If you’ve looked at the newest releases in Progressive Lens Designs, you will notice that you have approximately one bazillion choices when it comes to choosing the corridor length in your favorite Progressive Lens. If you’re not 100% certain on how to make the best choice for your patient regarding corridor length, here are a few tips to help clear the sometimes muddy water.
What Does The Patient Want? What Does The Patient Need?
I know you hear this from me often, but we must not forget how important lifestyle dispensing continues to be in our industry. I would argue that today with the advent of online eyewear companies, the most important thing we can offer our patients is the experience of working with an expert who is going to help them design lenses that will be perfectly suited for their needs. This can only be done if we truly understand what their needs are. We must ask the in-depth questions needed for us to ascertain the information we need in order to truly customize these lenses. By the way, this is something the Internet will never be able to provide.
What information do we truly need? I’m glad you asked. We need to fully understand our patient’s computer use. How do they get along with the lenses they are currently using? What do they struggle with in terms of near vision? Are they using a stationary PC or are they using a laptop, tablet, or cell phone? What is their posture while using these devices? How many hours are these devices in use? What about other close work? Are they a hobby reader? Do they read books, or do they use some form of an e-reader? Do they sit in a particular chair for these tasks? What is their posture for this task? How far away do they sit from their screen, how do they hold their device? Do you follow where I’m going here?
So, the information you gather from asking these questions is going to tell you many things. 1) Do they have a greater need for intermediate or for near? 2) Do you need to recommend an additional small environment or ofﬁce design lens for their computer use? 3) What problems do they currently experience with their current PAL design while using computers and can they be remedied with a different lens design?
Crunching The Information
You’ve asked the right questions and have all of the information you need to make your patient a perfect pair of glasses, now is the time to put your information into action. If the information your patient has provided you with indicates that your patient has a great need for near vision (i.e. uses their cell phone primarily throughout the day and for extended periods of time and holds it higher and closer than if they were reading a book) this indicates the need to place their near vision a bit higher within the lens. You should certainly consider a shorter corridor PAL for this patient. A good rule of thumb that has worked well for me is to take a normal segment height and then subtract 5mm to ensure you have full utilization of the near (as most PAL designs need at least 5mm of near vision to give enough reading room within the PAL to ensure the patient can use the lens comfortably.) This will give you a good idea of what corridor length to choose.
For example, let’s say you have measured a 20mm segment height, if you subtract 5mm from this to ensure you’ve got enough near coverage, you can roughly estimate that a 15mm corridor will be the longest corridor you will want to choose for this patient in this frame. Now, you might choose a shorter corridor based on further information, but I wouldn’t suggest choosing a corridor any longer than that.
Further information that will impact your corridor choice has to do with overall lens power, how the patient uses their devices, and how much intermediate the patient needs. As a general rule of thumb, keep in mind that a patient who still needs a good bit of intermediate vision will want as long of a corridor as you can provide them without putting the near vision so low in the lens that it will become unreachable, or uncomfortable for the patient’s eye to turn and reach. Also, speaking in general terms, Hyperopes tend to like longer corridors and Myopes tend to like shorter corridors.
There are many other items that will factor in to which corridor to ultimately choose so while these are generalities, none of these tips is an absolute. Patients like what they like and we must be able to listen and digest the information appropriately. Some things to consider are the shorter you make the corridor, the more peripheral distortion you will create within the lens, so it is always a good idea to remember that shorter isn’t always better. Also, remember that larger fashion frames will require a different way of thinking. For a patient with a segment height of 35, the subtract 5mm rule simply won’t work as you shouldn’t consider a 30mm corridor as the patient would never reach the full add comfortably and for that matter a 20mm corridor is about the longest you’re likely to be able to order anyway.
If in doubt or if you have a question about what the current corridor length is of the lens is that you’re using, don’t be afraid to call your lab and ask these questions.
Johnna Dukes, ABOC is currently the owner and operator of an optical boutique, with experience in both the private practice sector as well as the retail chain setting. She has a wide range of experience varying from optical support staff to dispensary management to practice ownership. She lives in Okoboji, Iowa.