The sensitivity of the human eye extends over a range of 10–11 log10 units. Cones and rods adapt to different levels of background light through neural mechanisms and through the bleaching and regeneration of visual pigments. Clinical dark adaptometry primarily measures the absolute thresholds of cone and rod sensitivity.
Dark adaptation can be measured and quantified with the Goldmann-Weekers (G-W) adaptometer; however, it is neither widely available or used. Although newer instruments have been introduced, they have yet to gain widespread acceptance, and the majority of the research literature is devoted to the G-W.
Dark adaptometry is useful in assessing patients with night blindness. Although it is a subjective test, dark adaptometry can complement the ERG; as a focal test (relevant when interpreting results from patients with local rather than generalized retinal dysfunction), it can be a more sensitive indicator of pathology than the ERG, especially early in the disease process. Dark adaptometry can also demonstrate the degree of cone adaptation in the evaluation of cone dysfunction syndromes.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.