Impaired dark adaptation in polycythemia. Improvement after treatment.

Purpose: To determine if dark adaptation is reduced in individuals with polycythemia and if so whether there is any improvement in dark adaptation after treatment.

Methods: Dark adaptation was recorded monocularly by automatic dark adaptometry in ten consecutive patients with polycythemia before and after treatment. Analogue investigations were performed in 31 healthy control subjects.

Results: Dark adaptation was markedly impaired in the patients as compared with the control subjects. After reduction of the red cell count and normalization of the hematocrit and hemoglobin the dark adaptation was markedly improved. There was no significant change in dark vision in the control subjects negating a confounding learning effect.

Conclusion: The findings indicate a sustained but reversible neuronal hypofunction secondary to polycythemia. As the rheological abnormality was normalized, dark adaptation was improved, probably secondary to normalized microcirculation within the retina or the brain, or both, possibly with reactivation of formerly inactive neuronal cells.