also been observed in those with Duane syndrome.

Aphakia is the absence of the lens of the eye, due to surgical removal, a perforating wound or ulcer, or congenital anomaly. It causes a loss of accommodation, far sightedness (hyperopia), and a deep anterior chamber. Complications include detachment of the vitreous or retina, and glaucoma.

Babies are rarely born with aphakia. Occurrence most often results from surgery to remove congenital cataract (clouding of the eye's lens, which can block light from entering the eye and focusing clearly). Congenital cataracts usually develop as a result of infection of the fetus or genetic reasons. It is often difficult to identify the exact cause of these cataracts, especially if only one eye is affected.

People with aphakia have relatively small pupils and their pupils dilate to a lesser degree.

Without the focusing power of the lens, the eye becomes very farsighted. This can be corrected by wearing glasses, contact lenses, or by implant of an artificial lens. Artificial lenses are described as "pseudophakic." Also, since the lens is responsible for adjusting the focus of vision to different lengths, patients with aphakia have a total loss of accommodation.

Some individuals have said that they perceive ultraviolet light, invisible to those with a lens, as whitish blue or whitish-violet.

CSR is a fluid detachment of macula layers from their supporting tissue. This allows choroidal fluid to leak beneath the retina. The buildup of fluid seems to occur because of small breaks in the retinal pigment epithelium.

CSR is sometimes called "idiopathic CSR" which means that its cause is unknown. Nevertheless, stress appears to play an important role. An oft-cited but potentially inaccurate conclusion is that persons in stressful occupations, such as airplane pilots, have a higher incidence of CSR.

CSR has also been associated with cortisol and corticosteroids. Persons with CSR have higher levels of cortisol. Cortisol is a hormone secreted by the adrenal cortex which allows the body to deal with stress, which may explain the CSR-stress association. There is extensive evidence to the effect that corticosteroids (e.g. cortisone), commonly used to treat inflammations, allergies, skin conditions and even certain eye conditions, can trigger CSR, aggravate it and cause relapses. In a study documented by Indian Journal of Pharmacology, a young male was using Prednisolone and began to display subretinal fluid indicative of CSR. With the discontinuation of the steroid drop the subretinal fluid resolved and did not show any sign of recurrence. Thus indicating the steroid was the probable cause of the CSR. A study of 60 persons with Cushing's syndrome found CSR in 3 (5%). Cushing's syndrome is characterized by very high cortisol levels. Certain sympathomimetic drugs have also been associated with causing the disease.

Evidence has also implicated helicobacter pylori (see gastritis) as playing a role. It would appear that the presence of the bacteria is well correlated with visual acuity and other retinal findings following an attack.

Evidence also shows that sufferers of MPGN type II kidney disease can develop retinal abnormalities including CSR caused by deposits of the same material that originally damaged the glomerular basement membrane in the kidneys.

Dichromacy ("di" meaning "two" and "chroma" meaning "color") is the state of having two types of functioning color receptors, called cone cells, in the eyes. Organisms with dichromacy are called dichromats. Dichromats can match any color they see with a mixture of no more than two pure spectral lights. By comparison, trichromats require three pure spectral lights to match all colors that they can perceive, and tetrachromats require four.

Dichromacy in humans is a color vision defect in which one of the three basic color mechanisms is absent or not functioning. It is hereditary and sex-linked, predominantly affecting males. Dichromacy occurs when one of the cone pigments is missing and color is reduced to two dimensions.

The odd-eyed coloring is caused when either the epistatic (dominant) white gene (which masks any other color genes and turns a cat completely white) or the white spotting gene (which is the gene responsible for bicolor and tuxedo cats) prevents melanin (pigment) granules from reaching one eye during development, resulting in a cat with one blue eye and one green, yellow, or brown eye. The condition only rarely occurs in cats that lack both the dominant white and the white spotting gene.

An odd-eyed cat is a cat with one blue eye and one eye either green, yellow, or brown. This is a feline form of complete heterochromia, a condition that occurs in some other animals. The condition most commonly affects white-colored cats, but may be found in a cat of any color, provided that it possesses the white spotting gene.

The most common symptoms of cone dystrophy are vision loss (age of onset ranging from the late teens to the sixties), sensitivity to bright lights, and poor color vision. Therefore, patients see better at dusk. Visual acuity usually deteriorates gradually, but it can deteriorate rapidly to 20/200; later, in more severe cases, it drops to "counting fingers" vision. Color vision testing using color test plates (HRR series) reveals many errors on both red-green and blue-yellow plates.

Central serous retinopathy (CSR), also known as central serous chorioretinopathy (CSC or CSCR), is an eye disease which causes visual impairment, often temporary, usually in one eye. When the disorder is active it is characterized by leakage of fluid under the retina that has a propensity to accumulate under the central macula. This results in blurred or distorted vision (metamorphopsia). A blurred or gray spot in the central visual field is common when the retina is detached. Reduced visual acuity may persist after the fluid has disappeared.

The disease is considered of unknown cause. It mostly affects white males in the age group 20 to 50 and occasionally other groups. The condition is believed to be exacerbated by stress or corticosteroid use.

There are various kinds of color blindness:

- Protanopia is a severe form of red-green color blindness, in which there is impairment in perception of very long wavelengths, such as reds. To these individuals, reds are perceived as beige or grey and greens tend to look beige or grey like reds. It is also the most common type of dichromacy today. This problem occurs because patients do not have the red cone cells in the retina. Protanomaly is a less severe version.

- Deuteranopia consists of an impairment in perceiving medium wavelengths, such as greens. Deuteranomaly is a less severe form of deuteranopia. Those with deuteranomaly cannot see reds and greens like those without this condition; however, they can still distinguish them in most cases. It is very similar to protanopia. In this form, patients do not have green cone cells in the retina, which makes it hard to see the green color.

- A rarer form of color blindness is tritanopia, where there exists an inability to perceive short wavelengths, such as blues. Sufferers have trouble distinguishing between yellow and blue. They tend to confuse greens and blues, and yellow can appear pink. This is the rarest of all dichromacy, and occurs in around 1 in 100,000 people. Patients do not have the blue cone cells in the retina.

At least one type of autosomal dominant cone-rod dystrophy is caused by mutations in the guanylate cyclase 2D gene (GUCY2D) on chromosome 17.

The cause is unclear. The underlying mechanism is believed to involve excessive excitability of neurons within the cortex of the brain.

Specifically the right lingual gyrus and left cerebellar anterior lobe of the brain.

Persisting visual snow can feature as a leading addition to a migraine complication called persistent aura without infarction, commonly referred to as persistent migraine aura (PMA). In other clinical sub-forms of migraine headache may be absent and the migraine aura may not take the typical form of the zigzagged fortification spectrum, but manifests with a large variety of focal neurological symptoms.

The role of hallucinogens in of visual snow is not clear. Hallucinogen persisting perception disorder (HPPD), a condition caused by hallucinogenic drug use, is sometimes linked to visual snow, but both the connection of visual snow to HPPD and the cause and prevalence of HPPD is disputed. Most of the evidence for both is generally anecdotal, and subject to spotlight fallacy.