Blindness can occur in combination with such conditions as intellectual disability, autism spectrum disorders, cerebral palsy, hearing impairments, and epilepsy. Blindness in combination with hearing loss is known as deafblindness.

It has been estimated that over half of completely blind people have non-24-hour sleep–wake disorder, a condition in which a person's circadian rhythm, normally slightly longer than 24 hours, is not entrained (synchronized) to the light/dark cycle.

Cortical visual impairment (CVI) is a form of visual impairment that is caused by a brain problem rather than an eye problem. (The latter is sometimes termed "ocular visual impairment" when discussed in contrast to cortical visual impairment.) Some people have both CVI and a form of ocular visual impairment.

CVI is also sometimes known as cortical blindness, although most people with CVI are not totally blind. The term neurological visual impairment (NVI) covers both CVI and total cortical blindness. Delayed visual maturation, another form of NVI, is similar to CVI, except the child's visual difficulties resolve in a few months. Though the vision of a person with CVI may change, it rarely if ever becomes totally normal.

The major causes of CVI are as follows: asphyxia, hypoxia (a lack of sufficient oxygen in the body’s blood cells), or ischemia (not enough blood supply to the brain), all of which may occur during the birth process; developmental brain defects; head injury; hydrocephalus (when the cerebrospinal fluid does not circulate properly around the brain, and collects in the head, putting pressure on the brain); a stroke involving the occipital lobe; and infections of the central nervous system, such as meningitis and encephalitis.

Symptoms of CVI usually include several (but not necessarily all) of the following:

- The person with CVI exhibits variable vision. Visual ability can change from one day to the next but it can also fluctuate from minute to minute, especially when the person is tired. When undertaking critical activities, people with CVI should be prepared for their vision to fluctuate, by taking precautions such as always carrying a white cane even if they don't always use it to the full, or always having very large print available, just in case it's needed. (For example, consider the consequences of losing vision while giving a public speech). Managing fatigue can reduce fluctuations but does not eliminate them. Changes in environment, even minor, are mostly responsible for what appears to be variable vision.

- One eye may perform significantly worse than the other, and depth perception can be very limited (although not necessarily zero).

- The field of view may be severely limited. The best vision might be in the centre (like tunnel vision) but more often it is at some other point, and it is difficult to tell what the person is really looking at. Note that if the person also has a common ocular visual impairment such as nystagmus then this can also affect which part(s) of the visual field are best. (Sometimes there exists a certain gaze direction which minimises the nystagmus, called a "null point.")

- Even though the field of view may be very narrow indeed, it is often possible for the person to detect and track movement. Movement is handled by the 'V5' part of the visual cortex, which may have escaped the damage. Sometimes a moving object can be seen better than a stationary one; at other times the person can sense movement but cannot identify what is moving. (This can be annoying if the movement is prolonged, and to escape the annoyance the person may have to either gaze right at the movement or else obscure it.) Sometimes it is possible for a person with CVI to see things while moving their gaze around that they didn't detect when stationary. However, movement that is too fast can be hard to track; some people find that fast-moving objects "disappear." Materials with reflective properties, which can simulate movement, may be easier for a person with CVI to see. However, too many reflections can be confusing (see cognitive overload).

- Some objects may be easier to see than others. For example, the person may have difficulty recognising faces or facial expressions but have fewer problems with written materials. This is presumably due to the different way that the brain processes different things.

- Colour and contrast are important. The brain's colour processing is distributed in such a way that it is more difficult to damage, so people with CVI usually retain full perception of colour. This can be used to advantage by colour-coding objects that might be hard to identify otherwise. Sometimes yellow and red objects are easier to see, as long as this does not result in poor contrast between the object and the background.

- People with CVI strongly prefer a simplified view. When dealing with text, for example, the person might prefer to see only a small amount of it at once. People with CVI frequently hold text close to their eyes, both to make the text appear larger and to minimise the amount they must look at. This also ensures that important things such as letters are not completely hidden behind any scotomas (small defects in parts of the functioning visual field), and reduces the chances of getting lost in the text. However, the simplification of the view should not be done in such a way that it requires too rapid a movement to navigate around a large document, since too much motion can cause other problems (see above).

- In viewing an array of objects, people with CVI can more easily see them if they only have to look at one or two at a time. People with CVI also see familiar objects more easily than new ones. Placing objects against a plain background also makes them easier for the person with CVI to see.

- For the same reason (simplified view), the person may also dislike crowded rooms and other situations where their functioning is dependent on making sense of a lot of visual 'clutter'.

- Visual processing can take a lot of effort. Often the person has to make a conscious choice about how to divide mental effort between making sense of visual data and performing other tasks. For some people, maintaining eye contact is difficult, which can create problems in Western culture (for example, bonding can be difficult for some parents who have an infant with CVI, and lack of contact in an older child can cause others to regard him or her with suspicion).

- It can also be difficult for some people with CVI to look at an object and reach for it at the same time. Looking and reaching are sometimes accomplished as two separate acts: look, then look away and reach.

- People with CVI can sometimes benefit from a form of blindsight, which manifests itself as a kind of awareness of one's surroundings that cannot consciously be explained (for example, the person correctly guesses what they should do in order to avoid an obstacle but does not actually see that obstacle). However, this cannot be relied on to work all the time. In contrast, some people with CVI exhibit spatial difficulties and may have trouble moving about in their environment.

- Approximately one third of people with CVI have some photophobia. It can take longer than usual to adjust to large changes in light level, and flash photography can be painful. On the other hand, CVI can also in some cases cause a desire to gaze compulsively at light sources, including such things as candle flames and fluorescent overhead lights. The use of good task lighting (especially low-temperature lamps which can be placed at very close range) is often beneficial.

- Although people (with or without CVI) generally assume that they see things as they really are, in reality the brain may be doing a certain amount of guessing and "filling in", which is why people sometimes think they see things that turn out on closer inspection not to be what they seemed. This can occur more frequently when a person has CVI. Hence, a person with CVI can look at an optical illusion or abstract picture and perceive something that is significantly different from what a person without CVI will perceive.

The presence of CVI does not necessarily mean that the person's brain is damaged in any other way, but it can often be accompanied by other neurological problems, the most common being epilepsy.

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 most common cause of cortical blindness is ischemia (oxygen deprivation) to the occipital lobes caused by blockage to one or both of the posterior cerebral arteries. However, other conditions have also been known to cause acquired and transient cortical blindness, including:

- Bilateral lesions of the primary visual cortex

- Side effect of some anti-epilepsy drugs (AEDs)

- Creutzfeldt–Jakob disease, in association with a rapid onset of dementia

- Infection

- Head trauma to the occipital lobe of the brain

- Congenital abnormalities of the occipital lobe

- Eclampsia and, rarely, pre-eclampsia

- Hyperammonemia

The most common causes of congenital cortical blindness are:

- Traumatic brain injury (TBI) to the occipital lobe of the brain

- Congenital abnormalities of the occipital lobe

- Perinatal ischemia

- Encephalitis

- Meningitis

The prognosis of a patient with acquired cortical blindness depends largely on the original cause of the blindness. For instance, patients with bilateral occipital lesions have a much lower chance of recovering vision than patients who suffered a transient ischemic attack or women who experienced complications associated with eclampsia. In patients with acquired cortical blindness, a permanent complete loss of vision is rare. The development of cortical blindness into the milder cortical visual impairment is a more likely outcome. Furthermore, some patients regain vision completely, as is the case with transient cortical blindness associated with eclampsia and the side effects of certain anti-epilepsy drugs.

Recent research by Krystel R. Huxlin and others on the relearning of complex visual motion following V1 damage has offered potentially promising treatments for individuals with acquired cortical blindness. These treatments focus on retraining and retuning certain intact pathways of the visual cortex which are more or less preserved in individuals who sustained damage to V1. Huxlin and others found that specific training focused on utilizing the "blind field" of individuals who had sustained V1 damage improved the patients' ability to perceive simple and complex visual motion. This sort of 'relearning' therapy may provide a good workaround for patients with acquired cortical blindness in order to better make sense of the visual environment.

Vitamin A supplementation plays an important role, specifically vitamin A deficiency is a top causes of preventable childhood blindness. Though in measles cases, the administration of the vitamin to offset visual impairment has not been proven effective, as of yet.

Nystagmus is a relatively common clinical condition, affecting one in several thousand people. A survey conducted in Oxfordshire, United Kingdom found that by the age of two, one in every 670 children had manifested nystagmus. Authors of another study in the United Kingdom estimated an incidence of 24 in 10,000 (~0.240 %), noting an apparently higher rate amongst white Europeans than in individuals of Asian origin.

It may be acquired from:

- Diseases. Some of the diseases that present nystagmus as a pathological sign:

- Aniridia

- Toxic or metabolic reasons could be the result of the following:

- Central nervous system (CNS) disorders, such as with a cerebellar problem, the nystagmus can be in any direction "including" horizontal. Purely vertical nystagmus is usually central in origin, but it is also a frequent adverse effect of high phenytoin toxicity. Causes include:

There are many causes of blindness in children. Blindness may be due to genetic mutations, birth defects, premature birth, nutritional deficiencies, infections, injuries, and other causes. Severe retinopathy of prematurity (ROP), cataracts and refractive error are also causes.

The most frequently affected parts of the eyes are:

- Whole globe (36%)

- Cornea (36%)

- Lens (11%)

- Retina (6%)

- Optic nerve (5%)

- Uvea (2%)

Mobility can be difficult for people with homonymous hemianopsia. “Patients frequently complain of bumping into obstacles on the side of the field loss, thereby bruising their arms and legs.”

People with homonymous hemianopsia often experience discomfort in crowds. “A patient with this condition may be unaware of what he or she cannot see and frequently bumps into walls, trips over objects or walks into people on the side where the visual field is missing.”

A related phenomenon is Hemispatial neglect, the possible neglect of the right or left. The patient is not conscious of its existence. The right side of the face is not shaven, make up is applied to one side of the face only and only half of a plate of food is eaten. This, however, is not necessarily due to a sensory abnormality, and is therefore distinct from hemianopsia.

Hemianopsia or hemianopia is a visual field loss on the left or right side of the vertical midline. It can affect one eye but usually affects both eyes. Homonymous hemianopsia, or homonymous hemianopia, is hemianopic visual field loss on the same side of both eyes. Homonymous hemianopsia occurs because the right half of the brain has visual pathways for the left hemifield of both eyes, and the left half of the brain has visual pathways for the right hemifield of both eyes. When one of these pathways is damaged, the corresponding visual field is lost.

Oscillopsia is a visual disturbance in which objects in the visual field appear to oscillate. The severity of the effect may range from a mild blurring to rapid and periodic jumping. Oscillopsia is an incapacitating condition experienced by many patients with neurological disorders. It may be the result of ocular instability occurring after the oculomotor system is affected, no longer holding images steady on the retina. A change in the magnitude of the vestibulo-ocular reflex due to vestibular disease can also lead to oscillopsia during rapid head movements. Oscillopsia may also be caused by involuntary eye movements such as nystagmus, or impaired coordination in the visual cortex (especially due to toxins) and is one of the symptoms of superior canal dehiscence syndrome. Sufferers may experience dizziness and nausea. Oscillopsia can also be used as a quantitative test to document aminoglycoside toxicity. Permanent oscillopsia can arise from an impairment of the ocular system that serves to maintain ocular stability. Paroxysmal oscillopsia can be due to an abnormal hyperactivity in the peripheral ocular or vestibular system.

Binasal hemianopsia (or binasal hemianopia) is the medical description of a type of partial blindness where vision is missing in the inner half of both the right and left visual field. It is associated with certain lesions of the eye and of the central nervous system, such as congenital hydrocephalus.

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

In binasal hemianopsia, vision is missing in the inner (nasal or medial) half of both the right and left visual fields. Information from the nasal visual field falls on the temporal (lateral) retina. Those lateral retinal nerve fibers do not cross in the optic chiasm. Calcification of the internal carotid arteries can impinge the uncrossed, lateral retinal fibers leading to loss of vision in the nasal field.

Note: Clinical testing of visual fields (by confrontation) can produce a false positive result (particularly in inferior nasal quadrants).

Distorted vision is a symptom with several different possible causes.

Ocular stability is maintained by three different ocular motor systems

1. The fixation system and its deficit

2. The visuo-vestibular stabilizing systems and their deficits

3. The neural integrator and its deficit

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.

In general, approximately one-third of congenital cataracts are a component of a more extensive syndrome or disease (e.g., cataract resulting from congenital rubella syndrome), one-third occur as an isolated inherited trait, and one-third result from undetermined causes. Metabolic diseases tend to be more commonly associated with bilateral cataracts.

Dyslexic children require special instruction for word analysis and spelling from an early age. While there are fonts that may help people with dyslexia better understand writing, this might simply be due to the added spacing between words. The prognosis, generally speaking, is positive for individuals who are identified in childhood and receive support from friends and family.

The predominant cause of nutritional optic neuropathy is thought to be deficiency of B-complex vitamins, particularly thiamine (vitamin B), cyanocobalamin (vitamin B) and recently copper Deficiency of pyridoxine (vitamin B), niacin (vitamin B), riboflavin (vitamin B), and/or folic acid also seems to play a role. Those individuals who abuse alcohol and tobacco are at greater risk because they tend to be malnourished. Those with pernicious anemia are also at risk due to an impaired ability to absorb vitamin B from the intestinal tract.

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.

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 several causes of toxic optic neuropathy. Among these are: ingestion of methanol (wood alcohol), ethylene glycol (automotive antifreeze), disulfiram (used to treat chronic alcoholism), halogenated hydroquinolones (amebicidal medications), ethambutol and isoniazid (tuberculosis treatment), and antibiotics such as linezolid and chloramphenicol. Tobacco is also a major cause of toxic optic neuropathy.