Pharmacological Strategies for Treating Presbyopia

Abstract and Introduction

Abstract

Purpose of Review: Presbyopia is the normal progressive loss of accommodation, which leads to the inability to focus clearly on objects located at different distances. Some of the accepted methods for treating this condition are glasses, contact lenses, and surgery. Pharmacological treatments are a new and promising noninvasive option for dealing with presbyopia. The aim of this review is to provide an update on some recent advances in this field.

Recent Findings: Currently, there are three different strategies for the pharmacological treatment of presbyopia. The first one aims to produce miosis and increase depth of focus through a pinhole effect, therefore improving uncorrected near visual acuity. The second one tries to restore the elasticity the lens has lost due to aging. Finally, the third strategy is based on rehabilitating accommodation; which is to say, in a binocular way, allowing for good vision at all distances.

Summary: Pharmacological treatments are a new alternative that expands the diversity of existing strategies for treating presbyopia. These treatments are based on the instillation of eyedrops with different compositions, which vary according to the different strategies. Many of these developments will most likely be on the market in the next few years. If the process of patient selection is done properly, any one of these three strategies can be used successfully.

Introduction

The term presbyopia, which means 'old eye', comes from the Greeks: 'presbys ', meaning old man and, 'oops ', meaning eye. It is a refractive condition in which the amplitude range of accommodation becomes too narrow to focus clearly on objects located at different distances. It appears in patients between 45 and 50 years. Although the inability to focus on objects is a phenomenon that appears suddenly, loss of accommodation is a slow and progressive process that begins many years before, in childhood.

Despite our greater technological advances, many aspects of accommodation, and how it varies with age, are far from being understood and are yet to be revealed. However, Von Helmoltz's accommodation theory, stated more than a century ago, is still the most accurate description of this phenomenon. According to Von Helmoltz, during the accommodation that takes place when the eye is focusing on objects that are near, the contraction of the ciliary muscle causes a centripetal movement (inwards, toward the center of the eye), as well as an anterior movement (toward the cornea) of ciliary muscle mass. This causes an increase in the thickness of the lens, as well as a reduction of its diameter. The anterior and posterior curvature intensify, which in turn leads to the power of the crystalline lens to increase.^[1] The active movement is mediated by the contraction of both the ciliary muscle and the sphincter of the iris, due to the stimulation of the parasympathetic cholinergic muscarinic receptors, causing the activation of the accommodation center.^[2] Meanwhile, the passive movement of the lens is then accompanied by the contraction of the iris sphincter, as well as the convergence of both eyes.

In a world where life expectancy is growing and birth rates are dropping, it is estimated that the average age of the population in 2050 will be 36 years old, very close to the onset of presbyopia.^[3] We are undergoing the Fourth Industrial Revolution: this means that an older, vital, active, and presbyopic working population will become even more screen dependent. Presbyopia treatment is, therefore, one of the challenges of the 21^st century.

During the 20^th century, we saw an unprecedented expansion of new options for treating presbyopia. Nonsurgical optical methods are still dominated by corrections through prescription lenses, such as reading spectacles, as well as bifocal, trifocal, or progressive spectacles, which offer quality vision in most circumstances. There are many surgical options, including corneal refractive surgery, intracorneal inlay, implantation of phakic and/or pseudophakic intraocular lens as monofocal, extended depth of focus, and multifocal.^[4] It should be noted that these options are not suitable for all patients, and that each technique has its own limitations.

In the last decade, a new approach for treating presbyopia has emerged: pharmacological treatments, which are topical, noninvasive, reversible, and do not require prosthetic devices. Within the realm of pharmacological treatments, there are currently three different branches. Although they may seem similar at first glance, they arise from different concepts. The first one aims to produce miosis and increase the depth of focus through a pinhole effect, therefore improving uncorrected near visual acuity (UNVA). The second one tries to restore the elasticity the lens has lost due to aging. Finally, the third strategy is based on rehabilitating accommodation; which is to say, in a binocular way, allowing good vision at all distances.^[5] This article reviews the pharmacological treatments that are available for treating presbyopia, in order to provide recent advances for an 'old' problem in this field, which is constantly growing.