Focusing on Color

A new study published in Science Advances by Drs. Benjamin Chin, Martin Banks, Derek Nankivil, Austin Roorda, and Emily Cooper investigates an open question: what wavelength is brought into best focus by the human eye?

Abstract

Humans can see in exquisite detail despite the fact that the eyes’ optics can only focus light at a single wavelength at a time. It remains an open question what wavelength is brought into best focus by the human eye. Here, we investigate this question. We used a custom optical apparatus to measure the eye’s focusing response (accommodation) to a range of stimuli with different wavelength compositions. We then developed a biologically informed model of the measured responses. Conventional wisdom holds that accommodation works to maximize visual acuity, but our findings suggest otherwise. Rather, our results support alternative lines of evidence that accommodation is guided by chromatic mechanisms that maximize signal quality in a color-opponent channel. Our results challenge prevailing views of oculomotor control and can inform therapeutic interventions for slowing the development and progression of myopia.

Images

Just like a prism, the lens of the human eye (light blue oval) refracts different wavelengths of light by different amounts; a phenomenon known as chromatic aberration. Thus, only one wavelength of light can be in focus at a time. Differences in blur across wavelengths due to chromatic aberration create distinct patterns of color fringes in images formed on the retina of the eye. In daily life, the wavelength in focus varies constantly due to the eye constantly changing its focal power: a process known as ocular accommodation.