Refractive errors

Short-sightedness (myopia)

There are several classifications. According to the strength of the prescription, myopia is commonly described as low, below -3.00 dioptres, moderate, from -3.00 to -6.00 dioptres, or high, above -6.00 dioptres.

Another distinction is between school-age, usually lower, myopia and high degenerative myopia. High degenerative myopia is associated with excessive elongation of the eyeball and may be accompanied by changes at the back of the eye that require monitoring.

Typical symptoms are blurred distance vision and clearer near vision. Assessment includes measurement of visual acuity, cycloplegic refraction using eye drops to temporarily relax focusing, and automated keratorefractometry. Depending on the degree of myopia and the findings of the examination, correction may involve glasses, contact lenses or laser vision correction such as PRK or LASIK.

Long-sightedness (hypermetropia)

Long-sightedness is a refractive error in which, without accommodation, parallel light rays entering the eye would focus behind the macula. Accommodation is the eye's reflex ability to keep objects at different distances clear by changing the shape and focusing power of the natural lens.

Long-sightedness may occur because the eye is anatomically shorter in relation to its focusing power, because the cornea and lens bend light less strongly, because accommodation is reduced, because of certain medicines, or in conditions where the natural lens is absent.

Symptoms may include eye strain, frontal headaches and blurred near vision. Diagnosis includes measurement of visual acuity, cycloplegic refraction and keratorefractometry. Depending on the degree of long-sightedness and the clinical findings, correction may involve glasses, contact lenses or laser vision correction, most often a LASIK procedure.

Presbyopia

Presbyopia is the natural, age-related reduction in accommodation. It causes difficulty focusing on nearby objects, makes reading harder and leads people to hold text farther away in order to see it clearly. The reduction in accommodation begins earlier in life but usually becomes noticeable at about the age of forty-five. Presbyopia may be corrected with glasses or contact lenses, while selected patients may discuss surgical options such as the Supracor procedure after a full assessment.