From the etymological point of view, the term asthenopia means “limited vision,” though it does not refer to the decline of visual function, but rather is a very broad, poorly defined concept. Asthenopia encompasses all of the disorders and problems that arise in relation to looking at objects up close such as eye discomfort, blurred vision, sporadic double vision, premature tiredness, the inability to maintain a consistently clear image
from a specified distance, headaches, retroocular pain (pain behind the eyes), etc.

Asthenopia is a frequent problem among those whose work requires looking at objects up close for prolonged periods of time, for example, computer users. Some research has estimated that up to 40% of computer users suffer symptoms of asthenopia on a daily basis.

SYMPTOMS AND SIGNS OF ASTHENOPIA
*A heavy feeling in the eyes
*Eye tension
*Consciousness of the existence of one’s eyes
*Red eyes
*Stinging eye pain
*Increased watering of the eyes (Epiphora)
*Headaches
*A decrease in the sharpness of vision
*Blurred vision
*Sporadic double vision

These symptoms can be due to various factors:
*The state of the visual system
*Personal factors
*Factors inherent in the working environment such as light, color, position, the size of
one’s personal working space, posture, etc.
*Environmental factors: temperature, relative humidity, ventilation, etc.
*The work is done on vertical, versus horizontal, surfaces (computers)

ACCOMMODATIVE ASTHENOPIA

A) Hyperopia. Patients with slight hyperopia (up to 3D) rarely suffer problems in the first 20 years of life, except if they have a job that requires looking at objects up close for prolonged periods of time in bad light or those who suffer physical or mental exhaustion.

The most frequent complaints seen in medical examinations are not specifically visual, but headaches, generally in the front of the head, including in the eyeballs. In addition to an eye exam, it is essential to evaluate the mental aptitudes of the patient and their abilities for facing their personal, social and work circumstances.

At times, the intensity of the headaches associated with asthenopia can be considerable and may even result in migraines with nausea and vomiting.

B) Myopia. Some patients with inadequate, improperly corrected or uncorrected myopia refer to feelings of pressure in the eye related to work that requires looking at objects up close for long periods of time. In these cases, the pain is most likely due to a lack of coordination of the eyes (fusional vergence) together with an inadequate
accommodation.

C) Astigmatism. The rates of astigmatism are variable according to its impact on visual performance.

The discomforts and pains that come from astigmatism are due to the efforts of the patient to reestablish the visual axis or adjust between astigmatic axes. This requires prolonged effort by the ciliary muscle, yet produces minimal positive effect.

D) Anisometropia. When the refractive powers of the two eyes are different (anisometropia), an accommodative asthenopia can result with a dull pain that can become piercing in the head or the eyes. Frequently, the functional level of each eye is different and one of the eyes may be either dominant or lazy.

E) Presbyopia. It is essential to visually correct the accommodative insufficiencies that come with age. The patient with presbyopia must hold objects at a distance in order to see them well. This becomes a particular problem when the patient’s work requires looking at objects up close. This situation occurs frequently in some professions, such as
musicians, computer users, painters, etc.

MUSCULAR ASTHENOPIA

Heterophoria

Heterophoria, a condition in which the motion of the eyes are not parallel, is normally offset by fusional vergence (offsets increasing tone of certain eye muscles, it can be induced to develop the impression of muscular asthenopia). The strained efforts of the eye muscles to maintain the visual axis can then lead to muscular asthenopia. At times muscular asthenopia can in turn cause an artificial heterophoria when the patient’s glasses are poorly located or off-center, resulting in eye strain. The resulting asthenopic problems can be accompanied by eye pressure or discomfort, headaches, drowsiness, general discomfort or difficulty concentrating, and may eventually cause deep depression.

Insufficient Convergence

This deficiency, like heterophoria, produces asthenopic problems, principally double vision.

The decline in the power of convergence (ability of the eyes to turn towards one another) tends to manifest itself in patients that have physical disabilities or neurogenetic exhaustion, in addition to a reduced power of fusion (coordination of the eyes), and often accompanied by exophoria. It is necessary to correct, in all cases, the refractive disorders, taking into account the relationship with the convergence accommodation, as an improperly corrected myopia can lead to defective convergence. These patients frequently complain of psychological problems such as inferiority complexes and hypochondria.