Most children come to the optometrist year after year not complaining of any visual symptoms at all. Complaints often occur at an advanced stage in the progression of many eye conditions. In children, binocular anomalies can occur without any serious symptoms, because of sensory adaptations. This means the patient gets used to the anomaly and is not bothered by it anymore. The onset of a strabismus, or eye turn, for example at an early age is seldom accompanied by any symptoms.

However, a high percentage of patients will come to an eye exam because they are having symptoms that they associate with the eyes and vision. The single most important factor in determining whether optometrists prescribe treatments such as spectacles or vision therapy are the symptoms that patients report.

The following are the more common binocular vision symptoms that children report when visiting the eye doctor.

Headaches

Headache is a very common symptom reported during eye examinations. It may be caused by a very large variety of problems, many of which have nothing to do with the eyes or vision. It is important to determine if any headache is associated with the use of the eyes. It is common for decompensated heterophoria, uncorrected hyperopia, or astigmatism to cause some headache that occurs after prolonged use of the eyes, often under difficult visual conditions.

A heterophoria is a type of eye condition where when the eyes are at rest, or not working together under binocular conditions, there is some deviation in their alignment.  For example some patients may have one eye that turns in very slightly in relationship to the other eye.  This is not always obvious.  When the patient is alert and focused on task, both eyes appear straight.  When fusion is broken such as being tired, or under a cover test, or being "zoned out", one eye appears to turn in.  Heterophorias can have one eye turning in, out, up or down, or a combination.  The visual system has to exert effort to keep the eyes aligned, resulting in mild headaches for some patients.

This type of headache is more likely to be in the frontal region of the head. Usually, headache due to binocular vision problems is less intense or absent in the morning after a good night’s sleep and gets worse as the day progresses on and the patient is engaged in prolonged near vision tasks such as screens and phones.

Double Vision

Diplopia, or double vision, is a less usual symptom in a long-standing strabismus, as sensory adaptation occurs. Its presence indicates a eye deviation of recent onset, although about two-thirds of cases of acquired strabismus from brain damage such as trauma or stroke do not report any double vision. Deviations of recent onset may have a pathological cause and careful attention is given to the tests for comitancy. Comitancy means the eye deviation or turn is the same in all directions of gaze. The patient may sometimes report that the double vision is greater in one direction of gaze than in another. The patient should also be asked if the double vision is constant or intermittent. whether it is horizontal, vertical or both. If it is associated with any particular use of the eyes. Incomitant deviations are more likely to have a vertical component, double vision up and down. Double vision in heterophoria indicates that it is intermittently breaking down into a strabismus. This may be because the factors causing the decompensation have reached a serious state and sometimes it is an early indication of an active pathological cause. In the event of serious pathology, the onset of intermittent diplopia is likely to be more sudden and dramatic.

Blurry Vision

Blurred vision is a common symptom in heterophoria. It can be associated with accommodative, or focusing difficulties, such as under corrected presbyopia or hyperopia. In these cases, the blurred vision is more likely to be noticed by the patient during close work. Patients may also report general tiredness or soreness of the eyes or lids. The significance of blurred vision should not be underestimated. Having blurred vision more than once or twice a month has a detectable and significant impact on school work and overall well being.

Poor Stereo Acuity

Poor stereopsis, the inability to see objects in 3-D, or stereo, occurs with some binocular vision problems in which the patient reports difficulty in judging distances. Patients often do not notice this symptom because of the many monocular clues to depth perception. The symptom of monocular occlusion is a relatively common sign of a binocular anomaly and may be described as closing one eye when reading or adopting an unusual head posture so that the nose occludes the view of one eye when reading or writing.

Eyestrain

Asthenopia is a term used to describe any symptoms associated with the use of the eyes, typically eyestrain and headache. Asthenopic symptoms can result from either internal binocular and accommodative disorders, or external problems such as dry eyes. The term asthenopia means weakness of the eyes or vision, so the term may be best confined to symptoms arising from a visual or ocular anomaly rather than from purely outside factors. Symptoms of eyestrain, tired eyes, irritation, redness, blurred vision and double vision associated with the use of display screen equipment have been collectively referred to as computer vision syndrome, which has been largely attributed to the eyes becoming dry.

Reading Problems

Reading difficulty (dyslexia) may be reported as a symptom as this occurs in about 5% of children. Patients with dyslexia are particularly likely to suffer from binocular instability although, in most cases, this is unlikely to be a major cause of the dyslexia. If patients with reading difficulties report asthenopia, this can be the result of binocular or accommodative anomalies.

Feeling Dizzy

Dizziness and vertigo may occur in incomitant heterophorias. Incomitant means the deviation of the eyes changes depending on viewing direction. This can be an indication of muscle paralysis. Vertigo can also be caused by variations to the blood supply to the brain, middle ear defects or alterations in magnification from eyeglass prescription changes, particularly astigmatic changes.

Excessive Squinting

Closing one eye or squinting is used by some patients with refractive error to improve acuity and in other cases to reduce illumination, particularly glare from the superior visual field. It is a common symptom in sunlight and in strabismus, particularly intermittent exotropia. Most of the time squinting occurs to reduce light sensitivity rather than to avoid double vision. Eye squinting under normal lighting conditions can occur to avoid diplopia or other visual symptoms associated with binocular vision anomalies. If your child appears to have any of these symptoms it is prudent to contact an eyecare professional for further evaluation.