If you are able to read and see the world with ease and clearly, you should be grateful for having a good eye sight. Do you know that there are at least 2.2 billion people in the world who have vision impairment? Being able to see well is something that should not be taken for granted. If you have eye problems, you should definitely ask a doctor immediately. In this article, we will learn about eye conditions that can cause problems with vision known as diplopia.

To understand how diplopia actually affects a person, do you know how we are able to see things through the eyes? First, light passes through the cornea (the clear front part of the eyes). Some of the light enters through an opening known as the pupil. The iris (the coloured part of the eyes) controls the amount of light entering the eyes. The light then passes through the lens (a transparent part of the eyes). Lens and cornea work simultaneously to focus light onto the retina. Light needs to be focussed on the retina (layer of tissue at the back of the eyes) in order for the brain to perceive the image seen. There are many photoreceptors, special cells on the retina that turn light into electrical signals.  The electrical signals travel from the eye to the brain via an optic nerve. The brain will translate these signals into images.

Diplopia refers to seeing 2 images of a single object. It can affect 1 eye or even both eyes at the same time. It can be difficult for children with diplopia to let know if they have diplopia but there are things parents can see to suspect if their child might experiencing diplopia such as squinting eyes to see better, covering 1 eye with their hand, turning head in unusual ways constantly and looking sideways instead of facing upfront. Diplopia is often known as double vision.

There are 2 kinds of diplopia which are monocular diplopia and binocular diplopia. Monocular diplopia occurs when something distorts light transmission through the eyes to the retina. Monocular diplopia may produce more than 2 images at a time with one image in normal quality and the rest are poor one. Common causes for monocular diplopia are cataract, corneal shape problems such as keratoconus and uncorrected refractive error such as in astigmatism. Binocular diplopia is the breakdown in the fusional capacity of the binocular system. Binocular diplopia only produces 2 images with equal quality. There are many possible causes for binocular diplopia, common ones are myasthenia gravis and palsy of cranial nerves.

Speaking of cranial nerves, do you know what cranial nerve is affected in diplopia? The common cranial nerve causing diplopia is when there are problems with the 3^rd, 4^th or 6^th cranial nerve. Cranial nerves III, IV and VI are known as oculomotor, trochlear and abducens respectively. These 3 cranial nerves play a role in the eye muscle, specifically extraocular muscles. These nerves work to maintain both eyes in primary position and aligned with each other. Thus, when there is an issue with any of these cranial nerves, it will cause eye misalignment. The eye misalignment itself will then affect the way images fall on the retina and the way a person perceives images.

Symptoms of diplopia are double vision with more than one image seen. Binocular diplopia is present when both eyes are open at the same time and the double vision goes away when one eye is covered. Monocular diplopia persists in one eye even if the other eyes are covered. Other symptoms include droopy eyelids (ptosis), headache, crossed eyes, nausea, pain with eye movement and weakness of the eyes.

Double vision may result from minor eye problems such as dry eyes but due to the fact that it can be caused by many reasons, it is important to get checked by a doctor for diplopia when it occurs. Thorough eye examination can help assess eye health and eye movement. Monocular diplopia is common and is the most serious condition as it is often caused by underlying diseases that can be life-threatening.

The underlying cause of diplopia will determine the treatment. For complex cases such as diabetes, treatment for the condition is needed. Common treatment includes usage of eye patch, occlusive lens or Fresnel prism on glasses and injection of botox. Surgery may be offered in certain cases.

In essence, diplopia is the double vision which is characterised by the images seen as two or more for one object. There are many causes that can lead to diplopia, either harmless such as dry eyes or dangerous such as stroke. It is best to get checked by a doctor when diplopia occurs to mitigate risk for life-threatening events. Monocular diplopia is said to be more dangerous than binocular diplopia despite being the common type seen in clinical settings.