"The most beautiful things in this world cannot be seen nor touched, but are felt in the heart," wrote Helen Keller who, in spite of losing her vision and hearing to what may have been meningitis or scarlet fever, was an author, political activist and lecturer.
Though few will contest her claim, new research from the School of Medicine has shed light - literally - on what ailed Keller, along with approximately 1.3 million Americans who meet the criteria for being legally blind, and an additional 21.2 million over the age of 18 who have experienced significant vision loss.
One of the most common causes of vision loss is cataracts, when the lens in the eye becomes cloudy and does not allow light to pass through as readily as in a healthy eye. Other common causes include uncorrected problems with vision, including astigmatism or far-sightedness, glaucoma, in which the optic nerve is damaged due to high levels of pressure within the eye, and macular degeneration, in which the central field of vision is lost.
Researchers at the School of Medicine worked with the Cole Eye institute at the Cleveland Clinic Foundation to investigate a curious phenomenon - reversible blindness. Some cases of below-optimal vision and blindness are caused by improper development in the blood vessels that supply oxygen and nutrients to the eye. Like any other tissue, the eye needs an adequate blood supply for proper function.
Jeremy Nathans, a professor of neuroscience and ophthalmology at the School of Medicine who led the study, discovered that an oxygen-starved eye can be coaxed to recover its function. Even if neurons in the retina, a membrane sensitive to light that covers the eye's back wall, are not active, their potential to be turned back on, restoring sight, is still retained for up to several months.
Development of blood vessels within the retina is attributed to three critical genes, Fz4, Ndp and Lrp5. Problems with any or all of these genes, including genetic defects, or lack of genes, result in the production of too few blood vessels in the retinas of laboratory mice, and blindness. The absence of the Fz4 does not directly cause blindness, but rather failure to produce enough blood vessels. Fz4 in blood vessels is responsible for picking up the signal produced by the gene Ndp in other retinal cells.
When electrical responses in retinas of mice lacking the Fz4 gene were measured, researchers found that signaling did not occur normally in the middle of the retina, which also happens to be the portion of the eye that does not contain blood vessels.
They proceeded to submerge these blood-starved retinas in a mixture of nutrients and oxygen to simulate the effect of an adequate blood supply. They discovered that the retinas regained light sensitivity and the ability to produce electrical responses to the degree that a healthy retina containing the Fz4 gene would.
The researchers concluded that the blood vessels defective in Fz4 can deliver enough oxygen to keep the retinal cells alive for up to several months, but not enough to allow the cells to sense light. Their findings have the potential to help humans who suffer vision impairment because of decreased blood supply to retinal cells.
