Ophthalmologist and Physician-Scientist
Night Vision in Humans

Night Vision in Humans

Recently, researchers from the United States and China announced they had endowed mice with the ability to see in the dark. According to the study, published in the February 2019 issue of the journal Cell, researchers injected nanoparticles into the eyes of a group of mice, which enabled them to see infrared light, a wavelength invisible to the naked eye. Here is a brief overview of how the scientists gave mice night vision and what it could mean for humans in the future.

The connection between light and vision.

In healthy eyes, vision occurs when light reflected off of an object in the field of vision enters the eye through the cornea, passes through the crystalline lens, and comes into sharp focus on the retina. The light is then converted by the retina into electrical signals, which are sent to the brain via the optic nerve. The brain processes these signals to create an image.

The reflected light enabling vision is actually a measure of electromagnetic radiation on the “visible spectrum” of light. The visible spectrum of light includes radiation from photons with wavelengths of between roughly 400 to 700 nanometers. Visible light photons have shorter wavelengths with a higher frequency (the measure of distance between a wavelength’s peaks), while longer wavelengths have a lower frequency. Infrared light (IR) wavelengths measure 700 nanometers to 1 millimeter, which falls outside the range of human vision.

How scientists gave mice night vision and the results of the study.

The experiment was undertaken by equipping the retinas of the mice with the tools necessary to detect IR. The study was conducted jointly by Gang Han, a biochemist at University of Massachusetts Medical School, and Tian Xue, a life science professor at University of Science and Technology of China.

The researchers developed unique, injectable photoreceptor-binding upconversion nanoparticles (UCNPs), which were coated with a protein that binds naturally to certain sugar molecules within the membranes of photoreceptors in the retina. Once the injectables were administered directly behind the retina of the test subjects, the UCNPs attached to the retina’s photoreceptor cells and acted as transducers for infrared light. Essentially, the nanoparticles acted like antennae for the longer waves of infrared light. Once the light was absorbed, the particles converted the long IR waves into shorter wavelengths.

As a result, the mice were able to detect IR in day and night conditions, and their night vision did not interfere with their ability to see light in the standard visible spectrum. Scientists identified that the mice could see using a number of tests, which included shining infrared light into their eyes, which resulted in the contraction of their pupils. Another test involved guiding the mice to a platform in a swimming test using an infrared light to signal where a submerged platform was located within a water maze. Mice injected with the UCNPs swam quickly and consistently toward a triangle projected on the wall of the maze using infrared light, which was associated with the safety of the platform.

The effects of the UCNPs lingered for approximately 10 weeks before diminishing. Overall, the researchers did not notice lasting side effects following the experiment, although it was noted some mice temporarily experienced cloudy corneas, which dissipated within two weeks after the injection. Cloudiness occurred at similar rates among the experimental and control groups.

Potential future uses for the research.

Scientists are excited about the potential implications of the experiment and are exploring the potential future uses of the new technology. The scientists involved in the study have considered next administering the test on dogs as subjects, which they believe could one day lead to the development of police K9 units to more easily identify and capture fleeing criminals in the dark. In humans, the technique could allow first responders and members of the military to see more effectively in the dark through the use of the UCNPs coupled with an infrared light, eliminating the need for devices such as night vision googles. The UNCPs advantage over the current night vision goggles is it does not require a power source and can be used either in the dark or daylight. In an academic setting, the discovery may enable researchers to develop a better understanding of visual perception in humans. In addition, it could lead to new treatments for ocular diseases such as macular degeneration. Lastly, the same technology that can alter the eye to take in light otherwise not visible may lay the groundwork for developing new treatments for people with red color blindness.