However well we think that we can see, every human eye contains defects that make our vision less than perfect.
Dr Juan Tabernero has dedicated his career to understanding these imperfections, but in his latest study he also took a major step towards discovering what causes them.
There is something magical about the moment when a person with poor eyesight wears glasses for the first time, and the world, previously blurred and indistinct, comes into focus. Imagine, though, if we could all experience that enhancement, even if our eyesight was perfectly good, so that suddenly we could see in higher definition.
This concept is actually less outlandish than it seems; in fact, scientists have for many years mooted the possibility of 'super-vision' that would enable everyone to see better. The reason is that however good our eyes seem to be, they always contain microscopic defects, which make our eyesight less than optimal. Understanding those imperfections, and how they might be corrected, has fascinated Dr Juan Tabernero ever since his academic career began.
“I started studying these tiny defects, which we call optical aberrations, when I began my PhD 15 years ago,” says Juan, who works in the Vision and Eye Research Unit (VERU), part of our Faculty of Medical Science. “The long-term ambition is to give everybody the best quality vision possible. The first step is understanding why these defects occur; then we can work out how to correct them.”
The blemishes that Juan studies are structural defects within the two lenses of the human eye – the outer cornea, and the inner, crystalline lens. The aberrations are almost imperceptibly small, usually just a few millionths of a metre in scale.
Their presence means that the curvature of our eyes is not quite ideal. As a result, a tiny fraction of the light passing into them does not concentrate as it should, causing imperfect vision. Most people will never be aware of this, but for some, aberrations will worsen their vision at night, when our pupils expand and try to take in more light. Aberrations are also a feature of some corneal diseases that distort the patient’s eyesight.
Until recently, it was assumed that aberrations formed by chance. The cornea itself is a malleable tissue, and could suffer tiny deformities as a result of constant strain on the eyes, or even random effects that occur when we are still a foetus in the womb.
Juan began to wonder, based on his wider research, if in fact many of these irregularities were determined less by our behaviour or environmental factors, than by genetics. A genetic cause, if it existed, could potentially be corrected.
To test this, Juan conducted a study which spanned his previous post at the University of Murcia, Spain, and his arrival in Cambridge. He analysed the ocular defects of 69 sets of twins, of whom 36 were identical. To his surprise, the identical twins, which share corresponding genes, had identical defects. This was not the case among non-identical twins, which only share 50% of their genes on average. The results suggest a strong genetic cause is behind the aberrations in our eyes.
“Because we thought these defects appear randomly, we were expecting the exact opposite result,” Juan says. “I was so surprised I had to check it with several colleagues. Fortunately, they were as impressed by what I had found as I was!”
Sadly, this does not mean that a future in which everyone has super-vision is imminent. Juan hopes to carry out further research to identify the genes that cause optical aberrations. Next, gene-editing techniques will need to be developed to prevent the very worst cases. Even if that were possible, we would also need to be able to control the way in which the brain presently compensates for these defects as it processes retinal signals from our eyes.
In recent years, however, there has been progress in all of these areas of research. “We have just completed the first stage of a long journey,” Juan says. “Personally, I think genetic testing for aberrations will happen within the next few decades. Whether we will then be able to edit the genes is really a question for geneticists. But there are some promising techniques, and it is likely that these will develop further.”
Twins provide researchers with the perfect natural experiment when they are trying to assess whether a particular characteristic is caused by genetic factors, or something else – as Juan was in his recent study. Identical twins always have the same genes, but non-identical subjects share 50% of genes on average. “That means that if identical twins have an identical characteristic, which non-identical twins do not, we have a strong indication of a genetic cause,” Juan explains. “The correlation is particularly striking when you are measuring something as minuscule as optical aberrations.”
Juan trained as a physicist, specialising in optical engineering. While many such researchers work on tools such as telescopes and microscopes, his interest is in the natural lenses of the human eye. This addresses problems from both the physical and life sciences, and demands a working environment involving interaction between both.
The Vision and Eye Research Unit enables exactly that sort of cross-boundary research: “We have great facilities, even in an area where every piece of equipment is expensive,” Juan adds. “We have labs and instruments, but also a clinic, and I can work directly with patients while also doing prototype testing. ARU really understood the multi-disciplinary approach, and that’s basically why I came here.”