Value of Inexpensive Digital Eye and Vision Photoscreening
“PPV of ADBC”
Robert W. Arnold, MD, Michelle Clausen, BA, Holly Ryan, Rachel E. Leman,
Diane Armitage, certified Orthoptist
Some consumer digital cameras have flash-lens distance ideal for photoscreening
so we adapted them to an ongoing state-wide vision screening program.
Digital cameras with short flash-lens distance were employed by lay screeners
trained by DVD movie. Confirmatory
exam by AAPOS criteria were sought from eye doctors.
2900 children were screened in 62 clinics by 14 screeners. 99% were readable
with 6% referred. The positive predictive value was estimated as greater
than 80%. The per-screening image cost was less than $100 including cameras.
Some screeners interpreted images similar to central reading center.
Pre-literate community photoscreening can be valid and cost-effective.
The American Academy of Pediatrics (AAP)
recommends a series of age-appropriate vision screens over the entire
course of a child’s first (amblyopia) decade1 however AAP was not
yet ready in 2002 to mandate preschool, objective photoscreening. The
NIH-supported Vision in PreSchoolers Studies (VIPS)
used disparate outcome measures to suggest that photoscreening, in the
hands of pediatric optometrists, was less sensitive than patched acuity
testing or remote autorefraction. This differs from the experience of
the initial large-scale validation. Small pediatric-office based validation
studies criticized the high variability of photoscreening image interpretation,
however large-scale centralized programs can achieve more consistently
high predictive value.
The issue of MTI photoscreener cost, and lack of availability, and the
experience with EyeDx digital camera, prompted investigation into certain
emerging commercial digital cameras with short flash-to-lens dimensions
as alternatives. In addition to two other short reports, this is the Alaska
Blind Child Discovery (ABCD) experience adapting inexpensive digital flash
cameras (Amblyopia Detection by
Camera- ADBC) to community pediatric vision screening.
ABCD has adapted several types of consumer digital flash cameras to screening
primarily including the JVC DVM70u, the Gateway DV-S20, and the Nikon
CoolPix S04. ABCD has calibrated these and other pediatric vision screening
devices for AAPOS-threshold levels of hyperopic anisometropia using a
normal subject and induced anisometropia via contact lens. Photoscreening
images are interpreted by the “Delta-Center
Crescent” method. Physicians at the ABCD coordinating center
use the delta center crescent method which can be taught to lay screeners
using an educational video DVD.
Digital photoscreening had a referral rate of about 9% with PPV of 87%
whereas MTI photoscreening had a referral rate of 7% and a PPV of 85%.
The inconclusive rate for digital was 1.1% and for MTI 0.6%. The slightly
higher PPV (94%) were for community JVC DVM70u screening and for school
Gateway and MTI photoscreening using a tent. The lowest PPV (60%) came
from community non-tent, Gateway photoscreening usually because of poor
fixation or too short a distance between camera and child, which washed
out the images.
Several photoscreener manufacturers are no longer financially viable.
The ideal photoscreener would be portable, child-friendly, fast, on-site
interpreted, referral-criteria modifiable, able to work in variable light
and noise environments. Technology representing many of these features
are still available at a cost. Until then, certain consumer digital flash
cameras with a small flash-to-lens can provide valid and inexpensive community
detection of amblyopia.
Arnold RW, Clausen M, Ryan H, Leman RE, Armitage D. Predictive Value
of Inexpensive Digital Eye and Vision Photoscreening: "PPV of ABCD".
Vis Strabismus Q 2007;22:148-52.