I just returned from the Academy of Pain Management meeting in Vancouver, B.C., where I presented some original research on adhesions of the temporomandibular joint and on measuring head posture. While attending some of the meetings I met a fellow from Norway who is doing some exciting research on reading difficulties following whiplash. So, to wrap up this series of articles on the fascinating relationship between the eyes and the spine, I'd like to tantalize your clinical thinking with an interesting interpretation of why some patients may complain of reading problems following (major) whiplash.
How Is "Reading" Actually Performed?
Reading is under the influence of the postural control system (PCS) and involves the ability of the eyes to perform what is called smooth pursuit. What is smooth pursuit? Imagine looking out a large window and watching a white dove gracefully fly across your field of vision. In the healthy visual system, the ability to faithfully follow the dove as it flies is accomplished by the smooth pursuit eye movement system (SPEMS).
SPEMS is important for the reading process too. It allows the eyes to fuse (focus in unison) on each word while they travel along the sentence, moving smoothly from word to word and then move down one line without loosing words or getting lost in the paragraph.
When all works well, we comprehend what we read by what is called the automotive reading process (ARP). Essentially ARP is a four-step process involving 1) information uptake (via smooth pursuit); 2) learning; 3) memory; and 4) concentration. A disturbance in any one of these four steps causes impairment in reading comprehension.
Reading and the Postural Control System
SPEMS relies heavily upon accurate information from the proprioceptive systems lying around the eyes (extraocular muscles) and the neck (those muscles which control head positioning). All this information is processed by the PCS.
Essentially, the PCS creates miniature postural memories and stores them in the pontine-reticular system. These postural memories are created as a result of a summation of all sensory input, particularly proprioceptive input.
When aberrant sensory input is sent to the PCS, strange things can occur. The most common example of what happens when the PCS receives aberrant input is vertigo or dizziness. Aberrant input can also prevent or hinder acquiring new psychomotor skills (imagine trying to learn to ride a bicycle while suffering from vertigo). It may also upset the functioning of existing skills. Have you ever tried to read a book while seasick?
Cognitive Dysfunction -- Can It Be a Result of a Major Neck Injury?
According to some preliminary work by Dr. Carsten Saunte, cognitive dysfunction (reading comprehension) can occur following major neck injury (whiplash). He explains that he studied over 50 patients diagnosed with whiplash injury to the neck who also complained of vertigo and who further reported they lost their ability to work or study. After carefully examining each patient he discovered that they all suffered from a disturbance in smooth pursuit.
From this he theorized the damaged neck causes aberrant proprioceptive input to be sent to the PCS. In turn, erroneous postural memories are created which impairs smooth pursuit and causes further errors in ARP. The net result, he claims, is an inability of the patient to accurately read and retain written information, hence, an inability to work or study.
Stay tuned to this very preliminary subject and be on the lookout for Dr. Saunte's article when it gets published. In the meantime, query your patients with any serious neck disorder (not just whiplash) to see if they have reading difficulties. If Dr. Saunte's work is on the right track, serious neck disorders should upset the normal smooth and effortless functioning of the eyes.
With each article I encourage you to write the questions you may have, commentaries on patient care, or thoughts to share with your colleagues, to me at the following address. Please include a self-addressed, stamped envelope.
Darryl Curl, DDS, DC
2330 Golden West Lane
Norco, California 91760
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