Presbyopia

Presbyopia is a normal part of aging, with most people noticing progressive changes in their near vision after the age of 40, worsening until age 65. Common symptoms include decreased focusing ability for near objects, eye strain, and headache. Eye strain is the feeling of soreness and tiredness in the eyes. When reading or doing close-up work, those with presbyopia may compensate with reading at brighter lights and holding material at an arm's length. Those with presbyopia may also have difficulties transitioning between seeing at a near and far distance. These issues focusing can also result in squinting and drowsiness while doing close-up tasks. Presbyopia generally does not affect a person's ability to focus on distant objects. == Causes ==

The main risk factor for presbyopia is being older than 40. include individuals with hyperopia, or farsightedness, who may experience symptoms of presbyopia earlier than individuals with myopia, or nearsightedness. ==Mechanism==

As a person ages, their eyes' accommodation reflex, which is the visual reflex for focusing on objects near the eye, becomes less capable. The expected, maximum, and minimum amplitudes of accommodation in diopters (D) for a corrected patient of a given age can be estimated using Hofstetter's formulas: expected amplitude (D) = 18.5 − 0.3 × (age in years); maximum amplitude (D) = 25 − 0.4 × (age in years); minimum amplitude (D) = 15 − 0.25 × (age in years). The main theory behind this age-related loss of accommodation is the stiffening of the crystalline lens. The lens in the eye is responsible for about one-third of the eye's total refractive power, with the cornea being responsible for the other two-thirds of refraction. When ciliary muscles contract, it causes the attached zonular fibers to loosen and round the lens for near vision. The round state of the lens is what allows for near vision. However, the lens is able to adjust its refractive power through changing its shape. With age, the lens loses flexibility through progressive nuclear sclerosis, a process in which the insoluble crystallin proteins in the eye aggregate and cross-link, causing rigidity and stiffness. When the lens is overly stiff, it is overly resistant to ciliary muscle contraction, meaning the zonular fibers remain stretched and the lens remains focused for more distant vision. ==Diagnosis==

is a device that measures refraction in the eyes and determines the correction necessary for adequate near and far sight. It is a common part of the refractive eye exam needed for presbyopia diagnosis. A comprehensive dilated eye exam including a refraction assessment and an eye health exam is used to diagnose presbyopia. Someone with presbyopia would have a near point of accommodation, or point at which an eye can focus at a near distance, recessed beyond the usual reading distance. Latent hyperopia, or uncorrected farsightedness, may also cause difficulties in near vision, especially as excessive accommodation of the lens leads to strain and fatigue of the eye. Other eye conditions affecting near vision include macular and retinal diseases, disease of the optic nerve, glaucoma, posterior subscapular cataracts, and astigmatism. ==Treatment==

To treat presbyopia, different methods are used to compensate for the eyes' poor accommodation. Images captured by the eye are translated into electric signals that are transmitted to the brain where they are interpreted. Presbyopia can be addressed in two components of the visual system, either improving the capturing of images by the eyes, or (in principle) image processing in the brain. Eye treatments include corrective lenses, eye drops, and surgery. If an individual with presbyopia already has an existing prescription for nearsightedness, farsightedness, or astigmatism, other forms of corrective lens can be used. These include bifocals, which are lenses that has an individual's distance prescription for nearsightedness above the midline, and an individual's reading prescription for farsightedness or presbyopia below the midline. Contact lenses Contact lenses can also be used to correct the focusing loss that comes along with presbyopia. Similarly to bifocal eyeglasses, bifocal contact lenses can be used to provide distance and near vision correction. Each bifocal contact lens is weighted on the bottom to keep the distance and near vision in alignment with the movement of the eye. Some people choose contact lenses to correct one eye for near and one eye for far with a method called monovision. Pilocarpine binds to muscarinic receptors in the eye, the pupillary sphincter muscle contracts and causes pupil constriction in the eye. Pupil constriction allows for an increase in focusing depth in the eyes and for an improvement in adaptability of the eyes to near vision, which drives the effectiveness of pilocarpine as a treatment for presbyopia. However, the effects of pilocarpine only last around 6-10 hours, with potential side effects of headache, brow discomfort, and diminished night vision. UNR844, a lipoic acid choline ester intended to restore lens elasticity, is also being investigated for efficacy. Phentolamine, a drug that induces vasodilation in the eye and causes pupil constriction without engaging the ciliary muscle to prevent retinal traction, is also being investigated. Compounds of carbachol and brimonidine as well as aceclidine and brimonidine also show promise in effectiveness and safety for presbyopia treatment. Concerns with refractive surgeries for presbyopia include people's eyes changing with time. Other side effects of multifocal corneal ablation include postoperative glare, halos, ghost images, and monocular diplopia. Conductive keratoplasty is a surgical treatment that does not use lasers. Instead, it uses radiofrequency radiation to increase the curvature of the central cornea to improve refractive power of the cornea. == Epidemiology ==

As of 2015, the prevalence of presbyopia was at 24.9%, or 1.8 billion people globally. While age is by definition the largest factor affecting prevalence of presbyopia, other factors have been seen to be associated with the condition. A greater prevalence of presbyopia has been seen in urban populations at 25-80%, while the prevalence of presbyopia in rural population varies between 25-67%. However, living in a rural area was associated with higher prevalence of uncorrected visual impairment. Women over 40 years old had a higher prevalence of presbyopia than men over 40 years old, hypothesized to be a result of differences in tasks performed and viewing distances rather than a physiological sex difference. ==Etymology==

The term presbyopia derives from and (GEN ). ==History==

The condition was mentioned as early as the writings of Aristotle in the 4th century BC. == See also ==