Presbyopia

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 muscles (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 dioptres (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).^[1]

The word presbyopia comes from the Greek word presbys (πρέσβυς), meaning "old man" or "elder", and the Neolatin suffix -opia, meaning "sightedness",^[2] giving rise to the laymen's definition often seen in consumer articles or medical glossaries, "old eyes".^[3]

Symptoms

The first symptoms most people notice are difficulty reading fine print, particularly in low light conditions, eyestrain 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.^[4]

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.^[5] 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 pupils.^[6] In particular, farmers and homemakers seek correction later, whereas service workers and construction workers seek eyesight correction earlier.

Focusing mechanism of the eye

Main article: Accommodation (eye)‎

In optics, 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 glasses.

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.^[7]

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.^{[citation needed]} 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 myopia (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.

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

The increased average age of the U.S. population and the lengthening of expected life span in the U.S. has given rise to an entire segment of the medical industry devoted to the needs of those over 40.^{[citation needed]} Nowhere is this more evident than in the wide and ready availability of inexpensive over-the-counter reading glasses with corrective lenses that cover a wide gamut of magnification levels. In addition to the availability of "vision centers" in many malls and shopping centers that provide walk-in Optometric care and rapid turnaround preparation of glasses, many large book sellers and most stores with a pharmacy section carry a selection of over-the-counter eye glasses with magnification lenses that provide a wide range of vision correction, some as high as +3.0 diopter. The internet provides those seeking even higher ranges of magnification lenses with sites that sell reading glasses of +4.0 diopter or higher. 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, some places and sites that sell over-the-counter reading glasses also sell bifocals (often a neutral lens with a magnification lens inset in the traditional bifocal position).

Contact lenses have 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.^[8]

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.^[9]

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 lenses (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.^[10] INTRACOR^[11] 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.^[12]

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. ^[13][14][15]

See also

• Adjustable-focus eyeglasses
• Astigmatism (eye)
• Conductive Keratoplasty
• Corrective lens
• Eye examination
• Eyeglass prescription, especially the section on Distant vision and near vision.
• Hyperopia
• Laser Blended Vision
• Lens (optics)
• Myopia
• Ophthalmology
• Optician
• Optometry
• Orthoptics
• PresbyLASIK
• Bates method

References

1. ^ Robert P. Rutstein, Kent M. Daum, Anomalies of Binocular Vision: Diagnosis & Management, Mosby, 1998.
2. ^ "presbyopia - Merriam-Webster Online Dictionary". Merriam-Webster.com. http://www.merriam-webster.com/dictionary/presbyopia. Retrieved 2009-04-03. 
3. ^ "presbyopia - definition of presbyopia in the Medical dictionary - by the Free Online Medical Dictionary, Thesaurus, and Encyclopedia". Farlex.com. http://medical-dictionary.thefreedictionary.com/presbyopia. Retrieved 2010-10-31. 
4. ^ Robert Abel, The Eye Care Revolution: Prevent and Reverse Common Vision Problems, Kensington Books, 2004.
5. ^ "Presbyopia: Patient Information". Marquette, Michigan, USA: Eye Associates of Marquette. 2008. http://www.marquetteeye.com/patientinfo/presbyopia.html. Retrieved 2010-10-31. 
6. ^ García Serrano, JL; López Raya, R; Mylonopoulos Caripidis, T (Nov 2002). "Variables related to the first presbyopia correction" (Free full text). Archivos de la Sociedad Espanola de Oftalmologia 77 (11): 597–604. ISSN 0365-6691. PMID 12410405. http://www.oftalmo.com/seo/2002/11nov02/03.htm. 
7. ^ "Sensory Reception Human Vision Structure and Function of the Eye" Encyolpaedia Britannica 1987
8. ^ Li, G; Mathine, DL; Valley, P; Ayräs, P; Haddock, JN; Giridhar, MS; Williby, G; Schwiegerling, J et al. (Apr 2006). "Switchable electro-optic diffractive lens with high efficiency for ophthalmic applications" (Free full text). Proceedings of the National Academy of Sciences of the United States of America 103 (16): 6100–4. doi:10.1073/pnas.0600850103. ISSN 0027-8424. PMC 1458838. PMID 16597675. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=16597675. 
9. ^ The lowdown on eye exercises, Harvard Medical School Family Health Guide http://www.health.harvard.edu/fhg/updates/update0903c.shtml
10. ^ Malecaze, FJ; Gazagne, CS; Tarroux, MC; Gorrand, JM (Dec 2001). "Scleral expansion bands for presbyopia". Ophthalmology 108 (12): 2165–71. doi:10.1016/S0161-6420(01)00591-7. ISSN 0161-6420. PMID 11733253. 
11. ^ www.technolaspv.com
12. ^ "LASIK and Presbyopia". Medical Management Services Group, The. http://www.seewithlasik.com/docs/lasik-presbyopia.shtml. Retrieved 2010-10-31. 
13. ^ Reinstein DZ, Couch DG, Archer TJ. LASIK for Hyperopic Astigmatism and Presbyopia Using Micro-monovision With the Carl Zeiss Meditec MEL80. J Refract Surg. 2009;25:37-58
14. ^ Reinstein DZ, Archer TJ, Gobbe M. LASIK for the correction of myopic astigmatism and presbyopia using aspheric ablation profiles and a micro-monovision protocol with the Carl Zeiss Meditec MEL80. J Refract Surg. [In Press]
15. ^ Reinstein DZ, Archer TJ, Gobbe M. Outcomes of Presbyopic Micro-Monovision LASIK for Myopia, Hyperopia and Emmetropia. ESCRS. Berlin, 2008

External links

• Presbyopia
• Vision Over 40
• Presbyopia at MedLinePlus Medical Encyclopedia
• Binocular Presbyopia Diagnosis with Dynamic Stimulation Aberrometry
• Ray Gottlieb, O.D., Ph.D. "Presbyopia Reduction" (PDF). http://www.i-see.org/gottlieb/presbyopia_chart.pdf. Retrieved 5 July 2009. —Chart with exercise proposed to reverse presbyopia.