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.

Many people with amblyopia, especially those who only have a mild form, are not aware they have the condition until tested at older ages, since the vision in their stronger eye is normal. People typically have poor stereo vision, however, since it requires both eyes. Those with amblyopia further may have, on the affected eye, poor pattern recognition, poor visual acuity, and low sensitivity to contrast and motion.

Amblyopia is characterized by several functional abnormalities in spatial vision, including reductions in visual acuity, contrast sensitivity function, and vernier acuity, as well as spatial distortion, abnormal spatial interactions, and impaired contour detection. In addition, individuals with amblyopia suffer from binocular abnormalities such as impaired stereoacuity (stereoscopic acuity) and abnormal binocular summation. Also, a crowding phenomenon is present.

These deficits are usually specific to the amblyopic eye. However, subclinical deficits of the "better" eye have also been demonstrated.

People with amblyopia also have problems of binocular vision such as limited stereoscopic depth perception and usually have difficulty seeing the three-dimensional images in hidden stereoscopic displays such as autostereograms. Perception of depth, however, from monocular cues such as size, perspective, and motion parallax remains normal.

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).

Amblyopia has three main causes:

- Strabismic: by strabismus (misaligned eyes)

- Refractive: by anisometropia (difference of a certain degree of nearsightedness, farsightedness, or astigmatism), or by significant amount of equal refractive error in both eyes

- Deprivational: by deprivation of vision early in life by vision-obstructing disorders such as congenital cataract

The signs and symptoms of far-sightedness are blurry vision, headaches, and eye strain. The common symptom is eye strain. Difficulty seeing with both eyes (binocular vision) may occur, as well as difficulty with depth perception.

Far-sightedness can have rare complications such as strabismus and amblyopia. At a young age, severe far-sightedness can cause the child to have double vision as a result of "over-focusing".

People with early keratoconus typically notice a minor blurring of their vision and come to their clinician seeking corrective lenses for reading or driving. At early stages, the symptoms of keratoconus may be no different from those of any other refractive defect of the eye. As the disease progresses, vision deteriorates, sometimes rapidly. Visual acuity becomes impaired at all distances, and night vision is often poor. Some individuals have vision in one eye that is markedly worse than that in the other. The disease is often bilateral, though asymmetrical. Some develop photophobia (sensitivity to bright light), eye strain from squinting in order to read, or itching in the eye, but there is normally little or no sensation of pain. It may cause luminous objects to appear as cylindrical pipes with the same intensity at all points.

The classic symptom of keratoconus is the perception of multiple "ghost" images, known as monocular polyopia. This effect is most clearly seen with a high contrast field, such as a point of light on a dark background. Instead of seeing just one point, a person with keratoconus sees many images of the point, spread out in a chaotic pattern. This pattern does not typically change from day to day, but over time, it often takes on new forms. People also commonly notice streaking and flaring distortion around light sources. Some even notice the images moving relative to one another in time with their heart beat.

The predominant optical aberration of the eye in keratoconus is coma. The visual distortion experienced by the person comes from two sources, one being the irregular deformation of the surface of the cornea, and the other being scarring that occurs on its exposed highpoints. These factors act to form regions on the cornea that map an image to different locations on the retina. The effect can worsen in low light conditions, as the dark-adapted pupil dilates to expose more of the irregular surface of the cornea.

An eye that has no refractive error when viewing distant objects is said to have "emmetropia" or be "emmetropic" meaning the eye is in a state in which it can focus parallel rays of light (light from distant objects) on the retina, without using any accommodation. A distant object in this case is defined as an object located beyond 6 meters, or 20 feet, from the eye, since the light from those objects arrives as essentially parallel rays when considering the limitations of human perception.

An eye that has refractive error when viewing distant objects is said to have "ametropia" or be "ametropic". This eye cannot focus parallel rays of light (light from distant objects) on the retina, or needs accommodation to do so.

The word "ametropia" can be used interchangeably with "refractive error". Types of ametropia include myopia, hyperopia and astigmatism. They are frequently categorized as spherical errors and cylindrical errors:

- Spherical errors occur when the optical power of the eye is either too large or too small to focus light on the retina. People with refractive error frequently have blurry vision.

- Nearsightedness: When the optics are too powerful for the length of the eyeball one has myopia or nearsightedness. This can arise from a cornea or crystalline lens with too much curvature (refractive myopia) or an eyeball that is too long (axial myopia). Myopia can be corrected with a concave lens which causes the divergence of light rays before they reach the cornea.

- Farsightedness: When the optics are too weak for the length of the eyeball, one has hyperopia or farsightedness. This can arise from a cornea or crystalline lens with not enough curvature (refractive hyperopia) or an eyeball that is too short (axial hyperopia). This can be corrected with convex lenses which cause light rays to converge prior to hitting the cornea.

- Presbyopia: When the flexibility of the lens declines, typically due to age. The individual would experience difficulty in near vision, often relieved by reading glasses, bifocal, or progressive lenses.

- Cylindrical errors cause astigmatism, when the optical power of the eye is too powerful or too weak across one meridian, such as if the corneal curvature tends towards a cylindrical shape. The angle between that meridian and the horizontal is known as the axis of the cylinder.

- Astigmatism: A person with astigmatic refractive error sees lines of a particular orientation less clearly than lines at right angles to them. This defect can be corrected by refracting light more in one meridian than the other. Cylindrical lenses serve this purpose.

Keratoconus (KC) is a disorder of the eye which results in progressive thinning of the cornea. This may result in blurry vision, double vision, nearsightedness, astigmatism, and light sensitivity. Usually both eyes are affected. In more severe cases a scarring or a circle may be seen within the cornea.

While the cause is unknown, it is believed to occur due to a combination of genetic, environmental, and hormonal factors. About seven percent of those affected have a family history of the condition. Proposed environmental factors include rubbing the eyes and allergies. The underlying mechanism involves changes of the cornea to a cone shape. Diagnosis is by examination with a slit lamp.

Initially the condition can typically be corrected with glasses or soft contact lenses. As the disease worsens special contact lenses may be required. In most people the disease stabilizes after a few years without severe vision problems. In a small number of people scarring of the cornea occurs and a corneal transplantation is required.

Keratoconus affects about 1 in 2000 people. It occurs most commonly in late childhood to early adulthood. While it occurs in all populations it may be more frequent in certain ethnic groups such as those of Asian descent. The word is from the Greek "kéras" meaning cornea and the Latin "cōnus" meaning cone.

The definition of visual impairment is reduced vision not corrected by glasses or contact lenses. The World Health Organization uses the following classifications of visual impairment. When the vision in the better eye with best possible glasses correction is:

- 20/30 to 20/60 : is considered mild vision loss, or near-normal vision

- 20/70 to 20/160 : is considered moderate visual impairment, or moderate low vision

- 20/200 to 20/400 : is considered severe visual impairment, or severe low vision

- 20/500 to 20/1,000 : is considered profound visual impairment, or profound low vision

- More than 20/1,000 : is considered near-total visual impairment, or near total blindness

- No light perception : is considered total visual impairment, or total blindness

Blindness is defined by the World Health Organization as vision in a person's best eye with best correction of less than 20/500 or a visual field of less than 10 degrees. This definition was set in 1972, and there is ongoing discussion as to whether it should be altered to officially include uncorrected refractive errors.

Refractive error, also known as refraction error, is a problem with focusing light accurately onto the retina due to the shape of the eye. The most common types of refractive error are near-sightedness, far-sightedness, astigmatism, and presbyopia. Near-sightedness results in far away objects being blurry, far-sightedness and presbyopia result in close objects being blurry, astigmatism causes objects to appear stretched out or blurry. Other symptoms may include double vision, headaches, and eye strain.

Near-sightedness is due to the length of the eyeball being too long, far-sightedness the eyeball too short, astigmatism the cornea being the wrong shape, and presbyopia aging of the lens of the eye such that it cannot change shape sufficiently. Some refractive errors occur more often among those whose parents are affected. Diagnosis is by eye examination.

Refractive errors are corrected with eyeglasses, contact lenses, or surgery. Eyeglasses are the easiest and safest method of correction. Contact lenses can provide a wider field of vision; however they are associated with a risk of infection. Refractive surgery permanently changes the shape of the cornea.

The number of people globally with 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 the most common disorder. Rates among adults are between 15-49% while rates among children are between 1.2-42%. Far-sightedness more commonly affects young children and the elderly. Presbyopia affects most people over the age of 35. The number of people with refractive errors that have not been corrected was estimated at 660 million (10 per 100 people) in 2013. Of these 9.5 million were blind due to the refractive error. It is one of the most common causes of vision loss along with cataracts, macular degeneration, and vitamin A deficiency.

Visual impairment, also known as vision impairment or vision loss, is a decreased ability to see to a degree that causes problems not fixable by usual means, such as glasses. Some also include those who have a decreased ability to see because they do not have access to glasses or contact lenses. Visual impairment is often defined as a best corrected visual acuity of worse than either 20/40 or 20/60. The term blindness is used for complete or nearly complete vision loss. Visual impairment may cause people difficulties with normal daily activities such as driving, reading, socializing, and walking.

The most common causes of visual impairment globally are uncorrected refractive errors (43%), cataracts (33%), and glaucoma (2%). Refractive errors include near sighted, far sighted, presbyopia, and astigmatism. Cataracts are the most common cause of blindness. Other disorders that may cause visual problems include age related macular degeneration, diabetic retinopathy, corneal clouding, childhood blindness, and a number of infections. Visual impairment can also be caused by problems in the brain due to stroke, premature birth, or trauma among others. These cases are known as cortical visual impairment. Screening for vision problems in children may improve future vision and educational achievement. Screening adults without symptoms is of uncertain benefit. Diagnosis is by an eye exam.

The World Health Organization (WHO) estimates that 80% of visual impairment is either preventable or curable with treatment. This includes cataracts, the infections river blindness and trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness. Many people with significant visual impairment benefit from vision rehabilitation, changes in their environment, and assistive devices.

As of 2015 there were 940 million people with some degree of vision loss. 246 million had low vision and 39 million were blind. The majority of people with poor vision are in the developing world and are over the age of 50 years. Rates of visual impairment have decreased since the 1990s. Visual impairments have considerable economic costs both directly due to the cost of treatment and indirectly due to decreased ability to work.

Optic ataxia is the inability to guide the hand toward an object using visual information where the inability cannot be explained by motor, somatosensory, visual field deficits or acuity deficits. Optic ataxia is seen in Bálint's syndrome where it is characterized by an impaired visual control of the direction of arm-reaching to a visual target, accompanied by defective hand orientation and grip formation. It is considered a specific visuomotor disorder, independent of visual space misperception.

Optic ataxia is also known as misreaching or dysmetria (), secondary to visual perceptual deficits. A patient with Bálint's syndrome likely has defective hand movements under visual guidance, despite normal limb strength. The patient is unable to grab an object while looking at the object, due to a discoordination of eye and hand movement. It is especially true with their contralesional hand.

Dysmetria refers to a lack of coordination of movement, typified by the undershoot or overshoot of intended position with the hand, arm, leg, or eye. It is sometimes described as an inability to judge distance or scale.

The reaching ability of the patient is also altered. It takes them longer to reach toward an object. Their ability to grasp an object is also impaired. The patient's performance is even more severely deteriorated when vision of either the hand or the target is prevented.

Bálint's syndrome symptoms can be quite debilitating since they impact visuospatial skills, visual scanning and attentional mechanisms. Since it represents impairment of both visual and language functions, it is a significant disability that can affect the patient's safety—even in one's own home environment, and can render the person incapable of maintaining employment. In many cases the complete trio of symptoms—inability to perceive the visual field as a whole (simultanagnosia), difficulty in fixating the eyes (oculomotor apraxia), and inability to move the hand to a specific object by using vision (optic ataxia)—may not be noticed until the patient is in rehabilitation. Therapists unfamiliar with Bálint's syndrome may misdiagnose a patient's inability to meet progress expectations in any of these symptom areas as simply indicating incapability of benefiting from further traditional therapy. The very nature of each Bálint symptom frustrates rehabilitation progress in each of the other symptoms. Much more research is needed to develop therapeutic protocols that address Bálint symptoms as a group since the disabilities are so intertwined.

This type of retinoschisis is very common with a prevalence of up to 7 percent in normal persons. Its cause is unknown. It can easily be confused with retinal detachment by the non-expert observer and in difficult cases even the expert may have difficulty differentiating the two. Such differentiation is important since retinal detachment almost always requires treatment while retinoschisis never itself requires treatment and leads to retinal detachment (and hence to visual loss) only occasionally. Unfortunately one still sees cases of uncomplicated retinoschisis treated by laser retinopexy or cryopexy in an attempt to stop its progression towards the macula. Such treatments are not only ineffective but unnecessarily risk complications. There is no documented case in the literature of degenerative retinoschisis itself (as opposed to the occasional situation of retinal detachment complicating retinoschisis) in which the splitting of the retina has progressed through the fovea. There is no clinical utility in differentiating between typical and reticular retinoschisis. Degenerative retinoschisis is not known to be a genetically inherited condition.

There is always vision loss in the region of the schisis as the sensory retina is separated from the ganglion layer. But like the loss is in the periphery, it goes unnoticed. It is the very rare schisis that encroaches on the macula where retinopexy is then properly used.

Retinoschisis is an eye disease characterized by the abnormal splitting of the retina's neurosensory layers, usually in the outer plexiform layer. Most common forms are asymptomatic, some rarer forms result in a loss of vision in the corresponding visual field.

Hallucinatory palinopsia consists of the following four symptom categories. A person often reports symptoms from multiple categories.

Formed image perseveration refers to a single, stationary object that remains fixed in one’s visual field. These pathological afterimages look realistic and have the same color and clarity as the original stimulus. The palinopsia lasts at least 15 seconds, but may persist for hours or days. For example, a patient sees a cat, and an identical copy of the cat remains fixed in the field of view for 30 minutes. A patient commonly complains of the perseverated fingers of an examiner. These afterimages often occur in visual field deficits but may occur anywhere in the visual field, regardless of the location of the original stimulus. The generation of the afterimages is not affected by external conditions such as the length of fixation, stimulus intensity, contrast, or motion. The palinoptic image can appear immediately after seeing the original image or may be delayed in time.

The hallmark sign of Alice in Wonderland syndrome (AIWS) is a migraine, and AIWS may in part be caused by the migraine. AIWS affects the sense of vision, sensation, touch, and hearing, as well as one's own body image.

A prominent and often disturbing symptom are experiences of altered body image. The person may find that they are confused as to the size and shape of parts of (or all of) their body. They may feel as though their body is expanding or getting smaller. Alice in Wonderland syndrome also involves perceptual distortions of the size or shape of objects. Other possible causes and signs of the syndrome include migraines, use of hallucinogenic drugs, and infectious mononucleosis.

Patients with certain neurological diseases have experienced similar visual hallucinations. These hallucinations are called "Lilliputian," which means that objects appear either smaller or larger than they actually are.

Patients may experience either micropsia or macropsia. Micropsia is an abnormal visual condition, usually occurring in the context of visual hallucination, in which affected persons see objects as being smaller than those objects actually are. Macropsia is a condition where the individual sees everything larger than it actually is.

A relationship between the syndrome and mononucleosis has been suggested.

One 17-year-old male, Michael Huang, described his odd symptoms. He said, "quite suddenly objects appear small and distant (teliopsia) or large and close (peliopsia). I feel as I am getting shorter and smaller 'shrinking' and also the size of persons are not longer than my index finger (a lilliputian proportion). Sometimes I see the blind in the window or the television getting up and down, or my leg or arm is swinging. I may hear the voices of people quite loud and close or faint and far. Occasionally, I experience attacks of migrainous headache associated with eye redness, flashes of lights and a feeling of giddiness. I am always conscious to the intangible changes in myself and my environment."

The eyes themselves are normal, but the person will often 'see' objects as the incorrect size, shape or perspective angle. Therefore, people, cars, buildings, houses, animals, trees, environments, etc., look smaller or larger than they should be, or that distances look incorrect; for example, a corridor may appear to be very long, or the ground may appear too close.

The person affected by Alice in Wonderland Syndrome may also lose the sense of time, a problem similar to the lack of spatial perspective. In other words, time seems to pass very slowly, akin to an LSD experience. The lack of time, and space, perspective leads to a distorted sense of velocity. For example, one could be inching along ever so slowly in reality, yet it would seem as if one were sprinting uncontrollably along a moving walkway, leading to severe, overwhelming disorientation. This can then cause the person to feel as if movement, even within his or her own home, is futile.

In addition, some people may, in conjunction with a high fever, experience more intense and overt hallucinations, seeing things that are not there and misinterpreting events and situations.

Other minor or less common symptoms may include loss of limb control and general dis-coordination, memory loss, lingering touch and sound sensations, and emotional experiences.

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.

Signs and symptoms of corneal abrasion include pain, trouble with bright lights, a foreign-body sensation, excessive squinting, and reflex production of tears. Signs include epithelial defects and edema, and often redness of the eye. The vision may be blurred, both from any swelling of the cornea and from excess tears. Crusty buildup from excess tears may also be present.

Another common form of synesthesia is the association of sounds with colors. For some, everyday sounds such as doors opening, cars honking, or people talking can trigger seeing colors. For others, colors are triggered when musical notes or keys are being played. People with synesthesia related to music may also have perfect pitch because their ability to see/hear colors aids them in identifying notes or keys.

The colors triggered by certain sounds, and any other synesthetic visual experiences, are referred to as "photisms".

According to Richard Cytowic, chromesthesia is "something like fireworks": voice, music, and assorted environmental sounds such as clattering dishes or dog barks trigger color and firework shapes that arise, move around, and then fade when the sound ends. Sound often changes the perceived hue, brightness, scintillation, and directional movement. Some individuals see music on a "screen" in front of their faces. For Deni Simon, music produces waving lines "like oscilloscope configurations – lines moving in color, often metallic with height, width and, most importantly, depth. My favorite music has lines that extend horizontally beyond the 'screen' area."

Individuals rarely agree on what color a given sound is. B flat might be orange for one person and blue for another. Composers Franz Liszt and Nikolai Rimsky-Korsakov famously disagreed on the colors of music keys.

In one of the most common forms of synesthesia, individual letters of the alphabet and numbers (collectively referred to as graphemes) are "shaded" or "tinged" with a color. While different individuals usually do not report the same colors for all letters and numbers, studies with large numbers of synesthetes find some commonalities across letters (e.g. A is likely to be red).

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.

Corneal abrasion is a scratch to the surface of the cornea of the eye. Symptoms include pain, redness, light sensitivity, and a feeling like a foreign body is in the eye. Most people recover completely within three days.

Most cases are due to minor trauma to the eye such as that which can occur with contact lens use or from fingernails. About 25% of cases occur at work. Diagnosis is often by slit lamp examination after fluorescein dye has been applied. More significant injuries like a corneal ulcer, globe rupture, recurrent erosion syndrome, and a foreign body within the eye should be ruled out.

Prevention includes the use of eye protection. Treatment is typically with antibiotic ointment. In those who wear contact lenses a fluoroquinolone antibiotic is often recommended. Paracetamol (acetaminophen), NSAIDs, and eye drops such as cyclopentolate that paralysis the pupil can help with pain. Evidence does not support the usefulness of eye patching for those with simple abrasions.

About 3 per 1,000 people are affected a year in the United States. Males are more often affected than females. The typical age group affected is those in their 20s and 30s. Complications can include bacterial keratitis, corneal ulcer, and iritis. Complications may occur in up to 8% of people.