Diplopia is one of the serious disorders of the eyes, which is associated with vision impairment. In common terms it is referred to as double vision. The occurrence of diplopia is closely associated with the cranial nerves. The effects caused by this optical disorder restrict normal activities of a person such as reading, walking and driving. The causes associated with diplopia when closely examined are myogenic and neurogenic in origin leading to an optical disruption both of vision and movement of the eyes.
Clinical manifestations and classification
Diplopia can be monocular or binocular in origin. Monocular Diplopia has preexisting-associated conditions such as cataracts, luxation of the lens and keratoconus, which results in light refraction within the eye. Macular degeneration and vitreous damage also causes light refraction retention inside eye causing blurred vision.
Binocular diplopia is caused by neurogenic impairments related to Oculomotor nerve damage, which is an important nerve in facilitating the movement of eye. The muscles associated with the respective functionality are also damaged in this condition. In most cases binocular diplopia is caused because of head injuries leading to cranial damage or traumas caused to the eyes. In some cases aniseikonia (condition which results in difference in the size of images as seen by the person) is also a predominant factor leading to binocular diplopia.
Diplopia occurrence and its respective effects can be further classified as sustained and short-lived forms. Intermittent or short-lived forms are usually a postoperative sequel especially in the case of cataract surgeries. However, diplopia of both continued and short-lived forms predominantly depend upon the thyroid hormone levels and underlying medical conditions such as myasthenia gravis.
Diagnosis of diplopia is a chronological aspect consisting of various factors. A patient complaining of blurred vision has to undergo series of medical and diagnostic investigations to rule out false positive findings. Since diplopia is associated with cranial nerves predominantly the oculomotor nerve, a gaze test is administered by the optometrist to estimate the functionality of nine cardinal vision factors.
This is prior to examining the patient history thoroughly in checking for conditions such as diabetes and hyperthyroidism. Important optometric examinations such as prism test, Bilshowsky test, Stereo acuity test and visual field testing are done to evaluate the impairments existing in the muscles associated with the eye. These tests are carried out after general examinations such as tonometry, fundoscopy and slit lamp examinations.
Corrective measures are incorporated to treat the movements of the eye, which is affected drastically in this condition. Refraction errors are analyzed and corrected in order to rectify the blurred vision. Patients are given eye exercises to facilitate proper oculomotor nerve functionalities and also to prevent squint occurrence.
All vision problems need not necessarily stem from the eye. Some vision problems involve the brain. Neuro ophthalmology is the sub specialty of both neurology and ophthalmology. A neuro ophthalmologist is a Physician who specializes in the diseases affecting vision that originates from the nervous system. Conditions such as optic nerve disorders, loss of vision from central nervous system disease, double vision diplopia and involuntary movement of the eyes nystagmus are some of the disorders under the purview of a neuro ophthalmologist. An ophthalmologist attends to patients with disease or injury in the eye ball, cornea and the lens or into the eyeball at the retina inside the eye. If any problem occurs behind the eye in the optic nerve or in some distinct visual pathways connecting the brain, it requires the special skills of a neuro ophthalmologist.
A neuro ophthalmologist could be an ophthalmologist or a neurologist with additional special training. After completing a residency program in any one of the two specialty areas, they take a fellowship in neuro ophthalmology for a year or two before starting to practice as a neuro ophthalmologist. A neuro ophthalmologist attends to a full spectrum of neuro ophthalmic conditions including evaluation, diagnostic and referral services of rare and complex disorders. A neuro ophthalmologist caters to:
In addition to the above, a neuro ophthalmologist provides emergency evaluation of a wide variety of disease that can cause visual loss. Unexplained visual loss can arise out of uncommon disease conditions like myasthenia gravis, multiple sclerosis, mitochondrial disease and other muscular diseases that affect the eye. The neuro ophthalmologist uses special testing techniques including visual fields, visual evoked response, imaging studies such as CT, MRI and Angiography and ultrasound to diagnose the disease patterns. It becomes necessary for the neuro ophthalmologist to work closely with other medical specialists to offer multidisciplinary care and solution for complex cases.
Bielschowsky test is a simple three step test to identify the paretic extra ocular muscle resulting in vertical ocular deviation. The fourth cranial nerve is responsible for controlling the extra ocular muscles and any damage caused to this cranial nerve results in vertical ocular deviation. With fourth cranial nerve palsy, the patient may have vertical and a torsional Diplopia - double vision and hence show an abnormal head posture with the head slightly tilted to the unaffected side with chin depression. Bielschowsky test or Park 3 Step Test provides useful information in assessing the affected muscle in case of ocular deviation.
While conducting Bielschowsky's (head tilt) test, examiner tilts the patient's head in both left and right directions and assesses if it improves or worsens double vision. Tilting the head toward weak or affected muscle will increase image separation and tilting the head toward unaffected muscle will decrease image separation.
First step: The Examiner identifies the hypertropic eye in primary position when the patient is looking in the distance. This implicates depressors of hypertropic eye or elevators of hypotropic eye.
Second step: Ascertains if hypertropia is worse on left gaze or right gaze. Increase on right gaze implicates either the right superior rectus or left superior oblique. Increase on left gaze indicates either a right inferior oblique or left inferior rectus.
Third step: Determines if hypertropia is worse on right head tilt or left head tilt. Increase of the left hypertropia on left head tilt implicates the left superior oblique. Increase of right hypertropia on left head tilt implicates the right inferior rectus. In the fourth cranial palsy, a deviation is better on opposite tilt.
Though Bielschowsky head tilt test is a standard diagnostic tool in isolating the palsied cyclovertical muscle, various other causes of vertical strabismus give rise to positive Bielschowsky head tilt test. Hence this test alone cannot be taken as a sole tool in identifying the fourth cranial palsy.
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Bibliography / Reference
Collection of Pages - Last revised Date: July 4, 2020