参考说明案例1

1、Optics and refractionDepartment of OphthalmologyContents1、ocular refractive system2、 refraction and modation3、ametropia (refractive errors) OPTICS AND THE EYEOcular Refractive SystemCornea n=1.3771Aqueous Humor n=1.3374Lens n=1.4371Vitreous n=1.3360(n: Index of refraction)(Air n=1, Water n=1.3329)Li

2、ght perceptive systemretinaoptic nerveGeometric OpticsSpeed, Frequency & Wavelength of light Frequency=Speed/WavelengthIndex of Refraction The effect of an optical substance on the speed of light is expressed as its index of refraction, n. Principal plane, Nodal pointPrimary focal point & Secondary

3、focal pointFocal lengthLaws of Refraction & ReflectionIncident, reflected and refracted rays all reside in a plane known as the plane of incidence, which is normal to the interfaceThe angle of incidence equals the angle of reflection but has the opposite signN sin I= n sin IOcular RefractionDefiniti

4、onpower or diopter(D)，the unit for refractive power DD= 1/F (m)Schematic eye and reduced eyeN: nodal point (5.6mm from cornea）E: principal pointF、F： front focal plane back focal planeThree factors of ocular refractionDiopter of the cornea: 43DLength of ocular axis: 24mm Diopter of the lens: 19D moda

5、tionThe eye changes its refractive power to focus on near objects by a process called modation. It is brought about by changes in the shape of the crystalline lensInvolved tissues lens zonules ciliary bodyProcess of the modationInnervational stimulus Ciliary muscle tonus increase Relaxation the zonu

6、les more biconvex state refractive powerAmplitude of modationAmplitude and ageHoffstetter Formula Least amplitude =15-0.25 Age Scope of modationFar point ：the point that is conjugate to the retina when the eye is not modationNear point：the nearest point at which the eye can maintain clear visionNear

7、 Reflex odationConvergence Miosis AmetropiaEmmetropia Parallel rays of light Passing through modated eyeFocus on the retina, the far point is infinityAmetropiaParallel rays of lightPassing through modated eyeCan not focus on the retinaTypes of ametropiaMyopiaHyperopiaAstigmatismMyopiaParallel rays o

8、f lightPassing through modated eyeFocus in front of the retinaClassifications of myopiaAxial myopia the eye is longer than average (For each additional millimeter of axial length, the eye is approximately 3D more myopic.)Refractive myopia (Curvature myopia) the refractive elements are more refractiv

9、e than averageDegrees of myopiaMild myopia: 3DMiddle myopia: 3D6DHigh myopia: 6DSymptoms Reduced the distant visual acuityVisual fatigueExophoria or exotropia Etiology of myopiaGenetic factors greater than environmental factorsComplications of high myopiaDystrophy of vitreous bodyDegeneration of ret

10、inaHigh myopiaMacular hemorrhageRetinal degenerationretinal tearretinal detachment TreatmentCorrections：minus (concave) lenses Objective and Subjective refraction Best visual acuity、lowest diopters HyperopiaParallel rays of lightPassing through modated eyeFocus behind the retinaClassifications of hy

11、peropiaAxial hyperopia: the eye is shorter than averageRefractive hyperopia: the refractive elements are less refractive than averageDegrees of hyperopiaMild hyperopia: 3DMiddle hyperopia: 3D5DHigh hyperopia: 5DSymptomsReduced both distant and near visual acuityVisual fatigueEsophoria or esotropia T

12、reatment Corrected by plus (convex) lenses: best visual acuity, greatest diopters AstigmatismThe curvature of the cornea or lens may vary in different meridians, Parallel rays of light focus with mutiple points or linescorneaNormalAstigmatismTypes of astigmatismRegular as. : there are two principal

13、meridians with constent power and orientation across the pupilIrregular as.: the power or orientation of the principal meridians changes across the pupilSimple myopic as.Complex myopic as.Simple hyperopicComplex hyperopicMixed astigmatismSymptoms of astigmatismBlurred visionVisual fatigueTreatmentRe

14、gular as. Corrected with cylindrical lensesIrregular as. corrected with RGP PresbyopiaDefinition: gradually loss of modation resulting from loss of elasticity of lens that comes with aging to all peopleSymptoms: decrease of near acuity TreatmentCorrected by Plus lenses (for near vision) 40-45 years old+1.0D increase 0.5D for every 5 yearsCorrection of Refractive ErrorsSpectacle lensesContact lensesKeratorefractive surgeryIntraoocular lensesSpectacle lensesTypes: minus lenses, plus lenses, cylindrical lensesMaterial: glass, resinDesign: spherical, non-spherical, bifocals, pr