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.
Resolution within 7–10 days is the norm. Individuals with persistent (chronic) erythema multiforme will often have a lesion form at an injury site, e.g. a minor scratch or abrasion, within a week. Irritation or even pressure from clothing will cause the erythema sore to continue to expand along its margins for weeks or months, long after the original sore at the center heals. Causes
Many suspected etiologic factors have been reported to cause EM. Infections: bacterial (including Bacillus Calmette–Guérin (BCG) vaccination, haemolytic Streptococci, legionellosis, leprosy, Neisseria meningitidis, Mycobacterium, Pneumococcus, Salmonella species, Staphylococcus species, Mycoplasma pneumoniae), chlamydial. Fungal (Coccidioides immitis)
Parasitic (Trichomonas species, Toxoplasma gondii), 
Viral (especially Herpes simplex)
Drug reactions, most commonly to: antibiotics (including, sulphonamides, penicillin), anticonvulsants (phenytoin, barbiturates), aspirin, modafinil, antituberculoids, and allopurinol and many others. Physical factors: radiotherapy, cold, sunlight
Others: collagen diseases, vasculitides, non-Hodgkin lymphoma, leukaemia, multiple myeloma, myeloid metaplasia, polycythemiaEM minor is regarded as being triggered by HSV in almost all cases. A herpetic etiology also accounts for 55% of cases of EM major. Among the other infections, Mycoplasma infection appears to be a common cause. Herpes simplex virus suppression and even prophylaxis (with acyclovir) has been shown to prevent recurrent erythema multiforme eruption. Treatment
Erythema multiforme is frequently self-limiting and requires no treatment. The appropriateness of glucocorticoid therapy can be uncertain, because it is difficult to determine if the course will be a resolving one. See also
Erythema multiforme major
Erythema multiforme minor
Toxic epidermal necrolysis
Stevens–Johnson syndrome

References


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