Preschool Vision Screening
There are two main types of vision screening devices available: photoscreeners and autorefractors. Photoscreeners assess both eyes simultaneously. They obtain an optical image of the eye's red reflex which is then interpreted by a trained operator or a computer to evaluate for refractive error, media opacities, ocular alignment, and other structural abnormalities. Autorefractors are used to evaluate the refractive error of each eye individually. Some of the more commonly used devices are discussed below.
The MTI photoscreener is probably the most evaluated of all screening instruments. It has been utilized in the largest screening programs and studies including the Iowa KidSight program, the Lions Clubs International Foundation Core Four Photoscreening program, and the Vision in Preschoolers Study. The MTI photoscreener is a handheld device that utilizes off-axis technology to obtain two polaroid photographs of the eyes which are then manually interpreted. Although the device is portable, easy to use, and has shown a reasonable positive predictive value for detecting amblyopia risk factors between the Polaroid film and the personnel required to interpret the photographs, it is a very expensive screening device (can cost approximately US$4.00 to US$9.00 per child screened). Also, there is significant time lag between screening and availability of results when there is an outsourced photographic interpretation center. For these reasons, the devices popularity has waned. Many units are still in use, but the company that manufactures the device is no longer in business.
The iScreen photoscreener relies on similar technology as the MTI photoscreener, but the images are electronically transferred to a centralized reading center for automated interpretation. Therefore, it does not require instant film. The latest model (iScreen Vision Screener 3000) was introduced in 2011. It is a handheld device and has similar sensitivity and specificity as the MTI Photoscreener.
The PlusoptiX Photoscreener (Plusoptix, Nuremberg, Germany) is the updated version of the PowerRefractor II, which is no longer in production. The PlusoptiX Photoscreener is a handheld infrared video recorder linked to a laptop computer. It measures refractive error, pupil size, pupil distance, and gaze deviation. The results are automatically analyzed by the software and an instant pass or fail determination is made. It does not require human interpretation. The machine was developed in Germany and the referral criteria set by the manufacturer have a high sensitivity, but low specificity resulting in high rates of unnecessary referrals. Also, the machine is not as accurate at detecting hyperopia. Therefore, modifications have been suggested to improve the specificity of the referral criteria with promising results.
The Welch Allyn SureSight is a handheld autorefractor that is used to estimate the refractive error under noncycloplegic conditions. Because it does not require film or photographic interpretation, it is less expensive and easier to use than photoscreeners. The Vision in Preschoolers Study Group found the SureSight to be among the most accurate tests studied. Multiple sets of referral criteria have been proposed to attempt to maximize the sensitivity of the instrument while limiting the overreferral. Some disadvantages of the instrument are that it tends to overestimate myopia and astigmatism, and it does not screen for nonrefractive amblyogenic risk factors.
The Retinomax is another handheld autorefractor that measures the refractive error monocularly. It was also found to have high accuracy in detecting refractive amblyopia risk factors in the Vision in Preschoolers Study.
Vision Screening Devices
There are two main types of vision screening devices available: photoscreeners and autorefractors. Photoscreeners assess both eyes simultaneously. They obtain an optical image of the eye's red reflex which is then interpreted by a trained operator or a computer to evaluate for refractive error, media opacities, ocular alignment, and other structural abnormalities. Autorefractors are used to evaluate the refractive error of each eye individually. Some of the more commonly used devices are discussed below.
MTI Photoscreener
The MTI photoscreener is probably the most evaluated of all screening instruments. It has been utilized in the largest screening programs and studies including the Iowa KidSight program, the Lions Clubs International Foundation Core Four Photoscreening program, and the Vision in Preschoolers Study. The MTI photoscreener is a handheld device that utilizes off-axis technology to obtain two polaroid photographs of the eyes which are then manually interpreted. Although the device is portable, easy to use, and has shown a reasonable positive predictive value for detecting amblyopia risk factors between the Polaroid film and the personnel required to interpret the photographs, it is a very expensive screening device (can cost approximately US$4.00 to US$9.00 per child screened). Also, there is significant time lag between screening and availability of results when there is an outsourced photographic interpretation center. For these reasons, the devices popularity has waned. Many units are still in use, but the company that manufactures the device is no longer in business.
iScreen
The iScreen photoscreener relies on similar technology as the MTI photoscreener, but the images are electronically transferred to a centralized reading center for automated interpretation. Therefore, it does not require instant film. The latest model (iScreen Vision Screener 3000) was introduced in 2011. It is a handheld device and has similar sensitivity and specificity as the MTI Photoscreener.
PlusoptiX
The PlusoptiX Photoscreener (Plusoptix, Nuremberg, Germany) is the updated version of the PowerRefractor II, which is no longer in production. The PlusoptiX Photoscreener is a handheld infrared video recorder linked to a laptop computer. It measures refractive error, pupil size, pupil distance, and gaze deviation. The results are automatically analyzed by the software and an instant pass or fail determination is made. It does not require human interpretation. The machine was developed in Germany and the referral criteria set by the manufacturer have a high sensitivity, but low specificity resulting in high rates of unnecessary referrals. Also, the machine is not as accurate at detecting hyperopia. Therefore, modifications have been suggested to improve the specificity of the referral criteria with promising results.
SureSight
The Welch Allyn SureSight is a handheld autorefractor that is used to estimate the refractive error under noncycloplegic conditions. Because it does not require film or photographic interpretation, it is less expensive and easier to use than photoscreeners. The Vision in Preschoolers Study Group found the SureSight to be among the most accurate tests studied. Multiple sets of referral criteria have been proposed to attempt to maximize the sensitivity of the instrument while limiting the overreferral. Some disadvantages of the instrument are that it tends to overestimate myopia and astigmatism, and it does not screen for nonrefractive amblyogenic risk factors.
Retinomax
The Retinomax is another handheld autorefractor that measures the refractive error monocularly. It was also found to have high accuracy in detecting refractive amblyopia risk factors in the Vision in Preschoolers Study.
Source...