This part two of three articles is from a CE course of the same title: Coping with Corridors by Barry Santini and is available at http://www.2020mag.com/ce/TTViewTest.aspx?LessonId=111755

Read part one here, and part two here.

Learning Objectives:

Upon completion of this program, the participant should be able to:

  1. Understand what opportunities are present for specifying progressive lens corridor lengths.
  2. Know when a specific corridor length is required.
  3. Learn the lenses and options when a specific corridor length is a requirement.

COPING WITH CORRIDORS

In traditional progressive lenses, the designer defines a series of performance goals, including a target corridor length and reading add, fixed lens areas, along with a merit weighting of various optical errors, and then enters into an iterative process to figure out which elements of progressive surface should be manipulated to achieve these goals.

Twenty years ago, when frame fashion took a left turn into small B dimensions, manufacturers responded with new, "shorter" corridor versions of their best-selling designs. For years afterward, ECPs often had only the choice between a normal, longer corridor design, or a compact, shorter corridor design. The optics of these early compact offerings, designed for fitting heights of 15 mm and less, were limited by the production constraints imposed by the manufacture of traditional molded surfaces. Often they were significantly compromised by poor peripheral acuity, in adequate intermediate utility, excessive swim and insufficient reading comfort, and therefore were only selected when fitting requirements absolutely demanded.

Although manufacturers could have produced a series of separate lenses with stepped corridor options, the economics of manufacturing and inventorying such an expanded series, further compounded by material and feature options, dictated a market reality where offering two corridor versions became the norm.

VARIABLE VERSUS FIXED CORRIDOR DESIGN

Knowing when to use a variable corridor versus a fixed corridor design is both a powerful and useful tool. The main distinction is that variable designs are often used to prioritize the quality of the distant and intermediate area, and fixed designs are used for prioritizing the reading area:

Variable Corridor Designs: Variable designs allow the ECP to adjust the corridor length as they desire. Longer corridors soften the progressive gradient across the lens, resulting in lower surface astigmatism. Benefits can include improved peripheral vision and an increase in the width of the intermediate and reading areas.

Fixed Corridor Designs: Fixed designs are used when prioritizing the size of the reading zone and/or the amount of eye declination required to reach the target add power. Fixed designs excel when fitting a mature add bifocal wearer — greater than 2.25D add —with their first progressive lens.

Fitting pearl:
Bifocal wearers, fitted with segments set 8 mm to 9 mm below pupil, are well-suited to using a 10 mm to 12 mm corridor referenced to a 95 to 100 percent target add value. (You're not still fitting bifocal segments using people's lower lids, without noting how far below their pupil the segment line is, are you?)

USING THE ADVANCED VARIABLE CORRIDOR

If you are ever intimidated or overwhelmed by the idea of juggling all the above factors in order to arrive at an optimal corridor length, then you can always consider selecting one of the advanced, premium class fully-optimized designs. These fully-personalized position of wear designs will automatically take all of the variables into account to strike an ideal balance between distance, intermediate and reading in selecting the final corridor length. You can maximize the customization by uploading the actual frame tracing, along with all the known position of wear variables. More advanced designs promise even greater wearer satisfaction by factoring in the wearer's previous lens design, corridor length, prescription, as well as center of rotation, eye dominance and head cape, if known. These highly customized designs may also feature the ability for dispensers to tweak the final reading height and corridor length by choosing from one of a variety of design priorities, including balanced, distance, intermediate or near.

FINDING THE MAGIC

The greatest challenge in progressive fitting remains the expert integration and assessment of an individual's posture, prescription, needs and wants, and mating that to a chosen lens design and frame style. As we begin to unleash the power of the corridor "genie," eyecare professionals can finally access one of the most powerful tools at their disposal for the fitting of progressive lenses. Don't remain a novice in your understanding of corridors, and have complaining patients swirling about your waiting room. Use the power of choosing corridor length to harmonize patient, prescription and lens design to frame choice. As patients discover the magic of true progressive satisfaction, so will your bottom line.


Barry Santini, ABOM, graduated from New York Technical College in 1975 with an AAS in Ophthalmic Dispensing. He is a New York State licensed optician with contact lens certification, is ABO certified and was awarded an ABO Master in 1994. As sales manager for Tele Vue Optics from 1987 to 2003, Santini developed his knowledge of precision optics and has been an owner of Long Island Opticians in Seaford NY, from 1996 to present. Recently The Society to Advance Opticianry named Barry Santini, OO, as the 2016 Ophthalmic Optician of the Year. In addition, Santini is an amatuer astronomer and lecturer and plays bass trombone in the Brooklyn Symphony.