We use cookies on the site for our own business purposes including keeping track of your preferences and collecting aggregated statistics to analyse how our site is used. By using this site you agree that a cookie is stored.

Main Viewing Distance vs. Working Distance: Know Which Multi-Focal Lenses to Prescribe

Main Viewing Distance vs. Working Distance: Know Which Multi-Focal Lenses to Prescribe

As an ECP, you already know that there are multiple indoor multi-focal lens designs within each manufacturer’s portfolio, and each is specifically designed to work best within a given main viewing distance. 

The problem is, many people are confused by the phrases “main viewing distance” and “working distance” when referring to indoor multi-focal lenses, such as iD Space, iD Screen, and iD Zoom

Let’s start with understanding the importance of these lenses. Download this PDF for a condensed version you can refer to as needed. 

Download One-Pager

The Perks of Indoor-Specific, Multi-Focal Lenses

Indoor multi-focal lens designs are a great solution for anyone spending most of their day viewing objects at a distance closer than 20 feet. These lenses give the wearer much wider fields of view, decreasing the need to turn the head from side to side in order to view objects out of the direct line of sight. 

They also allow a more natural posture, as the intermediate and near portions of the lens give the wearer the ability to achieve an ergonomically correct position at the workstation. To help patients understand the value in such a lens, highlight the increased field of view and ergonomics — key features of indoor-specific multi-focal lenses. 

Still, it hasn’t been clear to many ECPs about which types of indoor multi-focal lenses to prescribe to each patient. We will clear that up in this article.

“Main Viewing Distance” vs. “Working Distance” 

To adequately prescribe the right lens variation to a patient, you must understand these two phrases clearly. 

  • Main Viewing Distance: the distance at which the wearer will spend most of their time using the lens.
  • Working Distance: the minimum and maximum focal length of the lens.

When a wearer is having trouble adapting to one of these indoor-specific multi-focal designs, it may be that the wrong design was prescribed based on the misunderstanding of these two phrases.

Each lens has a working distance. Each lens design allows a clear view of the closest objects the wearer will be viewing. Therefore, we should go ahead and focus on the maximum viewing distance of each lens design first when prescribing. In other words, how far does the wearer need to clearly view an object looking through the fitting cross?

 

main-viewing-distance-vs-worki

Keep in mind that these lenses are technically regressive lenses. Not progressive lenses. In a progressive lens, the full distance power is the starting point and gets progressively stronger working down the corridor until we reach full add power. In a regressive lens, the full reading power (distance Rx + add power) is the starting point and the power becomes progressively weaker; or regresses.

Because each version — iD Space, iD Screen, and iD Zoom — has a different percentage of the total add power at the fitting cross, the working distance is proportionally affected by the total add power of the lens.

By contrast, the main viewing distance is simply where the wearer will spend most of their time using the lens we prescribe. Main viewing distance and working distancemust work in harmony for the patient to be a successful wearer of the indoor lens design we prescribe. 

For Example: When Your Patient Works at Varying Distances

Your patient says she spends most of her day viewing objects located no further than her computer screen. 

Your first inclination: use a lens that is intended for a main viewing distance of four to six feet, like the iD Zoom. 

Stop and think: Have we asked enough questions? Is this the only important visual task that she performs throughout the various situations in her work setting?

After more conversation, you find that she routinely collaborates with others in a large meeting room, where she needs to see a shared screen 10-12 feet away. You also learn that she is not interested in taking her glasses off to get up and move about the office. So, is the iD Zoom still a good lens choice here? It is not. Here’s why:

  • The 4-6 feet of working distance provided by the iD Zoom coincides with the main viewing distance. However, the working distance falls short of her other important visual tasks, like viewing the screen in the conference room. The iD Zoom will work wonderfully at the desk — it will not perform well in the conference room.
  • She prefers to avoid switching back and forth between multiple pairs of glasses throughout the day. The iD Zoom has a maximum working distance of about 8 feet. Remember, the add power directly affects this total working distance. A quick look at your patient’s RX tells you she has a +2.00 Add. This effectively reduces the total working distance to about 6 feet and will require switching to another pair of glasses to confidently move about the office.

Our solution, gleaned from this conversation, is the iD Screen. 

Here’s why: the main viewing distance recommendation will provide visual comfort where she needs it most. The working distance will allow her to view the screen in the conference room. Remember, she will likely be viewing the screen in the conference room at a slight up-gaze. If she were to use the lens at a gaze angle that took her line of sight above the fitting cross, it would extend her working distance slightly.

By choosing a lens that fits both her main viewing distance and total working distance needs, you have dramatically reduced any adaptation issues and provided an exceptional experience for your patient. Sure, she will have to use her everyday progressive to drive to and from work; however, she will be grateful that you have solutions that meet her individual visual needs.

Want more information about how to recommend the perfect pair of indoor-specific multi-focal lenses to your patients? Contact your HOYA Territory Sales Manager for more information.

Did you find this content helpful? Download this PDF for a condensed version you can refer to as needed. 
Download One-Pager