Refraction is the eye exam in which the correction for farsightedness (myopia) or nearsightedness (hypermetropia) and astigmatism is determined. Getting a refraction eye exam in Bourbonnais would determine what lens prescription will help you see best.
The first part of a refraction eye exam checks whether your eyes are straight, called orthophoria or orthoptics. Your doctor can check for this quickly by just asking you to read an eye chart while wearing your glasses, which, if it were not flat, would show a blurred image. If your eyes are straight, then you will see the large letters that make up the main part of the eye chart clearly, even though they may be blurry when looking directly at them without using your glasses. This also tells them whether any astigmatism in either eye is significant enough to affect vision.
If either eye has significant astigmatism, then it needs a different prescription from the other eye. There is usually no point wasting time doing a complete refraction exam on both eyes because there will be no meaningful difference between what could correct your vision and what needs to be corrected – the prescription will be essentially the same. With astigmatic eyes, most of the time, each eye must have a different lens prescription, so this is how refraction exams are usually done.
The second part of an eye exam refraction checks what your actual prescription is. The way this is done depends on whether you wear contact lenses or eyeglasses for your correction at present. If you wear glasses already, then you need to bring them because they’re required for making minor adjustments to get a perfect match with whatever lens power might be required if that becomes necessary during the exam. Imagine what it would be like to go to all that effort only to find out it’s been wasted by giving you precisely what you already had.
If you do not wear either glasses or contact lenses, then ideally, either you or someone with your exact prescription should bring in a lens to the exam and put it into one of your eyes. While it is in your eye, you will read an eye chart where the letters are clearly visible even when looking directly without any correction at all.
If you have been having trouble with your vision, then you will most likely find out that undergoing a refraction eye exam in Bourbonnais will be one of the first diagnostic tools put to use in figuring out the best course of action.