Ametropia-defective eyesight due to focusing, Physics

Assignment Help:

Defective eyesight due to focusing(refractive)problems- ametropia:


It is often possible to correct ametropia completely with glasses

There are four general types of ametropia:

  • Myopia (near sightedness) ,hyperopia or hypermetropia (far sightedness), astigmatism(asymmetrical focusing) and presbyopia (old sight) fig(2)  .

418_Ametropia-Defective eyesight due to focusing.png

 

 

2004_Ametropia-Defective eyesight due to focusing 2.png

 

  • The myopic individual usually has too long an eyebellor too much curvature of the cornea , distance objects come to focus in front of the retina, and the rays diverge to cause a blurred image at the retina .This condition is easily corrected with negative lens.
  • A hyperopic eye has a near point further away than normal and use some of its accommodation to see distance objects clearly ,the usual cause of  hyperopic is too short eye ball , a positive lens is used to correct this condition fig(3).
  • Inastigmatism ,the curvature of the cornea is uneven .Astigmatism cannot be corrected by a simple positive or negative lens, it is corrected with an  asymmetric lens in which the length is greater in one direction than in the perpendicular direction.

 

875_Ametropia-Defective eyesight due to focusing 3.png


Related Discussions:- Ametropia-defective eyesight due to focusing

Explain shifting pendulums, Explain Shifting pendulums?? Get two soda w...

Explain Shifting pendulums?? Get two soda water bottles that are exactly the similar size. Fill them with water and cork tightly. Place a rod across the back of two chairs. Sus

Dynamics, Action and reaction are always equal and opposite.Then,how does a...

Action and reaction are always equal and opposite.Then,how does a body moves?

Paper capacitors, In this type of capacitors the dielectric consists of one...

In this type of capacitors the dielectric consists of one or more layer of extremely thin craft paper which looks very much like cigarette paper. The metal plates consist of alumin

Projectile motion, in some case we take y=-g but in some case we take y=g.....

in some case we take y=-g but in some case we take y=g... why???

What do you mean by dispersion, What do you mean by dispersion? Describe a ...

What do you mean by dispersion? Describe a physical quantity which depends only on the material of the prism for its dispersion. Get an expression for it.

Bcs throry, bcs theory of superconductivity.

bcs theory of superconductivity.

Define polarization of ideal gas?, Define Polarization of Ideal Gas? Ev...

Define Polarization of Ideal Gas? Evaluate the electric polarization P of an ideal gas consisting of molecules having a constant electric dipole moment P in a homogeneous exter

Throttling process, In thermodynamics, the Joule-Thomson effect describes a...

In thermodynamics, the Joule-Thomson effect describes a process in which a fluid is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the

Flux of electric field strength vector across the circle , Two point charge...

Two point charges q and -q are splitted by distance 2l. Find the flux of electric field strength vector across the circle of radius R placed with its centre coinciding with the cet

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd