In the United States, testing for "horizontal gaze nystagmus" is one of a battery of field sobriety tests used by police officers to determine whether a suspect is driving under the influence of alcohol. The test involves observation of the suspect's pupil as it follows a moving object, noting

1. lack of smooth pursuit,

2. distinct and sustained nystagmus at maximum deviation, and

3. the onset of nystagmus prior to 45 degrees.

The horizontal gaze nystagmus test has been highly criticized and major errors in the testing methodology and analysis found. However, the validity of the horizontal gaze nystagmus test for use as a field sobriety test for persons with a blood alcohol level between 0.04–0.08 is supported by peer reviewed studies and has been found to be a more accurate indication of blood alcohol content than other standard field sobriety tests.

A test called the Bielschowsky Darkening Wedge Test can be used to reveal and diagnose the presence of dissociated vertical deviation, although any (or no) amount of dissociative occlusion may also prompt it to occur.

The patient is asked to look at a light. One eye is covered and a filter is placed in front of the other eye. The density or opacity of this filter is gradually increased, and the behaviour of the eye under the cover is observed not of the eye beneath the filter. Initially, if DVD is present, the covered eye will have elevated, but as the filter opacity is increased the eye under the cover will gradually move downwards. This "Bielschowsky phenomenon" is present in over 50% of persons with prominent DVD, all the more if the DVD is asymmetric and amblyopia is present as well.

The Bielschowsky phenomenon is also present in the horizontal plane in patients with prominent DHD (dissociated horizontal deviation).

DVD is often mistaken for over-action of the inferior oblique extra-ocular muscles. DVD can be revealed on ocular movement testing when one eye is occluded by the nose on lateral gaze. This eye will then elevate, simulating an inferior oblique over action. However, in a unilateral case, overaction of the superior rectus muscle in the unaffected dominant eye, can also be a causing factor as well as causing a V pattern exophoria.

Nystagmus is very noticeable but rarely recognized. Nystagmus can be clinically investigated by using a number of non-invasive standard tests. The simplest one is the caloric reflex test, in which one ear canal is irrigated with warm or cold water or air. The temperature gradient provokes the stimulation of the horizontal semicircular canal and the consequent nystagmus.

Nystagmus is often very commonly present with Chiari malformation.

The resulting movement of the eyes may be recorded and quantified by special devices called electronystagmograph (ENG), a form of electrooculography (an electrical method of measuring eye movements using external electrodes), or even less invasive devices called videonystagmograph (VNG), a form of video-oculography (VOG) (a video-based method of measuring eye movements using external small cameras built into head masks) by an audiologist. Special swinging chairs with electrical controls can be used to induce rotatory nystagmus.

Over the past forty years, objective eye-movement-recording techniques have been applied to the study of nystagmus, and the results have led to a greater accuracy and understanding of the condition.

Orthoptists may also use an optokinetic drum, or electrooculography to assess a patient's eye movements.

Nystagmus can be caused by subsequent foveation of moving objects, pathology, sustained rotation or substance use. Nystagmus is not to be confused with other superficially similar-appearing disorders of eye movements (saccadic oscillations) such as opsoclonus or ocular flutter that are composed purely of fast-phase (saccadic) eye movements, while nystagmus is characterised by the combination of a smooth pursuit, which usually acts to take the eye off the point of regard, interspersed with the saccadic movement that serves to bring the eye back on target. Without the use of objective recording techniques, it may be very difficult to distinguish between these conditions.

In medicine, the presence of nystagmus can be benign, or it can indicate an underlying visual or neurological problem.

According to a Cochrane review of 2012, controversies remain regarding type of surgery, non-surgical intervention and age of intervention.

The aims of treatment are as follows:

The elimination of any amblyopia

A cosmetically acceptable ocular alignment

long term stability of eye position

binocular cooperation.

The prognosis for each patient with esotropia will depend upon the origin and classification of their condition. However, in general, management will take the following course:

1. Identify and treat any underlying systemic condition.

2. Prescribe any glasses required and allow the patient time to 'settle into' them.

3. Use occlusion to treat any amblyopia present and encourage alternation.

4. Where appropriate, orthoptic exercises can be used to attempt to restore binocularity.

5. Where appropriate, prismatic correction can be used, either temporarily or permanently, to relieve symptoms of double vision.

6. In specific cases, and primarily in adult patients, botulinum toxin can be used either as a permanent therapeutic approach, or as a temporary measure to prevent contracture of muscles prior to surgery

7. Where necessary, extra-ocular muscle surgery can be undertaken to improve cosmesis and, on occasion, restore binocularity.

Controversy has arisen regarding the selection and planning of surgical procedures, the timing of surgery and about what constitutes a favourable outcome.

1. Selection and planning

Some ophthalmologists, notably Ing and Helveston, favour a prescribed approach often involving multiple surgical episodes whereas others prefer to aim for full alignment of the eyes in one procedure and let the number of muscles operated upon during this procedure be determined by the size of the squint.

2. Timing and outcome

This debate relates to the technical anatomical difficulties of operating on the very young versus the possibility of an increased potential for binocularity associated with early surgery. Infants are often operated upon at the age of six to nine months of age and in some cases even earlier at three or four months of age. Some emphasize the importance of intervening early such as to keep the duration of the patient's abnormal visual experience to a minimum. Advocates of early surgery believe that those who have their surgery before the age of one are more likely to be able to use both eyes together post-operatively.

A Dutch study (ELISSS) compared early with late surgery in a prospective, controlled, non-randomized, multicenter trial and reported that:

"Children operated early had better gross stereopsis at age six as compared to children operated late. They had been operated more frequently, however, and a substantial number of children in both [originally-recruited] groups had not been operated at all."

Other studies also report better results with early surgery, notably Birch and Stager and Murray et al. but do not comment on the number of operations undertaken. A recent study on 38 children concluded that surgery for infantile esotropia is most likely to result in measureable stereopsis if patient age at alignment is not more than 16 months.

Another study found that for children with infantile esotropia early surgery decreases the risk of dissociated vertical deviation developing after surgery.

Aside the strabismus itself, there are other aspects or conditions that appear to improve after surgery or botulinum toxin eye alignment. Study outcomes have indicated that after surgery the child catches up in development of fine-motor skills (such as grasping a toy and handling a bottle) and of large-muscle skills (such as sitting, standing, and walking) in case a developmental delay was present before. Evidence also indicates that as of the age of six, strabismic children become less accepted by their peers, leaving them potentially exposed to social exclusion starting at this age unless their eye positioning is corrected by this time ("see also:" Psychosocial effects of strabismus).

"Congenital esotropia," or "infantile esotropia," is a specific sub-type of primary concomitant esotropia. It is a constant esotropia of large and consistent size with onset between birth and six months of age. It is not associated with hyperopia, so the exertion of accommodative effort will not significantly affect the angle of deviation. It is, however, associated with other ocular dysfunctions including oblique muscle over-actions, Dissociated Vertical Deviation (DVD,) Manifest Latent Nystagmus, and defective abduction, which develops as a consequence of the tendency of those with infantile esotropia to 'cross fixate.' Cross fixation involves the use of the right eye to look to the left and the left eye to look to the right; a visual pattern that will be 'natural' for the person with the large angle esotropia whose eye is already deviated towards the opposing side.

The origin of the condition is unknown, and its early onset means that the affected individual's potential for developing binocular vision is limited. The appropriate treatment approach remains a matter of some debate. Some ophthalmologists favour an early surgical approach as offering the best prospect of binocularity whilst others remain unconvinced that the prospects of achieving this result are good enough to justify the increased complexity and risk associated with operating on those under the age of one year.

Since this condition is usually coupled with other neurological disorders or deficits, there is no known cure for cerebral polyopia. However, measures can be taken to reduce the effects of associated disorders, which have proven to reduce the effects of polyopia. In a case of occipital lobe epilepsy, the patient experienced polyopia. Following administration of valproate sodium to reduce headaches, the patient’s polyopia was reduced to palinopsia. Further, after administering the anticonvulsant drug Gabapentin in addition to valproate sodium, the effects of palinopsia were decreased, as visual perseveration is suppressed by this anticonvulsant drug. Thus, in cases of epilepsy, anticonvulsant drugs may prove to reduce the effects of polyopia and palinopsia, a topic of which should be further studied.

In other cases of polyopia, it is necessary to determine all other present visual disturbances before attempting treatment. Neurological imaging can be performed to determine if there are present occipital or temporal lobe infarctions that may be causing the polyopia. CT scans are relatively insensitive to the presence of cerebral lesions, so other neurological imaging such as PET and MRI may be performed. The presence of seizures and epilepsy may also be assessed through EEG. In addition, motor visual function should be assessed through examination of pupillary reactions, ocular motility, optokinetic nystagmus, slit-lamp examination, visual field examination, visual acuity, stereo vision, bimicroscopic examination, and funduscopic examination. Once the performance of such functions have been assessed, a plan for treatment can follow accordingly. Further research should be conducted to determine if the treatment of associated neurological disturbances can reduce the effects of polyopia.

If an optokinetic drum is available, rotate the drum in front of the patient. Ask the patient to look at the drum as you rotate it slowly. If an optokinetic drum is not available, move a strip of paper with alternating 2-inch black and white strips across the patient's visual field. Pass it in front of the patient's eye at reading distance while instructing the patient to look at it as it rapidly moves by. With normal vision, a nystagmus develops in both adults and infants. The nystagmus consists of initial slow phases in the direction of the stimulus (smooth pursuits), followed by fast, corrective phases (saccade). Presence of nystagmus indicates an intact visual pathway.

Another effective method is to hold a mirror in front of the patient and slowly rotate the mirror to either side of the patient. The patient with an intact visual pathway will maintain eye contact with herself or himself. This compelling optokinetic stimulus forces reflex slow eye movements.

OKN can be used as a crude assessment of the visual system, particularly in infants. When factitious blindness or malingering is suspected, check for optokinetic nystagmus to determine whether there is an intact visual pathway.

Diagnosing CVI is difficult. A diagnosis is usually made when visual performance is poor but it is not possible to explain this from an eye examination. Before CVI was widely known among professionals, some would conclude that the patient was faking their problems or had for some reason engaged in self-deception. However, there are now testing techniques that do not depend on the patient's words and actions, such as fMRI scanning, or the use of electrodes to detect responses to stimuli in both the retina and the brain. These can be used to verify that the problem is indeed due to a malfunction of the visual cortex and/or the posterior visual pathway.

The optokinetic response is a combination of a slow-phase and fast-phase eye movements. It is seen when an individual follows a moving object with their eyes, which then moves out of the field of vision at which point their eye moves back to the position it was in when it first saw the object. The reflex develops at about 6 months of age.

Optokinetic nystagmus (OKN) is nystagmus that occurs in response to a rotation movement. It is present normally. The optokinetic response allows the eye to follow objects in motion when the head remains stationary (e.g., observing individual telephone poles on the side of the road as one travels by them in a car, or observing stationary objects while walking past them).

Pseudomyopia refers to an intermittent and temporary shift in refractive error of the eye towards myopia, in which the focusing of light in front of the retina is due to a transient spasm of the ciliary muscle causing an increase in the refractive power of the eye. It may be either organic, through stimulation of the parasympathetic nervous system, or functional in origin, through eye strain or fatigue of ocular systems. It is common in young adults who have active accommodation, and classically occurs after a change in visual requirements, such as students preparing for an exam, or a change in occupation.

The major symptom is intermittent blurring of distance vision particularly noticeable after prolonged periods of near work, and symptoms of asthenopia. The vision may clear temporarily using concave (minus) lenses. The diagnosis is done by cycloplegic refraction using a strong cycloplegic like atropine or homatropine eye drops. Accommodative amplitude and facility may be reduced as a result of the ciliary muscle spasm.

Treatment is dependent on the underlying aetiology. Organic causes may include systemic or ocular medications, brain stem injury, or active ocular inflammation such as uveitis. Functional pseudomyopia is managed though modification of working conditions, an updated refraction, typically involving a reduction of a myopic prescription to some lower myopic prescription, or through appropriate ocular exercises.

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

Ocular hypertension is treated with either medications or laser. Medications that lower intraocular pressure work by decreasing aqueous humor production and/or increasing aqueous humor outflow. Laser trabeculoplasty works by increasing outflow. The cannabinoids found in cannabis sativa and indica (marijuana) have been shown to reduce intraocular pressure, by up to 50% for approximately four to five hours. But due to the duration of effect, significant side-effect profile, and lack of research proving efficacy, the American Glaucoma Society issued a position statement in 2009 regarding the use of marijuana as a treatment for glaucoma.

Typically a coloboma appears oval or comet shaped with round end towards the centre. There may be a few vessels (retinal or choroidal) at the edges. The surface may have irregular depression.

Amaurotic nystagmus is defined as the nystagmus associated with blindness or the central vision defects. It is characterized by the pendular or jerky movements of the eyes in the patients who have visual impairement for a long period of time.

Colobomas of the iris may be treated in a number of ways. A simple cosmetic solution is a specialized cosmetic contact lens with an artificial pupil aperture. Surgical repair of the iris defect is also possible. Surgeons can close the defect by stitching in some cases. More recently artificial iris prosthetic devices such as the Human Optics artificial iris have been used successfully by specialist surgeons. This device cannot be used if the natural lens is in place and is not suitable for children. Suture repair is a better option where the lens is still present.

Vision can be improved with glasses, contact lenses or even laser eye surgery but may be limited if the retina is affected or there is amblyopia.

Pendular nystagmus is a sinusoidal oscillation, which refers to the waveform of involuntary eye movements that may occur in any direction. It is characterized by the multidimensional slow eye movements of the eyes (1 Hz frequency) with an equal velocity in each direction that resembles the trajectory of a pendulum. These pattern of these movements may differ between the two eyes. Depending upon the pattern of movements, pendular nystagmus has been divided into different subtypes such as congenital nystagmus, acquired pendular nystagmus, and amaurotic nystagmus.

Differential diagnosis is rarely difficult in adults. Onset is typically sudden with symptoms of horizontal diplopia. Limitations of eye movements are confined to abduction of the affected eye (or abduction of both eyes if bilateral) and the size of the resulting convergent squint or esotropia is always larger on distance fixation - where the lateral rectii are more active - than on near fixation - where the medial rectii are dominant. Abduction limitations which mimic VIth nerve palsy may result secondary to surgery, to trauma or as a result of other conditions such as myasthenia gravis or thyroid eye disease.

In children, differential diagnosis is more difficult because of the problems inherent in getting infants to cooperate with a full eye movement investigation. Possible alternative diagnosis for an abduction deficit would include:

1. Mobius syndrome - a rare congenital disorder in which both VIth and VIIth nerves are bilaterally affected giving rise to a typically 'expressionless' face.

2. Duane's syndrome - A condition in which both abduction and adduction are affected arising as a result of partial innervation of the lateral rectus by branches from the IIIrd oculomotor cranial nerve.

3. Cross fixation which develops in the presence of infantile esotropia or nystagmus blockage syndrome and results in habitual weakness of lateral rectii.

4. Iatrogenic injury. Abducens nerve palsy is also known to occur with halo orthosis placement.The resultant palsy is identified through loss of lateral gaze after application of the orthosis and is the most common cranial nerve injury associated with this device.

The first aims of management should be to identify and treat the cause of the condition, where this is possible, and to relieve the patient's symptoms, where present. In children, who rarely appreciate diplopia, the aim will be to maintain binocular vision and, thus, promote proper visual development.

Thereafter, a period of observation of around 9 to 12 months is appropriate before any further intervention, as some palsies will recover without the need for surgery.

There have been cases of improvement in extra-ocular movement with botulinum toxin injection.

The eye findings of Parinaud's Syndrome generally improve slowly over months, especially with resolution of the causative factor; continued resolution after the first 3–6 months of onset is uncommon. However, rapid resolution after normalization of intracranial pressure following placement of a ventriculoperitoneal shunt has been reported.

Treatment is primarily directed towards etiology of the dorsal midbrain syndrome. A thorough workup, including neuroimaging is essential to rule out anatomic lesions or other causes of this syndrome. Visually significant upgaze palsy can be relieved with bilateral inferior rectus recessions. Retraction nystagmus and convergence movement are usually improved with this procedure as well.

Molecular (DNA) testing for PAX6 gene mutations (by sequencing of the entire coding region and deletion/duplication analysis) is available for isolated aniridia and the Gillespie syndrome. For the WAGR syndrome, high-resolution cytogenetic analysis and fluorescence in situ hybridization (FISH) can be utilized to identify deletions within chromosome band 11p13, where both the PAX6 and WT1 genes are located.

Cerebral polyopia is most often associated with occipital or temporal lobe lesions, as well as occipital lobe epilepsy. This condition is relatively uncommon, thus further research regarding its causes and mechanism has not been performed. Polyopia can be experienced as partial second or multiple images to either side (or in any eccentricity) of an object at fixation. Polyopia occurs when both eyes are open, or when one eye is open, during fixation on a stimulus. Known cases of polyopia provide evidence that, in relation to the stimulus at fixation, multiple images can appear at a constant distance in any direction; gaps in portions of an object at fixation can exist; multiple images can be overlaid vertically, horizontally, or diagonally on top of the stimulus; and the multiple images can appear different sizes, alignments, and complexities. The complexity of the stimulus does not appear to affect the clarity of the multiple images. The physical distance of the stimulus from the patient (near or far) also does not seem to affect the presence of multiple images. However, if the stimulus is swung or moved, multiple images of that object can either be extinguished or transformed into different objects, depending on the severity of the condition.

The onset of polyopia is not immediate upon perception of visual stimuli; rather, it occurs within milliseconds to seconds of fixation upon a stimulus. Polyopia has been described by patients as images “suddenly multiplying.” These multiple images can drift, fade, and disappear, depending on the severity of the condition. These episodes of polyopia can last from seconds to hours. In one specific case, a patient described difficulties reading due to letters “run[ning] together” and momentarily disappearing.

Most cases of polyopia are accompanied by another neurological condition. Polyopia is often accompanied by visual field defects (such as the presence of a scotoma) or transient visual hallucinations. Polyopic images often form in the direction and position of such visual field defects. Current research shows that when stimuli are close to the patient’s scotoma, the latency of polyopic images is much shorter than if the stimuli was far from the scotoma, and there is a higher probability that polyopic images will result.