Amblyopia

Amblyopia or lazy eye is clinically defined as the inability to see clearly through one eye. Amblyopia is considered the most common visual problem among children. The disorder seen in Amblyopia is due to the reduced coordination between the eyes and the brain.

Amblyopia is related to congenital processes. The incidence rate of the disease is defined as ca. 0 / 100.000.

Presentation

Patients suffering from amblyopia or lazy eye will usually present with an eye that is wandering inward or outward during visual examination. There is a marked discordance between the two eyes which may appear that both eyes may not work in coordination with each other. Patients will start to note that they have markedly poor visual depth perception of solid objects and things. Amblyopia frequently affects a single eye but in certain cases, this can affect both eyes. The outward signs typically seen in amblyopia requires a meticulous eye examination by a qualified medical professional to detect.

Workup

Amblyopia or lazy eye are commonly diagnosed clinically during a thorough eye examination. The different tests implored for the diagnosis of amblyopia is dependent on the age group of the patient:
Neonates – By flashing a penlight over the eyes of the newborn, a glaring red eye reflex may be seen connoting that are no impending congenital cataract in the eye that may advertently lead to amblyopia.
Infants – Infants are clinically tested for their inherent ability to gaze and follow moving objects with their eyeballs. This practical test will reveal the presence of strabismus among high risk patients.
Toddlers – The red reflex test is fervently done on toddlers to detect cataract formation. Photo screening and auto refraction is also implored to detect this visual anomaly [7].
Preschoolers – The older children will benefit from tests that makes use of pictures and letters. Both eyes are alternatively patched to check both eyes for visual defects at this age.

Treatment

By convention, amblyopia is treated in early childhood especially during the period where the brain and eye connections are starting to take form. The treatment options available for amblyopia is dependent on cause and the degree to which the child’s vision is affected. The following treatment options are available for amblyopia or lazy eye:

  • Eye patches – Eye patches may be worn over the child’s stronger eye to help visually stimulate the weaker eye and its visual pathways to the brain [8]. 
  • Eye drops – Patients suffering from amblyopia are given atropine drops on the normal eye one daily or twice weekly to blur the vision of the normal eye [9]. This will encourage the patient to use the other eye as well.
  • Corrective spectacles – This corrective glasses can by prescribed to the patient by the ophthalmologist to allay symptoms of lazy eye especially when it is caused by conditions like nearsightedness, farsightedness, or astigmatism [10].
  • Ophthalmic surgery – Amblyopia that are considered severe with eyes that are wondering may sometimes require surgery for the repair of the ocular muscles.

Prognosis

The earlier amblyopia is diagnosed and brought for professional medical intervention the sooner it is corrected. Amblyopia is no longer curable beyond the age of 8 years old when the visual pathways have reached full maturity. Best visual improvements are seen among patients who are treated before the fifth year of life. Treatments initiated when the child has not yet reached 2 years of age are likely to achieve full and complete recovery of the visual impairment.

Etiology

Clinically, any medical condition that blur’s the visual field or cause the eye to cross can possibly cause lazy eye or amblyopia. The following common causes can lead to Amblyopia:
Strabismus – This is the most common cause of amblyopia or lazy eye. Strabismus is clinically defined as an imbalance in the muscles that can make the eyes lead out or crossed externally [1].
Visual Deprivation – Lazy eye consequently develops in an eye when the other eye is deprived of vision like those found in cataract cases [2]. Clinical conditions associated with visual deprivation include congenital cataract, corneal opacities, and ptosis [3].
Eye Refraction – Amblyopia results when there is a significant difference between the visions both eyes. Common causes include nearsightedness, farsightedness, and astigmatism of the eye surface.

Epidemiology

The worldwide statistics for amblyopia is only 2-3% among children. They are found to occur predominantly before the second year of life. This visual anomaly may still be found in children up to the age of 8 years old although infrequent. Children are best treated before the age of 8 years old but in some cases, amblyopia persist until late childhood and adulthood which may now be very difficult to correct. There is no racial and sexual predilection found in amblyopia.

Sex distribution
Age distribution

Pathophysiology

The pathophysiology of primary amblyopia is referred to as a developmental disease of the brain rather than as an organic disease of the eyeball. Although some cases of amblyopia can result from an on-going organic problem that may persists long after the primary organic disease process has been resolved [4]. In cases where there are opacities that block visual images from the affected eye, the neural pathway becomes incompletely stimulated on one side. This disruption in the pathway will lead to the incomplete development of the affected visual cortex in the brain [5]. The stage in neural development that is grossly affected in amblyopia completely develops at the age of two, thus the visual pathways are most susceptible and fragile within the first two years of life [6].

Prevention

The early detection and treatment of amblyopia or lazy eye among the young children can greatly prevent permanent visual loss, It is imperative that all children should at least undergo one professional eye check-up between the age of 3 and 5 years old. Patients suspected of eye defects who are too young to speak should be brought to an eye specialist for a prompt eye evaluation.

Summary

The eye impairment found in Amblyopia is primarily due to the abnormal visual development occurring during the infancy or early childhood periods of growth. When amblyopia is left unchecked, an observable mild to moderate visual impairment is seen even among the younger age groups. Lazy eye develops when the nerve pathways between the brain and the eye is impaired causing the brain to ignore the defective eye and focuses on the functional eye. The consequent neural exclusion of the impaired eye makes it appear wandering externally and deviant from the actual object in focus, thus coined a “lazy eye”.

Patient Information

  • Definition: Amblyopia or lazy eye is clinically defined as the inability to see clearly through one eye due to an abnormal development in visual pathway in the brain.
  • Cause: Amblyopia is commonly brought about by any form of sight deprivation in one of the eyes. This can also be caused by strabismus and eye refraction. 
  • Symptoms: Patients with amblyopia or lazy eye will often times present with a wandering eye which deviates outwardly or inwardly. Eye coordination is markedly discordant in this condition. 
  • Diagnosis: The diagnosis of amblyopia is clinched through the early screening of the eyes for children. Red reflex is arbitrarily done especially during infancy. Photo screening and auto refraction can also be done to diagnose the disease.
  • Treatment and follow-up: Patients will benefit from eye drops and eye patches to temporarily deprive the stronger eye with normal vision and enhance the poorer eye. Corrective glasses can also be indicated to relieve the disease condition. Ophthalmic surgery may also be indicated to radically correct the visual impairment.

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References

  1. Kushner, BJ. Amblyopia. In: Nelson LB, ed. Harley's Pediatric Ophthalmology. 1998:125-39.
  2. Angell et al., Robb, RM, Berson, FG (1981). "Visual prognosis in patients with ruptures in Descemet's membrane due to forceps injuries". Arch Ophthalmol 99 (12): 2137–9.
  3. Lin LK, Uzcategui N, Chang EL. Effect of surgical correction of congenital ptosis on amblyopia. Ophthal Plast Reconstr Surg. Nov-Dec 2008; 24(6):434-6.
  4. McKee, SP., Levi, DM. Movshon, JA. (2003). "The pattern of visual deficits in amblyopia". J Vision 4 (5): 380–405.
  5. Lempert P. Retinal area and optic disc rim area in amblyopic, fellow, and normal hyperopic eyes: a hypothesis for decreased acuity in amblyopia. Ophthalmology. Dec 2008; 115(12):2259-61.
  6. Jeffrey Cooper & Rachel Cooper. "All About Strabismus". Optometrists Network. Retrieved 9 March 2008.
  7. McNamara D. Laser scanner tops comparison of preschool vision screens. Medscape Medical News. April 15, 2013.
  8. Holmes, Repka, Kraker & Clarke (2006). "The treatment of amblyopia". Strabismus 15 (1): 37–42.
  9. Wright, Kenneth W.; Spiegel, Peter H.; Thompson, Lisa S. (2006). Handbook of Pediatric Strabismus and Amblyopia. New York, New York: Springer. ISBN 978-0-387-27924-4.
  10. Taylor K, Powell C, Hatt SR, Stewart C. Interventions for unilateral and bilateral refractive amblyopia.Cochrane Database Syst Rev. Apr 18 2012;4:CD005137.

  • Commonly missed diagnoses in the childhood eye examination - S AMBLYOPIA - Am Fam Physician, 2001 - aafp.org
  • Behavioural studies of spatial vision in cats reared with convergent squint: Is amblyopia due to arrest of development? - SG Jacobson, H Ikeda - Experimental Brain Research, 1979 - Springer
  • Cranio-skeletal dysplasia - N Hajdu, R Kauntze - British Journal of Radiology, 1948 - Br Inst Radiology


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