Matta, Noelle S. CO, CRC, COT; Silbert, David I. MD, FAAP
Pediatric vision screening is intended to identify children with vision disorders including amblyopia, strabismus, significant refractive error, or other eye abnormalities. Vision screening can be carried out in community settings such as health fairs, preschools, grade schools, or can be carried out in medical homes. There are a variety of pediatric vision screening methods for programs to choose between, depending on the age of the children they plan to screen, the environment they are screening in, and the amount of money they have to invest. One of the keys to a successful pediatric vision screening program is ensuring that children who are identified as having potential amblyopia risk factors receive a complete pediatric ophthalmology examination, including a dilated fundus examination, a cycloplegic refraction, and fundus examination by an ophthalmologist comfortable with children.
Why We Need Pediatric Vision Screening
Pediatric vision screenings are essential to detect poor vision, refractive anomalies, and medically threatening eye disorders, most of which are treatable. Amblyopia, defined as reduced and uncorrected vision in a structurally normal eye, can be caused by significant refractive error, misalignment of the eyes, or deprivation such as visually significant ptosis (droopy eyelid) or a cataract.1 It is well documented that children who receive pediatric vision screening have a decreased prevalence of amblyopia and ocular disorders when compared with an unscreened population.2,3 Amblyopia is reversible with treatment during childhood, and it is generally believed that the earlier amblyopia risk factors are identified and amblyopia treatment is initiated, the more likely the child will develop normal vision.4 Left untreated amblyopia can lead to a permanent reduction in vision in one or both eyes and is the leading cause of vision loss in adults under the age of 40 years.5
Pediatric vision screening is extremely cost effective. The cost of pediatric vision screening is approximately $10 to $21 per child. The cost/Qualy ratio for amblyopia screening is estimated at $6000. This is significantly less than the same metric for annual screening for diabetics for retinopathy, which is estimated at $231,000, and considered a mandatory practice by many health care insurers and organizations. It is estimated that a single comprehensive eye examination on all 4-year-old patients would cost approximately $485 million.6 If children undergo 5 eye examinations from birth to the age of 10 years, as suggested by the American Optometric Association Guidelines, the cost would far exceed $1 billion.7
Subjective Pediatric Vision Screening
Subjective pediatric vision screening utilizing recognition acuity is the most widely used method. This method is inexpensive to perform, but can be difficult to execute properly. Over-referral or under-referral can have real economic costs. Subjective screening requires significant participation from a child. Subjective pediatric vision screening includes recognition acuity and stereoacuity. The testing distance can vary from 3 to 20 feet and it is critical that the child be tested at an appropriate distance from the chart. It is also important that an appropriate eye chart be selected. Appropriate optotypes for children include: Sloan (Fig. 1), HOTV (Fig. 2), Lea symbols (Fig. 3), and Patti Pics. The optotypes should be presented in a line or singly with crowding bars, as isolated optotypes may overestimate vision.8 The child should be seated comfortably in a chair or on their parents lap and encouraged not to lean forward. The testing distance needs to be measured from the child’s face to the eye chart, and if sitting on a parents lap this may alter the testing distance. A hand should never be used to cover the eye. It is best to use a stick on eye patch, which can be purchased or can be fashioned out of fabric tape and a tissue. It is important that the examiner pay close attention so that the child is not peaking from the side of the patch or holding their head sideways. Another alternative is pediatric occlusion glasses (Fig. 4), which have black plastic over the occluded eye and large foam animal shapes around the edges, making peaking nearly impossible. Children aged 3 to 5 years old should be considered if they do not correctly identify 4 of 6 optotypes on the 20/40 line with either eye or have a 2-line difference between the eyes (example 20/20 with the right eye and 20/30 with the left eye). Children aged 6+ years old should be considered if they do not correctly identify 4 of 6 optotypes on the 20/30 line with either eye or have a 2-line difference between the eyes.9
Computerized visual acuity testers are also available including: Vision Quest 20/20, Innova, and M&S. These devices automate the testing protocol and are performed utilizing a computer monitor. Vision Quest is fully automated and uses crowded HOTV letters in a matching game disguised as a video game.
Stereoacuity is often combined with recognition acuity to assess binocularity, although there is no good validation that it is an effective screening tool. An abnormal response might suggest strabismus, which would require a referral to a pediatric ophthalmologist. These forms of subjective pediatric vision screening tend to be most effective in verbal children aged 5 years and older, but may be attempted in younger verbal children.
Objective Pediatric Vision Screening
Objective screening requires less input from children and is faster. With objective screening, the child merely needs to focus on a device long enough to obtain a measurement. One of the most basic forms of objective pediatric vision screening is using the red reflex test to examine young children. The red reflex test looks at the light reflex through an ophthalmoscope. The examiner compares the brightness of the reflexes and determines whether they are normal and equal, otherwise the child is referred to a pediatric ophthalmologist.10 An abnormal finding could suggest a number of sight-threatening issues including media opacity, strabismus, or significant refractive error.
Another form of objective vision screening is autorefractive screening. There are a number of autorefractors, which can be used to evaluate for amblyopia risk factors. Most of these tests are conducted monocularly and therefore do not screen for strabismus. These devices are used on undilated eyes and will give the user an estimation of the child’s refractive error. On the basis of the predetermined referral criteria, the device or examiner can quickly determine whether the child passed the screening or should be referred for further evaluation by a pediatric ophthalmology for a cycloplegic refraction and comprehensive examination. The advantage to autorefractive screening is that it can be carried out not only on verbal children but also on preverbal and nonverbal children as well. It is also much faster than acuity screening.
Currently available autorefractors used for pediatric vision screening include: Grand Seiko binocular autorefractor,11 Retinomax, and the SureSight. Although the SureSight is specifically marketed as a vision-screening device, both the Retinomax and SureSight autorefractors were validated in the Vision in Preschoolers Study.12
Photoscreening is another form of objective vision screening for children. It uses a camera to take binocular images of a child’s undilated eyes by looking at the configuration of the crescents of light returning after a flash (red reflex). The devices can estimate refractive error; look for other amblyopia risk factors such as visually significant ptosis, strabismus, and media opacity; and determine which children are at risk for amblyopia. These images can be analyzed by a human interpreter at a reading center, or by software incorporated into the equipment to evaluate the alignment of the eye and estimate refractive error. If significant refractive error or a misalignment seems to be present, it can indicate amblyopia risk factors. If amblyopia risk factors are felt to be present, a referral should be made for the child to be seen by a pediatric ophthalmologist for a cycloplegic examination. Photoscreening has advantages to more traditional eye chart acuity screening, and is particularly useful on younger (age 3 to 5 years), preverbal children (under age 3 years), and nonverbal children.13 Photoscreening usually takes less than a minute to obtain the necessary images of a child. The only cooperation required is for the child to briefly look at the camera.
Currently available photoscreeners include: iScreen (Fig. 5), MTI (Fig. 6), plusoptiX (Fig. 7), Spot (Fig. 8), and Visiscreen. The MTI photoscreener, iScreen, and Visiscreen use a visible light flash, whereas plusoptiX and Spot utilize infrared light, which is not visible to the child. iScreen, plusoptiX, and Spot have been validated in many recent studies.
The iScreen photoscreener was first introduced in 2006. The first generation of the device was an off-axis binocular photoscreener taking 1 image, which is electronically transmitted for remote interpretation. The first generation iScreen was a tabletop device in which the child rests their head against a chin rest. The iScreen 3000, introduced in 2011, has been significantly redesigned and miniaturized.14 It is now a hand-held device, which takes 2 photographs in rapid succession in 2 axes with a separation of 90 degrees. Aiming beams placed on the child’s forehead focus the camera. A blinking fixation light, and sound attract the child’s attention. The images are then taken in such rapid succession that the child perceives just 1 flash before a blink. This is an improvement over the analog MTI photoscreener that required lens rotation before taking the second photograph, and prevents differential accommodative effort between photographs. The photograph can be reviewed immediately on the device and if the child is not fixating properly can be retaken. The final image is sent electronically to the company for interpretation, which provides the advantage of a consistent, expert interpretation of the images. A report is e-mailed securely that shows the results of the test and reason for the referral and also includes a picture of the child’s eyes.
The MTI photoscreener was first introduced in 1995.15 The camera uses special high-resolution black and white polaroid style instant film with an off-axis flash that rotates 90 degrees between images. Focus and fixation are similar to the iScreen with aiming beams and a flashing fixation target and noise to attract the child’s attention. Two consecutive photographs are taken of each patient resulting in a photograph showing the first image on the top and the second image on the bottom printed on a special high-resolution instant film.16 On the basis of the shape, size, and location of the crescents, a determination can be made as to whether the child has significant refractive error or strabismus. The MTI is no longer being manufactured but is still in use.
The plusoptiX photoscreener uses an infrared video recorder to obtain images on 3 axes. The device produces a noncycloplegic autorefractive reading, which is then compared with preset referral criteria. If the refractive values exceed the referral criteria, the device will trigger a referral. The referral criteria are user modifiable. The device also creates a scatter plot of the location of the pupillary light reflex and a photographic image of the eyes. A printout is created with the referral advice. The plusoptiX will also trigger a referral if 1 eye deviates by >10 degrees (suggesting strabismus) or if 2 round pupils cannot be seen (such as in a child with an iris coloboma, visually significant ptosis, or if the child will not look at the camera). An advantage to the plusoptiX is the use of infrared light, which is not perceived by the child as a flash. This allows the device to take a number of photographs in multiple axis rather than just 2. It does, however, take longer to acquire the image than the iScreen, which can be an issue with an uncooperative child. The classic plusoptiX is a desktop self-contained Linux-based computer with a hand piece resembling a small radar gun attached. A monitor is provided to view the child during image acquisition. The child fixates on the Smiling “Lucy Face” while noises are playing to attract the child’s attention. The spinning infrared beams are also slightly visible that may further attract the child’s attention. The device gives audible and visual cues to the tester to focus the device and will not acquire the images until optimal focus is obtained. The device is based originally on the Power Refactor. There have been 4 different variations of the plusoptiX marketed, the S04, S08 (screening models), the S09 and A09 (autorefractor model), and the S12 and A12 handheld model. This newest model has not been as well studied as the desktop units. All desktop models function similarly with similar results.17 The plusoptiX is marketed by plusoptiX, but was previously comarketed by Pediavision.
The Spot is a new hand-held infrared digital photoscreener developed and marketed by Pediavision.18 It functions similarly to the plusoptiX but has been significantly miniaturized. Rather than having the infrared elements on the face of the unit flanking the camera aperture, the Spot places the infrared elements below and in front of the camera aperture. The infrared light is then reflected off of a 45% 2-way mirror. The design allows for eye tracking. The device creates a diagram with the location of the eyes, demonstrating any strabismus present and an autorefractive reading. Spot creates a report that can be printed, recommending referral, based on preset criteria.
The Visiscreen is a 35-mm camera with a databack recorder attached to a 500-mm telephoto lens.19 There is an electronic strobe light located below the lens and a flashing light-emitting diode located above the lens. The camera is mounted on bars ensuring it is exactly 8 feet and 3 inches away from a headrest the patients place their chin on.
Another type of objective vision screening is to utilize visually evoked potential/response. There is currently 1 device available from Diopsys, which estimates visual acuity, or the difference in visual acuity between 2 eyes utilizing a sweep visually evoked potential. The machine analyzes the results and gives the user a pass/refer result. Few validation studies, however, have been conducted.20
Barriers to Comprehensive Eye Examinations
There are a number of barriers to comprehensive eye examinations.21–23 Parental understanding, insurance issues involving routine versus medical examinations, transportation, and scarcity of pediatric ophthalmologists for confirmatory examinations. Parents and health care providers often do not realize the importance of vision screening. There is a prevalent attitude that if a child can function adequately, they must be seeing well; however, children can function adequately in early grades of school with very poor vision or with good vision in 1 eye alone. After testing failure, the primary care provider, the school, or the testing site must determine whether and where to refer a child or whether to rescreen. Often a referral is made but not followed through with. A referral to an eye-care provider with little experience with amblyopia or young children may lead to a missed diagnosis of amblyopia. It is critical that children who fail a vision screening have a cycloplegic refraction24 to determine their refractive state, as noncycloplegic refractions in children can lead to significant errors in refraction.25
Vision Screening Program Models
There are many types of screening program models. Vision screening can be carried out by the pediatrician, by the school nurse, by organizations coming into preschools, or at community events such as health fairs. All children who are referred from a screening should either have a repeat screening or be referred for a comprehensive examination including cycloplegic refraction. Completed examinations can be tracked to improve the sensitivity and specificity of the screening program, and to encourage parents who have not had a follow-up examination yet to do so.
The American Association for Pediatric Ophthalmology and Strabismus have devised standards for comparing pediatric vision screening methods.26 These guidelines are set against a child’s cycloplegic pediatric ophthalmology examination to determine whether the child’s vision screening should have prompted a referral to a pediatric ophthalmologist or whether they should have passed the screening. These guidelines suggest that all children should be referred who have manifest strabismus of >8 prism diopters in primary position and a media opacity of >1 mm. They also suggest that all children should be referred based on their cycloplegic refractive error in diopters and age on the following guidelines (Table 1).
Pediatric vision screening is safe and effective when carried out properly and when parents follow through on referred screenings with a pediatric ophthalmologist. Programs should consider having objective instrument-based pediatric vision screening options for young children and children with behavioral issues or developmental delays as well as for children who fail subjective vision screening. Programs may consider subjective recognition acuity vision screening for older children as it may do a better job at detecting mild-moderate but symptomatic myopia and astigmatism that becomes more symptomatic in older children. Objective instrument-based screening though can also be utilized in older children.
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