Most of the corrective eyeglasses should be checked and prescribed by eye doctors, which are called prescription glasses. There are 4 types of prescription glasses which are designed and made to correct vision based on different circumstances.
The mostly used prescription glasses are for single vision. Most of eyeglasses wearers fit in this category. Single myopia, hyperopia and astigmatism only needs single correction. This group of prescription glasses is the easiest portion with the least return and complaints.
The second type is called double focal of bifocal prescription glasses. Bifocals were invented by Benjamin Franklin. He fused the farsighted lenses with the nearsighted one, thus he freed himself from interchanging two prescription glasses frequently. This type of prescription glasses are used by patients of presbyopia who are generally over 40s and are synchronously near- and far-sighted. Bifocal prescription glasses have two pairs of optical centers, which are equal to two pairs of eyeglasses.
Trifocal prescription glasses mean there are three pairs of optical centers. Its basic function is similar to bifocal prescription glasses except that trifocal possesses the center focal point which is for intermediate vision for a smoother transit from near to far.
The fourth is called progressive prescription glasses. This is also called no-line bifocals, for use by presbyopia patients to have a better look, as bifocal prescription glasses give other people a sign of being “old”!