This study compared the effectiveness of a newly developed semiautomated static perimeter, the preferential looking perimeter (PLP), to that of confrontation visual field testing in young and/or developmentally delayed children with and without visual field deficit. The results indicate that the preferential looking perimeter (PLP) is a useful new technique for assessing significant visual field loss in young or developmentally delayed children, with many advantages over confrontation testing.
Subjects were 74 children between 3 and 10 years of age, including 32 controls and 42 children with neurological and ocular disorders that could cause significant visual field deficit.
The PLP uses observation of the child's natural eye movement response to an appearing target to determine the peripheral visual field. It consists of a flat plasma screen with a modified webcam mounted just below the central point of the screen. This screen size allows 80 degrees of peripheral visual field in the horizontal meridian and 60 degrees on the vertical meridian to be tested when viewed from a distance of 0.5 m. A computer drives the plasma screen and an independent monitor on which the live image from the webcam superimposed with the position of the peripheral targets is seen by the clinician. A video of the device can be seen at www.cam.ac.uk/research/news/researchers-develop-new-test-for-children-with-vision-loss.
Using confrontation testing as the gold standard, the PLP was 100 percent sensitive and 100 percent specific, with excellent interobserver agreement. An interpretable result was achieved in 15 (71 percent) of the 21 children in whom confrontation testing was unhelpful, with PLP interpretable in 31 percent more patients than confrontation.
The authors note that the PLP has been designed to appeal to children. The child can sit on the parent's lap without restraint and he/she can choose a cartoon of interest rather than a plain target. Other advantages included automatic saving of a video that can be reviewed after testing, and the generating of a printout for the clinical notes, making it possible to compare serial tests.
A disadvantage of the design is that although large areas of dense visual field loss will be detected, milder losses of sensitivity or scotomata will be missed.
Many of the children who participated in the study have subsequently had repeat PLP testing as part of their ongoing clinical care, with the results of initial testing confirmed. The authors say that most will never be able to undergo confirmatory automated static perimetry because of their cognitive impairment.
The authors conclude that the PLP should be considered as an alternative to automated static perimetry for the screening and detection of significant visual field loss in young and developmentally delayed children.