Amblyopia is diagnosed by identifying low visual acuity in one or both eyes, out of proportion to the structural abnormality of the eye and excluding other visual disorders as causes for the lowered visual acuity. It can be defined as an interocular difference of two lines or more in acuity (e.g. on Snellen chart) when the eye optics is maximally corrected. In young children, visual acuity is difficult to measure and can be estimated by observing the reactions of the patient reacts when one eye is covered, including observing the patient's ability to follow objects with one eye.

Stereotests like the Lang stereotest are not reliable exclusion tests for amblyopia. A person who passes the Lang stereotest test is unlikely to have strabismic amblyopia, but could nonetheless have refractive or deprivational amblyopia. It has been suggested that binocular retinal birefringence scanning may be able to identify, already in very young children, amblyopia that is associated with strabismus, microstrabismus, or reduced fixation accuracy. Diagnosis and treatment of amblyopia as early as possible is necessary to keep the vision loss to a minimum.

Screening for amblyopia is recommended in all people between three and five years of age.

During an eye examination, the presence of suppression and the size and location of the suppression scotoma may be the Worth 4 dot test (a subjective test that is considered to be the most precise suppression test), or with other subjective tests such as the Bagolini striated lens test, or with objective tests such as the 4 prism base out test.

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.

Diagnosis of convergence insufficiency is made by an eye care professional skilled in binocular vision dysfunctions to rule out any organic disease. Convergence insufficiency characterized by one or more of the following diagnostic findings: Patient symptoms, High exophoria at near, reduced accommodative convergence/accommodation ratio, receded near point of convergence, low fusional vergence ranges and/or facility. Some patients with convergence insufficiency have concurrent accommodative insufficiency—accommodative amplitudes should therefore also be measured in symptomatic patients.

Suppression may treated with vision therapy, though there is a wide range of opinions on long-term effectiveness between eye care professionals, with little scientific evidence of long-term improvement of suppression, if the underlying cause is not addressed (strabismus, amblyopia, etc.).

The appropriate treatment for binocular diplopia will depend upon the cause of the condition producing the symptoms. Efforts must first be made to identify and treat the underlying cause of the problem. Treatment options include eye exercises, wearing an eye patch on alternative eyes, prism correction, and in more extreme situations, surgery or botulinum toxin.

If diplopia turns out to be intractable, it can be managed as last resort by obscuring part of the patient's field of view. This approach is outlined in the article on diplopia occurring in association with a condition called "horror fusionis".

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.

Diplopia has a diverse range of ophthalmologic, infectious, autoimmune, neurological, and neoplastic causes.

A comprehensive eye examination including an ocular motility (i.e., eye movement) evaluation and an evaluation of the internal ocular structures will allow an eye doctor to accurately diagnose the exotropia. Although glasses and/or patching therapy, exercises, or prisms may reduce or help control the outward-turning eye in some children, surgery is often required.

There is a common form of exotropia known as "convergence insufficiency" that responds well to orthoptic vision therapy including exercises. This disorder is characterized by an inability of the eyes to work together when used for near viewing, such as reading. Instead of the eyes focusing together on the near object, one deviates outward.

"Consecutive exotropia" is an exotropia that arises after an initial esotropia. Most often it results from surgical overcorrection of the initial esotropia. It can be addressed with further surgery or with vision therapy; vision therapy has shown promising results if the consecutive exotropia is intermittent, alternating and of small magnitude. (Consecutive exotropia may however also spontaneously develop from esotropia, without surgery or botulinum toxin treatment.)

Because of the risks of surgery, and because about 35% of people require at least one more surgery, many people try vision therapy first. This consists of visual exercises. Although vision therapy is generally not covered by American health insurance companies, many large insurers such as Aetna have recently begun offering full or partial coverage in response to recent studies.

Strabismus surgery is sometimes recommended if the exotropia is present for more than half of each day or if the frequency is increasing over time. It is also indicated if a child has significant exotropia when reading or viewing near objects or if there is evidence that the eyes are losing their ability to work as a single unit (binocular vision). If none of these criteria are met, surgery may be postponed pending simple observation with or without some form of eyeglass and/or patching therapy. In very mild cases, there is a chance that the exotropia will diminish with time. The long-term success of surgical treatment for conditions such as intermittent exotropia is not well proven, and surgery can often result in a worsening of symptoms due to overcorrection. Evidence from the available literature suggests that unilateral surgery was more effective than bilateral surgery for individuals affected with intermittent exotropia.

The surgical procedure for the correction of exotropia involves making a small incision in the tissue covering the eye in order to reach the eye muscles. The appropriate muscles are then repositioned in order to allow the eye to move properly. The procedure is usually done under general anesthesia. Recovery time is rapid, and most people are able to resume normal activities within a few days. Following surgery, corrective eyeglasses may be needed and, in many cases, further surgery is required later to keep the eyes straight.

When a child requires surgery, the procedure is usually performed before the child attains school age. This is easier for the child and gives the eyes a better chance to work together. As with all surgery, there are some risks. However, strabismus surgery is usually a safe and effective treatment.

When this magnification difference becomes excessive the effect can cause diplopia, suppression, disorientation, eyestrain, headache, and dizziness and balance disorders.

In general, strabismus can be approached and treated with a variety of procedures. Depending on the individual case, treatment options include:

- Correction of refractive errors by glasses

- Prism therapy (if tolerated, to manage diplopia)

- Patching (mainly to manage amblyopia in children and diplopia in adults)

- Botulinum toxin injection

- Surgical correction

Surgical correction of the hypertropia is desired to achieve binocularity, manage diplopia and/or correct the cosmetic defect. Steps to achieve the same depend on mechanism of the hypertropia and identification of the offending muscles causing the misalignment. Various surgical procedures have been described and should be offered after careful examination of eyes, including a detailed orthoptic examination focussing on the disturbances in ocular motility and visual status. Specialty fellowship trained pediatric ophthalmologists and strabismus surgeons are best equipped to deal with these complex procedures.

Treatment is done by changing the optical magnification properties of the auxiliary optics (corrective lenses). The optical magnification properties of spectacle lenses can be adjusted by changing parameters like the base curve, vertex distance, and center thickness. Contact lenses may also provide a better optical magnification to reduce the difference in image size. The difference in magnification can also be eliminated by a combination of contact lenses and glasses (creating a weak telescope system). The optimum design solution will depend on different parameters like cost, cosmetic implications, and if the patient can tolerate wearing a contact lens.

Note however that before the optics can be designed, first the aniseikonia should be known=measured. When the image disparity is astigmatic (cylindrical) and not uniform, images can appear wider, taller, or diagonally different. When the disparity appears to vary across the visual field (field-dependent aniseikonia), as may be the case with an epiretinal membrane or retinal detachment, the aniseikonia cannot fully be corrected with traditional optical techniques like standard corrective lenses. However, partial correction often improves the patient's vision comfort significantly. Little is known yet about the possibilities of using surgical intervention to correct aniseikonia.

Quantitative comparisons between different eyes and conditions are usually made using RMS (root mean square). To measure RMS for each type of aberration involves squaring the difference between the aberration and mean value and averaging it across the pupil area. Different kinds of aberrations may have equal RMS across the pupil but have different effects on vision, therefore, RMS error is unrelated to visual performance. The majority of eyes have total RMS values less than 0.3 µm.

The most common method of classifying the shapes of aberration maps is to consider each map as the sum of fundamental shapes or basis functions. One popular set of basis functions are the Zernike polynomials. Each aberration may be positive or negative in value and induces predictable alterations in the image quality.

Because there is no limit to the number of terms that may be used by Zernike polynomials, vision scientists use the first 15 polynomials, based on the fact that they are enough to obtain a highly accurate description of the most common aberrations found in human eye. Among these the most important Zernike coefficients affecting visual quality are coma, spherical aberration, and trefoil.

Zernike polynomials are usually expressed in terms of polar coordinates (ρ,θ), where ρ is radial coordinate and θ is the angle. The advantage of expressing the aberrations in terms of these polynomials includes the fact that the polynomials are independent of one another. For each polynomial the mean value of the aberration across the pupil is zero and the value of the coefficient gives the RMS error for that particular aberration (i.e. the coefficients show the relative contribution of each Zernike mode to the total wavefront error in the eye). However these polynomials have the disadvantage that their coefficients are only valid for the particular pupil diameter they are determined for.

In each Zernike polynomial formula_1, the subscript n is the order of aberration, all the Zernike polynomials in which n=3 are called third-order aberrations and all the polynomials with n=4, fourth order aberrations and so on. formula_2 and formula_3 are usually called secondary Astigmatism and should not cause confusion. The superscript m is called the angular frequency and denotes the number of times the Wavefront pattern repeats itself.

List of Zernike modes and their common names:

Convergence insufficiency may be treated with convergence exercises prescribed by an eyecare specialist trained in orthoptics or binocular vision anomalies. Some cases of convergence insufficiency are successfully managed by prescription of eyeglasses, sometimes with therapeutic prisms.

Pencil push-ups therapy is performed at home. Patient brings a pencil slowly to within 2–3 cm of the eye just above the nose about 15 minutes per day 5 times per week. Patients should record the closest distance that they could maintain fusion (keep the pencil from going double as long as possible) after each 5 minutes of therapy. Computer software may be used at home or in an orthoptists/vision therapists office to treat convergence insufficiency. A weekly 60-minute in-office therapy visit may be prescribed. This is generally accompanied with additional in home therapy.

In 2005, the Convergence Insufficiency Treatment Trial (CITT) published two randomized clinical studies. The first, published in Archives of Ophthalmology demonstrated that computer exercises when combined with office based vision therapy/orthoptics were more effective than "pencil pushups" or computer exercises alone for convergency insufficiency in 9- to 18-year-old children. The second found similar results for adults 19 to 30 years of age. In a bibliographic review of 2010, the CITT confirmed their view that office-based accommodative/vergence therapy is the most effective treatment of convergence insufficiency, and that substituting it in entirety or in part with other eye training approaches such as home-based therapy may offer advantages in cost but not in outcome. A later study of 2012 confirmed that orthoptic exercises led to longstanding improvements of the asthenopic symptoms of convergence sufficiency both in adults and in children. A 2011 Cochrane Review reaffirmed that office-based therapy is more effective than home-based therapy, though the evidence of effectiveness is a lot stronger for children than for the adult population.

Both positive fusional vergence (PFV) and negative fusional vergence (NFV) can be trained, and vergence training should normally include both.

Surgical correction options are also available, but the decision to proceed with surgery should be made with caution as convergence insufficiency generally does not improve with surgery. Bilateral medial rectus resection is the preferred type of surgery. However, the patient should be warned about the possibility of uncrossed diplopia at distance fixation after surgery. This typically resolves within 1–3 months postoperatively. The exophoria at near often recurs after several years, although most patients remain asymptomatic.

Refractive errors such as hyperopia and Anisometropia may be associated abnormalities found in patients with vertical strabismus.

The vertical miscoordination between the two eyes may lead to

- Strabismic amblyopia, (due to deprivation / suppression of the deviating eye)

- cosmetic defect (most noticed by parents of a young child and in photographs)

- Face turn, depending on presence of binocular vision in a particular gaze

- diplopia or double vision - more seen in adults (maturity / plasticity of neural pathways) and suppression mechanisms of the brain in sorting out the images from the two eyes.

- cyclotropia, a cyclotorsional deviation of the eyes (rotation around the visual axis), particularly when the root cause is an oblique muscle paresis causing the hypertropia.

Low order aberrations (hyperopia, Myopia and regular astigmatism), are correctable by eyeglasses, soft contact lenses and refractive surgery. Neither spectacles nor soft contact lenses nor routine keratorefractive surgery adequately corrects high order aberrations. Significant high order aberration usually requires a rigid gas-permeable contact lens for optimal visual rehabilitation.

Customized Wavefront-guided refractive corneal laser treatments are designed to reduce existing aberrations and to help prevent the creation of new aberrations. The wavefront map of the eye may be transferred to a Lasik system and enable the surgeon to treat the aberration. Perfect alignment of the treatment and the pupil on which the Wavefront is measured is required, which is usually achieved through iris feature detection. An efficient eye tracking system and small spot size laser is necessary for treatment . Wavefront customization of ablation increases the depth of ablation because additional corneal tissue must be ablated to compensate for the high order aberrations. Actual results with Wavefront guided LASIK showed that not only it cannot remove HOA but also the optical aberrations are increased. However, the amount of increase in aberrations are less than conventional Lasik. Corneal optical aberrations after photorefractive keratectomy with a larger ablation zone and a transition zone are less pronounced and more physiologic than those associated with first-generation (5 mm) ablations with no transition zone. An upcoming systematic review will seek to compare the safety and effectiveness of wavefront excimer laser refractive surgery with conventional excimer laser refractive surgery, and will measure differences in residual higher order aberrations between the two procedures.

Aspherical intraocular lenses (IOLs) have been used clinically to compensate for positive corneal spherical aberrations. Although Aspherical IOLs may give better contrast sensitivity, it is doubtful, whether they have a beneficial effect on distance visual acuity. Conventional (not Aspherical) IOLs give better depth of focus and better near vision. The reason for improved depth of focus in conventional lenses is linked to residual spherical aberration. The small improvement in depth of focus with the conventional IOLs enhances uncorrected near vision and contribute to reading ability.

Wavefront customized lenses can be used in eyeglasses. Based on Wavefront map of the eye and with the use of laser a lens is shaped to compensate for the aberrations of the eye and then put in the eyeglasses. Ultraviolet Laser can alter the refractive index of curtain lens materials such as epoxy polymer on a point by point basis in order to generate the desired refractive profile.

Wavefront customized contact lenses can theoretically correct HOA. The rotation and decentration reduces the predictability of this method.

"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.

Macropsia is generally diagnosed once a patient complains of the characteristic symptoms, such as disproportionally large objects in their visual field. The Amsler Grid test can be used to diagnose macropsia, along with other visual maladies depending on the subjective disturbance reported by the patient after looking at the Amsler Grid. Outward bulging of the lines on an Amsler Grid is consistent with patients experiencing macropsisa. The New Aniseikonia Test (NAT) can quantify the degree of macropsia or micropsia independently in the vertical and horizontal meridians. The test consists of red and green semicircles on a black background with a white round fixation target. The size of the red semicircle is held constant while the green semicircle is varied in size in 1% increments. The patient wears a pair of red/green goggles so that one eye is tested at a time, and the patient attempts to determine when the semicircles are the same size. This is termed the reversal threshold and the size difference between the semicircles is reported as the degree of aniseikonia. A positive value indicates that the object was perceived bigger and thus corresponds to macropsia, and conversely a negative value indicates micropsia. The Aniseikonia Inspector contains an aniseikonia test based on the same principles as the NAT, but the test is run on a computer screen, it is based on a forced choice method, and it can measure the size difference as a function of the size of the objects. The functionality of being able to measure the size difference as function of the size (i.e. field dependent testing) is especially important when the macropsia (or micropsia) has a retinal origin.

While preventive measures, such as taking breaks from activities that cause eye strain are suggested, there are certain treatments which a person suffering from the condition can take to ease the pain or discomfort that the affliction causes. Perhaps the most effective of these is to remove all light sources from a room and allow the eyes to relax in darkness. Free of needing to focus, the eyes will naturally relax over time, and relieve the discomfort that comes with the strain. Cool compresses also help to some degree, though care should be taken to not use anything cold enough to damage the eyes themselves (such as ice). A number of companies have released "computer glasses" which, through the use of specially tinted lenses, help alleviate many of the factors which cause eye strain, though they do not completely prevent it. Rather, they just make it harder to strain the eye.

Sometimes asthenopia can be due to specific visual problems—for example, uncorrected refraction errors or binocular vision problems such as accommodative insufficiency or heterophoria. It is often caused by the viewing of monitors such as those of computers or phones for prolonged periods of time.

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.

Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia and usually involves more severe axis deviation than exophoria. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision. Infantile exotropia (sometimes called "congenital exotropia") is seen during the first year of life, and is less common than "essential exotropia" which usually becomes apparent several years later.

The brain's ability to see three-dimensional objects depends on proper alignment of the eyes. When both eyes are properly aligned and aimed at the same target, the visual portion of the brain fuses the forms into a single image. When one eye turns inward, outward, upward, or downward, two different pictures are sent to the brain. This causes loss of depth perception and binocular vision. There have also been some reports of people that can "control" their afflicted eye. The term is from Greek "exo" meaning "outward" and "trope" meaning "a turning".

Aponeurotic and congenital ptosis may require surgical correction if severe enough to interfere with vision or if cosmetics is a concern.

Treatment depends on the type of ptosis and is usually performed by an ophthalmic plastic and reconstructive surgeon, specializing in diseases and problems of the eyelid.

Surgical procedures include:

- Levator resection

- Müller muscle resection

- Frontalis sling operation (preferred option for oculopharyngeal muscular dystrophy)

Non-surgical modalities like the use of "crutch" glasses or Ptosis crutches or special scleral contact lenses to support the eyelid may also be used.

Ptosis that is caused by a disease may improve if the disease is treated successfully, although some related diseases, such as oculopharyngeal muscular dystrophy currently have no treatments or cures.

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

Surgeons can remove or peel the membrane through the sclera and improve vision by 2 or more Snellen lines. Usually the vitreous is replaced at the same time with clear (BSS) fluid, in a vitrectomy. Surgery is not usually recommended unless the distortions are severe enough to interfere with daily living, since there are the usual hazards of surgery, infections, and a possibility of retinal detachment. More common complications are high intraocular pressure, bleeding in the eye, and cataracts, which are the most frequent complication of vitrectomy surgery. Many patients will develop a cataract within the first few years after surgery. In fact, the visual distortions and diplopia created by cataracts may sometimes be confused with epiretinal membrane.