The term lazy eye is slang or lay term that describes reduced vision in one eye caused by the failure of the vision in that eye to develop. The one eye is considered weaker or “lazy” and this eye often wanders inwards or outwards. The other eye is considered the strong or good eye. There is no standard definition of lazy eye but the following are terms that often describe this condition. It is better to use the correct medical terms to describe these eye conditions. Amblyopia and strabismus are the typical eye conditions people refer to when discussing lazy eye. Other conditions can include ptosis.
Early diagnosis and treatment can help prevent long-term problems with the child’s vision. Treatment can usually be correct with glasses or contact lenses, syntonics (optometric phototherapy) and vision therapy. Patching may be part of a vision therapy program. Less obtrusive patches called “bi-nasal occlusion” are commonly in the clinic. A child's first eye exam should be scheduled at 6 months of age and at least once per year after that.
Amblyopia is referred to a condition where there is poor vision in one or rarely both eyes without any underlying structural or pathological cause. There are three types: refractive amblyopia, strabismic amblyopia and deprivation amblyopia. If visual acuity is normal in both eyes by the age of 5, it is extremely unlikely amblyopia can occur.
Refractive amblyopia can result in some situations that prevents the eyes from focusing clearly. If there is difference in refractive error, this is called anisometropia. In myopia difference of refraction between the eyes of as little as -3D will cause amblyopia in one eye. Farsighted (hyperopia) this difference can be as little as +1D. These refractive errors need to be present up to 5 years of age to cause amblyopia. When both eyes have a very high refractive error amblyopia may occur in both eyes otherwise known as bilateral amblyopia. Eye glasses (often with prism lenses) and contact lenses are nearly always required.
Strabismic amblyopia can result when one eye is not straight. Typically one particular eye will turn in towards the nose or outwards. This eye turn is called strabismus. Amblyopia occurs when the eye turn is constant. Common eye turns are called esotropia (cross eyed) or exotropia. If both eyes are aligned at least some of the time, this is called intermittent strabismus. In this case amblyopia is unlikely present, however testing and treatment is required.
Deprivation amblyopia can be caused by form deprivation. Deprivation amblyopia is caused by a physical obstruction of vision, which prevents a well focused, high contrast image on the retina. This type of amblyopia is relatively rare, found in only about 0.1% of the population, and is associated with conditions such as, cataract, blood in the eye, corneal opacities, vitreous opacities or significant ptosis (drooping eyelid) occurring early in life.
Convergence insufficiency does not cause to amblyopia. This is a common non-strabismic binocular vision problem. Normal convergence is the coordinated movement and focus of our two eyes inward on close objects, including phones, tablets, computers, and books. It is one of many vital visual skills learned during our early years, as we begin to make sense of the world and how to use our eyes to take it all in. When convergence is insufficient, it means that the eyes do not come together closely enough when looking at a near object (dashed lines in above image), so the eyes are essentially looking "past" the target focal point. The American Optometric Association and the 2008 Convergence Insufficiency Treatment Trial clearly support the superiority of office-based vision therapy, supplemented by at-home vision therapy, for treatment of convergence insufficiency.
When we are not able to converge our eyes easily and accurately, problems may develop, such as: