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. 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 Hofstetters 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). Diagnosis
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: image capturing by the optical system of the eye and image processing in the brain.
Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long sight in the UK), it affects many adults over the age of 40. A common sign of presbyopia is difficulty reading small print which results in having to hold reading material farther away. Other symptoms associated can be headaches and eyestrain. Different people will have different degrees of problems. Other types of refractive errors may exist at the same time as presbyopia. This condition is similar to hypermetropia or far-sightedness which starts in childhood and exhibits similar symptoms of blur in the vision for close objects. Presbyopia is a typical part of the aging process. It occurs due to age related changes in the lens (decreased elasticity and increased hardness) and ciliary muscle (decreased strength and ability to move the lens), causing the eye to focus right behind rather than on the retina when looking at close objects. It is a type of refractive error along with nearsightedness, farsightedness, and astigmatism. Diagnosis is by an eye examination.Presbyopia can be corrected using glasses, contact lenses, multifocal intraocular lenses, or LASIK (presbyLASIK) surgery. The most common treatment is glass correction using appropriate convex lens. Glasses used to correct presbyopia may be simple reading glasses, bifocals, trifocals, or progressive lens.People over 40 are at risk for developing presbyopia and all people become affected to some degree.