Eco-Optics Part 9

You’ve probably noticed by now that the ecological approach to visual perception, or eco-optics, isn’t formulaic.  It is much more of a qualitative than quantitative approach, and that dovetails nicely with the way we’ve been approaching patients.  Conceptually we know that all our objective measures, be they based on auto-refractors, wavefront aberrometers, or traditional retinoscopy can’t substitute for putting contemplated lenses and/or prisms in front of a patient’s eyes and asking them how things looks and feel in a variety of environments.  Ranges of performance through the 38 mm holes of a phoropter, or seated in a confined stereoscope belie the complexity of the environment and, in Gibsonian terms, its affordances.

For many of our patients having a look out the window at traffic, or walking down the hallway, is infinitely more important than what we derive through the phoropter, which is a very important starting point, but only that.  Few if any of our patients are “routine” these days.  And what is the patient doing when they look around through the window at people or cars moving, or walking down the hallway?  They are interacting with the ambient optic array.  The “stimulus” that they are responding to through lenses or prisms isn’t a central point; there are multiple stimuli to process in parallel in the optic array.

ambient optic array

In this regard our diagnostic measures leave something to be desired.  Out of the phoropter = Outside of the box.  I’ve suggested some basic measures that help us get closer to what Gibson was introducing through ecological optics, and one of them is motion parallax.  We take advantage of this as a binocular feature in therapy, and it should be done as more of a routine in testing.  The target that I favor is the Marco stereopsis test projected at distance.  There are four concurrent levels of depth to resolve based on the increasing disparity as the patient scans around.  We look for the patient to be able to sort out the top line (with least disparity) is further back and the left line (with greatest disparity) is closest.

Stereo Distance

The key is to do this procedure with polaroids in place, over relevant lenses or prisms, out of the phoropter so that we can probe motion parallax.  Gauging the patient’s initial sensitivity to this during the evaluation, and using it at some point subsequently to assess progress is an important component of applied Eco-Optics.  Think of all the procedures that the patient undertakes in the vision therapy environment, and how few of them have a direct analogue in the evaluation.  Clearly there isn’t enough time in the day to, for example, have a probe like Inifinity Walk as part of the diagnostic battery.  But for select patients that might that be more important in an assessment than anything you could do through the constrained environment of a phoropter or stereoscope.  It is, for example, why the Useful Field of View Test was introduced as more indicative of visual readiness for driving than traditional visual field measures in a ganzfeld bowl with fixed head position.  Designers of that test understood at some level the importance of eco-optics.

After reading the first few installments of Eco-Optics, my colleague Dr. Stuart Rothman pointed out the type of technology that might loom in the future for having a more immersive and integrative assessment.  As a concept, take a look at this setup from Bertec Balance.  Though it’s way too pricey for private optometric practice at this point, the concepts are important.

Dynamic Product Package

The job ahead of us is to reverse engineer the process so that more of our diagnostic battery is indicative of what we do in therapy to help the patient interact with the environment.  What if we simply noted performance on Brock String with the patient seated vs. standing at different distances and in different angles of gaze?  Or had the patient look at a letter chart of Worth 4 Dot target while walking toward and then away from the chart?  Much like therapy, it needn’t be complex at the outset.

5 thoughts on “Eco-Optics Part 9

      • Unlikely, but the concept is that for patients with movement disturbances, the phoropter measurements are highly artificial relative to use of vision in the natural environment. Phorometer is a step in the right direction, but loose lenses/prisms in less obtrusive trial frames that allow natural movement are even better!

      • I always had pairs of plus lenses around the office for VT AND Retinoscopy.

        Good hint for some myopes do retinoscopy without lenses and move closer to the patient until your preferred result is reached. Or, for very high myopes, start at their nose and move outward. In both cases measure final distant and compute optical power.

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