User:Woundspirit

The Human Eye

How does the eye work alike a camera? The way in which the eye works similar to a camera is elucidated herewith by taking into consideration the entire process of eyesight being perceived, from the time light reflection, refraction and emission by varied items located around occurs and would reach surface of the eyes. Pathway of the light ray is tracked further within.

Explanation of vision defects :

Nearsightedness (myopia) People with myopia can see clearly up to a certain distance, beyond which objects begin to appear fuzzy or out of focus. In this case the eye has become elongated, compared to the normal, spherical eye. This causes the focal point of incoming light to not lie on the retina, but in front of it. The more extreme the nearsightedness, the higher the (negative) value and the thicker the optical glasses needed. In order to focus better, the focal point must be shifted towards the retina at the back of the eye. http://lancastria.net/blog/wp-content/uploads/2010/09/myopia_lancastria.jpg

Farsightedness (hyperopia) People with hyperopia can see distant objects clearly, but closer objects appear blurred. In the case of hyperopia the eye is usually too short; light entering the eye does not come to focus until behind the retina. The natural lens can its shape (accommodate) and compensating for the deficient refractive power of the hyperopic eye when looking at distant objects. The solution for wearers of glasses or contact lenses is a convergent lens with a corrective value expressed in "plus" dioptres.

http://www.drugs.com/health-guide/images/205058.jpg

Uneven curvature of the cornea (astigmatism) All objects, both near and far, are seen distorted. The cause is usually the shape of the cornea, which is more like an egg than a sphere. This irregular shape prevents light from focusing properly at one point on the back of the eye. Instead, it disperses on the retina. Uneven curvature of the cornea often occurs together with near- and farsightedness.This deficiency is corrected by restoring the eye's normal curvature and its ability bring images into focus.

http://www.lens-saver.com/wp-content/uploads/2012/01/astigmatism.jpg

 Convex Lens 

Lenses work by refracting light at a glass-air boundary. Although refraction occurs at the boundary, we will treat all lenses as bending the rays at the lens axis. The lens in the eye is a convex or converging lens. This means that the lens makes rays of light come together, or converge. http://www.webanswers.com/post-images/5/5D/F8A3EE3E-B990-4D68-8A52B62B975C2C9A.jpg The rays parallel to the principal axis are converged onto the principal focus. The focal length is the distance between the lens axis and the principal focus (strictly speaking, the focal plane). Thicker lenses bend light more, and are therefore described as more powerful. Powerful lenses have short focal lengths.

With long sight, a (converging lens) is used to make the eye more powerful.

Short sight is corrected by using a concave (diverging lens) to make the parallel rays move apart. The optician will find the far point, which is the furthest distance that the unaided eye can focus a clear image.

Astigmatism Correction Astigmatism, like nearsightedness and farsightedness, usually can be corrected with eyeglasses, contact lenses or refractive surgery.

questions :

1-	people with hyperopia can see distant objects blurred ? ( False - Closer Objects )

2-	there are three types of vision defects ? ( Yes, Nearsightedness - Farsightedness - astigmatism )

3-	Lenses work by refracting light at a glass-air boundary ? ( True )

4-	Short sight is corrected by using a concave (converging lens) ? ( False )

5-	Farsightedness accommodate when looking into distance object ? ( True )

6-	People with astigmatism see all objects, both near and far distorted ? ( True )

7-	which kinds of lenses are needed to correct the astigmatism vision defects ? ( eyeglasses, contact lenses or refractive surgery )

8-	Another name for Nearsightedness is (myopia) ? ( False )

'''Done by :

Ahmed Mohammed Khalifa

ID:ST1031090061

Grade:12.08'''