Researchers in Turkey have found a relationship between photopic pupil diameters and the timing of visual evoked potential (VEP) waveforms in eyes with early glaucoma. They also observed significantly reduced pupil constriction after illumination in eyes with glaucoma.

The study tested 24 patients with early stages of glaucomatous optic neuropathy using VEP, standard automated perimetry and a pupillometer. Patients with a mean deviation less than -2dB and greater than -6dB were included. The researchers took pupil size measurements under photopic conditions at 60cd/m², 100cd/m² and 130cd/m² luminance levels.

When the study compared age-corrected values in the glaucoma group with an age-matched control group, the differences in P100 latency and amplitudes were statistically significant. As the luminance level increased, the correlation between pupil diameters and VEP parameters also increased. The difference between glaucomatous eyes and healthy eye pupil diameters was the highest in the 130cd/m² luminance level.

The researchers noted that this relationship suggests that photopic pupil diameter measurements may be useful for the evaluation of damage to retinal ganglion cells and optic nerve axons due to glaucoma and may be used in glaucoma screening.

The team concluded that further research should evaluate pupil diameter in larger populations of healthy individuals and in different categories of glaucoma patients. They pointed out that factors that do not relate to optic nerve damage, such as mechanical properties of the iris, systemic conditions or medications, may result in variable responses in pupillary light responses.