Visual looming syndrome is a problem with visual perception that causes people to inaccurately think that a stationary object is moving towards them, and might poke their eyes.

It is a neurological and muscular state, where faulty eye coordination causes the brain to interpret incoming information as a visual looming event (i.e. feeling that an object is approaching and might hit the eye). Because this condition is muscular in nature, anything that causes eye cooperation to fail, such as being tired, under the of narcotics or alcohol, or even minor differences in eye pressure or eyesight (e.g. nearsightedness), may be the cause of an episode. The is usually a narrow or pointy object which is near enough to cause confusion in the eyes, or which is in front of an undetermined or busy background. Some peer to peer studies have indicated that certain conditions, such as nyctalopia or night blindness, may worsen the syndrome.

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.

There have been hypotheses about visual looming syndrome to be linked with several neural and gastroenterology diseases, such as celiac disease, epilepsy and migraines. Also physical differences between the eyes, such as astigmatism may be a factor. There have not been any empirical medical studies about the syndrome, though the consensus is all these may have affect on the muscular function of the eye, but most likely the visual looming syndrome is a separate symptom. There have been studies of a similar neurological situation. Gabbiani Peron has studied the "looming stimulus selectivity in a collision-detecting neuron". Beverley Regan has studied "Binocular and monocular stimuli for motion in depth". Moors P, Huygelier H, Wagemans J, de-Wit L, van Ee R; "Suppressed visual looming stimuli are not integrated with auditory looming signals"

Peer to peer studies have shown many common symptoms, such are "fear of pointy objects hitting the eye", "weird sensation behind the eyes", "difficulty in focusing on objects nearby, which are moving and are not operated by the observer, such as windscreen wipers or a pencil someone else is holding". In these studies visual looming syndrome is often referred as sharp edges eye syndrome (SEES).

In studies of the genetic predisposition of refractive error, there is a correlation between environmental factors and the risk of developing myopia. Myopia has been observed in individuals with visually intensive occupations. Reading has also been found to be a predictor of myopia in children. It has been reported that children with myopia spent significantly more time reading than non-myopic children who spent more time playing outdoors. Socioeconomic status and higher levels of education have also been reported to be a risk factor for myopia.

Between 2 and 5% of the population in western countries have amblyopia. In the U.K., 90% of visual health appointments in the child are concerning amblyopia.

Depending on the chosen criterion for diagnosis, between 1 and 4% of the children have amblyopia.

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%)

Amblyopia, also called lazy eye, is a disorder of sight due to the eye and brain not working well together. It results in decreased vision in an eye that otherwise typically appears normal. It is the most common cause of decreased vision in a single eye among children and younger adults.

The cause of amblyopia can be any condition that interferes with focusing during early childhood. This can occur from poor alignment of the eyes, an eye being irregularly shaped such that focusing is difficult, one eye being more nearsighted or farsighted than the other, or clouding of the lens of an eye. After the underlying cause is fixed, vision is not restored right away, as the mechanism also involves the brain. Amblyopia can be difficult to detect, so vision testing is recommended for all children around the ages of four to five.

Early detection improves treatment success. Eye glasses may be all the treatment needed for some children. If this is not sufficient, treatments which force the child to use the weaker eye are used. This is done by either using a patch or putting atropine in the stronger eye. Without treatment, amblyopia typically persists into adulthood. Evidence regarding treatments for adults is poor.

Amblyopia begins by the age of five. In adults, the disorder is estimated to affect 1–5% of the population. While treatment improves vision, it does not typically restore it to normal in the affected eye. Amblyopia was first described in the 1600s. The condition may make people ineligible to be pilots or police officers. The word amblyopia is from Greek ἀμβλύς "amblys" meaning "blunt" and ὤψ "ōps" meaning "sight".

The number of people globally with refractive errors that have not been corrected was estimated at 660 million (10 per 100 people) in 2013.

The number of people globally with significant refractive errors has been estimated at one to two billion. Rates vary between regions of the world with about 25% of Europeans and 80% of Asians affected. Near-sightedness is one of the most prevalent disorders of the eye. Rates among adults are between 15-49% while rates among children are between 1.2-42%. Far-sightedness more commonly affects young children, whose eyes have yet to grow to their full length, and the elderly, who have lost the ability to compensate with their accommodation system. Presbyopia affects most people over the age of 35, and nearly 100% of people by the ages of 55-65. Uncorrected refractive error is responsible for visual impairment and disability for many people worldwide. It is one of the most common causes of vision loss along with cataracts, macular degeneration, and vitamin A deficiency.

Six genes have been found to be associated with the condition. These genes include BANP-ZNF469, COL4A4, FOXO1, FNDC3B, IMMP2L and RXRA-COL5A1. Others likely also exist.

Synesthesia is found in at least 4.4% of the population, as a high estimate, which is equivalent to 1 in 23 people. This study had also concluded that one common form of synesthesia—grapheme-color synesthesia (colored letters and numbers) – is found in more than one percent of the population, and this latter prevalence of graphemes-color synesthesia has now been independently verified in a yet larger sample. Earlier estimates of the prevalence of synesthesia were based on "best-guess" estimations only ("e.g." 1 in 250,000) or had limitations in their methodologies because they required synesthetes to refer themselves for study ("e.g." 1 in 2000) and for this reason the authors of those studies had been moderate in their claims. Also, some individuals will not self-classify as synesthetes because they do not realize that their perceptions are different from those of everyone else.

The most common forms of synesthesia are those that trigger colors, and the most prevalent of all is day-color. Also relatively common is grapheme-color synesthesia. We can think of "prevalence" both in terms of how common is synesthesia (or different forms of synesthesia) within the population, or how common are different forms of synesthesia within synesthetes. So within synesthetes, forms of synesthesia that trigger color also appear to be the most common forms of synesthesia with a prevalence rate of 86% within synesthetes. In another study, music-color is also prevalent at 18–41%. Some of the rarest are reported to be auditory-tactile, mirror-touch, and lexical-gustatory.

There is research to suggest that the likelihood of having synesthesia is greater in people with autism.

The National Eye Institute reports keratoconus is the most common corneal dystrophy in the United States, affecting about one in 2,000 Americans, but some reports place the figure as high as one in 500. The inconsistency may be due to variations in diagnostic criteria, with some cases of severe astigmatism interpreted as those of keratoconus, and" vice versa". A long-term study found a mean incidence rate of 2.0 new cases per 100,000 population per year. Some studies have suggested a higher prevalence amongst females, or that people of South Asian ethnicity are 4.4 times as likely to suffer from keratoconus as Caucasians, and are also more likely to be affected with the condition earlier.

Keratoconus is normally bilateral (affecting both eyes) although the distortion is usually asymmetric and is rarely completely identical in both corneas. Unilateral cases tend to be uncommon, and may in fact be very rare if a very mild condition in the better eye is simply below the limit of clinical detection. It is common for keratoconus to be diagnosed first in one eye and not until later in the other. As the condition then progresses in both eyes, the vision in the earlier-diagnosed eye will often remain poorer than that in its fellow.

Far-sightedness, also known as hyperopia, is a condition of the eye in which light is focused behind, instead of on, the retina. This results in close objects appearing blurry, while far objects may appear normal. As the condition worsens, objects at all distances may be blurry. Other symptoms may include headaches and eye strain. People may also experience accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus.

The cause is an imperfection of the eyes. Often it occurs when the eyeball is too short, or the lens or cornea is misshapen. Risk factors include a family history of the condition, diabetes, certain medications, and tumors around the eye. It is a type of refractive error. Diagnosis is based on an eye exam.

Management can occur with eyeglasses, contact lenses, or surgery. Glasses are easiest while contact lenses can provide a wider field of vision. Surgery works by changing the shape of the cornea. Far-sightedness primarily affects young children, with rates of 8% at 6 years and 1% at 15 years. It then becomes more common again after the age of 40, affecting about half of people.

This may be present in conditions causing traction on the retina especially at the macula. This may occur in:

a) The vitreomacular traction syndrome; b) Proliferative diabetic retinopathy with vitreoretinal traction; c) Atypical cases of impending macular hole.

It is estimated that this much less common form of retinoschisis affects one in 5,000 to 25,000 individuals, primarily young males. "Schisis" is derived from the Greek word meaning "splitting", describing the splitting of the retinal layers from each other. However, "schisis" is a word fragment, and the term "retinoschisis" should be used, as should the term "iridoschisis" when describing splitting of the iris. If the retinoschisis involves the macula, then the high-resolution central area of vision used to view detail is lost, and this one form of macular disease. Although it might be described by some as a "degeneration", the term "macular degeneration" should be reserved for the specific disease "age-related macular degeneration".

Retinoschisis can be caused by an X-linked genetic defect, affecting the vision of men who inherit the disease from their unaffected carrier mothers. The genetic form of this disease usually starts during childhood and is called X-linked Juvenile Retinoschisis (XLRS) or Congenital Retinoschisis. Affected males are usually identified in grade school, but occasionally are identified as young infants.

Very few affected individuals go completely blind from retinoschisis, but some sufferers have very limited reading vision and are "legally blind". Visual acuity can be reduced to less than 20/200 in both eyes. Individuals affected by XLRS are at an increased risk for retinal detachment and eye hemorrhage, among other potential complications.

Retinoschisis causes acuity loss in the center of the visual field through the formation of tiny cysts in the retina, often forming a "spoke-wheel" pattern that can be very subtle. The cysts are usually only detectable by a trained clinician. In some cases vision cannot be improved by glasses, as the nerve tissue itself is damaged by these cysts.

The National Eye Institute (NEI) of the National Institutes of Health (NIH) is currently conducting clinical and genetic studies of X-Linked Juvenile Retinoschisis. This study is currently recruiting patients. A better understanding of why and how XLRS develops might lead to improved treatments. Males diagnosed with X-linked juvenile retinoschisis and females who are suspected carriers may be eligible to participate. In addition to giving a medical history and submitting medical records, participants submit a blood sample and the NEI will perform a genetic analysis. There is no cost to participate in this study.

As hyperopia is the result of the visual image being focused behind the retina, it has two main causes:

- Low converging power of eye lens because of weak action of ciliary muscles

- Abnormal shape of the cornea

Far-sightedness is often present from birth, but children have a very flexible eye lens, which helps to compensate. In rare instances hyperopia can be due to diabetes, and problems with the blood vessels in the retina.

The genetic mechanism of synesthesia has long been debated. Due to the prevalence of synesthesia among the first-degree relatives of synesthetes, there is evidence that synesthesia might have a genetic basis, however the monozygotic twins case studies indicate there is an epigenetic component. Synesthesia might also be a oligogenic condition, with Locus heterogeneity, multiple forms of inheritance (including Mendelian in some cases), and continuous variation in gene expression.

Bálint's syndrome has been found in patients with bilateral damage to the posterior parietal cortex. The primary cause of the damage and the syndrome can originate from multiple strokes, Alzheimer's disease, intracranial tumors, or brain injury. Progressive multifocal leukoencephalopathy and Creutzfeldt–Jakob disease have also been found to cause this kind of damage. This syndrome is caused by damage to the posterior superior watershed areas, also known as the parietal-occipital vascular border zone (Brodmann's areas 19 and 7).

Lack of awareness of the syndrome may lead to misdiagnosis such as blindness, psychosis, or dementia. Symptoms of Bálint's syndrome are most likely to be noticed first by therapists providing rehabilitation following brain lesions. However, due to the scarcity among practitioners of familiarity with the syndrome, the symptoms are often explained away incorrectly without being considered as a possibility and followed by medical confirmation of clinical and neuroradiological findings. Any severe disturbance of space representation, spontaneously appearing following bilateral parietal damage, strongly suggests the presence of Bálint's syndrome and should be investigated as such. One study reports that damage to the bilateral dorsal occipitoparietal regions appeared to be involved in Bálint's syndrome.

Of the published cases of palinopsia from posterior cortical lesions or seizures, 93% described hallucinatory palinopsia. Hallucinatory palinopsia may be caused by many types of posterior cortical lesions such as neoplasms, infarctions, hemorrhages, arteriovenous malformations, aneurysm, abscesses, and tuberculomas. Hallucinatory palinopsia from seizures may be secondary to a focal cortical lesion or may be secondary to a non-structural disturbance. Causes of seizures that are reported to cause palinopsia include metabolic disturbances (hyperglycemia, carnitine deficiency), ion channel disturbances, Creutzfeldt–Jakob disease, and seizures of unknown cause.

Hallucinatory palinopsia is a dysfunction of visual memory, caused by localized cortical hyperexcitability or hyperactivity in the posterior visual pathway. Post-geniculate cortical lesions or seizures may cause cortical deafferentation, focal cortical irritation, and epileptic discharges, the proposed mechanisms of hallucinatory palinopsia.

Alice in Wonderland syndrome is a disorienting neuropsychological condition that affects perception. People experience size distortion such as micropsia, macropsia, pelopsia, or teleopsia. Size distortion may occur of other sensory modalities.

It is often associated with migraines, brain tumors, and the use of psychoactive drugs. It can also be the initial symptom of the Epstein–Barr virus (see mononucleosis). AiWS can be caused by abnormal amounts of electrical activity causing abnormal blood flow in the parts of the brain that process visual perception and texture.

Anecdotal reports suggest that the symptoms are common in childhood, with many people growing out of them in their teens. It appears that AiWS is also a common experience at sleep onset, and has been known to commonly arise due to a lack of sleep.

Whatever the cause, the bodily related distortions can recur several times a day and may take some time to abate. Understandably, the person can become alarmed, frightened, and panic-stricken throughout the course of the hallucinations—maybe even hurt themselves or others around them. The symptoms of the syndrome themselves are not harmful and are likely to disappear with time.

Corneal abrasions are generally a result of trauma to the surface of the eye. Common causes include being poked by a finger, walking into a tree branch, and wearing old contact lenses. A foreign body in the eye may also cause a scratch if the eye is rubbed.

Injuries can also be incurred by "hard" or "soft" contact lenses that have been left in too long. Damage may result when the lenses are removed, rather than when the lens is still in contact with the eye. In addition, if the cornea becomes excessively dry, it may become more brittle and easily damaged by movement across the surface. Soft contact lens wear overnight has been extensively linked to gram negative keratitis (infection of the cornea) particularly by a bacterium known as "Pseudomonas aeruginosa" which forms in the eye's biofilm as a result of extended soft contact lens wear. When a corneal abrasion occurs either from the contact lens itself or another source, the injured cornea is much more susceptible to this type of bacterial infection than a non-contact lens user's would be. This is an optical emergency as it is sight (in some cases eye) threatening. Contact lens wearers who present with corneal abrasions should never be pressure patched because it has been shown through clinical studies that patching creates a warm, moist dark environment that can cause the cornea to become infected or cause an existing infection to be greatly accelerated on its destructive path.

Corneal abrasions are also a common and recurrent feature in people who suffer specific types of corneal dystrophy, such as lattice corneal dystrophy. Lattice dystrophy gets its name from an accumulation of amyloid deposits, or abnormal protein fibers, throughout the middle and anterior stroma. During an eye examination, the doctor sees these deposits in the stroma as clear, comma-shaped overlapping dots and branching filaments, creating a lattice effect. Over time, the lattice lines will grow opaque and involve more of the stroma. They will also gradually converge, giving the cornea a cloudiness that may also reduce vision. In some people, these abnormal protein fibers can accumulate under the cornea's outer layer—the epithelium. This can cause erosion of the epithelium. This condition is known as recurrent epithelial erosion. These erosions: (1) Alter the cornea's normal curvature, resulting in temporary vision problems; and (2) Expose the nerves that line the cornea, causing severe pain. Even the involuntary act of blinking can be painful.

Boehm Syndrome defines erosion events that occur only during periods of sleep.

Lattice corneal dystrophy type, also known as Biber-Haab-Dimmer dystrophy, is a rare form of corneal dystrophy. It has no systemic manifestations, unlike the other type of the dystrophy, Lattice corneal dystrophy type II. Lattice corneal dystrophy was first described by Swiss ophthalmologist Hugo Biber in 1890.

Lattice dystrophy gets its name from an accumulation of amyloid deposits, or abnormal protein fibers, throughout the middle and anterior stroma.

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

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