Short sighted
The corrective lenses have a negative optical power (i.e. These work by reducing the blur circle formed on the retina, but their adverse effects on peripheral vision, contrast and brightness make them unsuitable in most situations. For people with a high degree of myopia, very strong eyeglass prescriptions are needed to correct the focus error.Orthokeratology is the practice of using special rigid contact lenses to flatten the cornea to reduce myopia. With myopia, the eyeball is too long, or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye.
The opposite defect of myopia is hyperopia or farsightedness or long-sightedness —this is where the cornea is too flat or the eye is too short. Mainstream eye care professionals most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. Occasionally, pinhole glasses are used by patients with low-level myopia.
Myopia (Greek: μυωπία, muōpia, nearsightedness ), also called nearsightedness or shortsightedness, is a refractive defect of the eye in which collimated light produces image focus in front of the retina when accommodation is relaxed. Those with myopia see nearby objects clearly but distant objects appear blurred. Jensen believes that this indicates myopia and IQ are pleiotropically related as they are caused or influenced by the same genes.
This prismatic distortion is visible to the wearer as color fringes around strongly contrasting colors. However, strong eyeglass prescriptions have a negative side effect in that off-axis viewing of objects away from the center of the lens results in prismatic movement and separation of colors, known as chromatic aberration.
A 1997 review of this biofeedback research concluded that controlled studies to validate such methods .. No specific mechanism that could cause a relationship between myopia and IQ has yet been identified. Also other personal characteristics, as value systems, school achievements, time spent in reading for pleasure, language abilities and time spent in sport activities correlated to the occurrence of myopia in studies. Because in the most common, simple myopia, the eye length is too long, any etiologic explanation must account for such axial elongation.
However, the efficacy of these practices is disputed by scientists and eye care practitioners. In the 1980s and 1990s, there was a flurry of interest in biofeedback as a possible treatment for myopia. Australian researchers had concluded that exposure to daylight appeared to play a critical role in restricting the growth of the eyeball, which is responsible for myopia or short-sightedness. Various methods have been employed in an attempt to decrease the progression of myopia. The terms myopia and myopic (or the common terms short sightedness or short sighted) have also been used metaphorically to refer to cognitive thinking and decision making that is narrow sighted or lacking in concern for wider interests or longer-term consequences. eyelid: inflammation (Stye, Chalazion, Blepharitis) · Entropion · Ectropion · Lagophthalmos · Blepharochalasis · Ptosis · Blepharophimosis · Xanthelasma · eyelash (Trichiasis, Madarosis) lacrimal system: Dacryoadenitis · Epiphora · Dacryocystitis · Xerophthalmia orbit: Exophthalmos · Enophthalmos Paralytic strabismus: Ophthalmoparesis · Progressive external ophthalmoplegia · Palsy (III, IV, VI) · Kearns-Sayre syndrome Other strabismus: Esotropia/Exotropia · Hypertropia · Heterophoria (Esophoria, Exophoria) · Brown s syndrome · Duane syndrome Other binocular: Conjugate gaze palsy · Convergence insufficiency · Internuclear ophthalmoplegia · One and a half syndrome .
have been rare and contradictory. There is no universally accepted method of preventing myopia. The relationship also holds within families, and siblings with a higher degree of refraction error average higher IQs than siblings with less refraction error.
To date, no single theory has been able to satisfactorily explain this elongation. In the mid-1900s, mainstream ophthalmologists and optometrists believed myopia to be primarily hereditary; the influence of near work in its development seemed incidental and the increased prevalence of the condition with increasing age was viewed as a statistical curiosity . Among mainstream researchers and eye care professionals, myopia is now thought to be a combination of genetic and environmental factors. There are currently two basic mechanisms believed to cause myopia: form deprivation (also known as pattern deprivation Many people with myopia are able to read comfortably without eyeglasses even in advanced age. The fringes move around as the wearer s gaze through the lenses changes, and the prismatic shifting reverses on either side, above, and below the exact center of the lenses.
Myopes considering refractive surgery are advised that this may be a disadvantage after the age of 40 when the eyes become presbyopic and lose their ability to accommodate or change focus. A diagnosis of myopia is typically confirmed during an eye examination by an ophthalmologist, optometrist or orthoptist. are concave) which compensates for the excessive positive diopters of the myopic eye. Myopia has been classified in various manners. Borish and Duke-Elder classified myopia by cause: Various forms of myopia have been described by their clinical appearance: Myopia, which is measured in diopters by the strength or optical power of a corrective lens that focuses distant images on the retina, has also been classified by degree or severity: Myopia is sometimes classified by the age of onset: The global prevalence of refractive errors has been estimated from 800 million to 2.3 billion. In some areas, such as China, India and Malaysia, up to 41% of the adult population is myopic to -1dpt, A recent study involving first-year undergraduate students in the United Kingdom found that 50% of British whites and 53.4% of British Asians were myopic. In Australia, the overall prevalence of myopia (worse than −0.50 diopters) has been estimated to be 17%. In Brazil, a 2005 study estimated that 6.4% of Brazilians between the ages of 12 and 59 had −1.00 diopter of myopia or more, compared with 2.7% of the indigenous people in northwestern Brazil. In Greece, the prevalence of myopia among 15 to 18 year old students was found to be 36.8%. In India, the prevalence of myopia in the general population has been reported to be only 6.9%. A recent review found that 26.6% of Western Europeans aged 40 or over have at least −1.00 diopters of myopia and 4.6% have at least −5.00 diopters. In the United States, the prevalence of myopia has been estimated at 20%. A study of Jordanian adults aged 17 to 40 found that over half (53.7%) were myopic. The prevalence of myopia has been reported as high as 70–90% in some Asian countries, 30–40% in Europe and the United States, and 10–20% in Africa. Myopia is less common in African people and associated diaspora. A number of studies have shown that the incidence of myopia increases with level of education and many studies have shown a relationship between myopia and IQ. According to Arthur Jensen, myopes average 7–8 IQ points higher than non-myopes.
Many myopia treatment studies suffer from any of a number of design drawbacks: small numbers, lack of adequate control group, failure to mask examiners from knowledge of treatments used, etc. Pirenzepine eyedrops had a limited effect on retarding myopic progression in a recent, placebo-control, double-blinded prospective controlled study. Daylight may prevent myopia. Color fringing can make accurate drawing and painting difficult for users of strong eyeglass prescriptions. Strongly nearsighted wearers of contact lenses do not experience chromatic aberration because the lens moves with the cornea and always stays centered in the middle of the wearer s gaze. Practitioners and advocates of alternative therapies often recommend eye exercises and relaxation techniques such as the Bates method.
Frequently an autorefractor or retinoscope is used to give an initial objective assessment of the refractive status of each eye, then a phoropter is used to subjectively refine the patient s eyeglass prescription. Eyeglasses, contact lenses, and refractive surgery are the primary options to treat the visual symptoms of those with myopia. It may also be corrected by refractive surgery, such as LASIK.
