DISKUSI TOPIK 2

8/17/2019 DISKUSI TOPIK 2

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REFRACTION ERROR

LEO RINALDI


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KEY

Introduction of RefractionMedia of RefractionRefraction Procces

Refraksi ErrorMiopiHipermetropiPresbiopi

Astigmatism


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REFRACTION

Sinar/cahaya adalah suatu bentuk radiasielektromagnetik yang terdiri dari paket-paket energimirip partikel yang d inamai foton yang b erjalan dalambentuk gelombang.Berbeloknya berkas sinar dikenal sebagai refraksi(pembiasan). .Cahaya yang tampak is a sevagian kecil of theelectromagnetic spectrum with a wavelengthrange between 400 and 700 nm.


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REFRACTINGThe eye i s a n optical instrument.The correc t interpretation of visual informationdepends on the ey e's a bility to focus i ncoming rays oflight on the ret ina.


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REFRACTIVE MEDIA

The t wo s tructures m ost important in the eye’ srefractive a bility are t he corn ea and the lens.The cor nea and lens r efract light rays f romdistant objects s o t he i mage i s f ocused on thereti na


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PROCESS OF REFRACTION


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HOW IT WORKS...

When we view nearby objects the ciliarymuscles contract reduce t he t ension on thezonular bers of the s uspensory ligament the

lens becomes more rounded and convex thelens sh ortens i ts f ocal length more ref ractionWhen we s ee d istant objects, the c iliary musclesare r elaxed t he lens i s re latively at a littl erefraction focal length is at its g reatest.The p rocess of changing the s hape of the l ensand hence adjusting its f ocal length is ca lled

accommodation .


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REFRACTION ERROR (AMETROPIA)

A mismatch between the axiaand the r efractive p ower of the l ens an d cornea Ametropia axial (common)

Ametropia refractive (


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1. MYOPIA

A mismatch between the refaxial length of the eye so an image convergesin front of reti naMyopic p erson s c an see cl ose o bjects c learly, butnot distant objects.Type:

Miopia axialMiopia refractive


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WHAT DO THEY SEE?


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MYOPIA

Degree :Low myopia (6.00 D)


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2. HYPEROPIA

A mismatch between the refaxial length of the eye so an image convergesbehind the re tina.

Types: Axial hyperopiaRefractive hyperopia


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WHAT DO THEY SEE?

Farsightedness Vision Normal Vision


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HYPEROPIA

DegreeLow hyperopia consists of an error of +2.00 diopters(D) or l ess.Moderate h yperopia includes a range of error from+2.25 to +5.00 D.High hyperopia consists of an error over +5.00 D.


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HYPEROPIA AND ITS CORRECTION


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3. PRESBYIOPI

Presbyopia inability of the eye to focus(accommodate) due t o h ardening of thecryst alline l ens w ith age.When t he eye can no longer accommodate at thereading distance, positive spectacle l enses o fabout 2–3 D a re p rescribed to correc t thedifficulty.


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PRESBYOPI

Once a p erson has a p resbyopia, each eyeremains focused permanently a t an almostconstant distance w hich be d ifferentof eachperson ’s eyes.The eyes can no longer accommodate for bothnear and far vision.


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CORRECTION OF PRESBYOPI

AGE Lensa (D)

40 +1

45 +1,5

50 +2

55 +2,560 +3


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4. ASTIGMATISM

In astigmatism the curvature of the cornea isuneven, so l ight rays a re u nequally refracted. Therefractive a bility of a person ’s c ornea remainsconstant, because t he curvature of the corneanever changes.


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WHAT DO THEY SEE?


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Astigmatic errors cylindrical lenses, frequently in combination withspherical lenses. Because t he b rain is c apable ofadapting to t he v isual distortion of anuncorrected astigmatic er ror, new glasses t hat docorrect the er ror may cau se t emporarydisorientation, particularly a n apparent slantingof images.


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OVERVIEW


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OVERVIEW


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TERIMA KASIH


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REFERENCES

Sherwood, Lauralee, 2010, Human Physiology: From Cells to Systs Seventh Edition,

Brooks/Cole, Cengage Learning, Singapore, 197-202Paul Riordan-Eva a nd John P. Whitcher, 2007,Vaughan & Asbury's General Ophthalmology ,17th Edition, The McGraw-Hill Companies, Ch.20

Myron Yannof & Jay S . Duker, 2008,Opthalmology , Third Edition, El-Sevier, Ch. 21

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DISKUSI TOPIK 2