The word asthenopia means a sense of strain and weariness in the eyes and the head set up by the use of the eyes.
The various types of asthenopia met with can be classified as follows:-
1. Asthenopia Simplex. – In this the feeling of eyestrain is there but no apparent cause for it is noticeable. General constitutional weakness affecting the nervous system in general is supposed to be the cause.
2. Asthenopia dolens – It is associated with the pain in the eyeballs. Commonly secondary to all types of inflammatory conditions of the structures of the eyes and cases of glaucoma, etc.
3. Asthenopia Cephalgica. – It is associated with headache, the nature of which may be from slight to very severe type. Very common is reflex irritation of the different branches of the trigeminal nerve.
4. Asthenopia Irritants. – Here the sense of eye – strain is accompanied by signs of irritations, redness and burning sensation in the eyes as well as in the eye – lids.
5. Asthenopia Accommodative – This is a very common variety caused by the presence of refractive errors such as hypermetropia and astigmatism.
6. Asthenopia Muscularis – Caused by the anomalies of the external ocular muscles. These anomalies appear as convergence in – sufficiency, Divergence – in – sufficiency and Hyperphoria. Symptoms commonly noticed besides pain in the eyes, conjunctival irritation, headache – specially located in supra – orbital, orbital, temporal, and occipital regions. Spasms of the facial muscles are also noticed in some cases. A distinguishing feature of the asthenopic muscularis is that they disappear if one eye is closed.
7. Asthenopia Nervosa – Symptoms complained by this group which is hysterical or neurasthenic in nature, are marked amblyopia or even amaurosis and the disturbances of sight being often associated with contraction of the visual fields and occasionally by diminution of light sense and of colour sense. They are incapable of doing any eye work for any length of time, though no abnormalities of organic or refractive nature are present.
8. Asthenopia Photogenous – This is caused by excessive or improper illuminations. These may be natural or artificial in nature. Ultraviolet or infrared rays outside the spectrum can cause irritation and symptoms when falling on the external parts of the eye affecting the skin, lid and conjunctiva and when enters the eye cause changes and irritation to the lens and the retina.
9. Reflex Asthenopia – These are secondary to the pathological conditions of the adjoining organs such as nose and its accessory air sinuses and teeth.
10. Panorama Asthenopia – These cases generally suffer from some sort of refractive errors or muscular or motor anomalies, and the eyes get fatigued when watching continually some moving objects, travelling in railway train, motoring, riding, walking in crowded streets, even in ballroom dancing.