Myopia Done by: Ang Wee Shuen (01) 3P1

Agenda Introduction Spectacles Our Eye - Cornea Ray diagrams LASIK Facts Bibliography

Introduction What is myopia? Also known as short/nearsightedness Farsightedness is known as hyperopia Common in many countries, affects: 40% in Europe 70-90% in Asian countries such as Singapore Is a visual defect in which distant objects appear blurred Shape of the eye causes the retina to be out of place Images are focused in front or behind retina

Introduction Risk factors Exact cause is unknown Heredity and environment plays a role Parents nearsighted = greater risk Reading in dim light Excessive amounts of close work Symptoms Squinting eyes to see properly Placing a book very close to the face

Introduction From the diagram on the left, the light rays converge in front of the retina. However, light rays converge behind the retina on the diagram on the right. For a person to see distant objects clearly, the images should be focused on the retina, and this can be done by using convex or concave lens so that light rays will converge onto the retina.

Spectacles Spectacles Also known as eyeglasses Many use it to correct eyesight Works by correcting the path of light rays So that light rays will converge onto the retina forming a clear image There are 5 types of lens materials Optical crown glass Plastic Trivex Polycarbonate High-index plastics

Spectacles Most common material for the lenses in spectacles is plastic Refractive index of 1.498 Low cost Easy production Outstanding optical quality

Our Eye – the Cornea Cornea Where light undergoes most of its refraction (the Lens in the eye also refracts light) Refractive index: Approximately 1.34 Distance between cornea and retina: Approx. 2.4 cm

Our Eye Cornea / Lens Retina

Normal Eye (perfect eyesight) Cornea f Retina This diagram shows briefly on how the cornea converges light rays onto the retina (focal point).

Myopia (nearsightedness) Cornea f Retina However, the retina is now behind the focal point. In order to focus the light rays onto the retina, concave/diverging lens are needed to correct the path of the light rays so that it converges onto the retina. Retina For most people suffering from nearsightedness, the shape of their eyeball causes the retina to be behind its actual position. Thus, light rays converge in front of the retina.

Hyperopia (farsightedness) Cornea f The retina is now in front of the focal point. In order to focus the light rays onto the retina, convex/converging lens are needed to correct the path of the light rays so that it converges onto the retina. On the other hand, for most people suffering from farsightedness, the shape of their eyeball causes the retina to be in front of its actual position. Thus, light rays converge behind the retina. Retina

Brief introduction on LASIK What is LASIK? Stands for Laser-Assisted In Situ Keratomileusis Surgery to reshape cornea To produce clearer images by adjusting the focal length of the eye Many prefer LASIK to wearing spectacles/contact lens Spectacles/Contact lens may drop off or get scratched Less troublesome

However, LASIK surgery reshapes the cornea such that the focal point is now at where the retina is. This saves the trouble of having converging lens to correct one’s vision. LASIK (simplified diagram) This diagram shows how a farsighted person is suffering from myopia. Retina f f

LASIK (simplified diagram) Similarly, this diagram shows how a nearsighted person is suffering from myopia. f f Retina

LASIK Short video clip on LASIK procedure and how it corrects your vision http://www.youtube.com/watch?v=a7VRghAtwXU&feature=related

Fun Facts Did you know…? The more education you have, the more myopic you may be The rationale is that more education means you read more, which puts stress on the eye Steve Wozniak had a pair of “Apple Glasses” Co-founder of Apple, Inc. Had a pair of eyeglasses with its lenses made in the shape of the apple logo

Bibliography http://retina.anatomy.upenn.edu/~lance/eye/cornea.html http://www.docshop.com/education/vision/refractive/lasik/surgery/ http://en.wikipedia.org/wiki/Corrective_lens http://en.wikipedia.org/wiki/File:Schematic_diagram_of_the_human_eye_en.svg http://www.articlesbase.com/health-articles/why-myopia-is-such-a-big-problem-519607.html http://www.glenbrook.k12.il.us/GBSSCI/PHYS/class/refrn/u14l6c.html http://ezinearticles.com/?What-Does-Lasik-Stand-For?&id=338544

Bibliography http://www.babble.com/CS/blogs/strollerderby/lasik.jpg http://www.youtube.com/ http://vision.healthcommunities.com/refractiveerrors/myopia.shtml