Orthoptic work up is a battery of tests done to check the muscle balance of the eyes. These are done in some specific situations like constant headaches which gets precipitated by reading or computer work etc, intermittent eye deviation etc. 
There are various focussing mechanisms that work in the eye which enable us to see clearly.  However, these are different from just checking the glass power of the eyes.

The basic tests which are performed as part of the orthoptic evaluation include the following-

1. Stereopsis- Checking depth perception or 3D vision using special charts
2. Binocular single vision- This test is done to check whether both eyes are being used together. Any misalignment of the eyes can cause a break in this function
3. Near point of convergence- When we focus on a closer object both our eyes need to come slightly inwards so that the eyes can focus clearly on a near object. This is measured on a special ruler called the RAF ruler. The normal near point of convergence is 8 to 10 cm.
4. Near point of accommodation- Accommodation is a function where in the lens-ciliary body complex within the eye moves slightly forward to enable clear focussing of near objects. RAF ruler is used to measure the same. Normal values vary depending on the age
5. Amplitude of accommodation- It is a measure to calculate the strength of the accommodative process using age appropriate formulas. 
6. Accommodative lag- In this test a light is shone through a specific instrument inside the eye to see whether this function of accommodation is initiated on focussing at a near target. The decrease in this function can seriously impair near work and can just be corrected with glasses and exercises.
7. Fusional vergences- These measure the strength of the eyes to converge when focusing on a near target called as the positive fusional vergence as well as the measure of strength of the eyes to diverge while focussing on a distant target. Reduced amplitudes of these can predispose a person to develop squinting of eyes.
8. Accommodative facility- This function tests the ability of our accommodative examination to work as well as relax. This should happen at a particular speed in one minute. 
9. Accommodative vergence facility- This is a measure of the speed of our eyes being able to converge as well as diverge in one minute tested with specific prisms.

Weakness in any of these functions can cause eye strain as well as headaches as well as visual complaints.

The brighter side about these problems is that most of these can be corrected with simple eye exercises.

So if the initial eye power check-up and the eye test is not helping then you may need the orthoptic test. Orthoptic evaluation can be performed at any good eye hospital under the guidance of the squint specialist. The test results allow the eye doctor to guide and advise on the eye exercises that need to be performed.