The Power and Politics of the PD

By Barry Santini, ABOM

Release Date: November 1, 2015

Expiration Date: December 31, 2017

Learning Objectives:

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

  1. Understand the political history of the federal trade regulations for eyecare products
  2. Understand the science, metrics and statistical validity of the major current methods used to measure PD.
  3. Understand and learn how regulators are using evidence-based risk assessment to re-evaluate the degree of oversight needed to protect the public's health with eyeglasses.

Course Description:

As consumers begin to ask offices for their prescription and their PD, eyecare profes-sionals are seeing a threat both to the public's eye health and their bottom line. But re-fusing to give out a person's PD is inconsistent with the spirit the Spectacle Release Rule. Explore the history of regulatory politics and understand the main measuring mo-dalities used for determining a person's PD.

Faculty/Editorial Board:

Barry Santini, ABOM

Credit Statement:

This course is approved for one (1) hour of CE credit by the American Board of Opticianry (ABO). Course SWJHI419



Probably no question elicits more surprise and emotion from eye care professionals than when they're asked: “Can I have a copy of my Rx and PD?” Why? Because this innocent request is really an arrow aimed straight at the heart of historical "control" ECPs have had over the sale of prescription eyewear. If we step back and take a longer perspective, we can see that this is just the latest manifestation of a consumer empowerment process that began more than three decades ago.

In 1977, reacting to a rising tide of complaints that consumers were having trouble comparing eyewear prices because their eye care providers were reluctant to give up their prescriptions, the Federal Trade Commission took decisive and corrective action by issuing Eyeglasses I, also known as the Spectacle Prescription Release Rule, 16 CFR 456.1. Twenty-five years later, the FTC addressed a similar situation for contact lens wearers through the Fairness to Contact Lens Consumer’s Act. Importantly, both of these rules were designed to pry open an industry seen as unfairly acting in its own self-interest. Fast-forward to today, with the arrival of prescription eyeglasses offered online, and consumers find themselves once again squaring off for battle with their eye care professional. This time, they're being far more vocal in asking their government officials for help in freeing their PD from the clutches of their local eyewear establishment. NB: On September 4, 2015, the FTC, within their systematic review of current rules and regulations, again began soliciting public comments regarding the efficiencies, costs, benefits and impact of the regulations currently n place for eyewear and contact lenses.

The Battle for the PD

Eye care professionals argue that the pupillary distance is not, nor ever has been, a prescription parameter mandated for release under Eyeglasses 1. Consumers counter that only by having the Rx and their PD will they be able to freely shop the eyewear market. That this is clearly the intent of Eyeglasses 1 can best be seen in the latest revision from 2004 of Part g of 16 CFR 456.1, which states:

A prescription is the written specifications for lenses for eyeglasses which are derived from an eye examination, including all of the information specified by state law, if any, necessary to obtain lenses for prescription eyeglasses.”

ECPs respond that by releasing the PD to a supplier outside their office, consumers are, in essence, removing them from responsibility as the eyewear's "general contractor" ー leaving unanswered the question of who is ultimately accountable for ensuring product quality, prescription efficacy and overall visual comfort. Additionally, eye care professionals admonish that by sourcing prescription eyewear online, consumers are separating out and thereby fragmenting the try-on, consultative, fitting, warrantee and other related services that have traditionally constituted most of the added-value and therefore increased cost represented in their office’s higher asking prices. ECPs see an obvious message is here: If you pay less, you’ll get less.

But as household discretionary income comes under greater downward pressure than ever before, consumers today are actively vetting the value they receive for every dollar spent. It's really no secret that the public views eyewear prices as arbitrarily high, and a recent CBS 60 MINUTES segment echoes this sentiment.

The New Eyeglass Consumer

Striving to obtain maximum value, shoppers today are increasingly willing to experiment with making trade-offs to enjoy lower prices. But most optical store owners have yet to begin to strategize how they will cope with a far more vigilant consumer. Unfortunately, by neglecting to outline even a simple fee schedule for eyewear related services, eye care professionals have inadvertently created a climate of resentment between themselves and their patients.

Today, as the consumer’s desire to obtain their PD runs smack into an eye care professional’s reluctance to hand it over, its time to take a look at exactly where the majority of money is made in optical.

The Business of PD

The sale of eyeglasses has been the single greatest revenue generator for optical stores. But you can't begin the sale of glasses without first having an Rx, and eye exams are financed in large part through participation in vision care plans (VCPs). For most consumers, the scheduling of exams and availability of eyewear allowances is set through the VCP’s logistics. With plan benefits usually timed to one or two year intervals, it’s easy to see why leveraging the exam visit into a pair of revenue-generating eyewear is very important. So when someone’s Rx appears to be walking out the door, business owners also see the single most important contributor to their bottom line walking out with it.

With the plethora of lower eyewear prices available online, even longtime clients are beginning to question why their “trusted” eye care professional charges more for what appears to be the same product. And contained within that one word — product— is the biggest mistake the optical industry has ever made. By bundling all the consultative, fitting, adjustment, warrantee and other services into a one-price, product-centered transaction, ECPs did themselves a great disservice. Without a separate pricing schedule for services that covered adjustments, repairs, replacement parts, warrantee coverage, consultative time, etc., included in the asking price of eyeglasses, consumers were left with only one thing with which to compare prices and gauge value: the eyewear product alone.

Smell the Coffee

Insulated for years from the competitive realities of the free market, and in part protected by regulations and licensure, ECP’s had little motivation to change the status quo. But although the arrival of big box chains in the 1980s brought independents their first real taste of competition, ECPs were still slow to begin adapting to a new disrupter in their midst. Today, with a variety of alternate channels of distribution for Rx eyeglasses beginning to spring up, eye care professionals are still slow to realize that these new competitors are essentially capitalizing on one thing: The ECP’s mistaken assumption that its customer base had always appreciated all their services were included in the cost of their glasses.

Politics and the PD

The dispensing of prescription eyeglasses, a Class 1 medical device, has been regulated in part by some state requirements that a licensed optometrist or optician to oversee the process of dispensing. As a medical device, any records kept by ECPs are considered medical records, and as such, must be made available to the patient on demand. This would also include the patient's PD. Even in view of this, consumers continue to encounter difficulties obtaining their PD when requested. Therefore the question of what consumers are rightfully entitled to in their eyeglass record is far from being clearly answered. But with consumers becoming comfortable with buying other types of medical products online, they're beginning to ask their government representatives the toughest question: Do prescription eyeglasses really require regulatory oversight?

Product Safety and Regulation

Product safety and efficacy are important concerns for both consumers and eye care professionals. But while the dispensing of eyeglasses by opticians is only licensed in approximately half of all states, there is yet new pressure to remove regulation altogether. While the FDA ensures that consumers face reduced risk from the consequences of compounded injury through their impact resistance requirement, they have not begun to question whether eyewear that lacks compliance with ANSI standards for power or PD will pose a threat of harm.

Evidence-Based Risk Assessment

In our current regulatory environment, efforts to control costs and limit government involvement are constantly under scrutiny and review. Today, regulations are increasingly vetted toward optimal balancing of cost-versus-risk-of-harm. This is the main metric for determining the degree of oversight, regulation and recommendation for medical drugs, tests, procedures and devices. Notwithstanding anecdotes that ECPs recite about patients who needlessly suffered from poorly fitted or miss-fabricated eyewear, there remains a distinct lack of consensus or hard evidence of the risk of long term harm accompanying poorly made eyewear. And hard evidence is what regulators need to substantiate hard regulation.

In 2005, the Canadian Ophthalmological Society issued guidelines for the frequency of oculovisual examinations, including those exams intended to screen individuals for eye disease, provide secondary control of existing disease or tertiary prevention in reducing the consequential harm of chronic disease. In developing their guidelines, the COS employed real-world, evidence-based risk assessment studies. Here is a short excerpt of their surprising conclusions:

Healthy adults, who do not notice anything wrong with their eyes, should see an eye doctor according to the following schedule:

  • Age 19 to 40 - at least every 10 years
  • Age 41 to 55 - at least every 5 years
  • Age 56 to 65 - at least every 3 years
  • Over Age 65 - at least every 2 years

NB: Within these same recommendations, the COS cited sufficient evidence-based data to recommend at least one complete eye exam for children before age 5. Meanwhile in the US, only 3 states —Kentucky, Illinois and Missouri — have seen fit to mandate a complete eye exam before a child enters kindergarten.

Changing Atmosphere

If we look at the dynamics of oversight for prescription eyewear worldwide, we note how the regulatory atmosphere is changing with the arrival of online prescription eyewear. For example, in 2010, the Canadian Health Minister in British Colombia, responding to a court case involving a prominent online optical retailer, was prompted to review the current regulations concerning eyeglasses contained in the applicable Canada's Health Professionals Act. Subsequently, changes were instituted to allow BC consumers to order eyewear online without providing the seller a copy of their prescription. The new regulations stipulated that all patients must be given a copy of their Rx for free — regardless of whether requested or not. Commenting on these changes, the Health Minister noted: “With advances in technology and more consumers turning to the Internet, it makes sense to modernize a decades-old system to give British Columbians more choice...”.

The End of Primacy in PD

With the legalization of the sale of over-the-counter reading glasses in the late 1980s, the decline in the importance of accurate pupillary measurement had begun. Some states tried to limit the perceived risks of OTCs by forbidding the sale of powers over 2.75 diopters. But is this anything more than a superficial gesture, based on a "feeling" that consumers needing stronger powers should be seeing an eye doctor? As far as the potential negative effects of inaccurate PDs in OTCs is concerned, a 2009 OTC reading glass study concluded that most spectacle wearers would tolerate “up to 0.50D vertical prism [imbalance] and up to 1.0D horizontal prism (imbalance)” without marked discomfort.

Today, as OTC reading glasses approach $800 million in sales and more than 46 million units sold annually (Source: Vision Watch 2012), it is clear that consumers are willing to trade imprecise centering in return for low price.

A Primer on PD Tech

Ask any eye care professional if accurate PDs are important in satisfying an eyewear consumer, and they’ll no doubt respond with an overwhelming chorus of “Yes!” But hanging your professional hat on the hook of PD’s primacy today is a risky undertaking. To better appreciate a PD’s nuanced and multi-layered character, let's take a look at the science, anatomy and measuring techniques surrounding the pupillary distance.

PD Facts

Quite a bit of research has been done into the science of pupillary measurement. The importance of needing to define the extremes, age and gender distribution of PDs can be found within the disciplines concerned with stereoscopic displays. Here, whether considerations are binocular or bi-ocular — two eyes sharing the same entrance pupil — knowledge of the range to be accommodated is essential in designing these devices. Because of this, almost all PD research concentrates on the importance of binocular rather than monocular values. Here is a short summary of their findings:

General Recommandations:  
Extremes for all adults (Age 18 and over):
95th Percentile for all adults
Minimum values for children (Age 0 - 5)
Mean and median adult PD (all races and sexes included)
45 - 80 mm
70 mm
30 - 40 mm
63 mm

The PD:

  • Changes most from birth to age 5 (up to 10 mm growth)
  • Reveals second greatest change from age 5-18 (up to 7.5 mm)
  • Slowing in females at age 14; males at age 18 - reflecting earlier female maturation
  • Average is smaller in females than males
  • Continues to change between the ages of 18-50 with most of the delta occurring in ages 18-30, and the average change is 3%
  • Changes more slowly in the age group over 60 (up to 1.2 mm)

The Metrics of Pupillary Distance

By definition, the taking of a PD suggests that we are determining the distance between eye’s pupils. But within the last 20 years, as the optics and sophistication of eyeglass lenses have tremendously advanced, ECPs are having to advance their understanding of how designers use references beyond simple pupil location to help optimize a lens’s acuity, comfort and utility.

Pupillary Axis - A line drawn perpendicular to the corneal surface through the center of the eye’s (entrance) pupil.

Visual Axis - This is the actual sight-line of the eye, running from center of the fovea, through the eyes nodal points, and out to the object of regard. This is where the brain is actually looking. The point where the visual axis intersects the cornea is thought to almost coincident with the corneal apex, and therefore the corneal reflex. As the fovea is displaced temporally from the intersection of the pupillary axis with the retina, the corneal reflection/visual axis is normally found approximately 3-5 degrees nasal of the pu-pillary axis intersection with the cornea. The angle between these two axes is known as angle kappa, and has linear values at the respective corneal and spectacle planes (VD = 13 mm) of approximately 0.25 mm and 0.50 mm.

Corneal Reflection - also known as the corneal reflex, it is the image formed by a light source shining upon the cornea. If the examiner is co-axial with this light source, then the position of corneal reflection is where the visual axis exits the eye. This is important for determining prismatic effects and optimizing placement of a progressive lens’s intermediate corridor.

Center of Rotation - This is the virtual point around which the eye appears to rotate during its excursions. Its importance in lens design is twofold: It allows designers a proper reference for optimizing a lens’s off axis performance, and it is essential for maximizing binocular performance within a pair of lenses. A line drawn from the object/fixation point through the Cr (center of rotation) is called the fixation axis. The Cr provides a stable framework for the comparison mapping of corresponding points on each eye’s retina. Specific equipment, Rx parameters and other anatomical factors are required to assess the precise location of the center of rotation.

Measuring PD

For eye care professionals, it wasn't until the arrival of progressive lenses in the 1960s that the importance of an accurate monocular PD for obtaining optimal intermediate and reading utility was fully appreciated. Before that time, measurements primarily centered on obtaining binocular PDs. Using a millimeter ruler, monocular values, if desired, were derived by halving this value.

Measuring Methods and Accuracy

Several studies in the last twenty years have attempted to scientifically analyze the accuracy and repeatability of obtaining PDs using three primary methods:

  1. PD Ruler - Used to measure the distance between pupils, corneal reflections, iris margins and particularly in the case of small children, the inner and outer can-thus. A study completed in 2002 assessed that the ruler method can yield values accurate to within 1.54 mm of a gold standard (see below) with 68% confidence.
  2. Pupillometer - Primarily measures the distance between corneal reflections. Overall values were found to be within 0.74 mm accurate with 95% confidence.
  3. Digital Centration Devices - These may use either corneal reflections or iris borders for determining PD. The user should be aware if the device's software employs an internal calculation to extrapolate at the visual axis location from the pupil/iris center. DCDs were found to be very accurate instruments, with binocular PDs found to be within 0.40 mm with 95% confidence.

There's a pattern here: Pupillometers appear more accurate than millimeter rulers and digital centration devices appear more accurate than pupillometers. But before you ditch your PD ruler, remember that the ruler and manual measurements will always play an important role in an ECP’s toolkit. Both objective and subjective verification and troubleshooting of prescription eyewear will continue to require expertise in the use of ruler and pen. Because of this, some practitioners prefer to use an enhanced manual method, which employs a mirror to subjectively determine the visual axis at the spectacle plane. Each method has to consider variables that may impact accuracy and efficacy. Below is a summary of the most important factors affecting pupillary measurement:

  1. Device Calibration - While obviously important when using instruments, parallaxic errors can arise when using the ruler method if there are differences between the PDs of tester and subject. These are avoided by using Jalie's Rule of Sixteenths, which states that every millimeter difference PD requires an adjustment of 1/16mm to the end result.
  2. Instrument Operator skill/experience -
    1. Repeatability - Can a single operator take several similar measurements from the same patient?
    2. Serial - Can multiple operators take similar measurements from the same patient?
  3. Near and Intermediate Considerations-
    1. Vertex distance - Generally based on an average value of 13 mm. However, if the fitted VD departs from this number by 4 mm or more, then values for near and intermediate use will not be optimal without recalculation.
    2. Pantoscopic Tilt-Improperly measured values can result in deviations that may require compensation.
  4. Frame Considerations - A person’s physiognomy or fitting preference may place the frame markedly off the facial median plane, a deviation that, can make the efficacy of the found values suspect.
  5. Head Cape - Defined as the habitual departure from the orthogonal facial plane, head cape compensation is important for both optimal binocularity and multifocal utility.
  6. Rounding Errors - present in all methods, rounding errors can affect accuracy.
  7. Patient Cooperation - This is one of the least controllable of all variables affecting PD measurements.

The Gold Standard in PD

In the 2009 study, 8 different devices, both pupillometers and DCDs, were used to help answer an important question: Considering all the variables affecting a PD measurement, can we be confident that using any method or instrument will result in the complete truth of a precisely accurate PD? The answer is no. Faced with determining the truth of an objectively unverifiable parameter, statisticians often turn to averaging all the measurements to a mean value, and then observing the distribution of all the values found to this mean. This “best possible compromise" is then referred to as the gold standard. The 2009 study sought to establish both device repeatability (9 subjects tested in 5 rounds by 8 different instruments) and serial consistency (80 subjects measured once by 8 different instruments). When the data was adjusted for various corrective factors, the average for all devices was found to be within 0.6 mm of the gold standard with 95% confidence. That's accuracy I'd take any day!, Barry Santini

PD and the Consumer as King

In our political system, consumers are not always active participants. Nevertheless, government officials recognize that consumer influence can be great if an issue surfaces with enough sizzle to stir these voters out of bed on election day. It's clear today that lawmakers increasingly tend to consider regulatory issues before them in “consumer-friendly” terms. In Utah for example, legislation is pending that makes room for advancements in technology that facilitate “alternate channels of distribution” for medical services, some of which had previously been done only by licensed professionals. Therefore, as consumers increasingly feel comfortable taking their own blood pressure and heart rate in a kiosk at a local mall, lawmakers are also considering allowing contact lenses and even eye exams to be made available in a similar manner.

Only two states, Kentucky and Massachusetts, mandate that a PD be entered on every eyeglass prescription. But if eye care professionals continue to ignore the growing demand for freedom of choice in buying prescription eyewear, they might just see their state government become both a consumer advocate and a professional adversary. More than ever, eye care professionals must reformulate their business strategy to successfully compete in an economy where consumers are infatuated with the low prices, wide selection and convenience of online.