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Lazy Eye

Strabismus Strabismus is a fancy word for eye turn. Whether the eye turns in or out, is constant, intermittent, alternates between each eye or not, it all falls under the general term of strabismus. It occurs mainly due to the following things, either the eye fails to have full range of motion(eye muscle problem), the information received through the eye does not correlate with the other eye(brain processing problem), or the visual system was "built" on a fragile foundation(developmental/gross motor problem). There are a small percentage of people who have strabismus due to structural eye muscle abnormalities. More commonly, those with strabismus fall under the other two categories.
The requirements for clear, single, binocular vision in all positions of gaze are very precise. We begin to learn how to coordinate our eyes during infancy. Sometimes, even for no reason, the wiring between eyes and brain get misguided. This does not exclusively mean eyesight, which is why those strabismics who have good eyesight in the strabismic eye still have an eye turn. For them, it doesn't have to do with clarity, it's about quality.
In addition to learning eye coordination, infants begin to learn body coordination and how that coordination relates to their spatial environment. 'If I can move this arm then I can reach this toy.' These gross motor developments lay the foundation for more precise fine motor developments such as hand and eye movements. It is commonly found in a strabismic patient that the eye turn is not the problem but a symptom of a weakly developed or fragile gross motor system usually on the same side of the body as the eye turn. Directing therapy only to the eye turn treats the recurring symptom instead of the cause. Thus therapy that is targeted first at controlling and directing body movement on the weaker side with only the strabismic eye. Then directing body movement with both eyes is much more beneficial.

Amblyopia As we go about our daily lives, objects in our environment are interpreted as one whether we view them with one eye or both. The reason things aren't doubled is because the seeing happens in our brain and not in our eyes. The key piece of information as it pertains to our topic is that we see one object whether both eyes are open or just one. Amblyopia is visual condition in which one or uncommonly both eyes have decreased eyesight in spite of perfect ocular health and full prescription correction. You might be asking yourself, "Then what is the problem?" Amblyopia has three main causes. The first is strabismic amblyopia which means that because one eye turns in or out the majority of the time, that eye will have poorer eyesight. The second is called form deprivation amblyopia which is the result of a blockage of visual information into the eye. For information to be collected clearly by the back of the eye, light must pass through the eye relatively undisturbed. This is why the cornea, lens and intraocular fluids are clear and free from blood vessels. If there is a problem with the clarity of these parts such as a cataract then visual deprivation occurs and there is residual loss of eyesight after the cataract is removed. The last type is refractive amblyopia which occurs when one eye has a large difference in prescription relative to the other eye. This is exactly why it is uncommon for a child to realize one eye doesn't work very well. With both eyes open the brain uses information from the better seeing eye. Kids don't often go around squinting one eye or the other to ever notice the difference. So what do we do about it? Nothing? Well, amblyopia will not harm anyone directly, but it definitely affects quality of life. Most of us take our binocular vision for granted, we make a thousand decisions a day based on the spatial orientation of things, the timing and depth. Those who have to make those decisions with only one eye are at a great disadvantage. The focus of therapy for amblyopia is aimed at the brain, more specifically the pathways between the brain and the eyes and working toward equality of strength or importance of those pathways.

Convergence Insufficiency Let's discuss some terminology. Convergence is the ability of the eye muscles to bring each eye inward in a smooth, coordinated movement to point the eyes at an object which is closer to you than other objects in the environment. Looking to the left or right is not convergence; each eye must move in toward your nose. If the eyes aren't coordinated with each other and one eye turns in more than the other, then the eyes are pointing at different things which often results in double vision. Binocular vision is the fusion of information seen by each eye into a single image. Working distance is the average distance, 16 inches, from your eyes to the magazines you read or desktop items you work on. Taller people with longer arms tend to have larger working distances and vice versa for shorter people with shorter arms.
People with convergence insufficiency (CI) usually have some degree of convergence ability. The symptoms of eyestrain, headaches, double vision, eye rubbing, etc. begin when that person is asked to read or perform some type of desk work. This requires the eyes to converge a certain amount. Their convergence ability may not allow clear, single, binocular vision at their working distance. Others may have the ability to converge to their working distance but lack the ability to sustain it for an extended period of time.
Recently, a study has been published on this topic. To read the complete publication click here.