[thedoc (OP)]

Manoj Tomar  asked the Naked Scientists:
   I want to ask a technical question about this problem called lazy eye or amblyopia.
In order to see we need four things.
1. Something to see.
2. Eyes to focus
3. Nerves to carry signals to/from brain/eyes
4. Finally brain to see what actually has been seen by eyes.

A reading chart test at doctor's clinic is an indication of what brain is seeing. It doesn't proves something is wrong with eyes.  So how can they prescribe a glass for eye?
What do you think?

[CliffordK]

The simple answer is that eyeglasses will only resolve focal problems with the lens.
If a person's eye sight improves with eyeglasses, then the person has a problem with the lens focus. 
If the sight does not improve with eyeglasses, then there may be another underlying cause.

A thorough eye exam will look for a number of potential problems including glaucoma, cataracts, aneurysms, peripheral vision deficits, binocular vision deficits, ability to track an object with the eyes, and etc.  Additional tests may be conducted based on a patient's symptoms.