====== Diplopia ======
Commonly known as [[double vision]], is the simultaneous perception of two images of a single object that may be displaced horizontally, vertically, diagonally (i.e., both vertically and horizontally), or rotationally about each other.

===== Classification =====


Diplopia (double vision) can be classified based on various criteria, including its origin, laterality, onset, and associated conditions. Here is a structured classification:

### 1. **Based on Origin**
   - **Monocular Diplopia**: 
     - Persists when one eye is covered.
     - Often due to ocular causes like refractive errors, corneal irregularities, cataracts, or lens dislocation.
   - **Binocular Diplopia**: 
     - Disappears when either eye is covered.
     - Caused by misalignment of the visual axes (e.g., strabismus, cranial nerve palsies).

### 2. **Based on Laterality**
   - **Unilateral Diplopia**: Affects one eye and suggests ocular pathology.
   - **Bilateral Diplopia**: Affects both eyes and usually indicates a neurological or muscular cause.

### 3. **Based on Onset and Duration**
   - **Acute Diplopia**: Sudden onset; may indicate stroke, trauma, or cranial nerve palsy.
   - **Chronic Diplopia**: Long-standing or progressive; associated with conditions like myasthenia gravis or thyroid eye disease.
   - **Intermittent Diplopia**: Comes and goes, often linked to fatigue, myasthenia gravis, or decompensating strabismus.

### 4. **Based on Etiology**
   - **Neurogenic Causes**:
     - Cranial nerve palsies (III, IV, VI)
     - Multiple sclerosis
     - Stroke
     - Brainstem lesions or tumors
   - **Myogenic Causes**:
     - Myasthenia gravis
     - Chronic progressive external ophthalmoplegia
     - Orbital myositis
   - **Mechanical Causes**:
     - Orbital fractures
     - Thyroid eye disease (Graves’ orbitopathy)
   - **Refractive Causes**:
     - Corneal irregularities (keratoconus, scarring)
     - Cataracts
     - Astigmatism

### 5. **Based on Direction**
   - **Horizontal Diplopia**: Suggests involvement of lateral or medial rectus muscles (e.g., VI nerve palsy).
   - **Vertical Diplopia**: Suggests involvement of superior or inferior rectus, or oblique muscles (e.g., IV nerve palsy).
   - **Oblique Diplopia**: Involves multiple muscles or oblique muscle dysfunction.



### 6. **Special Forms**
   - **Concomitant Diplopia**: Present in all gaze directions, usually in congenital strabismus.
   - **Incomitant Diplopia**: Varies with gaze direction, typically due to cranial nerve palsies or restrictive pathology.

Would you like a deeper explanation on any specific classification or an approach to diagnosis?


===== Etiology =====
Diplopia, or double vision, can be caused by various factors, and understanding its etiology involves considering both ocular and systemic conditions. Here are some common causes:

1. **Refractive Errors:**
   - **Astigmatism**: Irregularities in the cornea or lens that cause light to focus unevenly on the retina.
   - **Uncorrected Vision Problems**: Such as severe myopia or hyperopia.

2. **Ocular Muscle Disorders:**
   - **Strabismus**: Misalignment of the eyes due to muscle imbalances.
   - **Cranial Nerve Palsies**: Involvement of nerves controlling eye movements (e.g., oculomotor, trochlear, or abducens nerves).

3. **Neurological Conditions:**
   - **Stroke**: Can affect the brain areas responsible for eye movement control.
   - **Tumors**: In the brain or orbit that impact the ocular muscles or nerves.
   - **Multiple Sclerosis**: Can lead to demyelination affecting eye movement.

4. **Trauma:**
   - **Orbital Fractures**: Damage to the bones surrounding the eye.
   - **Head Injury**: Can affect the nerves or muscles controlling eye movement.

5. **Systemic Diseases:**
   - **Diabetes Mellitus**: Can cause diabetic ophthalmoplegia.
   - **Thyroid Eye Disease**: Often associated with hyperthyroidism, leading to inflammation and swelling of the muscles around the eyes.

6. **Infections and Inflammatory Conditions:**
   - **Orbital Cellulitis**: Infection of the tissues surrounding the eye.
   - **Giant Cell Arteritis**: Inflammation of blood vessels that can affect vision.

7. **Drug Side Effects:**
   - Certain medications can cause diplopia as a side effect.

8. **Other Causes:**
   - **Myasthenia Gravis**: An autoimmune disorder affecting neuromuscular transmission.
   - **Botulism**: Can cause temporary paralysis of the eye muscles.

Accurate diagnosis often involves a comprehensive eye exam, neuroimaging, and sometimes blood tests, depending on the suspected underlying cause.

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It is usually the result of impaired function of the extraocular muscles (EOMs), where both eyes are still functional but they cannot converge to target the desired object.

Problems with EOMs may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves (III, IV, and VI) that stimulate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.

Diplopia is often one of the first signs of a systemic disease, particularly to a muscular or neurological process, and it may disrupt a person’s balance, movement, and/or reading abilities.

see [[Abducens nerve palsy]].

see [[Vertical diplopia]].
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A clear and comprehensive history is the single most useful evaluation in treating patients with diplopia. The patient typically presents with a history of double vision, where single objects appear as double. Specific inquiry as to onset, progression, and variability with head posture or gaze direction, as well as previous similar episodes (especially if associated with other neurologic symptoms) and/or spontaneous resolution, is very helpful in the diagnosis and management of diplopia.
Three important symptoms should be elicited, as follows:

Does covering either eye make the diplopia disappear? This test helps to rule out monocular diplopia, which persists in one eye even if the other eye is covered.

Is the deviation the same in all directions of gaze or by tilting and rotating the head into different positions? This suggests a comitant deviation, with no difference in separation of the images in all directions of gaze. When the extent of deviation changes (and indeed possibly disappears in a given direction), then the deviation is incomitant and suggests a problem with innervation, most likely a paretic muscle.

Is the second object displaced horizontally (side-by-side images) or vertically (images above each other)? Oblique diplopia (images separated horizontally and vertically) should be considered as a manifestation of [[vertical diplopia]].