30107231 Strabismus and Ambliopia

8/7/2019 30107231 Strabismus and Ambliopia

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` An intermittent or constant misalignment of an eye

so that its line of vision is not pointed at the same

object as the other eye

` Can cause amblyopia (a decrease in vision) andpermanent loss of vision


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` Strabismus is caused by an imbalance in the

muscles that control the positioning of the eye.

` Symptoms include misalignment of the eyes,

double vision, and eye muscle paralysis.` The diagnosis is based on an eye examination.

` Strabismus sometimes resolves on its own, but in

most cases, eyeglasses, eye drops, or surgery is

needed.


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` Some types are characterized by inward turning of

the eye (esotropia) and some by outward turning

of the eye (exotropia).

` Others are characterized by upward turning of theeye (hypertropia) or downward turning of the eye

(hypotropia)


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` Strabismus may cause double vision (diplopia) in

an older child or amblyopia in a younger child.

` To examine an infant, a doctor shines a light into

the eyes to see whether the light reflects backfrom the same location on each pupil.

` Treatment depends on the characteristics of the

strabismus


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` Infantile Esotropia: Infantile esotropia is a constantinward turning of the eyes that develops before 6months of age it often runs in families and tends to be severe. The eyes often begin to turn inward by 3 months of age. The degree of turning is large and easily noticeable.

` Surgery, which is accomplished by altering the pull ofthe eye muscles, is usually needed to realign theeyes. Repeated operations may be necessary.

With the best possible treatment, strabismus may not be fullycorrected. Occasionally, amblyopia develops but usually responds to

treatment.


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` Accommodative Esotropia Accommodative esotropia is inward turning of the eyes that develops between the

ages of 6 months and 7 years, most often in children aged 2 to 3 years and isrelated to optical focusing (accommodation) of the eyes.

The misalignment is the result of how the eyes move when focusing on nearby ordistant objects.

Children with accommodative esotropia are farsighted. Although everyone's eyes turn inward when focusing on very close objects, eyes

that are farsighted also turn inward when looking at distant objects. In mild cases, the eyes may turn too far inward only when looking at nearby

objects. In more severe cases, the eyes turn too far inward all the time. With treatment, accommodative esotropia can usually be corrected. Eyeglasses

can help the child focus on objects, reducing the tendency for the eyes to turninward when viewing those objects. Many children outgrow farsightedness andeventually do not need eyeglasses.

` Occasionally, drugs (echothiophate) are used to help the eyes to focuson nearby objects.

` If eyeglasses and eye drops fail to properly align the eyes, surgery mayhelp.


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` Intermittent Exotropia

Intermittent exotropia is outward turning of the eyes that

occurs intermittently, usually when the child is looking at

distant objects or when the child is tired or ill.

Intermittent exotropia that is of small magnitude, occursinfrequently, and does not cause symptoms may not require

treatment because amblyopia does not usually develop.

If symptoms of eye strain from an uncorrected refractive error

become troublesome or if attempting to bring the eyes into

alignment becomes troublesome, eyeglasses may be used In severe cases, surgery may be needed.


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` Paralytic Strabismus In paralytic strabismus, one or more of the eye muscles that move the eye in different

directions become paralyzed.

As a result, the muscles no longer work in balance.

The eye muscle paralysis is usually caused by a disorder that affects the nerves to the eyemuscles, such as certain viral illnesses, brain injuries, or brain tumors that increase pressurewithin the skull and compress these nerves.

` In children with paralytic strabismus, movement of the affected eye is impairedonly when the eye tries to move in a specific direction, not in all directions.

` Amblyopia or double vision may develop. The double vision is made worse bylooking in directions normally controlled by the paralyzed eye muscles.

` Paralytic strabismus may resolve by itself over time. However, it may need to becorrected with eyeglasses and covering of the unaffected eye. Sometimeseyeglasses with prisms are used. Alternatively, surgery may be needed. Ifparalytic strabismus results from another condition affecting the nerves, such as

a brain tumor, the other condition also needs to be treated.


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` Amblyopia refers to a decrease of vision, either

unilaterally or bilaterally, for which no cause can

be found by physical examination of the eye.

` The term functional amblyopia often is used todescribe amblyopia, which is potentially reversible

by occlusion therapy.

` Organic amblyopia refers to irreversible amblyopia


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` Most vision loss from amblyopia is preventable or

reversible with the right kind of intervention.

` The recovery of vision depends on how mature

the visual connections are, the length ofdeprivation, and at what age the therapy is begun.


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` In general, amblyopia is believed to result from

disuse from inadequate foveal or peripheral retinal

stimulation and/or abnormal binocular interaction

that causes different visual input from the foveae` There are Three critical periods of human visual

acuity development During these time periods, vision can be affected by the

various mechanisms to cause or reverse amblyopia.


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` The development of visual acuity from the 20/200

range to 20/20, which occurs from birth to age 3-5

years.

` The period of the highest risk of deprivationamblyopia, from a few months to 7 or 8 years.

` The period during which recovery from amblyopia

can be obtained, from the time of deprivation up to

the teenage years or even sometimes the adultyears.


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` United States Prevalence of amblyopia is difficult to assess and varies in the

literature, ranging from 1-3.5% in healthy children to 4-5.3% inchildren with ophthalmic problems. Most data show that about 2%of the general population has amblyopia.

Amblyopia was shown in the Visual Acuity Impairment Surveysponsored by the National Eye Institute (NEI) to be the leadingcause of monocular vision loss in adults aged 20-70 years orolder. Prevalence of amblyopia has not changed much over theyears.

` Mortality/Morbidity Amblyopia is an important socioeconomic problem. Studies have

shown that it is the number one cause of monocular vision loss inadults. Furthermore, persons with amblyopia have a higher risk ofbecoming blind because of potential loss to the sound eye fromother causes.


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` Race No racial preference is known.

` Sex

No gender preference is known.` Age

Amblyopia occurs during the critical periods of visual

development. An increased risk exists in those children

who are developmentally delayed, were premature,

and/or have a positive family history


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` Ocular history Elicit any previous history of patching or eye drops as

well as past compliance with these therapies.

Document previous ocular surgery or disease.

` In addition to the routine information, obtaining a

family history of strabismus or other ocular

problems is important because the presence of

these ocular problems may predispose a child to

amblyopia.


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` Visual acuity Diagnosis of amblyopia usually requires a 2-line

difference of visual acuity between the eyes

Crowding phenomenon: A common characteristic of

amblyopic eyes is difficulty in distinguishing optotypes

that are close together. Visual acuity often is better when

the patient is presented with single letters rather than a

line of letters.

Diagnosis is not an issue in children old enough to reador with use of the tumbling E.


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` Testing in preverbal children If the child protests with covering of the sound eye, amblyopia

can be diagnosed if it is dense.

Fixation preference may be assessed, especially whenstrabismus is present.

Induced tropia test may be performed by holding a 10-prismdiopter before one eye in cases of an orthophoria or amicrotropia.

In infants who cross-fixate, pay attention to when the fixationswitch occurs; if it occurs near primary position, then visual

acuity is equal in both eyes. Caution should be used when obtaining Teller acuity in

children, as grating acuity may be less reduced than Snellenacuity, especially in strabismic amblyopia.


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` Contrast sensitivity: Strabismic and anisometropicamblyopic eyes have marked losses of thresholdcontrast sensitivity, especially at higher spatialfrequencies; this loss increases with the severity ofamblyopia.

` Neutral density filters: Patients with strabismicamblyopia may have better visual acuity or less of adecline of visual acuity when tested with neutraldensity filters compared to the normal eye. This wasnot found to be true in patients with anisometropic

amblyopia or organic disease.` Binocular function: Amblyopia usually is associated

with changes in binocular function or stereopsis.


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` Eccentric fixation: Some patients with amblyopia mayconsistently fixate with a nonfoveal area of the retina undermonocular use of the amblyopic eye, the mechanism of which isunknown. This can be diagnosed by holding a fixation light in themidline in front of the patient and asking them to fixate on it whilethe normal eye is covered. The reflection of the light will not be

centered.` Refraction: Cycloplegic refraction must be performed on all

patients, using retinoscopy to obtain an objective refraction. Inmost cases, the more hyperopic eye or the eye with moreastigmatism will be the amblyopic eye. If this is not true, oneneeds to investigate further for ocular pathology.

` Rest of examination: Perform a full eye examination to rule outocular pathology


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` Anisometropia Inhibition of the fovea occurs to eliminate the abnormal

binocular interaction caused by one defocused imageand one focused image.

This type of amblyopia is more common in patients withanisohypermetropia than anisomyopia. Small amounts ofhyperopic anisometropia, such as 1-2 diopters, caninduce amblyopia. In myopia, mild myopic anisometropiaup to -3.00 diopters usually does not cause amblyopia.

Hypermetropic anisometropia of 1.50 diopters or greateris a long-term risk factor for deterioration of visual acuityafter occlusion therapy.


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` Strabismus The patient favors fixation strongly with one eye and

does not alternate fixation. This leads to inhibition of

visual input to the retinocortical pathways.

Incidence of amblyopia is greater in esotropic patients

than in exotropic patients.


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` Strabismic anisometropia: These patients have

strabismus associated with anisometropia.

` Visual deprivation: Amblyopia results from disuse or

understimulation of the retina. This condition may be

unilateral or bilateral. Examples include cataract,

corneal opacities, ptosis, and surgical lid closure.

` Organic: Structural abnormalities of the retina or the

optic nerve may be present. Functional amblyopia

may be superimposed on the organic visual loss.


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` Imaging Studies If suspicion exists of an organic cause for decreased

vision and the ocular examination is normal, then furtherinvestigations into retinal or optic nerve causes should be

initiated.S

tudies to perform include imaging of the visualsystem through CT scan, MRI, and fluoresceinangiography to assess the retina.

` OtherTests Although differences in the electrophysiologic responses

of normal eyes versus amblyopic eyes have beenreported, these techniques remain investigational and thedifferences are controversial


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` Histologic Findings

Histologic studies of the lateral geniculate nucleus in

kittens with deprivation amblyopia have shown that cells

receiving input from the deprived eye were shrunken andatrophied, while cells receiving input from the

nondeprived eye were expanded.


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` Medical Care

` The clinician must first rule out an organic cause

and treat any obstacle to vision (eg, cataract,

occlusion of the eye from other etiologies).` Remove cataracts in the first 2 months of life, and

aphakic correction must occur quickly.


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` Treatment of anisometropia and refractive errors must occurnext. The amblyopic eye must have the most accurate optical correction

possible. This should occur prior to any occlusion therapy because visionmay improve with spectacles alone.

Full cycloplegic refraction should be given to patients with

accommodative esotropia and amblyopia. In other patients, a prescriptionless than the full plus measurement that was refracted may be prescribedgiven that the decrease in plus is symmetric between the two eyes.Because accommodative amplitude is believed to be decreased inamblyopic eyes, one needs to be cautious about cutting back too muchon the amount of plus. Refractive correction alone has been shown toimprove amblyopia in up to 77% of patients in a nationwide trial.

Patients with bilateral refractive amblyopia do well with spectaclecorrection alone, with most children aged 3-10 years achieving 20/25 orbetter within a year.


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` The next step is forcing the use of the amblyopic eye byocclusion therapy. Occlusion therapy has been the mainstay oftreatment since the 18th century. The following are generalguidelines for occlusion therapy: Patching may be full-time or part-time. Standard teaching has been that

children need to be observed at intervals of 1 week per year of age, if

undergoing full-time occlusion to avoid occlusion amblyopia in the soundeye. The Amblyopia Treatment Studies (ATS) have helped to provide newinformation on the effect of various amounts of patching.

Always consider lack of compliance in a child where visual acuity is notimproving. Compliance is difficult to measure but is an important factor indetermining the success of this therapy.

In addition to adhesive patches, opaque contact lenses, occluders

mounted on spectacles, and adhesive tape on glasses have been used. Establishing the fact that the vision of the better eye has been degraded

sufficiently with the chosen therapy is important.


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` The Amblyopia Treatment Studies have helped to define the role of full-timepatching versus part-time patching in patients with amblyopia. The studies havedemonstrated that, in patients aged 3-7 years with severe amblyopia (visualacuity between 20/100 and 20/400), full-time patching produced a similar effectto that of 6 hours of patching per day. In a separate study, 2 hours of dailypatching produced an improvement in visual acuity similar to that of 6 hours ofdaily patching when treating moderate amblyopia (visual acuity better than

20/100) in children aged 3-7 years.In this study, patching was prescribed incombination with 1 hour of near visual activities.

` Data from the Amblyopia Treatment Studies are also available for older patients.For patients aged from 7 years to younger than 13 years, the AmblyopiaTreatment Studies have suggested that prescribing 2-6 hours a day of patchingcan improve visual acuity even if the amblyopia has been previously treated.For patients aged from 13 years to younger than 18 years, prescribing 2-6 hoursa day of patching might improve visual acuity when amblyopia has not been

previously treated; however, this is likely to be of little benefit if amblyopia waspreviously treated with patching. Long-term results from these studies are stillpending.


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` The Amblyopia Treatment Studies have also found

that about one fourth of children with amblyopia who

were successfully treated experience a recurrence

within the first year after discontinuation of treatment.

Data from these studies suggest that patients treatedwith 6 or more hours a day of patching have a greater

risk of recurrence when patching is stopped abruptly

rather than when it is reduced to 2 hours a day prior to

cessation of patching. Randomized studies have stillyet to be performed.


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` Penalization therapy In the past, penalization therapy was reserved for

children who would not wear a patch or in whom

compliance was an issue. The Amblyopia Treatment

Studies, however, have demonstrated that atropinepenalization in patients with moderate amblyopia (defined

by the study as visual acuity better than 20/100) is as

effective as patching. The Amblyopia Treatment Studies

were performed in children aged 3-7 years


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` The Amblyopia Treatment Studies have alsodemonstrated that weekend use of atropine providedan improvement in visual acuity similar to that of dailyuse of atropine when treating moderate amblyopia inchildren aged 3-7 years.

` Atropine drops or ointment is instilled in thenonamblyopic eye. This therapy is sometimes used inconjunction with patching or occlusion of the glasses(eg, adhesive tape, nail polish) by individualpractitioners. In the Amblyopia Treatment Studies that

evaluated patching versus atropine penalization,atropine penalization and patching were used inconjunction with 1 hour of near visual activities.


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` This technique may also be used for maintenance

therapy, which is useful, especially in patients with

mild amblyopia.


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` Other options include optical blurring through contactlenses or elevated bifocal segments.

` The endpoint of therapy is spontaneous alternation offixation or equal visual acuity in both eyes.

When visual acuity is stable, patching may be decreasedslowly, depending on the child's tendency for the amblyopia torecur.

Because amblyopia recurs in a large number of patients (seePrognosis), maintenance therapy or tapering of therapy shouldbe strongly considered. This tapering is controversial, so

individual physicians vary in their approaches


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` Treatment of strabismus generally occurs last. The

endpoint of strabismic amblyopia is freely

alternating fixation with equal vision. Surgery

generally is performed after this endpoint hasbeen reached.


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` Surgical therapy for strabismus generally shouldoccur after amblyopia is reversed. Disadvantagesto surgical therapy prior to correction of amblyopiainclude difficulty in telling if amblyopia is present

because there is no longer a strabismus to assessfixation preference and higher potential to beinglost to follow-up, as the child cosmetically looksbetter. The improved cosmesis gives the parents a

false sense of security about the vision improving.


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` Pharmacologic treatment with levodopa has beeninvestigated and has showed transient improvement ofvision in amblyopic eyes. However, the exact role of suchpharmacologic agents has not been determined. Levodopacurrently is not being used clinically.

` Atropine penalization (with either ointment or drops) is analternative method of blurring vision in the sound eye ofpatients who refuse patching. It may be applied once a dayto patients in the preferred eye only.

` Cycloplegics These agents are used to blur vision in one eye to treat amblyopia

in the contralateral eye


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` Outpatient follow-up care needs to continue beyond theprimary completion of amblyopia treatment because visualdeterioration occurs in many children. In a multicenterstudy conducted as part of the Amblyopia TreatmentStudies, one fourth of patients experienced recurrence of

amblyopia within the first year after treatment, with the riskof recurrence greater if the treatment was stopped abruptlyrather than tapered. One study by Levartovsky et alshowed deterioration in 75% of children with anisometropiaof 1.75 diopters or more after occlusion

therapy. Recidivism can occur, even several years after theinitial treatment period, and is as high as 53% after 3 years.


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` Vision screening programs: Studies have shown these programsto be technically easy and that they help reduce cost as well asincidence of amblyopia because of early treatment and detection.Current programs include use of the photorefractor and schoolvision screening programs.

` Amblyopia after trauma Young patients who have trauma to their eyes often are at risk for

occlusion amblyopia. Possible reasons include lid edema, hyphema,occlusive dressing, vitreous hemorrhage, and traumatic cataract.

This amblyopia often is superimposed on a visual deficit caused by anystructural abnormality and needs to be taken into account when treatingthese children.

Vision needs to be monitored closely in children after ocular trauma,

especially in those aged up to 6 years and in nonverbal children.Occlusive therapy needs to be instituted if there is any suggestion ofdecreased vision in the injured eye.


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` Complications The main complication of not treating amblyopia is long-

term irreversible vision loss. Most cases of amblyopia are

reversible if detected and treated early, so this vision loss

is preventable.


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` Prognosis After 1 year, about 73% of patients show success after their

first trial of occlusion therapy. Studies have shown that thenumber of patients who retain their level of visual acuitydecreases over time to 53% after 3 years.

Risk factors for failure in amblyopia treatment include thefollowing:

x Type of amblyopia: Patients with high anisometropia and patientswith organic pathology have the worse prognosis. Patients withstrabismic amblyopia have the best outcome.

x Age at which therapy began: Younger patients seem to do better.

x Depth of amblyopia at start of therapy: The better the initial visualacuity in the amblyopic eye, the better the prognosis.

30107231 Strabismus and Ambliopia

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