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Eye Exams and New Prescriptions

Your vision is getting a little blurry and you're ready for new glasses. So, you make an appointment with your eye doctor for an eye exam.

Dilate the Eyes and Relax the Ciliary Muscles

Once you arrive at the office the nurse puts some drops in your eyes. These atropine drops are used to relax the ciliary muscles of the eyes and prevent the ciliary muscles from contracting to make the eyes lenses rounder. In their "flattened" state, the lenses are supposed to be ready for distant vision.

You probably know that when you leave the eye doctor's office everything sees unusually bright. Often you need to wear sun glasses to avoid discomfort seeing in daylight. This is because both the ciliary muscle (that controls the roundness of the lens) and the sphincter muscle that dilates the iris are controlled by the same nerve. That is, when the iris constricts and the pupil becomes smaller, the lens becomes rounder.

In the same way, in order for the lens to become rounder, the pupil must become smaller. This was not understood at the time Helmholtz developed his theory of accommodation. So, he thought that the eye focuses to obtain a clear image on the retina of nearby objects by increasing the curvature of the lens. We now know that the size of the pupil and the curvature of the lens work in synchrony and are determined by the amount of light entering the eye.

But, your eye doctor figures your prescription based on the theory that the curvature of the lens is determined by the distance of the object you are focusing on. And this the problem.

Your Eye Exam

The examination room is darkened. Darkness is comfortable because the ciliary muscle and lens are relaxed and the pupil is wide open, allowing the maximum amount of light into your eye.

The eye doctor normally has a screen positioned at a distance of 20 feet in front of you. He or she projects characters on the screen to gage how well you can see. Then, the doctor places a complex device in front of your face that uses a set of various lenses that are tested to see what strength of lens is necessary for you to see the 20/20 line clearly.

Then, your doctor tests you for astigmatism and determines the amount of correction to apply to correct this problem.

Your New Prescription

For those of us with myopia, the prescription the doctor writes is primarily based on the amount of correction required to see clearly at a distance of 20 feet in the dark.

The prescription may be good when we are under stress (as we are in the unfamiliar examination room), at night and looking in the distance. But, for all other conditions the prescription is too strong.

This adds stress, especially when looking close up like reading a book or looking at a computer screen. The external muscles of the eye, already under chronic stress, experience increased stress. And, before long the stress increases and you think you need yet stronger glasses.

The problem is that you are using your prescription under conditions it was not designed for. Remember, it was designed for seeing in the distance in the dark (and while under increased stress).

Reduced Prescription Lenses

If you can, you should request your eye doctor to write the prescription for reduced strength lenses. A strength that will make your site legal for driving should be adequate. This will reduce the stress your eyes are under when looking up close.

I personally add a pair of reading glasses, effectively reducing my prescription even more, while using the computer. This allows the external muscles of the eyes to relax while I'm focusing up close.

Helping you eyes relax while working up close will give you a boost in improving your vision in the long run. And, it will keep you out of the doctor's office for new, stronger glasses.

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