REFRACTION ERROR

LEO RINALDI

KEY Introduction of Refraction Media of Refraction Refraction Procces Refraksi Error Miopi Hipermetropi Presbiopi Astigmatism

REFRACTION Light is a form of electromagnetic radiation

composed of particle-like individual packets of energy called photons that travel in wavelike fashion.

The bending of a light ray is known as refraction. Visible light is a small portion of the

electromagnetic spectrum with a wavelength range between 400 and 700 nm.

REFRACTING The eye is an optical instrument. The correct interpretation of visual information

depends on the eye's ability to focus incoming rays of light on the retina.

REFRACTIVE MEDIA

The two structures most important in the eye’s refractive ability are the cornea and the lens.

The cornea and lens refract light rays from distant objects so the image is focused on the retina

PROCESS OF REFRACTION

ACOMODATION

REFRACTION ERROR (AMETROPIA) A mismatch between the axial length of the

eye and the refractive power of the lens and corneaAmetropia axial (common)Ametropia refractive (less frequent)

1. MYOPIA A mismatch between the refractive power

and axial length of the eye so an image converges in front of retina

Myopic persons can see close objects clearly, but not distant objects.

Type: Miopia axial Miopia refractive

WHAT DO THEY SEE?

MYOPIA Degree :

Low myopia (<3.00 D) Medium myopia (3.00 D-6.00 D) High myopia (>6.00 D)

MYOPIA AND ITS CORRECTION

2. HYPEROPIA A mismatch between the refractive power

and axial length of the eye so an image converges behind the retina.

Types:Axial hyperopiaRefractive hyperopia

WHAT DO THEY SEE?

Farsightedness Vision Normal Vision

HYPEROPIA Degree

Low hyperopia consists of an error of +2.00 diopters (D) or less.

Moderate hyperopia includes a range of error from +2.25 to +5.00 D.

High hyperopia consists of an error over +5.00 D.

HYPEROPIA AND ITS CORRECTION

3. PRESBYIOPI Presbyopia inability of the eye to focus

(accommodate) due to hardening of the crystalline lens with age.

When the eye can no longer accommodate at the reading distance, positive spectacle lenses of about 2–3 D are prescribed to correct the difficulty.

PRESBYOPI Once a person has a presbyopia, each eye

remains focused permanently at an almost constant distance which be differentof each person’s eyes.

The eyes can no longer accommodate for both near and far vision.

4. ASTIGMATISM In astigmatism the curvature of the cornea

is uneven, so light rays are unequally refracted. The refractive ability of a person’s cornea remains constant, because the curvature of the cornea never changes.

CLASIFICATTION AND CAUSEAccording to the etiology:External astigmatismInternal astigmatismAccording to the location of the meridian of greater refraction:With-the-rule astigmatism (most common form)Against-the-rule astigmatismOblique astigmatismAccording to the meridian involved:Regular astigmatismIrregular astigmatism

WHAT DO THEY SEE?

Astigmatic errors can be corrected with cylindrical lenses, frequently in combination with spherical lenses. Because the brain is capable of adapting to the visual distortion of an uncorrected astigmatic error, new glasses that do correct the error may cause temporary disorientation, particularly an apparent slanting of images.

OVERVIEW

OVERVIEW

TERIMA KASIH

REFERENCES Sherwood, Lauralee, 2010, Human

Physiology: From Cells to Systems, Seventh Edition, Brooks/Cole, Cengage Learning, Singapore, 197-202

Paul Riordan-Eva and 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