Lenses, Part 4: Progressive Bifocals: Vision Care Breakthrough or Visual Process Breakdown?

Originally posted on June 4th, 2012

Lenses – part 4

Why all this fuss about lenses?

Lenses are an incredibly powerful and safe tool for helping people of all ages improve their overall performance, their productivity and their comfort.  My previous posts on lenses included concepts such as lenses are medicine and lenses change the instructions to the brain.  It is important to appreciate that the visual process is not restricted to the eyes.  The intake and processing of visual information and subsequent action that comprises the visual process are processes of the brain.  Lenses should be considered medicine because they act on the brain.  Lenses act on the brain by changing the character and quality of the light (the information, signals and feedback from the environment) reaching the brain.  Therapeutic lenses do so in a purposeful way.  And while there is no way to predict the exact way any particular brain will respond, an experienced behavioral optometrist can help steer the process in the right direction by the careful choice of lenses and possibly vision therapy.

I want to introduce another crucial issue: It is not what a lens does to a person but what a person does in response to the effects of the lens.  Lenses affect light in a precise and predictable way.  The response of any given person to this specific change in feedback is much less predictable.  Finding a $100 bill increases any person’s wealth by $100; that $100 means very different things to different people.  Behavioral optometrists often use their knowledge of lenses to help people change behavior and performance.  Other effects of lenses occur by default, that is, without purposeful intent and without the person even knowing it.

Lenses are consistent and predictable; people’s responses to them are not.

Every lens transforms light precisely and predictably, as I stated above.  The brain (and therefore the person) must make adjustments in order for any lens – compensating or therapeutic – to have the desired effect.  Most compensating lenses seem to work automatically, but this is not the case.  There would be no improvement in clarity if the brain didn’t respond appropriately to the lens.  The whole point of therapeutic lenses is to stimulate the brain into creating new patterns of behavior.  Sometimes a person is unable to make use of the lenses they need and vision therapy is used to help them make the desired changes.

All lenses change the information and feedback to the brain.  Compensating lenses demand that the brain do what they tell it to do – there is little wiggle room.  Lenses intended to have a therapeutic effect provide feedback that stimulates the brain to ask new questions and create new patterns of behavior.  It is these new patterns of behavior that stimulate the visual process to become more efficient, more productive and more comfortable.  Next I would like to discuss the king of all compensating lenses – the invisible bifocal.

Progressive bifocals – great idea, but…

Most adults are familiar with invisible bifocals, also known as progressive bifocals.  This interesting technology allows many people to take advantage of the benefits of multi-focal lenses (bifocals or trifocals) without anyone else knowing they’re doing it.  This of course is mostly a matter of cosmetics.  Progressive bifocals also help people, especially those over forty, to see clearly at various distances without having to switch glasses.  Standard bifocals and trifocals also do this, but everyone can see you are wearing them.

People who regularly perform a wide variety of tasks at various distances often find progressive bifocals very helpful.  Very few technologies or luxuries come without a price as we all know.  A large percentage of people who try progressive lenses cannot tolerate them for a number of reasons.  Some people find them nauseating or disorienting; others simply cannot use them comfortably for their daily routine.  Progressive lenses have some concrete effects on the visual system that are at the root of this dissatisfaction.  Many people either get used to them  fairly easily or with great effort, convinced that it is something they need to do.  Just because you can get used to something doesn’t mean it’s a good idea or that it’s particularly good for you.

There are three foundational abilities that are critical for effortless, effective and comfortable use of the visual process:

  • Accurate eye movements – we must be able to point our eyes precisely at each object of interest to allow for maximum clarity and efficiency.
  • Effortless eye teaming is necessary for reliable depth perception to judge distances and making accurate movements.
  • Flexible and stable focusing is important for seeing clearly at various distances without interruption or fluctuation.

Progressive lenses adversely affect all of these fundamental aspects of the visual process.  Obviously the idea behind progressive lenses, besides helping people hide their age, is to make life easier for the busy modern human.  Few things come without a price.

I want to explain the price of progressive bifocals here because most doctors who prescribe them are either unaware of these issues or choose to keep what they know to themselves in the hope that no one will notice.  The problems inherent in this technology are very important in the context of behavioral optometry and all the issues we address with our patients.  These issues are also important to everyone who uses their eyes on a regular basis.  I’ll address each of the three facets of the visual process listed above and how each is impacted by progressive lenses.  Before I get into the big three I’ll start by saying that the distance prescription is generally not as precise with progressive lenses as it is with standard single-vision, bifocal or trifocal lenses.

Eye movements: Briefly, eye movements are foundational to all visual performance.  We must aim our eyes precisely for things to work smoothly.  People over the age of four should be able to smoothly track a moving target without moving the head (unless the object is quite far to one side or very high or low).  We should be able to shift our eyes quickly and accurately from one target to another, again without moving the head for the most part.  We also need to be able to keep our eyes fixed on a target for as long as we need or want.  Infants typically move their heads most of the time when they move their eyes.  It is expected that in fairly short order the head movement will cease as they learn to move the eyes independently of the head.  Those who fail to make this transition are very likely to experience reading difficulties and poor coordination among other possible visual problems.

Progressive lenses dramatically restrict eye movement due to the design of the lens.  This is an unavoidable drawback inherent in the technology because the bifocal portion is a very narrow channel.  There is also significant distortion all around that channel, which negatively impacts peripheral awareness.  I have had numerous adult patients inform me that they were told not to move their eyes when reading with their progressive lenses.  This is a step backwards developmentally and often leads to eye fatigue and neck problems.  Fatigue and neck injury aside, young people are likely to suffer long-term disruption of the visual process if they wear progressive lenses for prolonged periods of time due to the restriction of eye movements.

Eye teaming: Restricted eye movements are guaranteed to disrupt eye teaming.  We are meant to use our two eyes as an integrated unit.  Two eyes aiming at the same thing at the same time gives us high quality depth perception and enables us to accurately judge where things are so that we don’t walk into them.  Good depth perception also enables us to participate in sports with at least some proficiency, drive safely and enjoy all the new 3-D movies being produced.  Progressive lenses restrict the fluid nature of the visual process.  This means that every visual move we make takes more effort to achieve a lower quality result.

Focusing: The problem with focusing through progressive lenses is more of an issue with younger people, but these issues persist for people in their forties and fifties to some degree.  I will be addressing the younger wearers here because it is not uncommon for even behavioral optometrists to prescribe progressive lenses for young people who need bifocals.  It is my opinion that anyone wearing distance lenses should have bifocals since the distance lenses put excessive strain on the visual system when used for close work.  The focusing mechanism is meant to function with incredible speed and precision.  You should never notice things coming into focus when you switch from one distance to another.  Progressive lenses have a graded bifocal portion so that the closer you are looking, the stronger the power of the lens you are looking through.  This is essentially the whole point of this technology.  The appropriate flexing of the focusing system of young person using these lenses is completely disrupted as the lens attempts to do the work the visual system needs to be doing.

I do not want to create more visual problems so I don’t prescribe progressive lenses unless someone demands it.

I do not prescribe progressive lenses, except in very specific circumstances, for these reasons.  Many people have problems with eye movements, which interfere with their ability to do many things including reading, handwriting and sports activities to name a few.  I am not interested in creating more visual problems.  My work centers around helping people improve their eye movements, eye teaming and focusing skills among other things, usually with vision therapy.  I cannot in good conscience recommend progressive lenses knowing all the drawbacks built into the technology.

I am not in the cosmetics business – I’m a behavioral optometrist.  I have helped numerous people get relief from headaches, eye fatigue, general fatigue and neck pain by having them give up their progressive bifocals in favor of some other approach.  I know there are plenty of doctors out there that will disagree with my assessment of progressive lenses.  They cannot really argue with the functional issues I’ve raised, but they can downplay their importance.  It’s up to each person to decide what is really important to them.  But that’s very hard to do if you don’t understand all the issues involved or don’t have most of the facts, and my goal is to provide as many of the facts and issues as possible.  If and when the technology improves sufficiently I will gladly adjust my approach.  Until then I’m sticking with the things I trust to do no harm.

Next time:  The Visual Process and The Autism Spectrum


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