Presbyopia

Presbyopia

Small print ingredients list

The small print in an ingredients list is hard to read in patients with presbyopia.
Classification and external resources
Specialty Ophthalmology
ICD-10 H52.4
ICD-9-CM 367.4
DiseasesDB 29647
MedlinePlus 001026
eMedicine article/1219573
MeSH D011305

Presbyopia (from Greek presbys (πρέσβυς) = old man + ops (ὤψ) = see like, sight > meaning literally trying to see as old men do[1]) is a condition associated with aging in which the eye exhibits a progressively diminished ability to focus on near objects. Presbyopia’s exact mechanisms are not fully understood; 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.

The first signs of presbyopia – eyestrain, difficulty seeing in dim light, problems focusing on small objects and 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 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 x (age in years), Maximum amplitude (D) = 25 - 0.4 x (age in years), Minimum amplitude (D) = 15 - 0.25 x (age in years).[2]

Signs and symptoms

Presbyopia

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.[3]

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.[4] 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.[5] In particular, farmers and homemakers seek correction later, whereas service workers and construction workers seek eyesight correction earlier. Scuba divers with interest in underwater photography may notice presbyopic changes while diving before they recognize the symptoms in their normal routines due to the near focus in low light conditions.[6]

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, so candidates for this procedure can determine if they are prepared to have their corneas reshaped by surgery to cause this effect permanently.

Monovision does not work well for spectacles, since the user will not always look through the optical centres of the lenses, causing double images. That problem is not present with contacts or laser surgery.[7]

Mechanism

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.

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,[8] 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 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.

Treatment

In the visual system, images captured by the eye are translated into electric signals that are transmitted to the brain where they are interpreted. As such, in order to overcome presbyopia, two main components of the visual system can be addressed: 1) the optical system of the eye or 2) the visual processing of the brain.

  1. Image capturing in the eye - Solutions for presbyopia have advanced significantly in recent years, thanks to widened availability of optometry care as well as over-the-counter vision correction.
  2. Image processing in the brain - Scientific solutions for overcoming the symptoms of presbyopia were developed in recent years and tested successfully in multiple studies. These solutions are available thanks to significant progress in the understanding of the human brain plasticity and the field of perceptual learning.[9]

Corrective lenses

Corrective lenses provide a range of vision correction, some as high as +4.0 diopter. Some with presbyopia choose varifocal or bifocal lenses to eliminate the need for a separate pair of reading glasses; specialized preparations of varifocals or bifocals usually require the services of an optometrist. Some newer bifocal or varifocal spectacle lenses attempt to correct both near and far vision with the same lens.[10]

Contact lenses can also be used to correct the focusing loss that comes along with presbyopia. Multifocal contact lenses can be used to correct vision for both the near and the far. Some people choose contact lenses to correct one eye for near and one eye for far with a method called monovision.

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. 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]

Surgical procedures for the correction of presbyopia without reshaping the cornea, using scleral band expansion (SBE) were proposed by Scharcker and Lin, using a laser scleral ablation in US Pat # 6,258,082 (2001). These procedures are different from PresbyLasik, and claim to create the true increase of accommodation of the eye by increasing the space between the ciliary body and lens. SBEs have not been found to provide predictable or consistent results in the treatment of presbyopia.[13]

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 nondominant 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 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 one eye is out of focus.[14][15][16]

Surgically implanted corneal inlays are another treatment option for presbyopia. Corneal inlays typically are implanted in the nondominant eye to minimize impact to binocular uncorrected distance vision.[17] 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.[18]

See also

References

  1. ↑ "Presbyopia". Dictionary.reference.com. Retrieved 2013-04-19.
  2. ↑ Robert P. Rutstein, Kent M. Daum, Anomalies of Binocular Vision: Diagnosis & Management, Mosby, 1998.
  3. ↑ Robert Abel, The Eye Care Revolution: Prevent and Reverse Common Vision Problems, Kensington Books, 2004.
  4. ↑ "Presbyopia: Patient Information". Marquette, Michigan, USA: Eye Associates of Marquette. 2008. Retrieved 2010-10-31.
  5. ↑ 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 Española de Oftalmología 77 (11): 597–604. ISSN 0365-6691. PMID 12410405.
  6. ↑ Bennett QM (June 2008). "New thoughts on the correction of presbyopia for divers". Diving Hyperb Med 38 (2): 163–4. PMID 22692711. Retrieved 2013-04-19.
  7. ↑ Specsavers: Monovision in glasses, On 25 April 2013 by Simon Kay
  8. ↑ Gregory, Richard Langton (1977). Eye and brain : the psychology of seeing. (3rd ed. rev. and update. ed.). New York ; Toronto: McGraw-Hill. ISBN 0070246653.
  9. ↑ Polat, U., Schor, C., Tong, J., Zomet, A., Lev, M., Yehezkel, O., Sterkin, A., & Levi, D.M. (2012). Training the brain to overcome the effect of aging on the human eye. Scientific Reports 2, Article number: 278. doi:10.1038/srep00278
  10. ↑ 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.
  11. ↑ http://www.technolaspv.com
  12. ↑ "LASIK and Presbyopia". Medical Management Services Group, The. Retrieved 2010-10-31.
  13. ↑ 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.
  14. ↑ 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
  15. ↑ 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]
  16. ↑ Reinstein DZ, Archer TJ, Gobbe M. Outcomes of Presbyopic Micro-Monovision LASIK for Myopia, Hyperopia and Emmetropia. ESCRS. Berlin, 2008
  17. ↑ Chang, Clark. "Novel Approaches to Treating Presbyopia" Review of Cornea & Contact Lenses. September 2011
  18. ↑ Dalton, Michelle. "Intracorneal Inlays Showing Positive Outcomes" EyeWorld. June 2011

External links

Look up presbyopia in Wiktionary, the free dictionary.
Look up presbyopia in Wiktionary, the free dictionary.
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