Double Vision and Eye Alignment
Double vision should be considered an ocular emergency. Double vision is assessed by the Eye Doctor with extraocular muscle (EOM) testing, cover test and phoria testing.
During EOM testing the Eye Doctor moves a target up, down, and side to side. This test assesses the function of cranial nerves (3, 4, and 6) and the muscles they control. These are the muscles that move the eye in various directions.
The cover test is useful for testing eye alignment by measuring the phoria and tropia. A phoria or heterophoria is the natural position of eye alignment. If the eyes are naturally misaligned horizontally or vertically the EOMs can strain to some degree to correct this and keep vision single. If double vision is present, then a tropia is present.
For a tropia, eye misalignment is to large to be compensated for. Tropia is known as a strabismus or eye turn. For a new tropia or strabismus double vision results. The brain really dislikes double images and attempts to prevent double vision in two ways. For those with long term eye turns a head tilt or turn may develop or the brain stops processing visual information of both eyes together, instead using each eye individually.
Neither solution is ideal. A head tilt or turn can cause torticollis or permanent contracture of the neck muscles and postural problems. Using each eye individually results in a lack of depth perception and amblyopia if the brain prefers one eye over the other. Amblyopia is a diminished connection between the eye and brain resulting in the loss of detailed vision.
Abnormal findings can indicate anything from a thyroid condition to a brain aneursym. These findings are indentified by eye misalignment, double vision or eye pain. The muscles and cranial nerves involved help narrow down diagnoses.
The third cranial nerve plays the largest role in eye movement. It controls the upper eyelid, the pupil, inferior oblique, superior, medial and inferior recti. When the third nerve isn't functioning properly the eye turns down and outward. This can be monitored closely, but is not an emergency. If the eye turns down and out with a dilated pupil, this is an emergency and may indicate a brain aneursym.
The fourth cranial nerve controls the superior oblique. Poor function of the fourth nerve causes the affected eye to drift up. Blunt trauma to the back of the head is the most common cause of fourth nerve damage. Vertical double vision can also be caused by fracturing the delicate bones around the eye (blow-out fracture).
The sixth cranial nerve controls the lateral rectus. The eye turns in when the sixth cranial nerve or lateral rectus muscle aren't working properly. Microvascular disease (diabetes, high blood pressure) are the most common causes of poor sixth nerve function.
Double vision usually resolves in three months. Until resolution prism, patching or surgery can alleviate symptoms. Fresnel prism can be applied to the current glasses prescription. Prism alters the way images enter the eye. Prism allows a misaligned eye to focus the incoming image on the macula, so retinal images of both eyes match avoiding double vision. Patching covers one eye, so the retinal image of only one eye is used.
When double vision remains for over three months prism can be ground into a glasses prescription or eye muscle surgery can be done to balance the eye muscles and remove the eye turn.
Summary
Double vision can indicate a life threatening condition.
When experiencing double vision it is not safe to operate a motor vehicle
Most cases of double vision are due to microvascular disease
Most cases of double vision resolve within 3 months
Prism, patching or surgery can be utilized to treat double vision
During EOM testing the Eye Doctor moves a target up, down, and side to side. This test assesses the function of cranial nerves (3, 4, and 6) and the muscles they control. These are the muscles that move the eye in various directions.
The cover test is useful for testing eye alignment by measuring the phoria and tropia. A phoria or heterophoria is the natural position of eye alignment. If the eyes are naturally misaligned horizontally or vertically the EOMs can strain to some degree to correct this and keep vision single. If double vision is present, then a tropia is present.
For a tropia, eye misalignment is to large to be compensated for. Tropia is known as a strabismus or eye turn. For a new tropia or strabismus double vision results. The brain really dislikes double images and attempts to prevent double vision in two ways. For those with long term eye turns a head tilt or turn may develop or the brain stops processing visual information of both eyes together, instead using each eye individually.
Neither solution is ideal. A head tilt or turn can cause torticollis or permanent contracture of the neck muscles and postural problems. Using each eye individually results in a lack of depth perception and amblyopia if the brain prefers one eye over the other. Amblyopia is a diminished connection between the eye and brain resulting in the loss of detailed vision.
Abnormal findings can indicate anything from a thyroid condition to a brain aneursym. These findings are indentified by eye misalignment, double vision or eye pain. The muscles and cranial nerves involved help narrow down diagnoses.
The third cranial nerve plays the largest role in eye movement. It controls the upper eyelid, the pupil, inferior oblique, superior, medial and inferior recti. When the third nerve isn't functioning properly the eye turns down and outward. This can be monitored closely, but is not an emergency. If the eye turns down and out with a dilated pupil, this is an emergency and may indicate a brain aneursym.
The fourth cranial nerve controls the superior oblique. Poor function of the fourth nerve causes the affected eye to drift up. Blunt trauma to the back of the head is the most common cause of fourth nerve damage. Vertical double vision can also be caused by fracturing the delicate bones around the eye (blow-out fracture).
The sixth cranial nerve controls the lateral rectus. The eye turns in when the sixth cranial nerve or lateral rectus muscle aren't working properly. Microvascular disease (diabetes, high blood pressure) are the most common causes of poor sixth nerve function.
Double vision usually resolves in three months. Until resolution prism, patching or surgery can alleviate symptoms. Fresnel prism can be applied to the current glasses prescription. Prism alters the way images enter the eye. Prism allows a misaligned eye to focus the incoming image on the macula, so retinal images of both eyes match avoiding double vision. Patching covers one eye, so the retinal image of only one eye is used.
When double vision remains for over three months prism can be ground into a glasses prescription or eye muscle surgery can be done to balance the eye muscles and remove the eye turn.
Summary
Double vision can indicate a life threatening condition.
When experiencing double vision it is not safe to operate a motor vehicle
Most cases of double vision are due to microvascular disease
Most cases of double vision resolve within 3 months
Prism, patching or surgery can be utilized to treat double vision
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