Cataracts and the gift of sight
Jesus asked, “Do you see anything?”
– Mark 8:24
He looked up and said, “I see people; they look like trees walking around.”
Jesus had just spat in the blind man’s eyes and laid his hands on him. So Jesus lays his hands on him again. Now he sees clearly – but it required two treatments. Vision is a central concern in many of the miracles done by Jesus.
Cataract surgery is one of our medical success stories: it has improved patients’ vision and given them the ability to continue living productive lives. My understanding from people who have had this procedure is that it is quick, not very painful and life changing, a true blessing.
Usually cataracts develop later in life. Unfortunately, children can also be born with cataracts. With our medical system these babies are generally diagnosed quickly, undergo surgery and live with minimal long-term consequences. However, in countries with limited access to health care, these babies are sometime untreated and so grow up blind.
Past research has indicated that early visual input from the eyes is needed for the brain’s visual system to develop normally. In research done with animals by Torsten Wiesel and David Hubel, the absence of patterned input early in life meant that animals could not use their visual system effectively later. Researchers fit light-blurring covering over the animal’s eyes for the first few months of life, depriving the visual system of patterned information but not light. Upon removing the lenses, they discovered that the brain could not process visual patterns properly. The animal’s vision was impaired for life.
Hubel and Wiesel found that the visual cortex in the brain is plastic in very early life. Over a few months, the brain neurons wire themselves into effective modules that respond to visual information like lines, corners and movement. In the absence of patterned input, this wiring process is random, and an animal cannot respond properly to visual information. The work suggested that a critical period exists for the establishment of vision. In the absence of sight in this critical phase, nothing could be done later to restore vision. Thus doctors assumed that treating individuals with infant cataracts later in childhood would be useless; the brain would never learn how to use the visual information properly. Wiesel and Hubel were awarded the Nobel Prize in 1981 for their research and related work on the visual system of the brain.
Rewired
A recent Science article provides a hopeful counter to their findings. Rhitu Chatterjee reports on a research program in India (where untreated cataracts in children are unfortunately not an uncommon problem) that tested Hubel and Wiesel’s conclusions. Researchers led by Pawan Sinha removed cataracts from about 500 teenagers and found that their brains still had the ability to start using visual information, even at this late developmental stage. Slowly, over about a year or so, these youth started to see better and better. While they did not reach the visual acuity of individuals who see from birth, they were able to use visual information to ride a bike in a crowded market. Most had difficulty reading fine print, but newspaper headlines were fine. Like the blind man healed by Jesus, they first saw things unclearly and only slowly were able to come to “see” and use the visual information now supplied by their eyes.
Sinha and his associates suspect that the visual system gradually rewires in these individuals, making them able to integrate the new visual input with information from the other senses to give them a more complete appreciation of their world. Images of brain activity suggest that these youth gradually come to use the same parts of the brain in visual tasks (such as recognising faces) that are used by normally sighted individuals. This research suggests the human brain has a remarkable degree of plasticity even into adulthood.
Clearly, early treatment for cataracts is preferable, but this work gives hope to many individuals who were condemned to a life of blindness. While we do not know the nature of the blindness that Jesus healed in the specific incident recorded in Mark, we can be thankful that now doctors are able to help individuals with at least some specific types of blindness.
