What is a “lazy” eye?

Parents often mention the term “lazy eye” in my optometric practice, however few people really understand the word. The term “lazy eye” is misleading, as the eye is not lazy at all. “Lazy eye” is a condition where there is reduced vision present in one eye that is not correctable with glasses or contact lenses and is not due to any eye disease. The brain ignores that eye and focuses on the other eye. The uncorrectable and reduced vision is the result of a problem in the brain and not the eye itself. The correct term for a lazy eye is amblyopia. It is estimated that 3% of children at age six have some form of amblyopia.

Symptoms of lazy eye

In many cases the brain and the good eye compensate so well for the shortfall that the problem goes unnoticed and is only detected after a routine eye exam. Children will often not complain but possible signs and symptoms of lazy eye may include:

·      Blurred vision in one eye

·      Occasional double vision.

·      May close one eye or may have a head tilt to compensate

·      Poor depth perception: clumsy or poor fine motor skills

·      Eyes do not appear to work together

Causes of lazy eye

Children are not born with good eyesight but must learn how to use their vision and to use their eyes together. If something affects one of the eyes during development, the signal between the eye and the brain gets disrupted and the brain begins to ignore that eye and becomes increasingly reliant on the stronger eye.

The most common conditions that disrupt the development of vision and can cause lazy eye are:

·      Squint

A squint is a common condition where one eye looks straight ahead but the other eye looks off to the left or right, up or down. The brain will receive two very different images that it cannot combine. In children who are still developing, it will cause the brain to ignore the images from the squinting eye, leading to a lazy eye.

·      Refractive errors

Refractive errors occur when the shape of the eyeball is too flat or too curved resulting in the light rays entering the eye being not properly focused.  One sharp image seen with one eye and a blurred image seen with the other will result in the brain relying only on the signals from the eye with the clear image. The other eye will fail to develop properly.

Less common conditions that can cause a lazy eye include:

  • Childhood cataracts
  • Clouding of the lens in the eye that is present from birth
  • Droopy eyelid
  • One eyelid obstructs the pupil and interferes with vision

Diagnosis of a lazy eye

 It is important for children to have eye examinations. The sooner a problem that might interfere with visual development is identified, the better. The first eye examination should be before the age of 3 to rule out risk factors for the development of a lazy eye.  The potential risk for a lazy eye is higher if there is a family history of a lazy eye or squints.

Treatment of lazy eye

A commonly prescribed treatment for amblyopia is “occlusion therapy”. Occlusion Therapy or “patching” involves wearing an eye patch on the good eye for a number of hours a day to stimulate vision in the poorer eye. Although traditional patching forces the poorer eye to “work” and does improve vision clarity over time, it is considered an old-school approach. Other than being frustrating and emotionally upsetting for children, patching the poor eye for extended periods of time does not teach the child binocular (two-eyed) vision.

Newer approaches to amblyopia involve training with one eye at a time as well as two eyes working together through office-based vision therapy. This is done with a visual therapist under supervision of an Optometrist along with home visual activities that complement the weekly office sessions.

This treatment approach yields the best outcomes with the ultimate goal being normalization of eyesight in the poor eye and the development of stereo (3D) vision for the child.