Bifocal glasses are undoubtedly one of the most used types of reading glasses. They come in various shapes, sizes and designs. The placement of hyperopic lenses inside the frame of myopic lenses varies from design to design. Many times it is placed in the lower left corner of circular or rectangular frame, but it can be bigger in size covering the lower half of the myopic lens or be merged with each other in the form of concentric circles. The latter form of lens is called simultaneous lens, all the above lenses are very sensitive and hence you need to run some quality tests to get the perfect one.
By a technique called glazing, the fitting of a lens inside a frame is carried out. The edges of the lens must be thin to perfectly settle inside the frame without any gap. To check out if there is a gap between the lens and the frame, take a thin plane paper and try to pass it through the frame. If it passes, these bifocal glasses are not best for you.
The junction of myopic and hyperopic lens in your reading glasses should be sharp and clear. There should be uniformity throughout the lens, if you see some visual coloring, then the lenses are not fused well enough. Never ignore small pits and scratches on the lens as they indicate the use of poor polishing techniques.
One of the easiest quality tests is to try to look through lens, placed at one foot distance from the eye, while moving bifocal glasses from one side to another. If your vision of distant objects is blurry and interrupted by waves and breaks then your glasses are of poor quality.