A total of three prototypes were built serially improving upon the features and functions of the earlier versions. Prototypes II and III were used to obtain data and will be described (
Table 1). Both these prototypes have a hemispherical dome built with a steel skeleton having 120-cm diameter. This dimension was chosen to comfortably place the infant in a supine position. A black cloth covered the dome and the metal rods were padded with foam. The dome was divided into 24 equidistant meridians at angular intervals of 15° in the azimuthal direction (
Fig. 1). LEDs placed along the meridians were displayed sequentially from periphery toward center, as done in hybrid perimetry (static-kinetic perimetry).
10,14 The viewing distance from the infant to the central fixation and to the rest of LEDs was 60 cm for prototype II. For prototype III, we accounted for the different head sizes (occipital distance) in the algorithm, and the position of each LED (x, y, z) was calculated for each participant in order to map the precise location of the stimulus. The color setting for the RGB (red, green, blue) LEDs was set to match 550 nm using hexadecimal (#a3ff00) color conversion (
https://academo.org/demos/wavelength-to-colour-relationship/). The chosen wavelengths in both the prototypes were closer to the human peak spectral sensitivity (V
λ peaks at 555 nm).
15 It is known that infants' scotopic and photopic spectral sensitivity curves are similar to adults.
16–19 The luminance of the LEDs was set to 30 cd/m
2. This value was determined by subjectively measuring the luminance of the LED that did not cause scatter when projected on the blind spot of two adult subjects (PNS, SD). Testing was done in dark room (0.1 cd/m
2) mesopic-scotopic conditions.
20 An IR camera mounted at the apex of the dome provided a live video feed of the tested infant to the examiner's computer. Similar to previous studies,
10,11 detection of the peripheral target by the infant is registered by the examiner, upon observing the video of the infant's eye/head (gaze) movement toward the target. Unlike the previous studies, the examiner knew the position of the target in this testing. However, because the testing was video recorded it allowed independent verification for detection responses at a later time by another examiner (also a trained optometrist) to avoid bias. An excellent agreement (intraclass correlation = 0.9) was obtained between the two independent examiners from analyzing 20 pilot sample videos.