Caloric Test I thought that I would explain the caloric test in hopes that it will give some people a clearer understanding of the test, how it is performed, and what the results mean. You can drop to last two paragraphs for summary, if you do not want to wade through this rather long post. The caloric test is often part of the ENG battery of tests. In these tests a medical technician will place electrodes on a person’s head reasonably close to the eyes. These electrodes are sensitive to the electrical activity of the eye muscles. Instead of using electrodes some doctors are using a newer technique in which a person’s eye motions are recorded by a video camera. The patient wears goggles to shut out extraneous light. Since the videos are made in the infrared region, it looks dark to patient but not to a camera with infrared sensitive detectors. Of course, the video monitors will display image in visible portion of light spectrum so that the technician can see for himself how things are progressing. Besides a visual monitor, computer algorithms will analyze eye motions and thereby provide even more information on eye responses to various stimuli. You may be wondering why someone should look at your eyes when it is your ears that are bothering you. It turns out that there are nearly direct neural connections between the vestibular organs and the eye muscles. According to my neurologist, some of the vestibular neural signals go to a ganglion (web of neurons) in the brain stem where they switch through one or two synapses before heading towards the eyes. This is very fast processing for the brain, about 1/30 of a second. It is this rapid response that gives us exquisite control of eye motion. The eye muscles are the most highly enervated muscles in the human body. We have very fine control over them, some voluntary and some involuntary. As a result of their connections to the ears, our eye muscles will fire when our heads are accelerated in certain manners. This allows us to keep objects in clear focus despite moving about in all sorts of ways. No doubt this ability has evolutionary advantages for us and all the other mammals that share this system. The caloric test is a test in which warm and cool fluids, usually water but can be air under certain circumstances, are inserted into a person’s ears. This stimulates the vestibular organs, especially the lateral semicircular canal (LSC). One way that the LSC is stimulated by the fluid is through a thermal effect in which a portion of the fluid of the LSC is cooled or warmed, thereby changing its density and leading to convection of fluid inside canal. This fluid motion causes the cilia (hair) of the organ to flex and a neural signal to be sent to brain stem. The brain stem then emits signals to eye muscles (picked up by previously mentioned electrodes). The firing eye muscles cause eye motion. The LSC is the canal that detects the motion of the head when it rotates back and forth when nodding “no”. It is the organ that can give rise to vertigo if it goes haywire. However, it is important to realize that there are two other semicircular canals in each ear. They are the anterior semicircular canal (ASC) and the posterior semicircular canal (PSC). The ASC detects rotation of head as in nodding “yes” and the PSC detects rotation of head when we tilt head side to side as if to say “perhaps”.) Compared to the LSC, both the ASC and the PSC are weakly affected by the caloric test because they reside more deeply in the cranium. Additionally, the vestibular organ has two linear acceleration detectors: the utricle and saccule. Linear acceleration is when an object's speed increases or decreases while it travels in a straight line. We’ve all experienced this when our cars accelerate forward or when out cars decelerate to a stop. The saccule and utricle also respond to the direction of gravity; they are useful for orientating ourselves with respect to gravity. The saccule and utricle are only weakly affected by caloric test. When one ear is stimulated by either warm or cold water and the other ear is not, then there is an imbalance in the vestibular signals that the brain stem receives. This imbalance can cause an erratic, beating motion of the eyes. The patient may feel dizzy and maybe even nauseous, depending on how quickly his body has an emetic response. The dizziness usually dies away as thermal balance is achieved. If a person has an unresponsive ear, then that person will not feel dizzy and his eyes will not develop a beating motion. When a determination is made on how well a person’s vestibular organs are functioning, a doctor actually makes a comparison between the left and right ears using both the warm and cool water portions of test. If an ear is hyperactive, it results in one type of eye motion or if a person’s ear is hypoactive, it results in a different type of eye motion. In summary, the ear has three semicircular canals (lateral, anterior, and posterior) and two linear acceleration detectors (utricle and saccule). The caloric test principally probes the lateral semicircular canal by exciting the ear with warm and cool water and examining the resultant eye motion. The eye motion is either sensed indirectly by electrodes or directly by video techniques. The two ears are compared to see if one is acting abnormally. Having a negative result on this test is not proof that you do not have Meniere’s disease. It only shows that your lateral semicircular canal still has satisfactory performance. Remember that there are four other balance organs inside each ear. This test is just one bit of information to help your doctor reach a diagnosis or monitor your condition. The other portions of the ENG are involved with other aspects of the visual and vestibular systems. Joe PS I am posting this explanation because Gwen thought it would be a good idea. I welcome feedback, good or bad. You can PM me or post on this thread.
Joe, You have a talent at explaining complexities at a laymans level, You must have been a wonderful teacher, and I for one am very glad you continue to teach here!!!
Great info! Just in time I'm having a E.N.G next week. You explained it better then Web. M.D !! Venus
Just wanted to ad that this type of test is also done in as part of determining your "stage" of Meniere's Disease, in which the later stages after the vestibular system is pretty much shot, it will also have negative results. This, in addition to other "late stage symptoms" shows the extent of damage to the vestibular. Great information!
Thank you for explaining the test to me, I had it done back in 1993 and hated the feeling it gave me. I also had a few other tests back then and I can't remember what the actually were but I was diagnosed with bilateral Meniere's. I have just dealt with it the last 10 yrs (and not very well) with the help of my personal doctor and meds but I am going back to my specialist next week. I will ask him what test he had done on me then so I will know more about it. When I first got it, the doctors around here didn't have experience with it so I had to do phone book searching back then to fins a specialist, now the computer online stuff is so helpful and I just started finding this stuff in the last few weeks. This sight has been so good for me to know there are more people like me out there and that I am not crazy as some people think that I am. I have even tried to commit suicide twice because I could not deal with a cronic condition. Thanks you to people like you for you help and knowledge.....Cheryl
This is the best explanation I have received. I have read numerous articles, webistes, and spoken with my doctor and still did not understand completely until I read this. I actually showed a weakened response in my left ear which my doctor said meant she knew where the defect in my balance system was stemming from based on the results but until now I never quite understood. My doctor also lead me to belive that because my defect was in the LSC a low soduim diet/diuritics would probalby not make a difference and valium would be most effective. Does this seem accuarate to you?
Thanks for the explanation. You explained it better than the doctors and all the articles I have read! I have an ENG coming up on Wednesday that I am not looking forward to at all..
This is an excellent description of the caloric test! Very good and informative! Thanks------my dr also said you can still have mm with a normal caloric test, it takes years for mm to destroy an ear. Good thread.
Really good information! So clear and concise. Let's a newbie understand the procedure so well, maybe it'll relieve some stress over having these tests done and what the results really mean! With this forum, so many of us know more than the normal Dr. Who isn't up on new treatments. It is so important to keep informed. God Bless You, Ray, for this site!
