July 2014

 

CATARACT

 

A new vision for blind patients


by Maxine Lipner EyeWorld Senior Contributing Writer

 
   

Splatter painting as it appeared before cataract removal, with current vision, and how it is viewed by those with normal sight Source: Luis A. Lesmes, PhD

Rethinking the brain's plasticity limits

Just because a patient has been blind during the early years of development does not mean that he cannot develop functional vision later, according to Luis A. Lesmes, PhD, CEO of Adaptive Sensory Technology, Watertown, Mass.

He cited a new study published in the February issue of Proceedings of the National Academy of Sciences that indicates that surprising gains in contrast sensitivity can be made in some young cataract patients well after the brain's "critical developmental window" has passed.

The study was part of Project Prakash, a joint scientific and humanitarian effort aimed at addressing problems of treatable blindness in India. "Project Prakash was able to screen children in rural parts of India and find those who unfortunately have lived with correctable blindness for much of their lives," Dr. Lesmes said. As part of that effort, his group studied children ages 8 to 18 living with cataracts. The study subjects had early onset blindness, which began before the age of 1 and extended for a period from 8 to 17 years. "This is an extreme example of deprivation that goes well beyond what I think clinicians and researchers would call the critical period," Dr. Lesmes said. "The fundamental question that we were asking when we joined this investigation was, 'If blindness exceeds this critical period, is there any visual plasticity that can allow some further visual development?'"

Eyeing dogma

The long-held dogma was that this critical period of plasticity ended at around 7 or 8 years old, which is why for conditions such as amblyopia there is such a rush to treat, he said. Along these same lines, one of the challenges with teenage cataract patients found in the developing world has been whether it makes economic sense to treat them because of their advanced age, Dr. Lesmes said.

Investigators found that some children can develop usable vision. "There is a reserve there," he said. "There is plasticity that can develop a considerable amount of functional vision," although this vision will not be perfect. Dr. Lesmes acknowledged that not everyone was able to acquire new vision. This opens the door to the question of if there was something unique about those who did develop vision, he said.

The patient's age was not the critical factor here, he said. "In fact, the largest improvements were in a 15-year-old," he said. This patient experienced an incredible amount of development, with an approximate 30-fold improvement in his contrast sensitivity. "That's such a huge gainand he got this in 6 months." One of the other questions considered was once the cataracts are removed, what is the rate of visual development? Would it mirror normal development rates? "In fact, it was more accelerated than that," Dr. Lesmes said. Investigators found that rates could exceed those of a normally developing infant.

New testing

In addition, the study included a new contrast sensitivity test, which Dr. Lesmes designed. "We thought that some of the previous tests, particularly ones that had to use cards or charts, were too imprecise," he said. Instead, the new test uses an algorithm that can adapt to the person taking it, he explained. It is akin to academic testing algorithms where if someone gets a question wrong, it gets easier and if he gets it right, it gets harder, Dr. Lesmes said. "We developed this first as a research tool and then we started to realize that this could be useful in the clinic," he said. "That also motivated us to put it on an iPad so that it could be portable." Dr. Lesmes is excited about bringing this tool to the clinic, viewing this as something that may have an immediate impact. "We're measuring both monocular and binocular contrast sensitivity and evaluating whether that might present a more powerful visual outcome measure for amblyopia therapy," he said. With amblyopia, even after patching has ceased, there may still be room for improvement. Often there are contrast sensitivity deficits even after intraocular acuity criteria have been reached, he said, adding that with perceptual training regimens both contrast sensitivity and acuity can be improved further. "One basic issue to evaluate is whether clinicians are using the right criteria to start and stop treatment," he said. That is something they are currently exploring with the new technology. He views this new test as potentially having broader implications as well. "If someone gets multifocals or cataract surgery, there's a neural adaptation element. If they don't happen to neurally adapt, they may keep complaining," Dr. Lesmes said. "We're hoping that we can provide more information about what's happening and why this person isn't showing neural adaptation."

Dr. Lesmes is enthusiastic about the study results and what this could mean for humanitarian efforts. "Even if blindness extends from almost birth to the teenage years, there is still considerable hope that someone can develop functional vision," he said. "I think that plasticity is something that a lot of people are excited about these daysthey realize that maybe the brain is not as static as we think it is."

Reference

Kalia A, Lesmes LA, Dorr M, Gandhi T, Chatterjee G, Ganesh S, Bex PJ, Sinha P. Development of pattern vision following early and extended blindness. Proceedings of the National Academy of Sciences. 2014 Feb: 111(5): 20359.

Editors' note: Dr. Lesmes has financial interests in the new test developed by Adaptive Sensory Technology.

Contact information

Lesmes
: luis.lesmes@adaptivesensorytech.com