INTRODUCTION

Presbyopia, from the Greek présbys 'ancient' and opôs 'eye', is the most common cause of loss of accommodation. It is part of the normal aging process that all people experience, and it is characterized by a gradual loss of age-related accommodation amplitude¹, clinically translating by a progressive difficulty in focusing on nearby objects, with increased comfort distance of reading ('very short arms'), which occurs more frequently between the ages of 42 and 44².

Contributing to this loss of accommodation amplitude³ are: the reduction of age-related ciliary muscle length (extralenticular process)⁴; crystalline hardening⁵; increase in crystalline viscosity⁶ and stiffness⁷; as well as geometric changes such as the increase of the thickness and convexity of this same lenticular structure^8,9. In fact, its pathophysiology still continues to be undetermined.

EPIDEMIOLOGY

As the world population progressively increases, as well as their average life expectancy, and knowing that this disorder is ubiquitous from the age of 40, it is estimated that 1.4 billion people develop presbyopia by 2020, increasing that number to 1.8 billion by 2050¹². Presbyopia is an often-neglected health problem¹³, even in large population studies¹⁴, since there are several corrective modalities, such as glasses, contact lenses or intraocular lenses, which in developed countries are easily available to the population. In 2005, it was estimated that globally, 1.04 billion people had presbyopia, and of these 517 million had no glasses or these were unsuitable. Of these, 410 million were unable to perform the tasks they intended.

ERGO-OPHTHALMOLOGY

Uncorrected presbyopia – Functional presbyopia – is the most common cause of vision disturbance¹⁵, hence the World Health Organization (WHO) recommends measuring near vision in population studies, as it can couple with decreased vision for distance, which also contributes to loss of quality of life, regardless of the environment, lifestyle or sociodemographic status of the affected individual¹⁶. The prevalence of functional presbyopia is higher in elderly people in South Asia (63.8%), Sub-Saharan Africa (58.6%), Central Europe, Eastern Europe and Central Asia (51.9%) and lower in developed countries (12.2%), where in countries such as Finland, it may be as low as 1.8%¹⁷. In Tanzania, only 6% of the presbyopic population has glasses for correction^18,19. In Brazil, 55% of people have glasses for presbyopia, but only 71% have adequate correction (i.e. only 39% of Brazilian presbyopes have adequate correction)²⁰. Only 30% of presbyopes in India and 26% in Timor-Leste have adequate eyeglasses^21,22. One study concluded that the likelihood of having appropriate corrective spectacles is 30-39% in less developed countries and 84-96% in more developed countries.

The loss of accommodation is gradual, with the first symptoms occurring on average between the ages of 42 and 44. The majority of the population experiences these visual symptoms by the age of 51 years. There are several factors that influence the onset of these complaints: ability to focus²³, depth of focus, concomitant refractive error (hyperopes develop presbyopia earlier and myopes later)²⁴, pupil size, geographic location^25,26, climate^27-29, requirements and expectations³⁰, gender³¹ and ethnicity^33-36. There seems to be some consensus regarding the initiation, earlier with higher levels of melatonin in equatorial regions.

Historically, the first combination for treatment of presbyopia, was developed by Benjamin Franklin in 1784, joining two pairs of glasses in the first set of bifocals. There are several ways to correct presbyopia with glasses: 1. Simple monofocal lenses, commonly referred to as 'reading glasses'; 2. Bifocal lenses; 3. Progressive lenses and 4. Occupational or 'office' lenses. We should prescribe the smallest possible addition, which allows for a clear and comfortable near vision³⁷, and avoid over-addition, since although it may improve eyesight acuity for near, it will reduce comfort by limiting the visual field³⁸.

Simple monofocal lenses – commonly referred to as 'reading glasses' – may be used by emmetropes, or by individuals with a low degree of ametropia who do not feel the need for far-reaching correction and in whom both seek a simple, cost-effective solution for close addition³⁹. They may also be used by contact lens wearers who have entered presbyopia and are unwilling to stop wearing contact lenses (for distance) and / or have not coped well with multifocal contact lenses.

Conventional bifocal lenses offer two fixed vision zones (distance and near) separated by a visible 'line', which produces in the transition an abrupt change of vision that stimulates a prismatic effect. More recently on the market, there are bifocal lenses in which you cannot see the 'line' (i.e. Shamir Duo^™). This type of lenses is becoming less used, not only because of their inferior optical characteristics, but also because their use is very associated with an older age group.

In progressive lenses, the desired additive power is provided by increasing the power between the distance and the near areas on the lens surface^40,41. This way you can get an upper corridor, to see objects well in the distance, a more central corridor for intermediate view, and the lower portion to see near. It has the advantage of wearing only one pair of glasses, and of having focused vision for different distances. The differences between different types of progressive lenses, even within the same manufacturer, reflect the existence of different designs of the lenses and are related to the height and width of the corridor of the progressive power and how much of this is intended for each focal length. Different areas of the lens can be expanded, depending on the intended function of the lens and depending on the lens producer, i.e. Essilor, Varilux X Near Vision Behavior (NVB)^™, Zeiss Precision or Individual 2^™, Shamir Autograph InTouch^™. In a computer user, progressive lenses with wide channel should be used to facilitate the transition between far, intermediate and near vision. This modality of correction constitutes a great optical innovation, but it is not without difficulties for some people in adapting to this new neurosensorial reality – interindividual variability. The process of neuroadaptation is dynamic and not yet well known, and a process of neuroadaptation may still be involved that has not yet been fully clarified, and in which the adaptive role of vergences and forays seems to be involved in the adaptation of new visual environments⁴².

For better adaptation, perseverance is suggested: 1. wear glasses permanently; and 2. see 'with your eyes and head' by shaking your head looking for the best position to see sharp. Occupational or office lenses do not include far-away refraction in the upper portion, only for intermediate and close distance.

According to Minkwitz's law⁴³, the fact that there is less change in the dioptric power in the lens allows a reduction of the aberrations in the periphery of the same, and thereby obtain a greater and clearer field of vision for near and middle distance. They are particularly used by those who do not have far-reaching refractive error, or this is small^44,45 ,and by those who spend a lot of time at home or at the office because the wider field of intermediate vision makes use of this and other new technologies, more comfortable. Finally, they are also useful for example, for those who use not only the computer but have to read and interact with people simultaneously in a very confined space. Examples of occupational lenses are: Essilor Digitime^™, Zeiss DuraVision^™, Shamir Office^™. With the advent of digital technologies, not only did the methods of communication and information management change, but also the vision and posture habits of users. To meet this emerging need, the optical industry has evolved in the field of chemistry and optical designs with the aforementioned lenses – occupational lenses and progressive lenses with expanded areas for intermediate and near distances.

Visual and postural behaviors have also changed. In 2011, about 21 million people in Germany used computers^46,47, and of these about 80% used computers for more than 3 hours a day, complaining of visual effort, headache or pain in the neck or shoulders⁴⁸ – digital asthenopia syndrome and postural defects. According to Hayes et al, this correlation between eye and body symptoms is 81%, and 64% between eye strain and neck pain / shoulders⁴⁹.

We are now also exposed to brighter lights and different light sources, such as blue LED light, which emits potentially harmful light – violet blue light. Regarding ergonomics in the office⁵⁰, it is known that one should not face a window, but should be with the visual axis parallel to this window, so that there is no chaining light (direct or reflected), have a backrest that has an angle of 100 to 105 degrees and has lumbar support; the hip, knee, and tibiotarsal joints should be in a neutral position (Figure 1). The computer screen should be facing forward at a distance of 50-75 cm⁵¹ and slightly tilted up so as to be parallel to the face and perpendicular to the visual axis, adjust the contrast and brightness according to personal preferences. For progressive lens wearers, the monitor should be positioned a little lower (7.7º⁵² or 15 cm⁵³ below eye level) in order to look at the computer through the intermediate corridor (the appropriate one to focus on the screen), so as to facilitate the proper use of such lenses, avoiding the movement of the neck and head back and forth⁵⁴.

With occupational lenses that is not necessary, with the top of the screen being at eye level, since the upper aisle is already for intermediate distance. In addition, the work environment has changed. Ten years ago the eyes were exposed to natural light, or that emitted by incandescent light, and they are now exposed to brighter lights and different sources, such as the Light Emitting Diodes (LED) used in interior light, newer television screens, computers and smartphones, which emit potentially harmful light – blue-violet light. This is due to the European directives of the Ecodesign of Energy Using Products (2005/32/EU), which recommends replacing incandescent bulbs with more economical devices such as LEDs, in order to save energy.

However, these LED lights have a higher percentage of potentially harmful blue light: 1. potential association of the blue component of white LED light with retinal toxicity^55-57; 2. possible association with a new increase in exposure to the flickering effect, with increased risk of digital asthenopia, due to a longer duration of exposure to the screens. This effect can be obviated by filters on the spectacles (for presbyopia or not) for the blue light emitted by these devices: Essilor Crizal^™ Prevenience, Zeiss DuraVision^™ BlueProtect, Shamir Glacier Blue Shield^™; and / or installing software specifically designed to regulate the amount of blue light the computer user is exposed to throughout the day. Thus, in conclusion, presbyopia is part of the normal aging process, and is clinically characterized by a progressive difficulty in focusing on nearby objects.

Although in developed countries there are a number of solutions to their resolution, this is not the case in other parts of the world, where a large part of the population has no glasses, or these are inadequate. With the increasing use of new digital technologies, new challenges arise, forcing the industry to develop new optical designs and filters for blue light. Ergo-ophthalmologists advise slight postural variations to make the use of such technologies easier, with the least inconvenience.

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