YEDTEPE NVERSTES GZ HASTANES Refractive Errors Dr Canan

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Refractive Errors Dr. Canan Aslı UTİNE

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Aim Learning the types of refractive errors and mechanisms of occurrence in the optical system of the eye Learning the emetropisation and accommodation mechanisms Objective To be able to completely classify the refractive errors and completely list the mechanism of occurence of each refractive error of the eye To be able to completely list the concept, mechanism of occurrence and aim of emmetropisation process To be able to completely list the elements of near vision reflex triad To be able to completely list the changes in the eye when looking at distance and at near, according to von. Helmholtz theory 10/30/2021 2

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ 10/30/2021 3

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ 10/30/2021 4

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ 10/30/2021 5

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Refractive State of The Eye Corneal power (mean, 43 D) Anterior chamber depth (mean, 3. 4 mm) Crystalline lens power (mean, 21 D) Axial length (mean, 24 mm) 10/30/2021 6

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Distribution of refraction components 10/30/2021 7 Sorsby et al. 1957

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Refractive Error A mismatch between the refractive power and the focusing distance of the eye 10/30/2021 8

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Refractive Error Clinically, it is the variation from perfect coincidence of the principal focus of the eye with the retina Parallel rays of light fail to converge to a sharp focus on the retina Affects all ages, sex, race, ethnic groups and religions but with variable prevalence and distribution 10/30/2021 9

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Refractive status Emmetropia Ametropia Hyperopia Myopia Astigmatizm • • • 10/30/2021 Simple myopic Simple hyperopic Compound myopic Compound hyperopic Mixed 10

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Etiology of Ammetropia Axial ammetropia Curvature ammetropia Index ammetropia 10/30/2021 11

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Accomodation Von Helmholtz theory 10/30/2021 Near objects Far objects 12

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Presbyopia 10/30/2021 13

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ 10/30/2021 14

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Hyperopia The refractive power of the eye is too weak so that light focuses behind the retina Total Manifest Latent 10/30/2021 15

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Myopia The refractive power of the eye is too much so that light focuses in front of the retina Physiologic (Simple) Pathologic (Degenerative) 10/30/2021 16

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Myopia Causes of myopia ? ? Nature vs Nurture 10/30/2021 17

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Myopia Nature Genetic factors Interactive with environment 10/30/2021 18

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Myopia Nurture ? Visual task • Eg. Reading, writing, computer, TV, etc. No definite conclusions yet 10/30/2021 19

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Astigmatism The refractive power is different in different meridians 10/30/2021 20

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Astigmatism 10/30/2021 21

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction By changing the eyeball length By changing the refractive power Changing the power of the existing structure Adding extra refractive medium 10/30/2021 22

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Pin - hole 10/30/2021 23

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction Spectacles Myopia : Concave lenses 10/30/2021 24

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction 10/30/2021 25

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction Spectacles Hyperopia : Convex lenses 10/30/2021 26

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction Contact lenses Commonly used types Hard lens Rigid gas-permeable lens (RGP) Soft lens • Daily wear • Extended wear 10/30/2021 27

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Contact lens - Complications Change ocular surface environment Hypoxia Allergy & Toxic Mechanical trauma Infection 10/30/2021 28

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction Refractive surgery Radial keratotomy Photorefractive keratectomy (PRK) Laser assisted subepithelial keratomileusis (LASEK) Laser in situ keratomileusis (LASIK) 10/30/2021 29

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Radial keratotomy 10/30/2021 30

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ LASIK Refraction +6 D to -8 D Astigmatism <6 D Corneal thickness and biomechanical properties Pupil size 10/30/2021 31

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ LASEK 10/30/2021 32

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Refractive Surgery 10/30/2021 33

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Any question ?