Abstract
Purpose: :
To measure the effect of near-total occlusion on the dark-adapted pupil diameter (DAPD).
Methods: :
25 subjects were dark-adapted at 2, 7, 50, 100 and 300 lux sequentially. The right DAPD was measured with the NeurOptics pupillometer with the left eye fixating at 20 feet. The left eye was occluded except for a 3 mm pinhole aperture and the right DAPD was measured again. The difference in DAPD (occluded minus unoccluded) was calculated at each light level. Differences were compared using the student's 2-tailed t test
Results: :
The mean difference (95% CI) in DAPD was +0.064 mm (-0.01, +0.14) at 2 lux (p = 0.10); +0.20 mm (+0.11, +0.28) at 7 lux (p = 0.0001); +0.31 mm (+0.20, +0.41) at 50 lux (p = 0.0000); +0.65 mm (+0.49, +0.81) at 100 lux (p = 0.0000); +0.83 mm (+0.61, +1.06) at 300 lux (p = 0.0000). The mean difference was a linear function of room illumination up to 100 lux. At 2 lux, the maximum difference was +0.5 mm in 1 subject; at 7 lux it was +0.5 mm and +0.6 mm in 1 subject each.
Conclusions: :
At low ambient illumination, reducing retinal illuminance through occlusion rarely causes the DAPD to increase to a clinically significant degree. At higher room illumination a clinically significant increase may be induced. Clinicians should carefully define a standardized level of low room illumination for DAPD measurement.
Keywords: pupil • pupillary reflex • optical properties