Heterophoria is a condition that affects the alignment of the eyes. It occurs when one eye is slightly misaligned, causing the eyes to point in different directions. This can lead to various symptoms, such as headaches, dizziness, blurred vision, and eye strain.
How is Heterophoria is different from strabismus?
Heterophoria is different from strabismus, which is a condition where the eyes are visibly misaligned and point in different directions all the time. Strabismus can cause double vision, loss of depth perception, and amblyopia (lazy eye). Heterophoria is also known as latent squint, because the deviation of the eyes is not visible unless the fusion mechanism that keeps the eyes aligned is disrupted. For example, when one eye is covered or when looking at a very close or distant object.
Heterophoria is also called Latent squint
Heterophoria is also known as latent squint, because the deviation of the eyes is not visible unless the fusion mechanism that keeps the eyes aligned is disrupted. For example, when one eye is covered or when looking at a very close or distant object.
Types of Heterophoria
Heterophoria can be classified into different types depending on the direction of the deviation. The most common types are:
- Esophoria: The eye turns inward
- Exophoria: The eye turns outward
- Hyperphoria: The eye turns upward
- Hypophoria: The eye turns downward
Heterophoria can also be classified into comitant or incomitant, depending on whether the deviation is constant or varies with the direction of gaze.
Heterophoria can be caused by various factors, such as genetics, orbital asymmetry, muscle weakness, nerve damage, or trauma. Some people are born with heterophoria, while others develop it later in life due to aging, stress, illness, or injury.
compensated or de-compensated Heterophoria
Compensated heterophoria means that the person does not experience any symptoms because their fusion mechanism is strong enough to overcome the deviation.
De-compensated heterophoria means that the person experiences symptoms because their fusion mechanism is weak or overwhelmed by the deviation.
Let us read about it in details:
Heterophoria is a condition where the eyes are not aligned properly when they are not focusing on anything. This means that one eye may point inward, outward, up or down compared to the other eye. However, most people with heterophoria do not notice any problem with their vision because they can use their eye muscles to adjust their eye position and keep them straight when they look at something. This is called compensated heterophoria.
Compensated heterophoria is usually harmless and does not require any treatment. However, some factors can make it harder for the eye muscles to keep the eyes aligned and cause symptoms such as eye strain, headache, blurred vision, double vision, or difficulty reading. This is called decompensated heterophoria.
Decompensated heterophoria can occur due to various reasons, such as:
- Excessive use of vision under adverse circumstances, such as working too close to the eyes for long periods, poor lighting, glare, or fatigue.
- Reduced ability to focus the eyes, such as presbyopia (age-related loss of near vision), uncorrected refractive error (need for glasses or contact lenses), or accommodative insufficiency (difficulty changing focus from far to near).
- Reduced ability to fuse the images from both eyes, such as suppression (ignoring one eye), amblyopia (lazy eye), or poor binocular vision skills.
- Changes in the size or direction of the heterophoria, such as due to injury, disease, medication, or stress.
Decompensated heterophoria can be diagnosed by an eye doctor using various tests, such as the cover test or the cross-cover test. These tests measure how much the eyes deviate from each other when one eye is covered and then uncovered. The eye doctor may also check the patient’s visual acuity, refractive error, accommodation, fusion, and vergence (ability to converge or diverge the eyes).
The treatment of decompensated heterophoria depends on the cause and severity of the condition. Some possible treatments are:
- Correcting the refractive error with glasses or contact lenses. Sometimes, prism lenses may be prescribed to help align the eyes and reduce double vision.
- Performing eye exercises or vision therapy to improve the eye muscle coordination and binocular vision skills.
- Taking breaks from near work and adjusting the working distance, lighting, and posture to reduce eye strain and fatigue.
- Using artificial tears or lubricating eye drops to prevent dryness and irritation of the eyes.
- Consulting a doctor if there is any sign of infection, inflammation, or injury of the eyes.
The symptoms of heterophoria can include:
- Double vision
- Blurred vision
- Eyestrain and eye fatigue
- Difficulty in changing focus from near to far and vice versa
- Difficulty with depth perception and spatial awareness
- Intermittent squinting or closing one eye
- Head tilt or turn to compensate for the deviation
- Sensitivity to light
- Motion sickness
- Disorientation from too much visual stimuli
- Sinus pain or pressure around the top of the head
- Pain when moving the eyes
- Unsteadiness or dizziness when walking
- Uneasiness in spaces with tall ceilings
The symptoms of heterophoria can vary from person to person and can depend on factors such as the degree and type of deviation, the visual demand, the lighting conditions, and the emotional state. The symptoms can also fluctuate over time and can be triggered or worsened by fatigue, stress, illness, alcohol, medication, or hormonal changes.
Diagnosis of Heterophoria
Heterophoria can be diagnosed by an eye doctor who will perform a comprehensive eye exam and various tests to measure the alignment of the eyes, the strength of the fusion mechanism, and the presence of any other eye problems. Some of the tests that may be used are:
- Cover test: The doctor covers one eye and observes how the other eye moves to fixate on an object.
- Maddox rod test: The doctor places a red lens in front of one eye and asks the person to look at a white light. The person will see a red line and a white dot and will report their position relative to each other.
- Prism test: The doctor places prisms of different strengths in front of one eye and asks the person to look at an object. The doctor will measure how much prism is needed to eliminate any double vision or misalignment.
- Phoria test: The doctor uses a device called a phoropter to measure how much deviation occurs when fusion is disrupted by placing filters or lenses in front of one eye.
Treatment of Heterophoria
Heterophoria can be treated by various methods depending on the severity and type of deviation, as well as the individual’s needs and preferences. Some of the treatment options are:
- Glasses or contact lenses: These can correct any refractive errors that may contribute to heterophoria and can also provide prismatic correction to reduce or eliminate double vision and eyestrain.
- Vision therapy: This is a series of exercises and activities that aim to improve binocular vision skills, such as convergence, divergence, accommodation, fusion, and stereopsis. Vision therapy can help strengthen the fusion mechanism and reduce or eliminate symptoms of heterophoria.
- Eye muscle surgery: This is a procedure that involves adjusting the position or length of one or more eye muscles to improve alignment. Eye muscle surgery can be performed for cosmetic or functional reasons and can be combined with other treatments.
Image credit –Slideshare
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