1. Eye strain, headache and psychological factors
In high degrees of refractive errors the main symptom is D.V.
In low degrees of refractive errors the D.V. is only one of his symptoms, other symptoms like effort to see clearly in spite of the presence of the refractive error.
Condition of sustained use of accommodation in hyperopic persons and presbyopic persons in near work are typical circumstances that produce non-visual symptoms like eye pain and headache.
The fact that the pathological basis of these symptoms depend on fatigue of extra ocular muscles and intraocular muscles (like ciliary muscles) has led to the mechanical concept of the strain that named eye strain.

2. Symptoms of eye strain Visual symptoms Ocular symptoms
Referred symptoms

3. A- Visual symptoms
These symptoms are intermittent in small refractive error like 0.50 D astigmatism actual visual acuity forms little or no of the symptoms in normal conditions.
This defect can be compensated by the ciliary muscle effort and accommodation in normal conditions.
But in conditions of long near work and effort of study this small refractive error may result in marked symptoms.

4. There frequently comes in periods of:
Excessive visual strain,
During temporary deterioration of the general health like flu.
Fatigue comes on both eyes and vision fails.
This is especially occurs in persons who use eyes much for reading or study of small prints for long time or sewing or watching T.V. for long time, driving in difficult circumstance and all conditions associated with attention and anxiety.

5. Details of visual symptoms
Sensation of confusion
Temporary blurring
Tiredness of the eyes
Heaviness of eye lids
Sensation of weariness and drowsiness
These symptoms are relieved by rest but recur in continuation of the work.
Indeed the ciliary muscle can compensate by exerting extra accommodation till a time will come where ciliary muscle will fail to compensate (decompensation) and the symptoms could not be relieved easily until the patient decides to seek for treatment.
When reads small letters the patient sees the letters running together.

6. Ocular symptoms These together are called asthenopia
These symptoms arising from excessive work of eye muscles, in presence of a refractive error where muscles fatigue results.
In long period of close work the eyes feel
Tiredness
Hotness
Un comfort
Temporary relief by rest
In return to near work again the above symptoms develop to eye pain
The pain of the eyes due to eye strain is mild and aching but occasionally becomes severe and acute.

7. Referred symptoms The commonest one of these symptoms is headache
- This headache is localized around the eyes (frontal) but sometimes may be temporal, vertical or occipital. The nature of the headache is aching, boring and deep seated
It may be intermittent or constant, related to the amount of use of the eyes
The aggravating factors like eye fatigue and poor illumination are said to be common
2. Digestive upset (disorder, like dyspepsia and nausea)
3. Vague nervous symptoms like (dizziness and depression).