Head rotations, bar reading and bring on the prism flippers
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! 😀 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.
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.