can anyone give me information on eye on the give topics - defects of vision, remedial measures, precautions?

The issue of learning disorders, including dyslexia, has become a matter of increasing personal and public concern. Inability to read and comprehend is a major obstacle to learning and may have far-reaching social and economic implications. Concern for the welfare of children with dyslexia and learning disabilities has lead to a proliferation of diagnostic and remedial treatment procedures, many of which are controversial. This policy statement addresses these issues, which are of importance to affected individuals, their families, teachers, doctors, allied health personnel, and society.

A broad-based consensus of educators, psychologists, and medical specialists has recommended that individuals with dyslexia or related learning disabilities should receive 1) early comprehensive educational, psychological, and medical assessment; and 2) educational remediation combined with appropriate psychological and medical treatment.

Although it is obvious some children do not read well because they have trouble seeing, research has shown that the majority of children and adults with reading difficulties experience a variety of language defects that stem from complex, altered brain morphology and function, and that the reading difficulty is not due to altered visual function per se.

However, in spite of these facts, a certain number of children who experience reading difficulty may also experience a treatable visual difficulty in addition to their learning dysfunction. Doctors can identify the majority of those who have reduced visual acuity. However, in a small percentage of children, a visual abnormality such as farsightedness may not be detected during pediatric office screening procedures. Therefore, doctors who evaluate children for reading difficulties should consider referral to an ophthalmologist familiar with children's eye problems.

In their position statement on learning disabilities, dyslexia, and vision, the AAP, AAO, and AAPOS concluded the following:

Those considered to be at risk for learning disabilities, dyslexia or attention defects, should be thoroughly assessed by both educational and psychological specialists.

Learning disabilities, including dyslexia and other forms of reading or academic under-achievement, require a multidisciplinary approach to diagnosis and treatment, involving educators, psychologists, and physicians. Research has established that the basis of dyslexia and other specific learning disabilities is within the central nervous system and is multi-factorial and complex.

Unfortunately, however, it has become common practice among some to attribute reading difficulties to one or more subtle ocular or visual abnormalities. Although the eyes are obviously necessary for vision, the brain interprets visual symbols. Therefore, correcting subtle visual defects cannot alter the brain's processing of visual stimuli. Children with dyslexia or related learning disabilities have the same ocular health statistically, as children without such conditions. There is no peripheral eye defect that produces dyslexia or other learning disabilities and there is no eye treatment that can cure dyslexia or associated learning disabilities.

Ocular defects should be identified as early as possible and when correctable, managed by the ophthalmologist. If no ocular defect is found, the child should be referred to a primary care physician to coordinate required multidisciplinary care.

Eye defects, subtle or severe, do not cause reversal of letters, words, or numbers. No scientific evidence supports claims that the academic abilities of dyslexic or learning disabled children can be improved with treatment based on a) visual training, including muscle exercises, ocular pursuit, tracking exercises, or “training” glasses (with or without bifocals or prisms); b) neurological organizational training (laterality training, crawling, balance board, perceptual training), or c) tinted or colored lenses. Some controversial methods of treatment result in a false sense of security that may delay or even prevent proper instruction of remediation. The expense of these methods is unwarranted, and they cannot be substituted for appropriate remedial educational measures. Claims of improved reading and learning after visual training, neurological organization training, or use of tinted or colored lenses, are typically based upon poorly controlled studies that rely on anecdotal information or testimony. These studies are frequently carried out in combination with traditional educational remedial techniques.

Since remediation may be more effective during the early years, early diagnosis is paramount. The educator ultimately plays the key role in providing help for the learning disabled or dyslexic child or adult.

In a review on the applicability and effectiveness of eye exercises, Rawstron et al (2005) noted that eye exercises have been purported to improve a wide range of conditions such as vergence problems, ocular motility disorders, accommodative dysfunction, amblyopia, learning disabilities, dyslexia, asthenopia, myopia, motion sickness, sports performance, stereopsis, visual field defects, visual acuity, and general well-being. Small controlled studies as well as a large number of case reports support the treatment of convergence insufficiency. Less robust, but believable, evidence indicates visual training may be useful in developing fine stereoscopic skills and improving visual field remnants following traumatic brain injury. As yet, there is no clear scientific evidence published in the mainstream literature supporting the use of eye exercises in the remainder of the areas reviewed, and their use therefore remains controversial.

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Most people believe that once they are diagnosed with some vision problem and start wearing eye glasses or contact lenses to correct them, they will have to do so for life in order to see better. Those who want a permanent solution to improve eyesight typically resort to Lasik or other corrective eye surgeries. But you you can also improve your vision without surgery and can see perfectly well without using eyeglasses or contact lenses. You can check here to know how https://tr.im/73ed3

I think I can help you.So if you want my advice I would say you have to eat lots and lots of vegetables cos they have lot of vitamins in it and dont forget to eat carrot.

Usually eye defects are caused by watching television.Make sure that you adjust the brightness and contrast number properly.Try to lower them and stay away it at a distance of 7 meters.

Use a dark coloured wallpaper in your desktop cos they will absorb radiations.Wear a low powered specs cos it will reduce your eye to focus at different levels.Wash your eye gently at different intervals.

Please see the web pages for more details on Human eye, Eye examination, Visual acuity, Colour vision, Colour blindness, Myopia (Nearsightedness), Corneal surgery, Hyperopia (Farsightedness), Amblyopia, Strabismus, Eye muscle repair, Sixth nerve palsy and Laser-Assisted In Situ Keratomileusis (LASIK) eye surgery.

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Please consult some good eye specialist for full details.

Myopia, also called nearsightedness, 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 typically can see nearby objects clearly but distant objects appear blurred. 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 ophthalmologists and optometrists most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery, such as LASIK. The corrective lenses have a negative dioptric value (i.e. are concave) which compensates for the excessive positive diopters of the myopic eye. In some cases, pinhole glasses are used by patients with low-level myopia. These work by reducing the blur circle formed on the retina.

Hyperopia, also known as hypermetropia or colloquially as farsightedness , is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or when the lens cannot become round enough), causing inability to focus on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance. As an object moves towards the eye, the eye must increase its power to keep the image on the retina. If the power of the cornea and lens is insufficient, as in hyperopia, the image will appear blurred.

Hyperopia, and restoring of vision with convex lensPeople with hyperopia can experience blurred vision, asthenopia, accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus.[1]

Hyperopia is often confused with presbyopia [2][3], another condition that frequently causes blurry near vision. [4] Presbyopes who report good far vision typically experience blurry near vision because of a reduced accommodative amplitude brought about by natural aging changes with the crystalline lens.[4] It is also sometimes referred to as farsightedness, since in otherwise normally-sighted persons it makes it more difficult to focus on near objects than on far objects.[5]

Presbyopia (Greek word "presbyteros" (πρεσβύτερος), meaning "elder") is the eye's diminished ability to focus that occurs with aging. The most widely held theory is that it arises from the 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.

Presbyopia is not a disease as such, but a condition that affects everyone at a certain age. The first symptoms are usually noticed between the ages of 40-50, though in fact the ability to focus declines throughout life, from an accommodation of about 20 dioptres (ability to focus at 50 mm away) in a young person to 10 dioptres at 25 and levelling off at 0.5 to 1 dioptre at age 60 (ability to focus down to 1 -2 metres only). For those with good distance vision, it may start with difficulty reading fine print, particularly if the lighting is poor, or with eyestrain when reading for long periods. Many advanced presbyopes complain that their arms have become "too short" to hold reading material at a comfortable distance.[1]

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.

Presbyopia, like other focus defects, becomes much less noticeable in bright sunlight. This is not the result of any mysterious 'healing effect' but just the consequence of the iris closing to a pinhole, so that depth of focus, regardless of actual ability to focus, is greatly enhanced, as in a pinhole camera which produces images without any lens at all. Another way of putting this is to say that the circle of confusion, or blurredness of image, is reduced, without improving focusing.

A delayed onset of seeking correction for presbyopia has been found among those with certain professions and those with miotic pupils.[2] In particular, farmers and housewives seek correction later, whereas service workers and construction workers seek eyesight correction earlier

In optics, astigmatism is when an optical system has different foci for rays that propagate in two perpendicular planes. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances.

Contents [hide]

1 Forms of astigmatism

1.1 Third-order astigmatism

1.2 Astigmatism in systems that are not rotationally symmetric

1.2.1 Ophthalmic astigmatism

1.2.2 Astigmatism due to misaligned or malformed lenses and mirrors

1.2.3 Deliberate astigmatism in optical systems

2 References

[edit] Forms of astigmatism

There are two distinct forms of astigmatism. The first is a third-order aberration, which occurs for objects (or parts of objects) away from the optical axis. This form of aberration occurs even when the optical system is perfectly symmetrical. This is often referred to as a "monochromatic aberration", because it occurs even for light of a single wavelength. This terminology may be misleading, however, as the amount of aberration can vary strongly with wavelength in an optical system.

The second form of astigmatism occurs when the optical system is not symmetric about the optical axis. This may be by design (as in the case of a cylindrical lens), or due to manufacturing error in the surfaces of the components or misalignment of the components. In this case, astigmatism is observed even for rays from on-axis object points. This form of astigmatism is extremely important in ophthalmology, since the human eye often exhibits this aberration due to imperfections in the shape of the cornea or the lens.

[edit] Third-order astigmatism

Page explaining and illustrating astigmatism[1]In the analysis of this form of astigmatism, it is most common to consider rays from a given point on the object, which propagate in two special planes. The first plane is the tangential plane. This is the plane which includes both the object point being considered and the axis of symmetry. Rays that propagate in this plane are called tangential rays. Planes that include the optical axis are meridional planes. It is common to simplify problems in radially-symmetric optical systems by choosing object points in the vertical ("y") plane only. This plane is then sometimes referred to as the meridional plane.

The second special plane is the sagittal plane. This is defined as the plane, orthogonal to the tangential plane, which contains the object point being considered and intersects the optical axis at the entrance pupil of the optical system. This plane contains the chief ray, but does not contain the optic axis. It is therefore a skew plane, in other words not a meridional plane. Rays propagating in this plane are called sagittal rays.

In third-order astigmatism, the sagittal and transverse rays form foci at different distances along the optic axis. These foci are called the sagittal focus and the transverse focus, respectively. In the presence of astigmatism, an off-axis point on the object is not sharply imaged by the optical system. Instead, sharp lines are formed at the sagittal and transverse foci. The image at the transverse focus is a short line, oriented in the direction of the sagittal plane; images of circles centered on the optic axis, or lines tangential to such circles, will be sharp in this plane. The image at the sagittal focus is a short line, oriented in the tangential direction; images of spokes radiating from the center are sharp at this focus. In between these two foci, a round but "blurry" image is formed. This is called the medial focus or circle of least confusion. This plane often represents the best compromise image location in a system with astigmatism.

The amount of aberration due to astigmatism is proportional to the square of the angle between the rays from the object and the optical axis of the system. With care, an optical system can be designed to reduce or eliminate astigmatism. Such systems are called anastigmats.

This section is a stub. You can help by expanding it.

[edit] Astigmatism in systems that are not rotationally symmetric

Blur from astigmatic lens at different distances.If an optical system is not axisymmetric, either due to an error in the shape of the optical surfaces or due to misalignment of the components, astigmatism can occur even for on-axis object points. This effect is often used deliberately in complex optical systems, especially certain types of telescope.

In the analysis of these systems, it is common to consider tangential rays (as defined above), and rays in a meridional plane (a plane containing the optic axis) perpendicular to the tangential plane. This plane is called either the sagittal meridional plane or, confusingly, just the sagittal plane.

[edit] Ophthalmic astigmatism

Main article: Astigmatism (eye)

In ophthalmology, the vertical and horizontal planes are identified as tangential and sagittal meridians, respectively. Ophthalmic astigmatism is a refraction error of the eye in which there is a difference in degree of refraction in different meridians. It is typically characterized by an aspherical, non-figure of revolution cornea in which the corneal profile slope and refractive power in one meridian is greater than that of the perpendicular axis.

Astigmatism causes difficulties in seeing fine detail. In some cases vertical lines and objects such as walls may appear to the patient to be leaning over like the Tower of Pisa. Astigmatism can be often corrected by glasses with a lens that has different radii of curvature in different planes (a cylindrical lens), contact lenses, or refractive surgery.

Astigmatism is quite common. Studies have shown that about one in three people suffer from it [1][2][3]. The prevalence of astigmatism increases with age [4]. Although a person may not notice mild astigmatism, higher amounts of astigmatism may cause blurry vision, squinting, asthenopia, fatigue, or headaches [5] [6] [7].

There are a number of tests used by ophthalmologists and optometrists during eye examinations to determine the presence of astigmatism and to quantify the amount and axis of the astigmatism[8]. A Snellen chart or other eye chart may initially reveal reduced visual acuity. A keratometer may be used to measure the curvature of the steepest and flattest meridians in the cornea's front surface[9]. A corneal topographer may also be used to obtain a more accurate representation of the cornea's shape [10]. An autorefractor or retinoscopy may provide an objective estimate of the eye's refractive error and the use of Jackson cross cylinders in a phoropter may be used to subjectively refine those measurements[11] [12] [13]. An alternative technique with the phoropter requires the use of a "clock dial" or "sunburst" chart to determine the astigmatic axis and power[14][15].

[edit] Astigmatism due to misaligned or malformed lenses and mirrors

Grinding and polishing of precision optical parts, either by hand or machine, typically employs significant downward pressure, which in turn creates significant frictional side pressures during polishing strokes that can combine to locally flex and distort the parts. These distortions generally do not possess figure-of-revolution symmetry and are thus astigmatic, and slowly become permanently polished into the surface if the problems causing the distortion are not corrected. Astigmatic, distorted surfaces potentially introduce serious degradations in optical system performance.

Surface distortion due to grinding or polishing increases with the aspect ratio of the part (diameter to thickness ratio). To a first order, glass strength increases as the cube of the thickness. Thick lenses at 4:1 to 6:1 aspect ratios will flex much less than high aspect ratio parts, such as optical windows, which can have aspect ratios of 15:1 or higher. The combination of surface or wavefront error precision requirements and part aspect ratio drives the degree of back support uniformity required, especially during the higher down pressures and side forces during polishing. Optical working typically involves a degree of randomness that helps greatly in preserving figure-of-revolution surfaces, provided the part is not flexing during the grind/polish process.

[edit] Deliberate astigmatism in optical systems

Compact disc players use an astigmatic lens for focusing. When one axis is more in focus than the other, dot-like features on the disc project to oval shapes. The orientation of the oval indicates which axis is more in focus, and thus which direction the lens needs to move. A square arrangement of only four sensors can observe this bias and use it to bring the read lens to best focus, without being fooled by oblong pits or other features on the disc surface.

Some telescopes use deliberately astigmatic optics.

Cataract

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For other uses, see Cataract (disambiguation).

Cataract

Classification & external resources

Magnified view of cataract in human eye, seen on examination with a slit lamp using diffuse illumination

ICD-10 H25.-H26., H28., Q12.0

ICD-9 366

DiseasesDB 2179

MedlinePlus 001001

Human eye cross-sectional view, showing position of human lens. Courtesy NIH National Eye Institute

Human eye cross-sectional view, showing position of human lens. Courtesy NIH National Eye InstituteA cataract is an opacity that develops in the crystalline lens of the eye or in its envelope. Early on in the development of senile cataract the power of the crystalline lens may be increased, causing myopia, and the gradual yellowing and opacification of the lens may reduce the perception of blue colours. Cataracts typically progress slowly to cause vision loss and are potentially blinding if untreated.[1] Moreover, with time the cataract cortex liquefies to form a milky white fluid in a Morgagnian Cataract, and can cause severe inflammation if the lens capsule ruptures and leaks. Untreated, the cataract can cause phacomorphic glaucoma. Very advanced cataracts with weak zonules are liable to dislocation anteriorly or posteriorly. Such spontaneous posterior dislocations (akin to the earliest surgical procedure of couching) in ancient times were regarded as a blessing from the heavens, because it restored some perception of light in the bilaterally affected patients.

Cataract derives from the Latin cataracta meaning "waterfall" and the Greek kataraktes and katarrhaktes, from katarassein meaning "to dash down" (kata-, "down"; arassein, "to strike, dash"[2]). As rapidly running water turns white, the term may later have been used metaphorically to describe the similar appearance of mature ocular opacities. In Latin, cataracta had the alternate meaning, "portcullis"[3], so it is also possible that the name came about through the sense of "obstruction".

Contents [hide]

1 Causes

2 Epidemiology

3 Cataract surgery

4 Prevention

5 Recent research

6 Types of cataracts

7 Associations with systemic conditions

8 References

9 See also

10 External links

[edit] Causes

Normal vision. Courtesy National Institutes of Health, USA (NIH).

Hazy view as seen by a person with a cataract, Courtesy NIHCataracts develop from a variety of reasons, including long-term ultraviolet exposure, secondary effects of diseases such as diabetes, or simply due to advanced age; they are usually a result of denaturation of lens proteins. Genetic factors are often a cause of congenital cataracts and positive family history may also play a role in predisposing someone to cataracts at an earlier age, a phenomenon of "anticipation" in pre-senile cataracts. Cataracts may also be produced by eye injury or physical trauma. A study among Icelandair pilots showed commercial airline pilots as three times more likely to develop cataracts than people with non-flying jobs. This is thought to be caused by excessive exposure to radiation coming from outer space.[4] Cataracts are also unusually common in persons exposed to infrared radiation, such as glassblowers who suffer from "exfoliation syndrome". Exposure to microwave radiation can cause cataracts.

Cataracts may be partial or complete, stationary or progressive, hard or soft.

Some drugs can induce cataract development:

Corticosteroids[5]

Ezetimibe

There are various types of cataracts, e.g. nuclear, cortical, mature, hypermature. Cataracts are also classified by their location, e.g. posterior (classically due to steroid use[5][6]) and anterior (common (senile) cataract related to aging).

[edit] Epidemiology

Cataracts are the leading cause of blindness in the world.[7]

In the United States, age-related lenticular changes have been reported in 42% of those between the ages of 52 to 64[8], 60% of those between the ages 65 and 74[9], and 91% of those between the ages of 75 and 85[8].

[edit] Cataract surgery

Main article: Cataract surgery

Cataract surgery, using a temporal approach phacoemulsification probe (in right hand) and "chopper" (in left hand) being done under operating microscope at a Navy medical centerThe most effective and common treatment is to surgically remove the cloudy lens. There are two types of surgery that can be used to remove cataracts, extra-capsular (extracapsular cataract extraction, or ECCE) and intra-capsular surgery (intracapsular cataract extraction, or ICCE). Extra-capsular surgery consists of removing the lens but leaving the majority of the lens capsule intact. High frequency sound waves (phacoemulsification) are sometimes used to break up the lens before extraction. Intra-capsular surgery involves removing the entire lens of the eye, including the lens capsule, but it is rarely performed in modern practice. In either extra-capsular surgery or intra-capsular surgery, the cataractous lens is removed and replaced with a plastic lens (an intraocular lens implant) which stays in the eye permanently.

Cataract operations are usually performed using a local anaesthetic and the patient is allowed to go home the same day. Recent improvements in intraocular technology now allow cataract patients to choose a multifocal lens to create a visual environment in which they are less dependent on glasses. Under some medical systems multifocal lenses cost extra. Traditional intraocular lenses are monofocal.

Complications after cataract surgery, including posterior capsular opacification and retinal detachment, are possible.

In ICCE there is the issue of the Jack in the box phenomenon where the patient has to wear aphakic glasses - alternatives include contact lenses but these can prove to be high maintenance, particularly in dusty areas.

[edit] Prevention

Although cataracts have no scientifically proven prevention, it is sometimes said that wearing ultraviolet-protecting sunglasses may slow the development of cataracts.[citation needed] Regular intake of antioxidants (such as vitamin C and E) is theoretically helpful, but this is also not proven. Bilberry extract shows promise in a rat model.[10]

[edit] Recent research

Although statins are known for their ability to lower lipids, they are also believed to have antioxidant qualities. It is believed that oxidative stress plays a role in the development of nuclear cataracts, which are the most common type of age-related cataract. To explore the relationship between nuclear cataracts and statin use, a group of researchers took a group of 1299 patients who were at risk of developing nuclear cataracts and gave some of them statins. Their results suggest that statin use in a general population may be associated with a lower risk of developing nuclear cataract disease. [11]

[edit] Types of cataracts

Bilateral cataracts in an infant due to Congenital rubella syndrome, courtesy CDCThe following is a classification of the various types of cataracts. This is not comprehensive and other unusual types may be noted.

Classified by etiology

Age-related cataract

Immature Senile Cataract (IMSC) - partially opaque lens, disc view hazy

Mature Senile Cataract (MSC) - Completely opaque lens, no disc view

Hypermature Senile Cataract (HMSC) - Liquefied cortical matter: Morgagnian Cataract

Congenital cataract

Sutural cataract

Lamellar cataract

Zonular cataract

Total cataract

Secondary cataract

Slit lamp photo of Anterior capsular opacification visible few months after implantation of Intraocular lens in eye, magnified viewDrug-induced cataract (e.g. Corticosteroids)

Traumatic cataract

Blunt trauma (capsule usually intact)

Penetrating trauma (capsular rupture & leakage of lens material - calls for an emergency surgery for extraction of lens and leaked material to minimise further damage)

Classified by location of opacity within lens structure (However, mixed morphology is quite commonly seen, e.g. PSC with nuclear changes & cortical spokes of cataract)

Anterior cortical cataract

Anterior polar cataract

Anterior subcapsular cataract

Slit lamp photo of Posterior capsular opacification visible few months after implantation of Intraocular lens in eye, seen on retroilluminationNuclear cataract - Grading correlates with hardness & difficulty of surgical removal

1 - Grey

2 - Yellow

3 - Amber

4 - Brown/Black (Note: "Black cataract" translated in some languages (like Hindi) refers to Glaucoma, not the color of the lens nucleus)

Posterior cortical cataract

Posterior polar cataract (importance lies in higher risk of complication - posterior capuslar tears during surgery)

Posterior subcapsular cataract (PSC) (clinically common)

After-cataract - posterior capsular opacification subsequent to a successful extracapsular cataract surgery (usually within 3 months - 2 years) with or without IOL implantation. Requires a quick & painless office procedure with Nd:YAG laser capsulotomy to restore optical clarity