Overview
Definition:
Amblyopia, commonly known as lazy eye, is a developmental disorder of vision that results in reduced visual acuity in one or both eyes, despite adequate optical correction
It occurs when the brain favors one eye over the other, leading to impaired visual development in the less-favored eye
This condition arises from abnormal visual experience during the critical period of visual development, typically before the age of 7-9 years.
Epidemiology:
Amblyopia affects approximately 2-5% of the pediatric population worldwide
It is a leading cause of monocular visual impairment in children and young adults
Risk factors include strabismus, anisometropia (significant difference in refractive error between the eyes), significant refractive errors in one or both eyes (myopia, hyperopia, astigmatism), and visual deprivation (e.g., congenital cataracts or ptosis).
Clinical Significance:
Untreated amblyopia can lead to permanent visual deficits, including reduced visual acuity, impaired stereopsis (depth perception), and difficulty with visual tasks
Early diagnosis and intervention are crucial for maximizing visual recovery
The choice of treatment between patching and atropine depends on the type, severity, and cause of amblyopia, as well as patient compliance and age.
Clinical Presentation
Symptoms:
Often asymptomatic in the affected child, detected during routine screening
Parents may notice the child favors one eye
Poor depth perception
Head tilting to align the eyes
Drooping eyelid (ptosis) or cloudy cornea (cataract) may be apparent
Squint or eye turn (strabismus) may be present.
Signs:
Reduced visual acuity in one or both eyes on Snellen chart testing, despite best optical correction
Strabismus (misalignment of the eyes) may be observed
Poor fixation with the amblyopic eye
Reduced or absent stereopsis on testing (e.g., Titmus test)
Pupillary abnormalities are usually absent unless associated with optic nerve hypoplasia.
Diagnostic Criteria:
Visual acuity of 20/25 (6/7.5) or worse in one or both eyes
The cause is not attributable to structural abnormalities of the eye or neurological conditions
Occurs during the critical period of visual development (typically up to age 7-9 years).
Diagnostic Approach
History Taking:
Detailed birth history (prematurity, birth weight)
Family history of strabismus, amblyopia, or refractive errors
History of eye trauma, infections, or surgery
Presence of symptoms suggestive of visual impairment
Previous eye examinations or treatments.
Physical Examination:
Visual acuity assessment using age-appropriate charts (e.g., Snellen, HOTV, Lea Symbols)
Cover test to detect strabismus (esotropia, exotropia, hypertropia, hypotropia)
Refraction to determine refractive error (spherical, cylindrical, axis)
Examination of ocular media for opacities (cornea, lens, vitreous)
Red reflex testing to rule out media opacities
Palpation of orbits for masses
Neurological examination to rule out central causes.
Investigations:
Cycloplegic refraction is essential to accurately assess refractive errors
Fundus examination under mydriasis to rule out structural causes of reduced vision (e.g., retinal dystrophies, optic nerve hypoplasia)
Optical Coherence Tomography (OCT) or ultrasound may be used if media opacities prevent fundus view
Visual evoked potentials (VEPs) can objectively assess visual pathway function but are not routinely used for diagnosis.
Differential Diagnosis:
Uncorrected refractive error
Strabismus
Optic nerve hypoplasia
Congenital cataracts
Corneal opacities
Ptosis causing visual deprivation
Neurological conditions affecting visual pathways (e.g., cortical visual impairment, optic neuritis).
Management
Initial Management:
The primary goal is to achieve the best possible visual acuity in the amblyopic eye
This involves first correcting any underlying cause of amblyopia
This includes prescribing appropriate glasses or contact lenses for refractive errors and treating any visual deprivation (e.g., cataract surgery, ptosis repair).
Medical Management:
The mainstay of amblyopia treatment is to force the brain to use the amblyopic eye
This is achieved through: 1
**Patching (Occlusion Therapy):** A patch is placed over the good eye for a prescribed duration each day, forcing the brain to rely on the amblyopic eye
The duration and frequency depend on the age of the child and the severity of amblyopia (e.g., 2-6 hours per day for moderate amblyopia, full-time for severe amblyopia)
2
**Atropine Penalization:** Dilating drops of 1% atropine are instilled into the good eye, causing blurred vision
This pharmacologically penalizes the good eye, encouraging the use of the amblyopic eye
It is often used for milder amblyopia or when compliance with patching is an issue
For distance vision, atropine blurs distant objects
for near vision, it blurs near objects.
Surgical Management:
Surgery is indicated for underlying causes of amblyopia that require correction, such as strabismus surgery to align the eyes or surgery for congenital cataracts or significant ptosis that cause visual deprivation
Surgery is generally not a direct treatment for amblyopia itself but is a prerequisite for effective amblyopia treatment.
Supportive Care:
Regular follow-up visits are crucial to monitor visual acuity and compliance with treatment
Adjustments to the patching schedule or atropine dosage may be necessary
Parental education and support are vital for successful treatment adherence
Use of visual training or exercises may be considered in older children or for residual amblyopia.
Complications
Early Complications:
Skin irritation or breakdown from patching
Photophobia and blurred vision from atropine
Decreased binocularity or suppression of the treated eye if treatment is too aggressive or stops prematurely.
Late Complications:
Recurrence of amblyopia if treatment is discontinued too early or without adequate follow-up
Reduced visual acuity and stereopsis that persist into adulthood
Increased risk of visual impairment if the good eye is injured later in life.
Prevention Strategies:
Adherence to prescribed treatment regimens for the recommended duration
Regular ophthalmological follow-up to monitor progress and adjust treatment
Gradual reduction of patching time or atropine use under supervision
Encouraging binocular activities once visual acuity has improved.
Prognosis
Factors Affecting Prognosis:
Age at initiation of treatment (earlier is better)
Severity of amblyopia at diagnosis
Cause of amblyopia (deprivation amblyopia often has a poorer prognosis)
Duration and compliance with treatment
Presence of strabismus.
Outcomes:
With early and consistent treatment, visual acuity can improve significantly
Many children can achieve 20/20 vision
However, some residual amblyopia may persist, especially if treatment is delayed
Good stereopsis is more likely to be achieved with treatment for refractive amblyopia or mild strabismic amblyopia compared to severe strabismic amblyopia.
Follow Up:
Follow-up is typically required for several years, even after visual acuity has normalized
The frequency of follow-up decreases over time but may continue until visual maturity
Monitoring for recurrence is important, especially during periods of rapid growth or significant visual changes
Extended follow-up may be needed for patients with a history of severe amblyopia or strabismus.
Key Points
Exam Focus:
Understand the definition and critical period for amblyopia
Differentiate between patching and atropine penalization, including their indications, durations, and side effects
Recognize that treating the underlying cause (refractive error, strabismus, deprivation) is paramount before amblyopia therapy
Prognosis is age-dependent.
Clinical Pearls:
Always perform cycloplegic refraction in children suspected of amblyopia
Compliance is the biggest challenge
tailor treatment to the child and family
Consider atropine for older children or those with compliance issues with patching
Monitor for amblyopia recurrence even after initial success.
Common Mistakes:
Failing to perform cycloplegic refraction
Prescribing glasses without adequate trial period
Inadequate duration or frequency of patching/atropine
Discontinuing treatment prematurely
Attributing reduced vision to other causes without ruling out amblyopia.