Showing posts with label cranial nerves. Show all posts
Showing posts with label cranial nerves. Show all posts

Tuesday, March 3, 2015

Jaw clenching, Vision Therapy and earthquake resistant structures

Personally I learn a lot from reading/listening up on vision rehab and anatomy but I learn just as much from having conversations with other strabismics. I think it's a practice that could be useful to anyone with any problem. Don't compare yourself to people with a very differing, in this case neurological, background. Learn from people who are similar to you and dealing with similar day-to-day problems. What follows is a blog post constructed on this type of conversation.

PASQUALE: Hi Michael, in many blog entries you mention jaw clenching. I too have said that I engage numerous facial muscles while I try converging and diverging at different targets.  It feels like the brain is recruiting other muscles because it still hasn't figured out how to properly use the eye's extra-ocular muscles.

MICHAEL: I always think of it like learning how to do something with your left arm (unless you are left-handed). First you use your entire arm, often in a contorted way. Then you move on to more specialized movements of the joints and ultimately you can do things smoothly having very fine control over your arm, hand and fingers. Theoretically the potential for improvement is limitless.

Let's transpose this to the visual realm. At first, when trying to accomplish a visual task, you are doing it very clumsily and inefficiently. Your brain is trying to accomplish a task which requires fine ocular motor skill but it's not succeeding because of a lack of (lasting) control. Because many of us are hardheaded we redouble our effort and adjacent regions and resources like facial muscles are drawn into the process to little or no avail. Not good. Instead of redoubling our effort employing a very limited set of visual skills we should go back to the drawing board and improve and multiply our skills. Technique is more important than 'brute' force.

The visual system involves six of the the twelve cranial nerves. That's a lot of guns to fire and potentially misfire. When I experience jaw clenching after too much reading or just a visually or otherwise stressful situation, that implies I've gone beyond my current visual skill level and I need to back down.

Trigeminal nerve - 5th cranial nerve

PASQUALE: Have you figured out exercises that eliminate engaging other muscles except for those needed to coordinate the various components of the eyes.

MICHAEL: Well, any activity that encourages 'the eyes', meaning the appropriate muscles and neural processes associated, to do the work without recruiting other muscles. That implies not going too far beyond your current skill level and paying a lot of attention without getting frustrated. For me it means slowing down and lowering expectations while gathering finer motor control. As long as my jaw doesn't clench, I'm in the safe zone. Once I start hurting, I'm overdoing it. It's not always easy to be patient and sometimes there are just visually stressful tasks I have to deal with. Then I'm tired, dizzy and in pain.


When thinking about this problem I'm reminded of something I learned about earthquake resistent structures. There's no such thing as a completely earthquake resistent building but you can improve a buildings capacity to withstand external shifts to a large extent. There are various approaches you can adhere to when going about the seismic retrofitting of a structure.
- You can increase the global capacity of a structure. (strengthening)
- You can isolate the foundation so the structure can shake on it. (partial flexibility)
- You can impose intelligent structural changes. Structural vibration control technologies minimize forces and deformations. (flexibility)
The last option implies that various individual parts of the building can move or flex allowing for shock absorption.

Vision Therapy is akin to a seismic retrofit for the visual system. You make structural changes in how it works and learn how to control and flex individual parts. You learn to lean into a quake rather than stiffening up.  That way you can withstand more external demands, with reduced energy drainage and avoid collapse of the structure/system.


For me, eye teaming remains a big challenge but I'm getting there. A related challenge is to gain more independent control over vergence and accommodation, i.e. taking on any binocular stance while manipulating my eye lens as I please. Either component should have limited effects on the other one's performance and there should be a certain ease in doing this. Just like using indivudual fingers while playing the piano.  An increased 'isolation' of these visual components gives more freedom of movement. To continue the piano anology, you'll be able to play 'visual Mozart' instead of just hitting the keys indiscriminately with all fingers at once.

As far as particular exercises are concerned, there are plenty of options to choose from if you understand the underlying principle. Magic eye stereograms, prism/spherical flippers, Eccentric Circles, Aperture rule, even just playing freely with your vision, ... Many VT practices are grafted on this idea one way or another. They are looking to improve smooth eye teaming, lens focusing and then increasing skill level by adding more activities (balance, body coordination, cognitive skill, ...).

In that respect, I particularly liked a quote from the interview I did with Mark last month. It illustrates this point very nicely.
MARK: I still have strabismus but I have a greater degree of control. The reduced suppression helps. I can line everything up that I need for stereopsis (fixation on an object, in focus, no suppression, awareness of peripheral vision etc.). It can be an enormous effort but it's like any other form of learning. Repetition is the key and progress, however slow, will be made!
The only catch 22 when talking about all this 'control' is that you won't necessarily attain it by going about this like a control freak. Be relaxed, patient but determined.

One month later... 

PASQUALE: It has taken me over eight months to finally feel that my brain can move my eyes with better coordination without trying to recruit a battery of other facial, non ocular muscles. I have gone through an entire slew of other muscles including those around the temple region, jaw, even moving my ears. The worse was when I actually felt my upper jaw putting tremendous stress on my entire skull as if trying to separate one from the other. I have to say that I see more positive progress now that my brain isn't trying to move my eyes through the recruitment of all those other muscles.

Sunday, April 27, 2014

Head rotations, bar reading and bring on the prism flippers

Head rotations
Last week, for the first time, I had a completely stable percept while doing my head turns. I couldn't believe it!  I thought I was suppressing or something but I wasn't. Both eyes were just heedlessly adjusting to the head movements without error. It must be great to be able to take these reflexes for granted! I had predicted this milestone for the end of April et voila. Another hurdle taken. The reflexes are not equally reliable every day but that, again, is a matter of time.

Speaking of head turns... I'm reading this awesome book called 'Vision Rehabilitation: Multidisciplinary care of the patient following brain injury' which I will review properly later on. It had some interesting things to say about the anatomy of vision and head rotations.

The cortical or supranuclear influence on gaze is carried out by six distinct neural networks: (1) the saccadic eye system directs the fovea from one object to another object of interest; (2) smooth pursuits hold the image of a moving target on the fovea; (3) the vergence system acts to move the eyes in opposite directions (i.e., convergent and divergent) so that the image of a single object in space can be placed simultaneously on the fovea; (4) vestibulo-ocular holds images still on the retina during brief head movements driven by signals of the vestibular system; (5) optokinetic system holds the image still insofar as possible during sustained head rotation or watching a sustained stimulus going by, such as a train; and finally (6) the fixation system holds the fovea in place on a stationary target. These complex supranuclear networks result in eye movements coordinating whole muscle groups. With the exception of the vergence system, supranuclear eye networks mediate conjugate eye movements. Thus, other than vergence system disorders, supranuclear damage does not lead to diplopia, but to restrictions of conjugate gaze, as in loss of upgaze or downgaze.

Misalignment of the two visual axes with complaints of diplopia frequently results with lesions involving the infranuclear portion of the gaze system, including Cranial Nerve III, IV, or VI or the myoneural junction or extraocular muscles they innervate. Intranuclear lesions also result in diplopia. Innervation of extraocular muscles is ipsilateral to the CN nucleus for CN III and VI, and contralateral for CN IV. The infranuclear ocular motor system is a complex motor system requiring the coordination of twelve muscles to move the eyes.

So there you have it then... I've got problems with the supranuclear, ifranuclear and intranclear portions of the gaze system but the head rotations are on their way! :D In my case it was not a traumatic head injury but a combination of uncorrected developmental weakness and bad surgical intervention. The result for the visual system however is the same. I remember a number of ophthalmologists/strabologists giving me some spiel about third cranial nerve palsy 'with unknown cause'. Yeah, sure mate... Unknown cause. After the surgery there was not only horizontal misalignment but also vertical misalignment meaning the stress on that nerve had increased because the muscles had become so much harder to operate. Vertical alignment also meant that now CN IV had become affected. Overall visual stress on the visual system had become too much to bare as some parts of the system had been ignored and neglected whereas other parts had been damaged in surgery.



Bar reading
I'm a bit repetitive in my mentioning bar reading. I just love this exercise. Nowadays I just wake up, eat something and spend an hour or so bar reading until I get tired. Not completely exhausted though. Up until the point that I still got some juice left but it's time to go for some less visually stressful activities as the day progresses. The hardest part about bar reading is to stop and wait until the next day so I can do it all over again. That's just because I love reading too. I've gone from zero pages at the beginning of this year to 14 to 15 pages a day by the end of April. Hopefully things keep progressing at this pace. It's much more fun to read properly and binocularly than to read in a half assed way. The bars keep you tied up in a 'binocular straight jacket' preventing you from falling back to double vision and visual confusion. Reading while experiencing double vision and visual confusion feels like you are hurting yourself and giving yourself a headache on purpose. I've done this many times to study the things I needed to know to survive but it's not the way to live your life in the long haul. When my bar reading juice is up for the day, I resort to text to speech software, audiobooks or other normal day activities which can include less cognitively taxing forms of visual exercise.



Bring on the prism flippers
To enhance the bar reading progress and the elimination of my remaining convergence insufficiency I'm going to start using prism flippers by the end of May. Making it a little harder yet again. Going to the next level. The new normal.