Carried out by researchers at Rutgers University Behavioral Health Care, USA, and the Perception, Neuroscience and Behavior Laboratory, Brazil, the new small-scale study looked at 71 participants who had smoked less than 15 cigarettes ever in their lifetime and 63 who smoked more than 20 cigarettes a day.
The participants were between the ages of 25 and 45 and all classed as healthy with normal or corrected-to-normal vision. However, they had been diagnosed with tobacco addiction and reported that they had made no attempts to stop smoking.
During the study, the participants were asked to sit 59 inches away from a 19-inch cathode-ray tube monitor which displayed stimuli. The researchers monitored both of the participants’ eyes simultaneously to assess how well they discriminated between contrast levels – subtle differences in shading – and colours while watching the stimuli.
The findings, published in journal Psychiatry Research, showed that the group of heavy smokers, those smoking more than 20 a day, had a reduced ability to discriminate between contrasts and colours when compared to the non-smokers.
The researchers also found significant changes in the smokers’ red-green and blue-yellow colour vision, which they noted suggests a link between consuming substances with neurotoxic chemicals, such as those found in cigarettes, and overall colour vision loss.
“Cigarette smoke consists of numerous compounds that are harmful to health, and it has been linked to a reduction in the thickness of layers in the brain, and to brain lesions, involving areas such as the frontal lobe, which plays a role in voluntary movement and control of thinking, and a decrease in activity in the area of the brain that processes vision,” said co-author Steven Silverstein.
“Previous studies have pointed to long-term smoking as doubling the risk for age-related macular degeneration and as a factor causing lens yellowing and inflammation. Our results indicate that excessive use of cigarettes, or chronic exposure to their compounds, affects visual discrimination, supporting the existence of overall deficits in visual processing with tobacco addiction.”