Exophoria
Patients can overcome a
heterophoria by maintaining a contraction tone
in the extraocular muscles so that their visual
axes are parallel for distance and near vision.
This continuous task may cause symptoms
consisting of discomfort of varying degree and
location, the so-called asthenopic symptoms.
Patients always relate the symptoms to use of
their eyes and so-called eyestrain.
Complaints range from redness and a feeling of
heaviness, dryness, and soreness of the eyes, to
pain in and around the eyes, frontal and
occipital headaches, and even gastric symptoms
and nervous exhaustion. The eyes are easily
fatigued, and such patients often have an
aversion to reading and studying. Typically,
these complaints tend to be less severe or to
disappear altogether when patients do not use
their eyes in close work.
Asthenopic symptoms are less
frequent in distance vision than in near vision.
However, it can be distressing to watch moving
objects in the distance, such as in movies, on
television, or from fast-moving cars, or at a
ball game, since maintenance of fusion in such
circumstances is difficult and may produce
stress.
To decide whether a
patient’s asthenopia is caused by muscular or
refractive factors, it is advisable to have the
patient wear an occlusive patch over one eye. If
this patch test
relieves the symptoms, asthenopia is most likely
caused by muscular factors.
Most heterophoric patients experienced relief
of asthenopia with the correction of the
refractive error if present, others may need
orthoptic exercises, while surgery is only
indicated in manifest tropias.
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