A SUPPLEMENTAL MECHANISM FOR VO LENS DEFOGGING
Roy F. Sullivan, Ph.D. ©:1997
Fogging of the video otoscope frontal lens surface can obscure the video camera view when examination room temperature and humidity are significantly below that encountered within the patient's ear canal. Some VO systems are supplied with Siegle bulb connections to the VO head. One or more air puffs from the bulb will generally defog the lens surface. Unless the patient is warned, a startle response is often inadvertenently elicted. A number of VO systems do not provide Siegle bulb connections and require either temperature stabilization of the head when not in use or the physical clearing of fogging with lens tissue and alcohol. Deeper insertion of the VO speculum is more likely to result in defogging than shallow insertion.
A continuous defogging mechanism was improvised utilizing a low pressure fishtank pump and connectors found in aquarium and pet supply stores (Figure 1). Figure 1 shows a "Whisper 100" model fishtank pump (A). The bleed valve (B) limits airflow to reduce turbulence noise in the ear canal and to avoid a suprathreshold cool air caloric stimulation to the vestibular system of the ear under examination. The airflow can be fine tuned by observing nystagmus or heeding subjective report of vertigo from a test subject used for intial system calibration. A high pass acoustical filter, constructed of finger cot and pill container (C) inserted in series into the pressure line, limits low frequency noise transmitted through the flexible pressure tubing leading to the VO head.
A "T" connector is inserted in the Siegle Bulb connecting tubing (Figure 2). This allows a mild, continuously defogging air flow upon which can be manually superimposed a Siegle air pulse for observing tympanic membrane intactness and mobility. Figure 3A, below, illustrates the VO endoscopic image immediately upon inserting the VO rod with speculum into a patient's ear canal. Room ambient temperature at the time was 65 degrees with 55% relative humidity. The ear canal, which is used routinely used thermally indexing body temperature, can reach 98.6 degrees F when enclosed. Figure 3B shows the VO view after 3 seconds, cleared spontaneously with the mild fishtank pump airflow.
Figure 3 A/B
A keychain radio-frequency remote control, (Figure 4) conveniently mounted on the backrest of the examination chair, concurrently turns on or off the halogen light source with its cooling fan and the fishtank pump. It is likely that VO system manufacturers will incorporate this feature into their clinical units in the future. [Since this article was posted in 1997 on the Video Otoscopy website www.rcsullivan.com, At least one manufacturer, Starkey Laboratories, has included a defogging feature in its STARMED GENERATION 5 video otoscope.]