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 vonHelmholtz theory

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ

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)

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Distribution of refraction components Sorsby et al. 1957

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Refractive Error A mismatch between the refractive power and the focusing distance of the eye

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

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Refractive status Emmetropia Ametropia Hyperopia Myopia Astigmatizm Simple myopic Simple hyperopic Compound myopic Compound hyperopic Mixed

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Etiology of Ammetropia Axial ammetropia Curvature ammetropia Index ammetropia

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Accomodation Von Helmholtz theory Near objectsFar objects

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Presbyopia

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ

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

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)

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Myopia Causes of myopia ?? Nature vs Nurture

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Myopia Nature Genetic factors Interactive with environment

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Myopia Nurture ? Visual task Eg. Reading, writing, computer, TV, etc. No definite conclusions yet

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Astigmatism The refractive power is different in different meridians

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Astigmatism

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

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Pin - hole

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction Myopia : Concave lenses Spectacles

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction Spectacles Hyperopia : Convex lenses

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Correction Contact lenses Commonly used types Hard lens Rigid gas-permeable lens (RGP) Soft lens Daily wear Extended wear

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Contact lens - Complications Change ocular surface environment Hypoxia Allergy & Toxic Mechanical trauma Infection

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

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Radial keratotomy

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

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ LASEK

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Refractive Surgery

YEDİTEPE ÜNİVERSİTESİ GÖZ HASTANESİ Any question ?