Our success rates for screening were 94% with the MTI system and 90% with the VR system. In comparison, for those 5 years of age or less, the success rates were 96% with the MTI system and 83% with the VR system. Reported photoscreening success rates in preschool-aged children have ranged from 94–100%.28
The lower success rates in our study most likely relate to screening a more challenging patient population. This compares with our success rate of 40% for performing the traditional vision screening method of visual acuity testing with optotypes in our patient population, even with conduction of the tests in specialty pediatric ophthalmology clinics.
The operating characteristics of photoscreening in children with DS demonstrate its utility as a screening test following an initial complete ophthalmic exam. The sensitivity (the probability that a patient with the disease tested positive) and negative predictive value (the probability that a patient with a negative result did not have the disease) were very good. These results mean that few children with treatable ocular conditions were missed by photoscreening. These findings were similar to previous reports regarding photoscreening in preschool aged children without DS. Based on the high sensitivity and negative predictive value, photoscreening appears to be a suitable method to screen children with DS and normal baseline examination in terms of detecting the development of treatable ocular conditions.
These operating characteristics are dependent on the definition used for “treatable ocular conditions.” This study assumed that treatable ocular conditions are the same for children with and without DS; however, this assumption may not be the case. For instance, because of possible hypoaccommodation in children with DS, clinicians may have a lower threshold for the treatment of hyperopia. Most of the false positives were found in children with correctly identified refractive errors that failed to meet the significant criteria requiring treatment. Thus photoscreening’s sensitivity to lower amounts of hyperopia may actually be useful in the DS population.
Not surprisingly, the prevalence of ocular conditions requiring treatment was much higher in our DS patient population (60%) than that reported in preschool-aged children without DS (1% to 3%).29–31
The overall prevalence of ophthalmic disorders in previous studies on children with DS has ranged from 46% to 100%9
; however, some of these studies included conditions that do not affect vision, such as slanting palpebral fissures and epicanthal folds. The prevalence of specific ophthalmic conditions reported in previous studies is listed in . These ophthalmic conditions include diagnoses that may not be detected by photoscreening such as optic nerve abnormalities and hypoaccommodation, thus making a baseline complete ophthalmologic examination imperative in this patient population.
The economic impact of photoscreening with follow-up examinations for referred children compared to annual or biannual complete ophthalmologic examinations for all children with DS is difficult to assess. North Carolina, the state in which the study was conducted, already has a well-established preschool photoscreening program, making the start-up cost associated with photoscreening negligible. In this established program, the cost of photoscreening per child is $6.00 (Prevent Blindness North Carolina). This cost includes trained and certified personnel, administrative support, travel, film, and analysis. Photoscreening takes place in the schools en masse. The cost of a complete ophthalmologic examination is $75.00 (Medicaid Fee Schedule, http://www.cms.hhs.gov/home/medicaid.asp
). The savings per child screened in the first year after the baseline complete examination is given in e-Supplement 1
(available at jaapos.org). This saving depends not only on the cost of photoscreening and ophthalmologic examination but also on the referral rate after a normal baseline comprehensive ophthalmologic examination. The referral rate in our study was about 80%, but this rate included all comers, not just those with normal baseline complete examinations. If photoscreening was limited to “normals,” the photoscreening referral rate would likely be much lower. The cost savings with a referral rate of 80% is $9.00 per screened child.
These data can be used to calculate a referral rate breakeven point (). As the referral rate increases, the cost-effectiveness of screening decreases. The break-even point for photoscreening is a 92% referral rate. As long as referral rate is less than 92%, it is cost-effective to perform screening. As mentioned previously, the referral rate is highly likely to be less than 80% in those with a normal baseline comprehensive ophthalmologic examination.
FIG 1 Break-even point in terms of cost for photoscreening in children with DS (in a cohort of 40 patients). The cost of full examination is $75.00 and the cost of photoscreening is $6.00. The total cost is shown on the x-axis and the referral rate is shown (more ...)
Although the cost analysis appears favorable, in states without an established photoscreening program, investing in photoscreening devices specifically for children with DS requires careful consideration. Establishing the infrastructure necessary to administer a screening program also adds to screening expense. Hence, it is important for each state to independently determine the cost of instituting such a photoscreening program in the DS population.
It seems reasonable to consider time and effort in addition to cost regarding the use of photoscreening versus complete ophthalmologic examinations for children with DS. Photoscreening is portable, fast (it usually takes less than 5 minutes), and easy to administer. When performed at school, photoscreening does not require any additional travel for the patient or patient’s family. On the other hand, ophthalmologic examinations take longer (at least one hour with full cycloplegia) and require both the patient and at least one parent to travel to an ophthalmologist’s office. The time required for complete ophthalmologic examinations versus baseline ophthalmologic examinations with follow-up photoscreening is given in e-Supplement 2
(available at jaapos.org). Even with a referral rate of 80%, screening saves 15 minutes per DS patient. The break-even point for time occurs at a 90.7% referral rate (). Any referral rate of less than 90.7% saves time.
FIG 2 Break-even point in terms of time for photoscreening in children with DS (in a cohort of 40 patients). The time for a full examination is 140 minutes and cost of photoscreening is 13 minutes. The total time is shown on the x-axis and the referral rate (more ...)
In some instances, photoscreening may miss treatable ocular disease. However, even in missed cases, screening is not a one-time occurrence, so they would likely be detected as abnormal at future screenings. A complete exam at baseline with photoscreening as a follow-up for “normals” incorporates the strengths of both approaches.
In conclusion, we found that photoscreening is feasible in children with DS. The test is very sensitive but less specific in detecting treatable ocular conditions. In North Carolina, the use of photoscreening in the DS population showed savings in terms of both time and expense related to annual or biannual eye examinations in children with a normal baseline examination. The results from this study support the inclusion of children with DS in existing school-based, photoscreening programs; however, caution must be taken in applying these findings to all states. Future study should focus on the use of the photoscreening techniques to detect new-onset disease in children with DS following a normal baseline examination.