Week in Review: Number 9

Eye Doctors Save Lives
Researchers at the University of Michigan Health conducted a meta-analysis of 17 studies consisting of 48,000 people collectively to investigate the association between visual disability and risk of all-cause mortality on a global scale. They found that the risk of mortality was 29% higher for participants with mild vision impairment, compared to normal vision, and that the risk increased to 89% among those with severe vision impairment. Most of these cases, such as cataracts and unmet need for glasses, can be prevented or corrected. The study compliments the researchers' earlier work highlighting the impact of vision impairment on health and well-being. One of the investigators states, “It’s important these issues are addressed early on because losing your vision affects more than just how you see the world; it affects your experience of the world and your life. This analysis provides an important opportunity to promote not only health and well-being, but also longevity by correcting, rehabilitating, and preventing avoidable vision loss across the globe.”

Engineering Photovoltaic Retinal Prostheses
While efforts at retinal regeneration and retinal transplant are ongoing, another line of research looks into artificial vision using retinal prostheses. Engineers in Switzerland have created a prototype of one such retinal prosthesis and their preliminary tests in a virtual reality program are encouraging. The research team used two parameters to evaluate their system: image resolution and field of vision. The POLYRETINA implant contains 10,500 electrodes, each of which produces one dot of light. Patients would need to learn to interpret the signals from the array of electrodes, similar to recognizing constellations in the pattern of stars in the night sky. The researchers investigated number of electrodes and spacing to provide enough image resolution while keeping the electrodes spaced far enough apart to distinguish one dot from another. Their virtual reality program determined that 10,500 was a good amount of electrodes, and that each electrode stimulated a different part of the retina. In their system, adding more electrodes would not improve image resolution. The second parameter they investigated was field of vision. Tests of field-of-vision angles between 5 degrees and 45 degrees found that 35 degrees is the saturation point for stable object perception. This retinal prosthesis is still a long ways from clinical trials, but the project provides a look into the parameters that engineers consider in designing a system for artificial vision.

Neurological Agreement in Color Perception
This article from general science news is extra special in that the authors of the news article are also the authors of the research. The research was aimed at answering the question of color perception, both the purpose of color perception and the physiological agreement of color perception, from a neuroscience perspective. Two studies were discussed. In one study, by a different research team, participants were shown real-world stimuli illuminated by low-pressure-sodium lights (similar to the kind found in parking garages). The yellow light (perhaps any colored light) prevents the retina from properly encoding color. The participants could still recognize objects, such as fruits, but those fruits appeared unappetizing. The participants could still recognized faces, though those faces looked green and sick. The researchers think that when normal color perception expectations are violated, this sends an error signal to the brain to interpret the situation as amiss, that there is something wrong. In other words, such studies confirm that color perception encodes meaning.

But what about individual variations in perception of color? There is of course the physical basis of color in the wavelengths of visible light. But is one person's perception of red the same as another person's? In the second study, conducted by the authors, magnetoencephalography  (MEG) was used to measure participants' brain wave activity in response to different color relationships. Note that the study design does not answer the much tougher question of whether responses to specific colors are similar across people. Rather, it is a measure of responses to color relationships, such as a person's perception of the relationship between red and orange. The MEG results showed that a person's neurological response to more closely similar colors, such as light green and dark green, is more similar than the response to less closely similar colors, such as yellow and brown. Furthermore, these relationships are preserved across people. As the authors conclude, “Physiological measurements are unlikely to ever resolve metaphysical questions such as 'what is redness?' But the MEG results nonetheless provide some reassurance that color is a fact we can agree on.”

Gold-Infused Contact Lenses for Color Vision Correction
Researchers at the American Chemical Society have created a prototype of a contact lens using gold nanoparticles to correct red-green color vision deficiencies. Previously, colorblindness-correcting contact lenses using dyes as filters (to shift the color confusion curve and thereby enhance contrast between colors) had the problem of leaching the dyes. The advantage of using gold to produce the color filter is that gold is inert. For a quotidian example, one can recall the culinary use of gold leaf in more elegant dishes to add artistic flare, though the gold is not metabolized by the body in any way. The use of gold nanoparticles to produce a color-filtering rosy tint is also not surprising given the artistic use of gold particles to impart a red color to stained or blown glass. The rosy tint of the gold-infused contact lenses were matched with the wavelength profile of existing dyed contact lenses for correction of red-green color vision deficiency. The researchers found that 40 nm-wide gold nanoparticles were the most effective, as the particles did not clump or filter more color than necessary. Because gold is inert to the body, there is a lot of potential with this line of research, so it will be interesting to see its performance in real eyes.

Retinal Ischemic Lesions and Risk of Heart Disease
Researchers from the Shiley Eye Institute at UC San Diego recently published a small study to investigate the correlation between retinal ischemic perivascular lesions (RIPLs) and risk of cardiovascular disease. The microvasculature of the retina is a window to the health of larger vessels and organs in the body, so the research team sought to determine if it could serve as a biomarker of cardiovascular disease. They compared a cohort of 84 individuals with heart disease with 76 healthy individuals through chart review of ocular coherence tomography (OCT) findings between July 2014 and July 2019. An increased number of RIPLs was observed in the eyes of individuals with heart disease, which the researchers correlate with increased risk of heart disease. The study references the atherosclerotic cardiovascular disease (ASCVD) risk score calculator, the national guideline developed by the American College of Cardiology, as the guideline for assessing risk of cardiovascular events such as heart attack and stroke. The researchers found a positive correlation between the number of RIPLs in a patient’s eye and their ASCVD risk score. This study offers an interesting approach to the connection between retinal microvasculature and cardiovascular health. The population size is small and the study design and inferences are indirect. Nonetheless, it is a reminder of the eye's unique window to help reduce risk of disease in the rest of the body.

In Other News
(1) NEI launches data portal for macular degeneration research
(2) Vision impairment expected to rise in future decades
(3) The history of eye charts