There is not much you can do to determine the power of your spectacle lens without recourse to a professional, but you can still evaluate lens quality at home. Holding your glasses one foot away from your eyes, look at a distant lamp-post or other stationary object. Move the glasses gradually from side to side. If your view of the object is marred by irregular waves or breaks, it may indicate poor optical quality of the lens.
Observe carefully the lens surface. Are there any scratches or pits? Those are caused usually by incautious polishing or small accidents, and although they look minor they can lead to problems with vision.
Also examine the junction of the bifocal segment in your pair of spectacles. The lines ought to be clear and sharp, and the size and shape of the segment should be balanced equally on the right and the left. If there is any visible coloring, it is a sign of the poorly-fused bifocal blank.
How has the lens been fitted into the frame? This is what is technically known as glazing. The edge should ideally be of minimum thickness. It should fit closely into the frame. There should be no gaps. Try to slide the edge of a sheet of paper between frame and lens. Can you? If so, poor glazing technique is responsible.
The Fit of your Bifocal Glasses is Important
The fitting of most frames, particularly the newer, imported zylonite frames, won’t loosen or change for years. Fitting is done at the time of delivery. At this time it should be made sure that the spectacles feel comfortable to wear. Be quite sure of the fact that the tips of the earpieces do not poke into the skin behind your ears. Given time they might form deep grooves and induce much discomfort. If your glasses have frames with adjustable nose pads, this is also the ideal time to check the fitting of those. They should not be too tight or bent in too perceptibly on one side.
Bifocals are designed precisely so that you can see clearly when your eyes have swung down by 15 degrees and your head is held erect. Should your bifocals be too high, they will hinder good distance vision, forcing you to hilt your head to compensate. Should they be too low, you will have to dig your book into your chest just to read it. Another common problem is asymmetrical height segments. Make sure your bifocal segments are the same height, or they will lead to sight problems.
Most opticians worth their degree will check the patient’s glasses thoroughly before dispensing them. But time is at a premium and human beings make mistakes. You, as the wearer of the glasses, will have to cope with any resultant problems, so be careful. In case of lingering doubt, don’t hesitate to get your doctor to have them re-examined.
Bifocals continue to be popular as they are hassle-free to use. They let the patient keep their prescription eye glasses, if such are required. However, you can’t just buy a pair of bifocals that incorporate your individual eye glass prescription. Talk to your optician about your options.
Unfortunately, in spite of the popularity of bifocal reading glasses, many leading retailers of eyewear do not store them regularly. A convenient, simple alternative choice is to use a slim or half eye reader for intermediate or distance viewing. In which case, you won’t need a clear top on your reading lens at all.