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As with most things making spectacles or eyeglasses is a far more complex process than one would first imagine. The difficulty is that at first glance to the untrained eye, all lenses look pretty much the same which of course they are not! Each pair of lenses must be custom made to each individual’s needs to be truly effective. The common abundance of ready made reading glasses has probably altered the pulic perception of the complexity of glasses and the degree to which prescription glasses are customized for each and every wearer.

There are a number of areas in which ready made glasses fall short of the mark for providing optimum corrected vision.

1. They cannot take into account a difference in required lens power between the right and left eye.

2. They cannot correct for astigmatism.

3. They cannot account for accurate optical centre centration.

4. Lenses are generally made of inferior lens materials which even if were correct in power for the wearer would only give a second rate result due to the impurity of the material (low abbe number)

I will explain the spectacle making process from the manufacturing standpoint, that is everything after the eye examination and frame and lens dispensing process has been completed.

There are two main categories of spectacle lens available. They are stock lenses and grind lenses.

Stock lenses

Stock lenses are usually injection moulded lenses which are mass produced in varying powers in an enormous range of materials. There are hundreds of lens manufacturers worldwide producing millions of stock lenses annually. Most lines of stock lens are available in at least 300 different power combinations, of which 266 would be cylinder lenses that correct for astigmatism. Of that 266 lenses they can be set at nearly any angle (axis) from zero to 180 degrees.