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Overview of Presbyopia and Its Medical Management

Atalie C. Thompson, MD, MPH; Samuel Passi, MD; and Terry Kim, MD

The term presbyopia refers to the gradual loss of accommodation by the crystalline lens with advancing age. Patients typically become symptomatic when approaching middle age. They may report blurry vision when doing near work, headaches, asthenopia, squinting, and eye strain.¹ Identification of presbyopia is important because it is an easily correctable cause of vision loss in aging individuals, with many affordable nonsurgical and surgical management options. In developing nations, presbyopia remains widely undertreated due to limits in access to eye care.² In developed nations, patients have a variety of treatments available to improve their acuity at near and intermediate distances. Nonsurgical management options include inexpensive over-the-counter plus power reading glasses, prescription spectacles that incorporate a bifocal segment or progressive lens, multifocal or monovision contact lenses, and pharmacological drops.¹

For previously emmetropic patients, the experience of developing a new dependency on corrective lenses may be distressing. Health care providers should reassure patients that these changes in their vision are a normal part of the aging process and refer the patient to an eye care specialist in optometry or ophthalmology for further evaluation and treatment. Guiding the patient to the best option to correct his or her evolving refractive error can take some time and will require patience from the patient and provider as they move through an iterative process of trial and error. All decisions should be made in a patient-centered manner with the goal of improving his or her visual function.

This chapter will review the worldwide epidemiology of presbyopia, some of the theories behind the physiologic changes that may contribute to the onset of this condition, and the nonsurgical management options for presbyopic patients.

EPIDEMIOLOGY OF PRESBYOPIA

Presbyopia occurs in all adults, with the onset typically starting around 38 years of age and reaching a peak incidence around 42 to 44 years of age.³ Nearly 100% of patients will prove symptomatic by the time they are 52 years old.⁴ Despite the universal development of presbyopia in older adults, estimating the prevalence and incidence of presbyopia has proven challenging for a number of reasons. First, it is difficult to assess the precise onset of such a slowly developing chronic condition. Second, not all individuals with presbyopia will present for an examination to an eye care specialist to confirm their diagnosis. This is particularly true in developing nations, where 94% of the world’s burden of uncorrected vision impairment due to presbyopia exists.² Third, neither the definition of presbyopia nor the methods to measure presbyopia have been standardized.5 Census data frequently rely on subjective self-report of visual complaints, and few studies have attempted to correlate survey measures with clinical diagnosis.⁶

Nevertheless, as life expectancy increases, the proportion of aging individuals is growing worldwide and the prevalence of presbyopia is expected to rise. The United Nations estimates that in 2015, there were 901 million people aged 60 years or older. This constituted a 48% increase since the year 2000. By 2050, the global population of older adults is projected to double to nearly 2.1 billion.⁷

By combining data from multiple surveys, Holden and colleagues² have recently attempted to publish global estimates of presbyopia. They state that there were approximately 1.04 billion people with presbyopia in 2005. More than half of these patients either did not have glasses or had inadequate refractive correction, and 410 million had functional impairment when trying to perform near tasks.² Global health researchers should continue to work to improve access to inexpensive nonsurgical treatments for presbyopia, especially low plus power reading glasses. Such interventions stand to make a large impact on the burden of visual impairment in elderly patients worldwide.

Risk Factors for Presbyopia

In addition to age, several other factors can contribute to presbyopic symptomatology. Females are more likely to report presbyopia at an earlier age and may need a higher plus power corrective lens than males.⁸ This finding may stem from shorter arm lengths in women compared to men, rather than true anatomic differences in the eye.⁹ At baseline, hyperopic patients have greater accommodative demands, and thus they may present sooner with visual dysfunction from presbyopia. Patients whose vocation or avocation involves prolonged near work may begin to complain of asthenopia from accommodative fatigue as they approach middle age. Impaired accommodation is also an unwanted side effect of a number of major drug classes, including but not limited to antidepressants, antipsychotics, antispasmodics, antihistamines, anticholinergics, and anxiolytics. Any trauma to the lens, ciliary muscle, or zonules can also lead to earlier loss of accommodation as well as earlier development of cataract.¹

Physiology of Accommodation

The mechanism of accommodation has been a source of scientific inquiry for more than half a century. In 1855, a German physicist by the name of Hermann von Helmholtz proposed what has become the predominant paradigm used to explain the relationship between accommodation and the ciliary muscle.^10–12 According to von Helmholtz, whenever a subject is focused on a distant object, the relaxed ciliary muscle keeps the zonular fibers at a resting tension because the internal diameter of the ciliary muscle is maximized. This places tension on the lens equator, which flattens the lens and diminishes its dioptric power. During accommodation, the ciliary muscle, which is a sphincter muscle, contracts so that the internal diameter decreases, which releases tension on the zonules. As the zonules relax, the lens capsule constricts, leading to a decrease in the equatorial lens diameter and an increase in the convexity of the anterior and posterior lens surfaces. The end result is a rounder lens that increases the eye’s dioptric power so that one can focus on near objects (ie, accommodate).¹⁰

A rival theory of accommodation was almost immediately put forth by a Danish ophthalmologist named Marius Tscherning. In 1895, he published his theory that ciliary muscle contraction increases the tension in the zonules, which in turn pushes the cortex around the nucleus to reshape the lens without modifying its thickness.¹³ More recent adaptations of Tscherning’s theory have been proposed by Ronald Schachar. Schachar has postulated that ciliary muscle contraction during accommodation preferentially increases, rather than decreases, zonular tension at the equator of the lens. The lens curvature thus increases as the equatorial lens is pulled toward the sclera.¹⁴ Schachar believes that continued growth of the lens equatorial diameter over time leads to a decrease in the lens-ciliary body distance, such that the zonules display more slack with advancing age. This slackening of the zonules contributes to the loss of accommodation in his model.^14–16

Recent work on accommodation in nonhuman primates and humans, however, has served to challenge the Tscherning-Schachar theories of accommodation. For example, using ultrasound biomicroscopy and goniovideography, Glasser and Kaufman¹⁷ documented that both the lens equator and ciliary body moved away from the sclera during accommodation in monkeys. With the advent of more modern technology, such as optical coherence tomography (OCT), Scheimpflug imaging, and magnetic resonance imaging (MRI), researchers have been able to document in vivo dynamic changes in the lens and ciliary muscle during accommodation. For example, Baikoff et al¹⁸ used OCT to image increasing lens thickness and decreasing ciliary body diameter during accommodation in a 19-year-old albino patient. Strenk and colleagues¹⁹ have employed MRI to confirm that the ciliary muscle moves inward during accommodation. In another study, the lens diameter and surface area decreased with accommodation while the lens volume was constant on OCT, indicating that the lens was incompressible but the capsular bag elastic.²⁰ Such findings seem to support von Helmholtz’s understanding that the lens thickens and ciliary body diameter constricts during accommodation.

Goldberg and colleagues²¹ recently incorporated data from biometry, video ultrasound biomicroscopy, and endoscopy to design a Computer-Animated Model of Accommodation and Presbyopia (CAMA 2.0) that illustrates how the lens, ciliary muscle, and zonules interact during accommodation and disaccommodation. In this model, the anterior zonules and posterior zonules have reciprocal actions on the lens capsule. During ciliary muscle contraction, for example, the anterior zonules relax and lose tension, causing the lens to become rounder as they release tension on the anterior capsule. At the same time, the posterior zonules stretch and store energy for disaccommodation. Because the posterior zonules are attached to the elastic foundation in the Bruch’s membrane and choroid, they rebound back during ciliary muscle relaxation. The anterior zonules simultaneously increase their tension and pull on the lens in a reciprocal action during disaccommodation.21

Accommodation and Aging

Although presbyopia is due to a loss of accommodation in middle age, it is the result of a gradual process that begins in early childhood. On average, the accommodative amplitude declines -1.0 diopter (D) for every 4 years, falling to 6.0 D ± 2.0 D around the age of 40 years. Loss occurs at a faster rate of -1.5 D for every 4 years between the ages of 40 to 48 years, and then slows down to an average of -0.5 D decline every 4 years once one reaches 48 years old.²²

The reason for this natural decline in the amplitude of accommodation over time is not fully understood, but it is likely multifactorial. Histopathologic evidence of ciliary muscle atrophy and replacement of muscle with connective tissue over time originally led some to believe that presbyopia stems from ciliary muscle weakening.^23,24 However, such age-related tissue changes may be the result rather than etiology of presbyopia. Moreover, the decrease in accommodative amplitude begins in childhood, long before any atrophic changes occur in the ciliary muscle.²⁵ Well into the seventh decade of life, the ciliary muscle maintains a fairly constant contractile force as measured by impedance cyclography.²⁶ Recent MRI studies have failed to detect any significant relationship between age and the ability of the ciliary muscle to contract in humans.²⁷ This long-term constancy in ciliary muscle strength argues against a strong influence of the ciliary muscle in loss of accommodation, or presbyopia.

Rather, presbyopia is more commonly attributed to age-related changes in the lens. Throughout one’s life, the anterior lens epithelial cells act as progenitors that differentiate into elongated lens fibers layered around the lens nucleus like concentric rings in a tree. Studies using MRI and Scheimpflug photography have confirmed that the lens increases in its anterior-posterior diameter over time, while the unaccommodated adult diameter of the lens equator remains fairly constant around 9.0 mm.^27,28 The lens not only becomes thicker, but also stiffens and eventually opacifies into a cataract as the crystalline lens proteins undergo posttranslational changes from chronic oxidative damage.²⁹ Older lenses are markedly stiffer than younger lenses.³⁰ However, an interesting discovery is that the lens stiffness is not uniform within the lens itself over time. In young lenses, the stiffness gradient in the central lens nucleus appears to be lower than in the cortex. By around 40 years of age, the nucleus and cortex are equally firm, and after another 10 years, the lens nucleus becomes significantly stiffer than the cortex.^17,30

While this stiffening of the lens substance is likely the primary factor contributing to loss of accommodation over time, changes in the lens capsule may also contribute. Fincham¹² was the first to suggest that the lens capsule helped to maintain the shape of the lens. He noted that upon removal of the lens capsule, the lens material seemed to lose its shape. Von Helmholtz¹⁰ later suspected that presbyopia was due in part to loss of the elasticity of the lens capsule with age. Changes in the biomechanical properties of the lens capsule have been published and seem to corroborate this concept to an extent. For example, Krag and colleagues³¹ found that younger lens capsules are not only thinner but also stronger and more extensible, whereas older lens capsules are thicker, more brittle, and less extensible. In their study, changes in lens capsule elasticity notably started to decline beyond age 35. Thus, lens and lens capsule properties are likely the primary physiologic factors driving the loss of accommodation with age, which contributes to the onset of presbyopia.

Modern Visual Demands on Presbyopes

Because of the surge in digital and mobile device ownership, the average American is connected with a digital screen throughout the day for over 60 hours per week.³² Eighty-four percent of mobile technology owners use their devices as second screens while watching television at the same time.³³ Office work spaces are less likely to be cubicles with a desktop computer and a monitor on a desk. According to the Citrix Workplace of the Future report, by 2020, the average employee will access the company network from 6 different devices and one-third of employees will no longer work from a traditional office but rather at home, field sites, or alternate locations.³⁴ The tablet has changed the landscape of computing with exceptional portability. However, the ergonomics of tablets may be cumbersome. Tablets may be held at any angle for reading, but for typing, holding a tablet flat is bad for the neck and spine. Holding a tablet completely perpendicular is bad for the wrists. A compromise is to hold the tablet at a 30-degree angle when typing or using the touch screen.³⁵ Ergonomists suggest accessory keyboards be used for laptops and tablets to allow for better body positioning. This increases the working distance from the eye to the laptop screen and may elevate the height of the screen.

Smartphone ergonomists suggest holding the smart-phone at eye level, with font size, screen resolution, brightness, and browser setting enlarged for eye comfort held at arm’s length.³⁶ It has also been suggested that a smartphone be held while lying down, holding the phone over the face.³⁷ These recommendations may be more beneficial for posture, but they create significant problems with progressive spectacle lens wear. Traditional bifocals as well as progressive lenses require the eyes to drop down into the bottom of the spectacle lens to view the printed reading material. Computer glasses with blue blocker coatings or “office lenses” directly address this shortcoming, but patients may become frustrated with multiple pairs of glasses. These patients are more likely to pursue surgical correction.

In addition to postural problems, increased smart-phone usage can lead to increased ocular surface disease. In the Nielsen Total Audience Report of 2016, they found that the average American devoted more than 8 hours per day to screen time.38 Prolonged screen time can lead to a variety of symptoms including dry eyes, eye strain, headache, blurred vision, and neck and shoulder pain.³⁹ Reading reduces the overall blink rate, which is compounded by the eyes being open in primary rather than downward gaze. In addition to retinal damage reported with blue LED light exposure,⁴⁰ LED exposure has been found to increase ocular surface disease in mice.⁴¹ In a recent study by Lee and colleagues, LEDs of 630-, 525-, and 410-nm wavelengths were used to irradiate mice. Tear break-up time in the blue wavelength group was significantly decreased compared with the control and red wavelength groups. Increased corneal fluorescein staining scores, corneal levels of interleukin-1β and interleukin-6, reactive oxygen species production in the DCF-DA (dichlorofluorescin diacetate) assay, and inflammatory T cells in the flow cytometry were observed in the blue group compared with the other groups. The authors concluded that overexposure to blue light with short wavelengths can induce corneal oxidative damage and apoptosis, which may manifest as increased ocular surface inflammation and dry eye.⁴¹ In another study, increased smartphone usage and short duration of outdoor activity was strongly associated with pediatric dry eye disease. Moreover, symptoms improved when smartphone usage was reduced.⁴²

Increased ocular surface disease reduces the comfort of contact lens wear, a common vision correction method employed by middle-aged and older adults to avoid spectacles. Current presbyopic contact lens options are more successful than in years past. Modern contact lens materials often contain hydrogel and siloxane groups, and are termed SiHi lenses. While these materials allow greater oxygen transmission, are more hydrophobic, and stiffer than conventional hydrogel lenses, the material encourages lipid deposition, may suffer from poor wettability, and cause reduced comfort levels and mechanical complications.⁴³ While more patients are interested in presbyopic contact lens options, ocular surface disease limits wearing time and often results in contact lens drop out.⁴⁴ This also can result in an increased interest in surgical correction.

NONSURGICAL TREATMENT OF PRESBYOPIA

The nonsurgical management of presbyopia encompasses spectacles, contact lenses, and pharmacological agents. Selection of the appropriate therapy requires careful consideration of the patient’s goals for visual performance and desire for independence from glasses.

Spectacles

There are several options for optical correction of presbyopia with glasses. Single-vision spectacles for reading are a convenient first-line treatment option for patients who otherwise do not rely on glasses for distance vision. Patients who are emmetropic at distance can purchase relatively inexpensive, over-the-counter reading glasses that are a low plus power. Estimation of the appropriate dioptric power can be made by measuring the reading distance in meters and taking the reciprocal (eg, +3.0 D lenses correct for a 33-cm reading distance). Patients with additional refractive errors, such as hyperopia or astigmatism, can be prescribed a pair of reading glasses that adds the reading power to the sphere of their distance manifest refraction. Many myopic patients, on the other hand, may find it easier to read if they remove their distance glasses since their natural focal point is at near.

For patients who want to be able to focus at different focal lengths while wearing a single pair of glasses, there are several options (Figure 2-1). Traditional bifocal lenses preserve the top part of the lens for distance viewing and incorporate the reading segment into the lower part of the lens. Single-piece lenses are currently more common than fused bifocal lenses where the bifocal segment is fused into the convex part of the lens. Different shapes of reading segments may induce variable amounts of image jump or image displacement depending on the correction for distance. Image jump is caused by the prismatic power at the top of the bifocal segment and is worse if the optical center of the bifocal is near the bottom of the segment. Flat-top and executive reading segments minimize image jump because the optical center is near the top. Image displacement is caused by the combined prismatic effect of the distance lens and bifocal segment. This tends to be more problematic for patients than image jump. Round-top reading segments minimize image displacement for hyperopic patients who wear plus distance lenses but exacerbate image jump. Flat-top reading segments minimize image displacement and image jump for myopic patients who wear minus distance lenses.⁴⁵

Trifocal lenses have similar options for the shape of the reading segment but are composed of 3 sections: the large top section corrects for distance vision, a smaller middle segment corrects for intermediate distances, and the bottom segment for near vision (see Figure 2-1C). The trifocal add is usually half the bifocal add and allows a patient to focus at a distance that is approximately the length of the patient’s arm.⁴⁵

The progressive addition lens (PAL) provides clear vision for a range of distances via a narrow progressive corridor that smoothly transitions between the distance and near zones in the lens. One drawback of the PAL is that clear vision at the intermediate distance is attained within a narrow corridor (Figure 2-2). Patients may notice distortion in their peripheral vision from astigmatism.⁴⁵ While some patients may find it difficult to adapt to progressive lenses, many patients prefer this no-line alternative to the lined bifocal and trifocal lenses.⁴⁶ Selecting the appropriate lens style for new presbyopes may require trialing several different styles before the patient finds a corrective lens that is both comfortable and functional for his or her visual demands.

Most lens materials used in single-vision lenses are also available in bifocal platforms. High-index material is preferable for the patient whose lens power exceeds 3.0 D in magnitude. Also, any patient who is monocular or whose vocation or avocation involves shop-work should be prescribed polycarbonate lenses for eye protection.

Contact Lenses

For presbyopic patients who wish to wear contact lenses, several options are available. Presbyopic patients wearing contact lenses to correct for distance vision may wear single-vision reading glasses when performing near work. Since many presbyopes prefer to avoid spectacles altogether, other available options for near vision include monovision, bifocal, multifocal, and alternating vision contact lenses.

Monovision Contact Lenses

One common approach to increase the range of vision in patients with presbyopia is to prescribe monovision contact lenses. The nondominant eye is prescribed a contact lens that corrects for near vision, while the dominant eye is prescribed a contact lens that corrects for distance vision but leaves the patient with a small amount of residual myopia.⁴⁷ Patients can then have vision over a range of distances as long as adequate suppression of the more blurred image occurs. Interocular differences up to 1.5 D are usually well tolerated,^48–50 and binocular acuity typically matches that of the dominant eye. The depth of focus range for each eye should overlap, and patients may notice improved visual function during high lighting settings since constricted pupils will further enhance their depth of focus. If patients wish to further enhance their depth of focus, binocularity, and stereoacuity, one or both eyes can be fit with a bifocal or multifocal contact lens. To achieve extended or enhanced monovision, one eye is fit with a single-vision contact lens so that visual function is enhanced at the range most important to the patient, while the other eye is fit with a multi- or bifocal contact lens. For example, if the patient wishes to enhance vision at near, then the dominant eye is corrected for near and the other eye is provided a multi- or bifocal contact lens. Alternately, if the patient wishes to enhance vision at distance, the dominant eye is corrected for distance and the other eye is provided a multi- or bifocal contact lens. Intermediate distance can be improved by applying partial monovision, in which a weaker near add is prescribed in one eye. Modified monovision is another approach in which the dominant eye is center-distance and the nondominant eye is center-near using bi- or multifocal lenses. While a variety of monovision combinations exist to increase a patient’s range of vision, not all patients are able to adjust to monovision. Disturbance of stereopsis and spatial disorientation are particularly common for patients requiring adds that exceed +2.5 D.^50,51 This may place patients at a higher risk of tripping and falling.⁵² Other reported side effects include difficulty driving⁵³ and diminished contrast sensitivity.⁵¹ The reported success rate for monovision in presbyopes ranges from 60% to 80%.^48,49,55

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