Not too long ago in the field of opticianry, iseikonic lenses were a common topic. I asked some seasoned opticians and an optometrist to find out why iseikonic lenses have decreased in popularity.
For those of you who don’t know, iseikonic lenses are lenses in which the magnification has been balanced. Each lens produces a certain amount of magnification or minification (small-ification if you will). Differing magnifications become a problem if there is a significant disparity between the two lenses. Orthodoxy holds that a difference of 5% magnification or more is enough to break fusion in most individuals. The difference in image size produced by the difference in magnification is called aniseikonia. Fusion is the process in which the two eyes combine their respective images into one. When fusion breaks, people complain of diplopia, or double vision. Some people who do not break fusion, but still have magnification differences of over 1%, may complain of headaches and nausea when wearing glasses that do not correct for the magnification difference. Some people with a high astigmatism that significantly supercedes any astigmatism in the other eye will also experience similar problems. People in this category have meridional aniseikonia.
Getting back to the original topic, why has this aspect of opticianry tapered off? In my case, it may be the setting. I work in an optical chain that is geared more for retail. Where I work, we do not usually make iseikonic lenses for people, but I have done them and it is a real battle with the lab. Another reason as mentioned by the optometrist I work with, contact lenses have a high success rate in correcting the magnification imbalance. I would imagine that surgery would also be a factor. Another offered that many opticians simply do not know how to make iseikonic lenses and either refers it out or simply has the patient get used to it. This is not to say there are times that a patient who has had a change in their prescription needs time to adjust to their new Rx. Vision is a brain thing as much as it is an eye thing. I feel that in these cases, although somewhat rare, aniseikonia is a real problem for some since either they can’t wear (or don’t want to wear) contacts or there are other issues that surgery can not correct. This situation provides an opportunity for the optician to make a huge impact on someone’s life. Binocular vision is not overrated! Many people who do not have binocular vision may lose out on opportunities that require it. Making iseikonic lenses are a hassle, I know, but I actually provide some reprieve. On this site there is an Iseikonic Lens Calculator that should help out with the math. I originally made it as part of a project when I went to Raritan Valley Community College. It has been a lifesaver in terms of time. The only thing I would ask is that once you are done, double check the answer manually and let me know how it turns out (bear in mind things may be rounded). I want to make my programs as reliable and robust as possible. Email (at the bottom of the page) me if you want to know how to use the meridional aspect of the calculator.
Remember, what we do as opticians, in my opinion, is noble work and it is important to not lose sight of that.