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Amblyopia F. Kianersi M.D. Isfahan University of Medical Sciences 1390 / 1 / 25
Amblyopia Sometimes called “lazy eye” characterized by: Uncorrectable, decreased visual acuity in an otherwise normal eye. Definition includes an operated eye made “structurally normal” by surgery (e.g. post cataract surgery).
Amblyopia: History “When the doctor sees nothing and the patient sees nothing, the diagnosis is Amblyopia.” Hippocrates, 450 B.C.
Amblyopia. Onset early in life (typically before age 6). Amblyopia Amblyopia may be unilateral (most common) or bilateral. It is the most common cause of monocular vision loss in children and young adults. Prevalence: 2%-4% of population.
Amblyopia Best-corrected Snellen V/A in amblyopic eyes range from mild deficits (20/25) to severe vision loss (≤20/400). The accepted definition of clinically significant Amblyopia is BCVA ≤20/40 or a difference of 2 lines of Snellen acuity between the amblyopic eye and the normal eye.
Amblyopia Degree of Amblyopia Slight BCVA: Middle BCVA: Severe BCVA: ≤ 0.1
Neurophysiology Amblyopia is primarily a defect of central vision. Cells of the primary visual cortex can completely lose their innate ability or show significant functional deficiencies. Abnormalities also occur in neurons in the lateral geniculate body. Evidence concerning involvement at the retinal level remains inconclusive.
Amblyopia is usually classified on the basis of its associated clinical condition. Two basic conditions set up the developing visual system for failure and result in Amblyopia: Abnormal binocular interaction (eg, Strabismus), Blur/distortion of the visual image due to Uncorrected Refractive Errors or Media Opacities. Classification
1.Strabismus Amblyopia (Misaligned eyes) Amblyopia 2.Anisometropic Amblyopia (Refractive Amblyopia) 3.Deprivation Amblyopia (Media opacity) Multiple or “Mixed” mechanisms often are involved.
Amblyopia: Three Main Types Amblyopia Strabismic Amblyopia Amblyopia Anisometropia Amblyopia Deprivation Amblyopia
Strabismus Amblyopia The most common form of Amblyopia. Occurring in at least 40% of children with manifest Strabismus (usually Esotropia).
Strabismus Amblyopia Strabismic Amblyopia is thought to result from competitive or inhibitory interaction between neurons carrying the nonfusible inputs from the two eye. Which leads to domination of cortical vision centers by the fixating eye and chronically reduced responsiveness to the nonfixating eye input.
Strabismus: Esotropia Infantile Esotropia Poor ability to develop binocular fusion, Amblyopia or alternating fixation.
Strabismus: Esotropia Accomodative Esotropia Amblyopia common, More Hyperopic eye tends to cross and become Amblyopic.
Strabismus: Accomodative Esotropia If eyes straight with glasses: Amblyopia partly “self-treats” since both eyes are being used simultaneously. If eyes remain crossed with glasses: Fusion lost, Amblyopia worsens.
Strabismus: Exotropia Often have good fusional ability, Amblyopia less common than with Esotropia.
Amblyopia: Three Main Types Strabismic Amblyopia Anisometropia Amblyopia Deprivation Amblyopia
Anisometropia Amblyopia Second in frequency. Clear input to the visual cortex is required to develop good vision. Amblyopia When unequal refractive error in the tow eyes causes the image on the one retina to be chronically defocused Anisometropia Amblyopia develops.
Mild Hyperopic or Astigmatic Anisometropia (1-2D) can induce Mild Amblyopia. Mild Myopia Anisometropia (less than -3D) usually doesn't cause Amblyopia. Unilateral High Myopia (-6D) often result in Sever Amblyopic visual loss. Anisometropia Amblyopia
Ametropic Amblyopia Large, approximately equal, uncorrected refractive errors in both eyes of a young child cause Bilateral reduction in acuity that is usually relatively Mild. Hyperopia exceeding about 5 D and Myopia in excess of 10 D carry a risk of inducing Bilateral Amblyopia.
Meridional Amblyopia Uncorrected Bilateral Astigmatism in early childhood may result in loss of resolving ability limited to the chronically blurred meridians. The degree of Cylindrical Ametropia necessary to produce Meridional Amblyopia is not known, but most ophthalmologists recommend correction of greater than 2 D of cylinder.
Amblyopia: Three Main Types Strabismic Amblyopia Anisometropia Amblyopia Deprivation Amblyopia
It is usually caused by congenital or early acquired media opacity. This form of Amblyopia is the least common but most damaging and difficult to treat. Deprivation Amblyopia
Best example: Monocular Congenital Cataract. Any opacity preventing light from reaching the retina: Ptosis Corneal scar/opacity Forceps injury at birth Hereditary abnormalities Vitreous opacity, Hemorrhage Deprivation Amblyopia
The most severe vision loss due to Amblyopia can be found In cases of untreated pattern deprivation during the first 3 months of life, Vision may be reduced to HM or even LP. Deprivation Amblyopia
In children younger than 6 years, dense Congenital Cataract that occupy the central 3 mm or more of the lens must be considered capable of causing Sever Amblyopia. Small Polar Cataracts & Lamellar Cataracts may cause mild to moderate Amblyopia or may have no effect on visual development. Deprivation Amblyopia
Occlusion Amblyopia Occlusion Amblyopia is a form of deprivation caused by excessive therapeutic patching.
Amblyopia sometimes coexists with visual loss directly caused by an uncorrectable structural abnormality of the eye such as Optic Nerve Hypoplasia or Coloboma. When such a situation (“Organic Amblyopia") is encountered in a young child, it is appropriate to undertake a trial of occlusion therapy; improvement in vision confirms that Amblyopia was indeed present. Organic Amblyopia
Diagnosis Amblyopia is diagnosed when reduced V/A cannot be explained entirely on the basis of physical abnormalities and is found in association with a history or finding of a condition known to be capable of causing Amblyopia.
Diagnosis Characteristics of vision alone cannot be used to reliably differentiate Amblyopia from other forms of visual loss. The Crowding phenomenon is typical for Amblyopia but is not Patahogonomic. Afferent pupillary defect (RAPD) rarely occurred in Amblyopia.
Binocular fixation pattern is a test for estimating the relative level of vision in the tow eyes for children with strabismus who are under the age of about 3. Diagnosis – V/A in Preverbal Children
Diagnosis – V/A in 3-6 years old A variety of optotypes can be used to directly measure acuity in children 3-6 years old.
Diagnosis – V/A in 3-6 years old Often, however, only isolated letters can be used, which may lead to under estimated Amblyopia visual loss.
Diagnosis Crowding bar or contour interaction bars, may help alleviate this problem. Bar surrounding the optotype mimic the full of optotype to the amblyopia child.
Prevention / Screening
Nearly all Amblyopic Visual loss is Preventable or Reversible with timely detection and appropriate intervention. Children with Amblyopia or at risk for Amblyopia should be identified at a young age when the prognosis for successful treatment is best. Role of Screening is important.
Prevention / Screening In recent years, Amblyopia has become a topic of great interest in public health policy and discussions, beyond the domain of the treating ophthalmologist’s office.
Prevention / Early Treatment Overall affects 2-4% of population Awareness of problem
Prevention / Screening Birth First examination by primary care doctor before newborn leaves hospital. Look for clear, equal Red Reflex Congenital Cataract Hereditary Corneal Dystrophies Ocular alignment unreliable in first week of life.
Prevention / Screening Birth to 2 Years Examination at each well baby check Red reflex Ocular alignment should be orthophoric by 3-6 months Visual Acuity - Fix and Follow smoothly by 6 months
Prevention / Screening 3, 4, 5 Year Checks Red reflex Ocular alignment - should be perfect Visual Acuity - Allen figures or similar External, anterior segment Ophthalmoscopic exam
Treatment of amblyopia involves the following steps: Eliminating (if possible) any obstacle to vision such as a Cataract. Correcting Refractive error. Forcing use of the poorer eye by limiting use of the better eye.
Cataract Removal Cataracts capable of producing Amblyopia require surgery without unnecessary delay. Removal of significant congenital lens opacities during the first 2-3 months of life is necessary for optimal recovery of vision.
Cataract removal In symmetrical bilateral cases, the interval between operations on the first and second eyes should be no more than 1-2 weeks. Acutely developing severe traumatic cataracts in children younger than 6 years should be removed within a few weeks of injury, if possible. Significant cataracts with uncertain time of onset also deserve prompt and aggressive treatment during childhood.
Refractive correction In generally, optical prescription for amblyopic eyes should correct the full refractive error as determined with Cyclopagia. Both Anisometropic and Ametropic Amblyopia may improve considerably with Refractive correction alone over several months.
Occlusion and Optical Degradation
Full Time Occlusion of the Sound Eye Defined as occlusion during all waking hours. It is the most powerful means of treating Amblyopia by enforced use of the defective eye.
Full Time Occlusion of the Sound Eye If skin irritation, inadequate adhesion, or poor compliance proves to be a significant problem, Spectacle-mounted occluder or special opaque contact lenses can be used as an alternative to full-time patching.
Full Time Occlusion of the Sound Eye Full time patching runs a small risk of perturbing Binocularity. Full time patching should generally be used only when constant Strabismus eliminates any possibility of useful Binocular vision. The child whose eyes are straight should be given some opportunity to see Binocularly.
Full Time Occlusion of the Sound Eye Rarely, Strabismus may result from full-time patching. Modest reductions are employed by many ophthalmologists (removing the patch for an hour or two a day) to reduce the likelihood of occlusion Amblyopia or of inducing Strabismus.
Part-Time Occlusion Defined as occlusion for 1-6 hours per day. The children undergoing part time occlusion should be kept as visually active as possible when the patch is in place. The relative duration of patch-on and patch-off intervals should reflect the degree of Amblyopia; For Moderate to Severe deficits, at least 6 hours per day is preferred.
Part-Time Occlusion Recent experimental work in older children with Amblyopia has shown that the addition of the neurotransmitter precursor Levodopa/Carbidopa to part-time occlusion regimens may extend the effective age range for Amblyopia therapy.
Penalization Optical degradation of the better eye's image to the point that it becomes inferior to the Amblyopic eye's. Use of the Amblyopic eye is thus promoted within the context of Binocular seeing.
Penalization A Cycloplegic agent (usually Atropine 1% drops or Homatropine 5% drops) is administered daily to the better eye so that it is unable to accommodate. As a result, the better eye experiences blur. This form of treatment is as effective as patching for Mild to Moderate Amblyopia.
Penalization Alternative methods of treatment based on the same principle involve prescribing excessive plus-power lenses (fogging) or diffusing filters. These methods avoid potential pharmacologic side effects and may be capable of inducing greater blur.
Penalization Another benefit of Atropinization and other nonoccluding methods in patients with straight eyes is that: The eyes can work together, a great practical advantage in children with Latent Nystagmus.
Complications of Therapy
Any form of Amblyopia therapy introduces the possibility of over-treatment leading to Amblyopia in the originally better eye. Full-time occlusion carries the greatest risk of this complication and requires close monitoring, especially in the younger child.
Complications of Therapy The first follow-up visit after initiation of treatment should occur within: 1 week for an infant, An interval corresponding to 1 week per year of age for the older child. Subsequent visits can be scheduled at longer intervals based on early response.
Complications of Therapy Part-time occlusion and optical degradation methods allow for less frequent observation, but regular follow-up is still critical. The parents of a strabismic child should be instructed to watch for a switch in fixation preference and to report its occurrence promptly.
Complications of Therapy Iatrogenic Amblyopia Sometimes, simply stopping treatment altogether for a few weeks leads to equalization of vision. Iatrogenic Amblyopia can usually be treated successfully with judicious patching of the better-seeing eye or by alternating occlusion.
Endpoint of Therapy The desired endpoint of therapy for unilateral Amblyopia is free alternation of fixation. Linear Snellen acuity that differs by no more than 1 line between the 2 eyes, or both.
Endpoint of Therapy The time required for completion of treatment depends on: 1.Degree of Amblyopia 2.Choice of therapeutic approach 3.Compliance with the prescribed regimen 4. Age of the patient
Endpoint of Therapy More severe Amblyopia, less complete obstruction of the dominant eye's vision, and older age are all associated with a need for more prolonged treatment.
Unresponsiveness Complete or partial Unresponsiveness to treatment occasionally affect younger children but must often occurs in patients older than 5 years. Conversely, significant improvement in vision may be achievable with protracted effort even in adolescents. Primary therapy should generally be terminated if there is a lock of demonstrable progress over 6 months with good compliance.
Unresponsiveness Before it is concluded that Intractable Amblyopia is present, refraction should be carefully rechecked and the macula and optic nerve critically inspected for subtle evidence of Hypoplasia or other malformation that might have been previously overlooked. Neuroimaging might be considered in cases that inexplicably fail to respond to treatment.
Unresponsiveness Amblyopia associated with Unilateral High Myopia and extensive Myelination of Retinal Nerve Fibers is a specific syndrome in which treatment failure is particularly common.
Recurrence When Amblyopia treatment is discontinued after fully or partially successful completion, approximately half of patients show some degree of recurrence, which can usually be reversed with renewed therapeutic effort.
Acuity Maintenance Regimen Patching for 1-3 hours per day, Optical penalization with spectacles, or Pharmacologic Penalization with Atropine 1 days per week. This may require periodic monitoring until age 8-10 years.
Amblyopia: Conclusion Clear the Media Correct the Refractive Error Straighten the Eyes