Double Vision Symptoms & treatment
Double vision medically termed diplopia is a disorder that involves poor teaming between the two eyes. Even though we have two eyes and separate images are formed in the retina of each eye, the brain fuses the two images into a single unified percept. This fusion process is aided by the two eyes working as a team and rotating the eyeballs in desired directions to aid fusion. A command to make the eyes move is generated by the brain and it is executed to perfection by the six extraocular muscles that surround each eyeball. In most of us, this fusion process is completed within a few hundred milliseconds and we rarely experience double vision in our routine life.
The two eyes mayhowever not work well as a team in some of us. The improper teaming may manifest itself as an eye-turn or squint or strabismus and will lead to the perception of double vision. Both children and adults are equally susceptible to eye-turn and double vision and this may occur due to a variety of reasons including paralysis or excessive contraction of one or more extraocular muscles, abnormal positioning of extraocular muscles in the eyeball and improper commands from the brain to converge and diverge the eyes. Head trauma (e.g. following road traffic accident) or systemic disorders like diabetes and hypertension are the leading causes of eye turn and double vision in adults because of extraocular muscle paralysis. Some children may be born with abnormal extraocular muscles and this may lead to eye turn from birth. Other children may develop an eye turn and experience double vision around 3 - 4 years of age when they start going to school and near work activity intensifies. Double vision may also be experienced intermittently by those who spend extended periods of time in front of the computer. The constant stress in the eyes to focus and converge on the computer screen tends to fatigue the extraocular muscles and this may lead to intermittent double vision. Intermittent double vision may also progress into a relatively more permanent form of double vision, if not attended to properly.
The short and long term consequences of double vision are quite alarming and disturbing. The experience of double vision (see figure 1 for a computer simulation of double vision) will hinder us from performing many routine activities like driving, walking around the house without bumping into things, handling equipment around the house, reading, etc. When double vision is experienced over several weeks to months, the brain adapts to the situation by permanently ignoring information from one of the two eyes a condition called amblyopia or lazy eye. Children are most susceptible to amblyopia as the eye turn and double vision is experienced during a very plastic stage of their vision development. Research on monkeys and cats that were reared with eye-turn have clearly shown that the neurons in the brain that usually respond to information from both eyes become tuned to information from only one eye (the other eyes information is suppressed) in the presence of an eye-turn. A similar neurological effect is expected in humans as well.
It is a popular belief in some societies that eye turn is a gift from God and a sign of good luck. Such a belief system does not have any basis and it is purely a myth. Having an eye turn and experiencing double vision is not normal and the problem needs to be addressed by an eye care professional on a priority basis. As adults, we can verbalize our experience of double vision and can seek medical attention voluntarily. Children, however, do not verbalize such an experience and they tend to live with the perception of double vision for a long time. Usually problems of double vision get diagnosed in children only during school eye screenings; unfortunately, the long-term consequence of double vision amblyopia has usually set in by then and the problem has become harder to treat. Parents are therefore expected to be extra vigilant and look for any signs of eye turn in their children. In any case, it is a good practice to get yourself and your child examined by a qualified eye care professional (Optometrist or Ophthalmologist) on an annual basis where such problems of eye turn and double vision may be identified early.
The management and treatment of eye turn and double vision depends on the cause of the problem. The good news is that eye turn and double vision can be completely treated and normalcy in binocular vision can be restored. For those who experience double vision because of an eye turn, the treatment options range from surgery to fix the damaged extraocular muscle or prescribe spectacles that have prisms incorporated into them. For those who experience double vision intermittently with no obvious eye turn associated with it, vision therapy through non-invasive exercise may be offered to solve the problem. These exercises may be coupled with spectacle or contact lens correction to reduce eye fatigue and encourage eye teaming. Children who have an eye turn and an associated amblyopia may require surgical correction of their eye turn plus spectacles and vision therapy (involving patching of the good eye and encouraging the amblyopic eye to see better) to fix their problem.
Figure 1: Computer simulation of double vision. The left panel shows an image as seen by someone with normal binocular vision. The middle and right panel shows an image as seen by someone experiencing double vision in the horizontal and vertical direction, respectively.