Bifocal reading glasses were initially developed to offset a common problem among presbyopic individuals. There is now a considerable portion of folks in their 40s and 50s who start to suffer presbyopia. This visual condition will cause a difficulty in seeing close up objects. There is a common phrase that describes vividly the symptom caused by this eye problem: “too short arms”. This is because presbyopic patients are used to hold the reading materials at an arm’s length, in which position can they get a clear view. The need for bifocal eyeglasses is still driven by another visual problem, either nearsightedness or farsightedness. Some presbyopic patients have developed farsightedness or myopia at an earlier age. Without the help of bifocal glasses, they have to use two separate pairs of prescription glasses. That is really inconvenient if they have to make visual switches between different ranges.
While most people sing the praises of bifocal reading spectacles, this entity is actually far from perfect. Certain problems have been reported on these visual aid devices. Commonly heard ones include headaches, visual dizziness and image jump. What is the reason for these unwanted problems associated with bifocal eyeglasses? In most cases, factors of fashion will not cause problems that are associated with lens function. Those symptoms or side effects are closely linked with visual experience. So, it is the lens design that matters and leads to these bothersome or disappointing problems.
Bifocal eyeglasses now have different lens designs. The original design is Franklin bifocal, followed by variations with added reading segments in different shapes into a primary lens. Reading segments usually account for a small portion of the whole lens. Both of these designs may lead to the mentioned problems. The crossing line on a Franklin bifocal lens will cause frequent image jump. Headache and dizziness are actually subsequences of image jump that occurs from time to time. Bifocals with reading segments have a similar situation. It usually takes a period to adapt to bifocal spectacles.
C: Bifocal eyeglasses bring both significant benefits and unwanted problems. The most common problem is image jump, and subsequently headaches and dizziness will probably follow.