Device-Based Vision Screening for Children – Photoscreening
What is Photoscreening?
This text is one component of a paper by Dr. Sean Donahue, titled "Device-Based Vision Screening Comparison".
Photo refraction screening utilizes a flash of light and the observation of the reflection of that light from the blur circle of the fundus to detect ocular misalignment and refractive blur. Of the commercially available photoscreening instruments available, the most prominent are the MTI Photoscreener and the iScreen Photoscreener. These photoscreening systems require interpretation of the flash reflections and difficulties with interpretation currently limit the acceptance of photoscreening technology for widespread screening. The MTI Photoscreener is perhaps the most well evaluated automated visual screening instrument. It is an off-axis photoscreener that utilizes two photographs taken with an eccentric flash unit that rotates 90° for each pair of images. These two images are captured on Polaroid film for interpretation by trained personnel. The instrument is easy to use, portable, and although it has a dated analog output, the Polaroid film is available for immediate interpretation. Other limitation of this instrument include high costs ranging from $6-7 per child, lack of support for current instruments (old cameras need to be retrofitted to handle currently available film), and the lack of a company providing support or new investment (the company is no longer in business). Despite these limitations, there have been several large validation studies.
Field studies generally report positive predictive value (since normal children are not referred) while clinic-based studies report sensitivity and specificity (since predictive value depends upon disease prevalence). One large field-based vision screening program using the MTI Photoscreener began in Tennessee. Referred children were evaluated by local optometrists and ophthalmologists and the results are collected centrally. Over 200,000 children were screened using the MTI Photoscreener with a referral rate of 4%, a screenability rate of 96% and a positive predictive value of over 75%. This program has been expanded by the Lions’ Club International Foundation to include multiple other states and foreign countries. The results from the 17 programs that have screened over 400,000 preschool children show similar overall results with a referral rate averaging 5%, a screenability rate of 97% and a positive predictive value averaging 80%.
The VIP (Vision in Preschool) studies evaluated photoscreening with the MTI Photoscreener as one methodology in a prospective trial of over 1000 children with an enriched proportion of ocular pathology. In that study, photoscreening had a lower sensitivity than the Welch Allyn SureSight and the Nikon Retinomax when specificity was fixed retrospectively at 94% reporting an overall sensitivity of 37% and a 63% sensitivity for amblyopia. However, the relatively high sensitivity for these other instruments was likely a result of a retrospective reanalysis of the data using a set of referral criteria for the autorefractors (but not for the photoscreeners) that was determined by re-evaluating the study results. Other issues with respect to the methodology of the VIP study which biased against photoscreening technology have been discussed extensively in the literature. Plus Optix has recently introduced a photoscreening instrument (The Power Refractor II) that allows detection of ocular misalignment in addition to an automated calculation of refractive error. It is a handheld video/photorefractor that binocularly measures refractive error in 8 meridia and measures eye alignment. Although field evaluation of this instrument has only recently begun, there are many advantages to the Power Refractor including the ability to alter the referral criteria.
An earlier version of the Power Refractor was tested in the VIP studies. The purpose of the VIP study was to compare 11 preschool vision screening tests administered by licensed eye care professionals. Sensitivity for detecting children with one or more targeted conditions (amblyopia, strabismus, significant refractive error, and unexplained visual acuity) at selected levels of specificity was the primary outcome measure. The Power Refractor had a higher sensitivity than other photoscreening devices but was statistically significantly lower than the Retinomax autorefractor. The study reported a screenability rate of 98.5%, a positive predictive value ranging from 50-60%, and a sensitivity of 54% when specificity was set to 90%.
iScreen is a company which uses digital photography and a high quality photograph with off axis photo screening to detect amblyogenic factors. Their marketing plan typically places the screening device in the primary care doctor’s office with remote image transfer to a centralized location for interpretation. Referral criteria are proprietary and have not been published. Kennedy and Thomas demonstrated high sensitivity and specificity of the iScreen visual screening instrument when tested in the pediatric ophthalmologists’ office. Results reported a sensitivity of 92.4% at a specificity of 89.1% when a total of 449 consecutive patients (median age 7 years) from a private pediatric ophthalmology practice underwent screening with the iScreen photoscreener.i In the VIP study, the iScreen device had nearly identical sensitivity as MTI Photoscreening with a screenability rate of 99.9%. When failure criteria was set to obtain 94% specificity, the iScreen sensitivity for all of the targeted conditions was statistically significantly below the values of noncycloplegic retinoscopy, the Retinomax Autorefractor, the SureSight, and LEA Symbols Visual Acuity test.
An important advance in the interpretation of automated vision screening devices into primary care offices is a new CPT code for vision screening, 99174, which became effective January 1, 2008. Its RVU value (0.68) recognizes photoscreening as a useful adjunct in the primary care office. A statement encouraging the use of photoscreening for preschool vision screening has also been published by the American Academy of Pediatrics and is currently being updated.
Next Section, "Automated Refraction."