Chicago?Vision screening of children in the community has received attention for a great number of years, and because of that numerous instruments are commercially available to fill that need.
Chicago-Vision screening of children in the community has received attention for a great number of years, and because of that numerous instruments are commercially available to fill that need.
"Vision screening of children has been a topic of concern for more than 100 years since the first state-supported vision testing program was formed in 1899. The desire to detect amblyogenic factors in the preschool population has fueled the need for quick, easy, and reliable screening tests," Pfeifer said.
Three classes of photoscreeners emerged that were based on different optic designs. "The validity of photorefraction as a screening technique has exploded," said Pfeifer, who is clinic manager of the Pediatric Ophthalmology and Adult Strabismus Service, Department of Ophthalmology and Visual Sciences, University of Iowa Healthcare, Iowa City.
The MTI PhotoScreener, developed from the prototype Eyecor Camera system, has been studied extensively since it became commercially available. According to Pfeifer, it is a portable, light-weight, instant film device, which has a horizontal rotating flash and sliding film, and allows two photographs to be placed on one black-and-white instant film.
The focal length of 1.1 m is achieved with a parallax aiming system, and fixation is obtained by a flashing, light-emitting diode (LED) that is next to the lens aperture. The film is removed from the camera after both images are taken and allowed to develop for 45 seconds before separating the instant film, she explained. Primary care physicians, pediatricians, pediatric ophthalmologists, the organization Prevent Blindness America, and community service organizations use this camera.
"In addition, Lion's Club International has used the MTI PhotoScreener as its screening tool to provide free vision screening to children. Since 1997, the organization has screened more than 400,000 children in 16 states," Pfeifer explained.
The images provided by the MTI PhotoScreener can be graded for refractive errors, media opacities, and strabismus. The clinicians who interpret the photographs include ophthalmologists, optometrists, orthoptists, technicians, program coordinators, medical students, and a Vanderbilt University imaging center, according to Pfeifer.
"The cost per child of screening varies depending on the number of children screened. The manufacturer suggested retail price of the MTI PhotoScreener is $6,000," she said. The original film used with the camera, the Polaroid 337 film, was discontinued, and upgrades to the older models allow Polaroid 667 film to be used; upgrades cost about $1,200. The cost of film is about $0.88 cents per exposure.
The VisiScreen OSS-C (Vision Research Corp.) entered the market in 1989. The camera is an off-axis photorefractor, the technology of which was developed and patented by the National Aeronautical and Space Administration. The system, which requires only about 30 seconds to screen a child, comprises a single-flash 35-mm camera and telescopic lens with a headrest that is fixed 8 feet 3 inches from the lens. Five trained technicians at Vision Research Co. analyze the color photographs for refractive error, media opacities, and strabismus.
Primary care physicians and school systems are the primary users of this camera, according to Pfeifer.
"This system has been used extensively as a mass screening tool to screen entire geographic areas. To date this camera has been used to screen more than 2 million children in eight states," she said.
The cost per child varies based on the number of children screened and can range from $8 to $16 per child.
"The VisiScreen system continues to evolve with the manufacturer anticipating that within 2 years the system will become digital," she reported.