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Refractive errors in human eye : 

Refractive errors in human eye Made by: Shubham deshpande Kartik Lokhande Chirag Sanghvi Shubham Dosi

The errors of refraction: : 

The errors of refraction: The normal eye: The refractive components of the eye include the cornea, the crystalline lens (shown in white) and the vitreous gel (behind the crystalline lens). The combined refraction of these elements is thus that rays of light reflected off objects in the front of the eye are focused on the retina (the fovea centralis).

Hypermetropia or hyperopia : 

Hypermetropia or hyperopia What is it ? Also called far-sightedness, or far-sighted and hyperopia. Rays of light relected off objects in front of the eye are focused behind the retina as shown above. Such persons can see well in the distance provided they are young and the refractive error is not large. This error of refraction is corrected by a "+" (convex) lens.

Why does it occur? : 

Why does it occur? It was at one time accepted that in the majority of cases hypermetropia was axial, that is the length of the eyeball is shorter than it should be. But this is not always true, the corneal may be flatter than it should be. Hypermetropia actually forms a stage in normal development of the eyes. At birth practically all eyes are hypermetropic to the extent of 2.5 to 3.0 Diopters and as the growth of the body proceeds, the length of the eye increases until adolescence is passed, the eye should theoretically be "normal" in size and refraction.

What is presbyopia? : 

What is presbyopia? It is another form of hyperopia which affects individuals after or near 40 years of age. This is because age related loss of "accommodation" due to decreased elasticity of the crystalline lens surface (capsule). Persons with presbyopia have difficulty in reading/writing and doing near work. This refractive error is corrected by adding a "+" lens to the current refractive correction the person is wearing.

Symptoms of hyperopia &presbyopia : 

Symptoms of hyperopia &presbyopia The earliest symptoms of uncorrected hypermetropia are "eye-strain", "watering", "redness" of the eyes, and often headaches in the later part of the day. Presbyopic persons complain of blurring of text specially after some time. Young children with significant hypermetropia can also develop a convergent squint.

Myopia : 

Myopia What is it? Also called short-sightedness or short-sight, because the person affected is able to perform near work without correction, and has difficulty defining distance objects. Rays reflected off an object in front of the eye focus in front of the retina. A "-" or concave lens is needed for correction of this refractive state.

Why does it occur? : 

Why does it occur? In the great majority of cases the cause of myopia is an increased length of the eyeball. But it may also be due to an increase in the curvature of the cornea or the surfaces of the crystalline lens. Cataract can also produce myopia due to a change in the refractive index of the crystalline lens of the eye. Myopia is of two types. A simple myopia in which there is only a myopic state in the eye, the commonest form of myopia, and no damage to the retina, and pathological myopia in which there is damage to the retina of the eye. Myopia can also be progressive if the negative power continues to increase over a time period. Progressive myopia may require surgical intervention by a retina specialist.

Symptoms: : 

Symptoms: Typically uncorrected myopes do not have "eye-strain", "watering" of the eyes or headaches as often as hypermetropes do. The myopia is usually detected in the young when children playing with each other discover that they can not see distant objects as well as their friends do, or the class-teacher complains that the child makes too many mistakes copying things from the black-board.

Astigmatism: : 

Astigmatism: What is it? Rays of light reflected off objects in front of the eye are focused differently on the retina of the eye, because more than one focal point exists. Astigmatism is due to distortion of the corneal surface in one or multiple planes. A cylindrical lens with either "+" or "-" power is required to correct the refractive error. ?

Why does it occur? : 

Why does it occur? Astigmatism may either be an error of curvature, of centring, or of refractive index. Curvature astigmatism of any degree occurs in the cornea. The commonest error is one wherein the vertical curvature is greater than the horizontal. Injuries to the eyes can also cause astigmatism, so do surgeries to the eyes.

Symptoms: : 

Symptoms: Astigmatic persons often complain of headaches, low vision or reduced vision for distance and near, "watering", "redness", "foreign body sensation" in the eyes as the day progresses. Such persons may also complain of "running together of text" while reading. An astigmatic person can see well neither a distant nor a near object, more so the difficulty is with distant objects. In uncorrected astigmatism with oblique axes there may be a compensatory tilt in the head posture.

What are the way of treating refractive errors? : 

What are the way of treating refractive errors? spectacles{eye glasses} The advantages of using spectacles: Cost effective Freely available even in remote places Can be cleaned easily The disadvantages of using spectacles: Difficult to handle for children and sports persons Misplaced or lost easily Accidental breakage and "scratching" more common

Contact Lenses The Advantages: Better field of vision Overcome peripheral distortions in spectacles specially if the power requirement is high More suitable for sports persons and similar professions The Disadvantages Require more maintenance (or meticulous maintenance) Chances of infection in the eye are more common if cleanliness is inadequate Require better hand-eye co-ordination while wearing

The Surgical Correction of Refractive Errors : 

The Surgical Correction of Refractive Errors The Advantages; 1. In case of high refractive errors, the error may be brought down to a more manageable level so that it can be corrected by other means 2. No need for glasses, contact lenses, no maximum wearing time The Disadvantages; 1. All surgical procedures have a statistical failure rate which may range from improper correction to loss of the eye 2. Costly instrumentation and surgery

Thank you : 

Thank you

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