Interview with Dr. Christian Lappe, Director Scientific Affairs & Technical Communication | Principal - ZEISS Expert Ladder
What is peripheral vision?
To answer this question, we must first look more closely at a couple of fundamental aspects of visual perception. The macula lutea (sometimes called the "yellow spot") is located on the retina exactly on the visual axis. The fovea centralis is positioned in the center of the macula. This is where our vision is at its sharpest and where the retina has the densest concentration of color receptors (cones). If we focus our vision on something so we can observe the details, the corresponding image is generated in the region of the fovea. This is called foveal vision. The fovea is surrounded by two further zones, the parafovea and the perifovea which also play a certain part in enabling us to see objects in detail. The number of rods increases in this region and it is the rods which help us see at low ambient light levels. The retinal area outside the macula is called the retinal periphery; rods predominate here. Visual perceptions originating in the peripheral area of the retina and which therefore cannot be attributed to foveal vision are called "peripheral vision".
We need peripheral vision to be able to navigate through the world and move around. If we are concentrating on looking at our screen in front of us, we can nevertheless see that a small spider is moving on the left-hand edge of our desk. If we are walking in a straight line along the sidewalk and looking straight ahead, we can nevertheless notice if a dog wants to cut across our path from one side. But we can only say exactly what breed of dog it is if we look directly at it. Thus, depending on how we judge the situation, we can direct our attention to what we have just detected in our peripheral vision and thus see the object in our foveal vision.
Is peripheral vision now more important than ever?
We can't answer this question with statistics. But the figures of smartphones usage and the time we spend on our smartphones tell us, of course, that we now have a device to which we very often deliberately direct our visual attention. But also, even when we are moving around and preoccupied with our smartphone, we can still perceive people coming towards us either from in front or the side. Of course, not in so much detail as if we were looking straight at them. Peripheral vision is definitely important for these smartphone moments.
Does this mean that if we are immersed in our smartphone we can still perceive other visual stimuli?
Yes, exactly. Thanks to our peripheral vision we can, for instance, see immanent hazards which are not in the center of our attention. However, the smartphone, with all its various functions, demands so much of our attention that it still makes sense to take a look at our surroundings from time to time, particularly if our safety is at stake, for example when crossing the road.
In this connection are there particular problems for spectacle wearers?
In this case we must once again first separate two distinct facts: particularly in the case of progressive lenses there are central areas and corridors in which very precise (i.e. clear and sharp) , detailed vision is possible - and then there are the peripheral areas of the eyeglass lenses where the physical laws of optics imply a range of visual aberrations. These little undesirable yet unavoidable aberrations are normally the lower left and right outer areas of the eyeglass lens.
Irrespective of whether the eyeglass wearer is now deliberately looking through the central or peripheral areas (edge areas) of the eyeglass lens, he or she is using his foveal vision. The same applies the other way around: all areas of the eyeglass lens are used for peripheral vision depending on where the wearer's attention is targeted. A wearer of progressive lenses sees the spider on his desk through the peripheral area of the eyeglass lens - in this case possibly with more or less remarkable visual aberrations. But most eyeglass wearers adapt to these aberrations. If the observer wants to know in detail what the spider looks like and moves his eyes but does not move his head, he uses his foveal vision through the periphery of the eyeglass lens.
And what does that mean for smartphone users?
If we return to the earlier smartphone example we can understand that many targeted glances are made through the peripheral areas of the eyeglass lens. Our world is only getting more dynamic: we look to the right or left, upwards or downwards without moving our head just to spot if a door is opening or someone is approaching.
At the same time peripheral perception is generally made through areas of the eyeglass lens which are unable to generate a precise image because of physical and optical constraints. The importance of this peripheral perception is particularly increasing in the age of the ubiquitous smartphone because our attention is so often focused on the smartphone and mobile device itself.
This means that the optical design of the eyeglass lens should be adapted to this lifestyle considering both a clear foveal vision and also effortless peripheral perception.
Does ZEISS have a solution?
The new ZEISS SmartLife portfolio has integrated this new lifestyle, the associated visual behavior and the visual challenges it brings with it, into the eyeglass lens design. In fact, irrespective of the lens category - for single vision and progressive lenses. The design was modified to make vision relaxed in all directions and at all distances.
The efficiency of products and acceptance by eyeglass wearers is tested before the market launch in scientific studies, often with independent and external partners.
The studies demonstrated, for instance, that 4 out of 5 test wearers of ZEISS SmartLife progressive lenses experienced smooth vision from near to far across all viewing zones1. In a different study on the visual performance of contrast perception in the area of peripheral vision, it was confirmed that the new ZEISS SmartLife progressive lens design enables peripheral vision.2
How is peripheral vision and peripheral perception measured?
Some consumers are probably familiar with ophthalmological diagnosis of their visual field by the eye care professional or eye doctor - with the aid of what is called "perimetry". You have to look carefully at a fixed point through a special device. Points of light then flash on and off at various positions in the visual field. Every time the test subject detects one of these points, they have to register this by clicking on a button, for example.
This examination can reveal deficiencies in the visual field, both in the central and the peripheral areas. There are many different causes of limited visual field performances, for example retinopathy, macular degeneration, "green star" (glaucoma), neurological diseases, tumors, accidents, etc. Therefore, a regular check of apparently normal central and peripheral visual fields is a very important examination.
In more rigorous scientific studies conducted under strictly controlled conditions, eye tracking is also used to check whether the test subject is really concentrating his/her gaze on the fixed point; this is done to capture unintentional eye movements and to compensate for them if necessary.
Another interesting fact about peripheral vision - if there is sufficient light, central, i.e. foveal vision enables us to see sharp contrasts and a wide range of colors. However, if the ambient light level continuously dims, we first notice this by our color vision to gradually vanish ("at night all cats are gray") and a degrading perception of contrasts. At extremely low light levels at night we cannot see a faint star or point of light if we stare at it. On the other hand, in the periphery of the retina there are large numbers of light-sensitive rods and, for instance, we see the faintly luminous stars in the periphery. In complete darkness it can therefore sometimes be helpful not to look directly at a faint object but to look to one side of it. This is one way of putting peripheral vision to good use.
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