Before the age of forty, the flexibility of the crystalline lens manages to maintain on the retina, the image of an object that moves from far away to the reading distance. And the eye sees clearly at all distances.
There comes a day, when your arms are too short to read and you blame your computer screen for everything! But as Professor Pouliquen writes very nicely: “Presbyopia is only the border between two stages : before, during which man ignores his eye, and after, when he must necessarily have it checked, then assist him with the optical means that the modern world puts at his disposal (…)[1]. »
What are the questions that arise when presbyopia arrives?
What is going on?
With age, the structure of the crystalline lens inevitably changes and consequently, the distance at which we see clearly decreases as age progresses.
There are no practical solutions other than adding an “optical compensation”, a spectacle lens, between the eye and the object viewed in near vision to compensate the loss efficiency of the crystalline lens. At first, it is sufficient to use a low-power monofocal lens (generally 0.75 to 1 diopter) because the “accommodation reserve”, which remains of the lens’ flexibility, will do the rest for near vision. But as we get older, the accommodation reserve will no longer be enough and we will have to equip ourselves with progressive lenses.
[1] POULIQUEN Y. Member of the French Academy and Professor of Ophthalmology. The transparency of the eye. Edition Odile Jacob. Paris 1991. pp. 181 and 182.
What is the solution?
In 1959, Bernard Maitenaz invented the first progressive lens within Essilor: the Varilux®, which has evolved enormously over the past 60 years.
This lens allows you to see clearly from afar, straight ahead and to see clearly up close, at the bottom of the lens. Indeed, in a progressive lens, the power of the lens gradually increases from top to bottom. We can therefore consider that each angle is dedicated to a particular distance, from horizontal distance vision to downward near vision. The intermediate distances are gradually staggered from top to bottom, what explains why the “arm’s length” distance, which is the distance from the screen, is not at eye level but about ten degrees below the horizontal. This lens offers a kind of cone of good vision whose base, oriented and horizontally flared, is located at eye level and whose tip is on the computer keyboard or the document to be read.
What is the risk of a bad posture?
Young persons facing a screen at eye level have enough accommodation reserve to see the top their screen clearly, however, by making more demands on their accommodation. But as they get older, they will have to ask more and more (accommodative constraint) and finally, to escape this constraint, they will have no other solution than to slightly tilt their head backwards to raise the bottom of their lens between their eye and screen in order to increase the power of the area of the lens they will use to look at it (postural constraint).
How to avoid it?
The task content of people working on screens rarely requires perfect distance vision. A “social” distance of 2 to 3m is generally sufficient to perform the work. Therefore, optically, it is sufficient to reduce the power of the lens dedicated to distance vision in order to obtain an horizontal power that corresponds to the screen distance or, according to the job analysis, this “social” distance. These are the so-called degressive lenses.
Hence the dilemma: good vision at all distances, distance vision included or visual comfort when age comes?
From what age?
We are not all equal in the face of age. But we must take into consideration the fact that the number of older workers remaining at work has increased considerably over the past 15 years. Their accommodation reserve becomes marginal and the frequency of postural complaints increases proportionately. It is particularly important to pay attention to these workers in order to provide them with a lens that allows them to maintain their visual comfort at work.
What are these lenses?
Essilor, specifically for people working on computer screens, has launched the “Varilux® Digitime™” lens, to ensure visual comfort. It is important for the optician to know the workstation data in terms of distance and screen height in order to choose the most suitable lens to the person’s visual characteristics and the workstation.
Essilor Pro-Office™ lenses, available with or without vision correction, benefit from the latest technological innovations to ensure optimal comfort at all distances (near and far) and to protect against the blue-violet light emitted by the screens, which can cause vision problems and discomfort over time.
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