Presbyopia
Encyclopedia
Presbyopia is a condition where the eye
exhibits a progressively diminished ability to focus on near objects with age. Presbyopia’s exact mechanisms are not known with certainty; the research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens’s curvature from continual growth and loss of power of the ciliary muscle
s (the muscles that bend and straighten the lens) have also been postulated as its cause.
Like gray hair and wrinkles, presbyopia is a symptom caused by the natural course of aging. The first signs of presbyopia – eyestrain, difficulty seeing in dim light, problems focusing on small objects and/or fine print – are usually first noticed between the ages of 40 and 50. The ability to focus on near objects declines throughout life, from an accommodation
of about 20 dioptre
s (ability to focus at 50 mm away) in a child, to 10 dioptres at age 25 (100 mm), and levels off at 0.5 to 1 dioptre at age 60 (ability to focus down to 1–2 meters only). The expected maximum and minimum amplitudes of accommodation for a corrected patient of a given age can be determined using Hofstetter's formulas: Expected amplitude (D) = 18.5 - 0.3 x (age in years), Maximum amplitude (D) = 25 - 0.4 x (age in years), Minimum amplitude (D) = 15 - 0.25 x (age in years).
The word presbyopia comes from the Greek word presbys (πρέσβυς), meaning "old man" or "elder", and the Neolatin suffix -opia, meaning "sightedness", giving rise to the laymen's definition often seen in consumer articles or medical glossaries, "old eyes".
when reading for long periods, blur at near or momentarily blurred vision when transitioning between viewing distances. Many extreme presbyopes complain that their arms have become "too short" to hold reading material at a comfortable distance.
Presbyopia symptoms, like other focus defects, become much less noticeable in bright sunlight due to the action of the iris closing to a smaller diameter. As with any lens, increasing the focal ratio
of the lens increases depth of field by reducing the level of blur of out-of-focus objects (compare the effect of aperture on depth of field
in photography
).
A delayed onset of seeking correction for presbyopia has been found among those with certain professions and those with miotic pupil
s. In particular, farmers and homemakers seek correction later, whereas service workers and construction workers seek eyesight correction earlier.
, the closest point at which an object can be brought into focus by the eye is called the eye's near point. A standard near point distance of 25 cm is typically assumed in the design of optical instruments, and in characterizing optical devices such as magnifying glass
es.
Without correction, the near point is at 3 inches (7 cm) at age 10, to 6 inches (16 cm) at age 40, to 39 inches (1 meter) at age 60. As a result, a 60-year-old must use corrective lenses to read books or magazines at a comfortable distance.
There is some confusion in articles and even textbooks over how the focusing mechanism of the eye actually works. In the classic book, 'Eye and Brain' by Gregory, for example, the lens is said to be suspended by a membrane, the 'zonula', which holds it under tension. The tension is released, by contraction of the ciliary muscle, to allow the lens to become more round, for close vision. This implies that the ciliary muscle, which is outside the zonula must be circumferential, contracting like a sphincter, to slacken the tension of the zonula pulling outwards on the lens. This is consistent with the fact that our eyes seem to be in the 'relaxed' state when focusing at infinity, and also explains why no amount of effort seems to enable a myopic person to see farther away. Many texts, though, describe the 'ciliary muscles' (which seem more likely to be just elastic ligaments and not under any form of nervous control) as pulling the lens taut in order to focus at close range. This has the counter-intuitive effect of steepening the lens valve cytokinesis centrally (increasing its power) and flattening peripherally.
(near-sightedness) can read comfortably without eyeglasses or contact lenses even after age 40. However, their myopia does not disappear and the long-distance visual challenges remain. Myopes considering refractive surgery
are advised that surgically correcting their nearsightedness may be a disadvantage after age 40, when the eyes become presbyopic and lose their ability to accommodate
or change focus because they will then need to use glasses for reading. Myopes with astigmatism
find near vision better, though not perfect, without glasses or contact lenses when presbyopia sets in, but the more astigmatism the poorer their uncorrected near vision.
A surgical technique offered is to create a "reading eye" and a "distance vision eye", a technique commonly used in contact lens practice, known as monovision. Monovision can be created with contact lenses or spectacles so that candidates for this procedure can determine if they are prepared to have their corneas reshaped by surgery to cause this effect permanently.
Contact lenses can also been used to correct the focusing loss that comes along with presbyopia. Some people choose contact lenses to correct one eye for near and one eye for far with a method called monovision, which can interfere with depth perception due to loss of focusing ability in the other eye. There are also newer bifocal or multifocal contact lenses that attempt to correct both near and far vision with the same lens.
es (IOLs). Scleral expansion bands, which increase the space between the ciliary body and lens, have not been found to provide predictable or consistent results in the treatment of presbyopia.
INTRACOR has now been approved in Europe for treatment of both eyes (turning both corneas into multifocal lenses and so dispensing with the need for reading glasses).
Surgical treatments that reshape the cornea, such as PresbyLASIK
and Conductive Keratoplasty
, are also worth consideration, but some use of reading glasses will still remain when light is poor or when reading for extended periods of time, since such procedures do nothing for crystalline lens deterioration.
Another treatment option for the correction of presbyopia in patients with emmetropia as well as in patients with myopia, hyperopia and astigmatism is Laser Blended Vision
. This procedure uses laser refractive surgery to correct the dominant eye mainly for distance vision and the non-dominant eye mainly for near vision, while the depth of field (i.e. the range of distances at which the image is in focus) of each eye is increased. As a result of the increased depth of field, the brain merges the two images, creating a blend zone, i.e. a zone which is in focus for both eyes. This allows the patient to see near, intermediate and far without glasses. Some literature also suggests that the benefits achieved include the brain learning to adapt; assimilating two images, one of which is out of focus. Over time, many patients report they are unaware that one eye is out of focus.
Surgically implanted corneal inlays are another treatment option for presbyopia. Corneal inlays typically are implanted in the non-dominant eye to minimize impact to binocular uncorrected distance vision. They seek to improve near vision in one of three ways: The Flexivue Microlens
(Presbia) changes the central refractive index
, the Kamra (AcuFocus) increases the depth of focus through the use of a pinhole, and the Vue+ (Revision Optics) reshapes the central cornea.
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
exhibits a progressively diminished ability to focus on near objects with age. Presbyopia’s exact mechanisms are not known with certainty; the research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens’s curvature from continual growth and loss of power of the ciliary muscle
Ciliary muscle
The ciliary muscle is a ring of striated smooth muscle in the eye's middle layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humour into Schlemm's canal. It changes the shape of the lens within the eye not the size of the pupil which is...
s (the muscles that bend and straighten the lens) have also been postulated as its cause.
Like gray hair and wrinkles, presbyopia is a symptom caused by the natural course of aging. The first signs of presbyopia – eyestrain, difficulty seeing in dim light, problems focusing on small objects and/or fine print – are usually first noticed between the ages of 40 and 50. The ability to focus on near objects declines throughout life, from an accommodation
Accommodation (eye)
Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image on an object as its distance changes....
of about 20 dioptre
Dioptre
A dioptre, or diopter, is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres . It is thus a unit of reciprocal length. For example, a 3-dioptre lens brings parallel rays of light to focus at metre...
s (ability to focus at 50 mm away) in a child, to 10 dioptres at age 25 (100 mm), and levels off at 0.5 to 1 dioptre at age 60 (ability to focus down to 1–2 meters only). The expected maximum and minimum amplitudes of accommodation for a corrected patient of a given age can be determined using Hofstetter's formulas: Expected amplitude (D) = 18.5 - 0.3 x (age in years), Maximum amplitude (D) = 25 - 0.4 x (age in years), Minimum amplitude (D) = 15 - 0.25 x (age in years).
The word presbyopia comes from the Greek word presbys (πρέσβυς), meaning "old man" or "elder", and the Neolatin suffix -opia, meaning "sightedness", giving rise to the laymen's definition often seen in consumer articles or medical glossaries, "old eyes".
Symptoms
The first symptoms most people notice are difficulty reading fine print, particularly in low light conditions, eyestrainAsthenopia
Asthenopia or eye strain is an ophthalmological condition that manifests itself through nonspecific symptoms such as fatigue, pain in or around the eyes, blurred vision, headache and occasional double vision...
when reading for long periods, blur at near or momentarily blurred vision when transitioning between viewing distances. Many extreme presbyopes complain that their arms have become "too short" to hold reading material at a comfortable distance.
Presbyopia symptoms, like other focus defects, become much less noticeable in bright sunlight due to the action of the iris closing to a smaller diameter. As with any lens, increasing the focal ratio
F-number
In optics, the f-number of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter...
of the lens increases depth of field by reducing the level of blur of out-of-focus objects (compare the effect of aperture on depth of field
Depth of field
In optics, particularly as it relates to film and photography, depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image...
in photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
).
A delayed onset of seeking correction for presbyopia has been found among those with certain professions and those with miotic pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
s. In particular, farmers and homemakers seek correction later, whereas service workers and construction workers seek eyesight correction earlier.
Focusing mechanism of the eye
In opticsOptics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
, the closest point at which an object can be brought into focus by the eye is called the eye's near point. A standard near point distance of 25 cm is typically assumed in the design of optical instruments, and in characterizing optical devices such as magnifying glass
Magnifying glass
A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle ....
es.
Without correction, the near point is at 3 inches (7 cm) at age 10, to 6 inches (16 cm) at age 40, to 39 inches (1 meter) at age 60. As a result, a 60-year-old must use corrective lenses to read books or magazines at a comfortable distance.
There is some confusion in articles and even textbooks over how the focusing mechanism of the eye actually works. In the classic book, 'Eye and Brain' by Gregory, for example, the lens is said to be suspended by a membrane, the 'zonula', which holds it under tension. The tension is released, by contraction of the ciliary muscle, to allow the lens to become more round, for close vision. This implies that the ciliary muscle, which is outside the zonula must be circumferential, contracting like a sphincter, to slacken the tension of the zonula pulling outwards on the lens. This is consistent with the fact that our eyes seem to be in the 'relaxed' state when focusing at infinity, and also explains why no amount of effort seems to enable a myopic person to see farther away. Many texts, though, describe the 'ciliary muscles' (which seem more likely to be just elastic ligaments and not under any form of nervous control) as pulling the lens taut in order to focus at close range. This has the counter-intuitive effect of steepening the lens valve cytokinesis centrally (increasing its power) and flattening peripherally.
Interaction with myopia
Many people with myopiaMyopia
Myopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...
(near-sightedness) can read comfortably without eyeglasses or contact lenses even after age 40. However, their myopia does not disappear and the long-distance visual challenges remain. Myopes considering refractive surgery
Refractive surgery
Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea or cataract surgery. The most common methods today use excimer lasers to...
are advised that surgically correcting their nearsightedness may be a disadvantage after age 40, when the eyes become presbyopic and lose their ability to accommodate
Accommodation (eye)
Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image on an object as its distance changes....
or change focus because they will then need to use glasses for reading. Myopes with astigmatism
Astigmatism (eye)
Astigmatism is an optical defect in which vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina. This may be due to an irregular or toric curvature of the cornea or lens. There are two types of astigmatism: regular and...
find near vision better, though not perfect, without glasses or contact lenses when presbyopia sets in, but the more astigmatism the poorer their uncorrected near vision.
A surgical technique offered is to create a "reading eye" and a "distance vision eye", a technique commonly used in contact lens practice, known as monovision. Monovision can be created with contact lenses or spectacles so that candidates for this procedure can determine if they are prepared to have their corneas reshaped by surgery to cause this effect permanently.
Treatment
Treatment for presbyopia has advanced significantly in recent years, thanks to widened availability of Optometry care as well as over-the-counter vision correction.Corrective lenses
Corrective lenses provide a range of vision correction, some as high as +4.0 diopter. Some with presbyopia choose bifocal lenses to eliminate the need for a separate pair of reading glasses; while specialized bifocal preparations usually require the services of an optometrist.Contact lenses can also been used to correct the focusing loss that comes along with presbyopia. Some people choose contact lenses to correct one eye for near and one eye for far with a method called monovision, which can interfere with depth perception due to loss of focusing ability in the other eye. There are also newer bifocal or multifocal contact lenses that attempt to correct both near and far vision with the same lens.
Exercises
Controversially, eye exercises have been touted as a way to delay the onset of presbyopia, but their effectiveness has not been demonstrated in medical research.Surgery
New surgical procedures may also provide solutions for those who do not want to wear glasses or contacts, including the implantation of accommodative intraocular lensIntraocular lens
An intraocular lens is an implanted lens in the eye, usually replacing the existing crystalline lens because it has been clouded over by a cataract, or as a form of refractive surgery to change the eye's optical power. It usually consists of a small plastic lens with plastic side struts, called...
es (IOLs). Scleral expansion bands, which increase the space between the ciliary body and lens, have not been found to provide predictable or consistent results in the treatment of presbyopia.
INTRACOR has now been approved in Europe for treatment of both eyes (turning both corneas into multifocal lenses and so dispensing with the need for reading glasses).
Surgical treatments that reshape the cornea, such as PresbyLASIK
PresbyLASIK
PresbyLASIK is a surgical technique for presbyopic visual correction using Excimer LASER ablation.PresbyLASIK treatment uses the principles of LASIK surgery to create a multifocal corneal surface aimed at reducing near vision spectacle dependence in presbyopic patients...
and Conductive Keratoplasty
Conductive keratoplasty
Conductive keratoplasty is a type of refractive surgery that uses radio waves to adjust the contour of the cornea by shrinking the corneal collagen around it. It is used to treat mild to moderate hyperopia. It is a non-invasive alternative to other types of eye surgery....
, are also worth consideration, but some use of reading glasses will still remain when light is poor or when reading for extended periods of time, since such procedures do nothing for crystalline lens deterioration.
Another treatment option for the correction of presbyopia in patients with emmetropia as well as in patients with myopia, hyperopia and astigmatism is Laser Blended Vision
Laser blended vision
Laser blended vision, is a sophisticated laser eye treatment which rectifies short-sightedness in one eye and long-sightedness in the other eye...
. This procedure uses laser refractive surgery to correct the dominant eye mainly for distance vision and the non-dominant eye mainly for near vision, while the depth of field (i.e. the range of distances at which the image is in focus) of each eye is increased. As a result of the increased depth of field, the brain merges the two images, creating a blend zone, i.e. a zone which is in focus for both eyes. This allows the patient to see near, intermediate and far without glasses. Some literature also suggests that the benefits achieved include the brain learning to adapt; assimilating two images, one of which is out of focus. Over time, many patients report they are unaware that one eye is out of focus.
Surgically implanted corneal inlays are another treatment option for presbyopia. Corneal inlays typically are implanted in the non-dominant eye to minimize impact to binocular uncorrected distance vision. They seek to improve near vision in one of three ways: The Flexivue Microlens
Flexivue Microlens
The Flexivue Microlens, a corneal inlay treatment for presbyopia, is 3-mm in diameter and about 15 microns thick. The lens is placed about 280-300 microns deep in the cornea of the patient's non-dominant eye through a pocket created using a femtosecond laser. The specific vision-correcting...
(Presbia) changes the central refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
, the Kamra (AcuFocus) increases the depth of focus through the use of a pinhole, and the Vue+ (Revision Optics) reshapes the central cornea.
See also
- Adjustable-focus eyeglassesAdjustable-focus eyeglassesAdjustable focus eyeglasses are prescription eyeglasses with an adjustable focal length. They compensate for refractive errors by providing variable focusing, allowing users to adjust them for desired distance or prescription, or both....
- Astigmatism (eye)Astigmatism (eye)Astigmatism is an optical defect in which vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina. This may be due to an irregular or toric curvature of the cornea or lens. There are two types of astigmatism: regular and...
- Conductive KeratoplastyConductive keratoplastyConductive keratoplasty is a type of refractive surgery that uses radio waves to adjust the contour of the cornea by shrinking the corneal collagen around it. It is used to treat mild to moderate hyperopia. It is a non-invasive alternative to other types of eye surgery....
- Corrective lensCorrective lensA corrective lens is a lens worn in front of the eye, mainly used to treat myopia, hyperopia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye...
- Eye examinationEye examinationAn eye examination is a battery of tests performed by an ophthalmologist, optometrist, or orthoptist assessing vision and ability to focus on and discern objects, as well as other tests and examinations pertaining to the eyes....
- Eyeglass prescriptionEyeglass prescriptionAn eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist or ophthalmologist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient.If an examination indicates that...
, especially the section on Distant vision and near vision. - HyperopiaHyperopiaHyperopia, also known as farsightedness, longsightedness or hypermetropia, is a defect of vision caused by an imperfection in the eye , causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance...
- Laser Blended VisionLaser blended visionLaser blended vision, is a sophisticated laser eye treatment which rectifies short-sightedness in one eye and long-sightedness in the other eye...
- Lens (optics)Lens (optics)A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
- MyopiaMyopiaMyopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...
- OphthalmologyOphthalmologyOphthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
- OpticianOpticianAn optician is a person who is trained to fill prescriptions for eye correction in the field of medicine, also known as a dispensing optician or optician, dispensing...
- OptometryOptometryOptometry is a health care profession concerned with eyes and related structures, as well as vision, visual systems, and vision information processing in humans. Optometrists, or Doctors of Optometry, are state licensed medical professionals trained to prescribe and fit lenses to improve vision,...
- Orthoptics
- PresbyLASIKPresbyLASIKPresbyLASIK is a surgical technique for presbyopic visual correction using Excimer LASER ablation.PresbyLASIK treatment uses the principles of LASIK surgery to create a multifocal corneal surface aimed at reducing near vision spectacle dependence in presbyopic patients...
- Bates methodBates MethodThe Bates method is an alternative therapy aimed at improving eyesight. Eye-care physician William Horatio Bates attributed nearly all sight problems to habitual strain of the eyes, and felt that glasses were harmful and never necessary...
External links
- Presbyopia
- Vision Over 40
- Presbyopia at MedLinePlus Medical Encyclopedia
- Binocular Presbyopia Diagnosis with Dynamic Stimulation Aberrometry—Chart with exercise proposed to reverse presbyopia.