Free Space testing and Continuous Refraction
Reflecting on the Kraskin Memorial Lecture ICBO 2006
Bryan T Smith BOptom, FCOVD, FACBO (reprinted here with permission of the author)
At the 5th International Congress of Behavioural Optometry (ICBO) 2006, Dr. Robert B. Sanet presented the Kraskin Memorial Lecture, entitled, “Using Behavioral Probes to Understand Visual Spatial Thinking: Implications for Visual Therapy. Is the 21 OEP Analysis Enough?” In the abstract for this lecture Dr. Sanet made some profound statements and gave clear insights into the future direction Optometry should head, stating,
“The 21 Point Vision Analysis taken through a phoropter has several serious drawbacks including: Not allowing for normal Magno-Ambient processing, inducing an abnormal head and neck posture which may change the relationship between the vision and vestibular systems and the inability to evaluate facial expressions, stress or postural changes. In addition, the findings are taken at 40 cm, which may vary greatly from how the child visually functions at his habitual working distance.”
One of the main themes of the lecture was that it was time for the profession to put aside our phoropters and for us to conduct our visual analysis in free space using a trial frame, prism bars, and flippers. He made the point that the purpose of the visual analysis wasn’t just to collect a series of numbers, but to understand how the patient used their visual process to derive meaning and direct action. He recommended doing the visual evaluation in as natural or ergonomic a situation as possible, and one that mirrored the visual demands in free space and in the position of gaze and distance the patient needed to perform in real life.
I remember, soon after the 2006 ICBO, that my colleague at the time made a comment that my testing with a trial frame was antiquated and didn’t look professional when compared to his computer assisted motorised phoropter; he had totally missed the point. I just smiled and quietly got on with the job, changing nothing while my phoropter stood in disuse.
Almost seven years on, I often wonder how many delegates made the change into free space testing or like my colleague, gave it little credence. I personally had started free space testing some 17 years earlier, after attending, what was to me, a landmark workshop presented by Dr. Melvin Kaplan (1991) on the use of yoked prism. I remember one dramatic demonstration on how the visual process affects muscle tension and strain. He showed that while a patient observed an Elephant disc Rotator wearing prescribed yoked prism along with Red/Green goggles, symptoms of back and neck pain disappeared. To me this was remarkable; it demonstrated a clear link between vision and body. Today the Rotator can be replaced with observing into free space and the yoked prisms with prism bars to get the same result.
My experience has been that free space testing in a well-lit room puts the patient at ease with comparatively reduced prescriptions with respect to phoropter methodology. Patients generally report more comfortable vision.
I slowly found my free space refraction evolving. I initially started with monocular refraction with binocular balance, then I started doing a free space binocular refraction with +0.50D blur before the eye not being directly assessed, this was followed by binocular balance. This approach allowed greater comfort and coherence between the two eyes. Now, however through insights given by my colleague Michael G. Christian (2008), I conduct a pure free-space refraction we have coined a Continuous Refraction.
A Continuous Refraction is a binocular refraction and binocular balance done simultaneously. After objective retinoscopy evaluations, 0.25D is then added alternately while the patient makes subjective discriminations on clarity and comfort; typically this is in the direction of emmetropia. That is, in cases of hyperopia the patient prefers less plus power and in cases of myopia the patient prefers less minus power. With this method a symmetrical pattern usually emerges between the right and left sphere. Cross-Cylinder testing is also performed binocularly, alternating back and forth between right and left and again it is usual for a symmetrical pattern to appear. I find the patient more at ease and just the right amount of support is prescribed.
In his presentation, Dr. Sanet also stated, “Our understanding of the visual process and the interaction of processes both within the visual system and between the visual system and other systems has expanded dramatically”. Indeed that most dramatic of these being the discovery in 1968 by Dr. Colwyn B. Trevarthan, a neuroscientist at Harvard University. In his summary he stated:
“Experiments with split-brain monkeys led me to consider that vision of space and vision of object identity may be subserved by anatomically distinct brain mechanisms. In this paper I examine the visual mechanisms of the brain to test the idea that vision involves two parallel processes; one ambient, determining space at large around the body, the other focal which examines detail in small areas of space”.
A variety of experimental evidence in more recent years supports the two-visual system hypothesis and is aptly discussed by W.C. Maples (1995) and Rosen et al. (2001)
The focal visual system (or the “what” system of visual processing) enables object identification and perception of shape and colour. The focal visual system predominantly responds to focal lenses. The ambient visual system (or “where and how” system of visual processing), enables visually guided movement such as pointing, reaching and grasping along with posture, balance and movement. The ambient visual system predominantly responds to prism lenses.
Now that we have a scientific and anatomical explanation of how strongly vision and posture, balance, and movement are related. How do we test and treat it?
If we can answer this question, maybe the questions Dr. Sanet posed also get answered, namely:
- Should we be performing probes which allow for more natural peripheral, Magnocellular-Ambient function?
- Is the 21 Point Skeffington Analytical Sequence visual analysis enough?
- Do we need to update the model and data used?
- What would a prototype for a new behavioural optometric testing battery look like?
- Does it reflect visual functioning in free space?
- What test will give greater insights into the key aspects of an Optometric Vision Training Program?
The answer to the above questions can be quite simple and straight forward. By changing the emphasis from what is difficult for the patient to what is easy for the patient; a strategy for assessing the ambient visual system has been uncovered. I believe the goal of the visual analysis, like visual therapy, should not be the attainment of certain findings, but rather to produce an individual capable of thinking about and controlling his or her own visual situation. The goal should be to empower patients, to help make them to be more observant thinking individuals.
I agree the ambient visual system needs to be tested in free space, performing probes which allow for more natural peripheral, Magnocellular-Ambient function. And as Dr. Kaplan demonstrated to me many years ago, sometimes this process is not successfully achieved in the sitting position, but requires the patient to be moving around from place to place, assessing pointing, reaching and grasping along with posture, balance, and movement. It has been uncovered that these abilities intuitively reveal what prism is required to support the body as well as the visual system thereby reflecting visual functioning in free space.
Dr. Sanet stated that, “The Magnocellular-Ambient pathway is the main pathway for spatial vision and orientation. Interference with this system may dramatically affect eye movements, vergence, and spatial localization.” The flipside to this statement is that, supporting the ambient visual system may dramatically affect eye movements, vergence, and spatial localization. By assessing and treating the ambient visual system, a lens based Optometric Vision Training Program has emerged which Michael Christian calls Visuo-Somatic Realignment (VSR) or Vision Body Realignment. Given the right cues the body can determine the precise quality and quantity of horizontal and vertical prism required before each eye for vision and body realignment. A dynamic combination of prism is found which is typically asymmetric. Tight necks, sore hips and frozen shoulders disappear as a result and the patient’s attains freedom of movement and balance as well as comfortable and open vision, this is the essence of VSR.
As Dr. Sanet intended four years ago, if you haven’t already made the change, I hope this piece encourages you to start free space refraction, you’ll never look back.
- Sanet, R. B. Abstract for the Kraskin Memorial Lecture ICBO 2006.
- Kaplan, M. Visuo-Motor Management Workshop Sydney Australia 1991.
- Christian, M. G. Visuo-Somatic Realignment Workshop Queenscliff Australia 2008
- Trevarthen, C. B. The mechanism of vision in primates. Psychologische Forschung, 1968; 31: 299.
- Maples, W. C. Anatomy and Physiology of Eye Movements. NSUCO Oculomotor Test, OEP 1995; 2: 4-17
- Rosen, S. A., Cohen A. H., & Trebing, P. The Integration of Visual and Vestibular Systems in Balance Disorders-A Clinical Perspective. Visual & Vestibular Consequences of Acquired Brain Injury, OEP 2001; 179-182