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REFRACTIVE ERROR.pptx
This document discusses various topics related to optics and refraction, including: 1. The basic optics of refraction and lens properties, identifying different types of lenses, and the requirements for emmetropia. 2. The various types of refractive errors including myopia, hyperopia, astigmatism, and presbyopia as well as their clinical findings and methods of correction. 3. Accommodation reflex and how it allows the eye to focus at different distances, as well as the causes of its loss with age which leads to presbyopia.
REFRACTIVE ERROR.pptx
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- 2. INTENDED LEARNING OUTCOMES(ILOS) 01 DISCUSS IN BRIFE THE BASIC OPTICS OF REFRACTION & LENS PROPERTIES. 02 HOW TO IDENTIFY LENSES. 03 DISCRIBE THE EMMATROPIA AND ITS REQUIRMENTS.
- 3. INTENDED LEARNING OUTCOMES(ILOS) 04 DISTINGUISH THE VARIOUS TYPE OF REFRACTIVE ERROR & ITS CORRECTION. 05 LIST THE CLINICAL FINDINGS OF MYOPIC FUNDUS 06 EXPLAIN ACCOMODATION REFLEX.
- 4. What happen whenlight strike on surface ? Reflection Refraction
- 5. Refraction Refraction of lightis a phenomenon of change in the path of light when it passes from one medium to another due to change in velocity.
- 6. Refraction θ1 θ2 𝑺𝐢𝐧 𝜽𝟏 =𝒏 𝒙 𝑺𝐢𝐧 𝜽𝟐 𝒏 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕 𝒏 = 𝑽𝟏 𝑽𝟐
- 7. Refractive index Air 1.00 Water1.33 Cornea 1.37 Crystalline lens 1.39 – 1.40 Window glass 1.50 Diamond 2.50
- 8. LENS A lens isa transparent optical device, which has at least one curved surface. The lenses are made of either glass or plastic. LENS SPHERICAL CYLINDRICAL SPHEROCYLINDER convex concave convex concave Compound spherocylindrical Mixed spherocylindrical
- 9. The spherical lenseshave a single power in all meridians and bring the parallel rays to a pinpoint focus that may be real or virtual Unlike cylindrical lens has power only in one axis, which is at right angles to the long axis and forms a line of parallel rays, parallel to the axis of the cylindrical lens LENS
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- 15. So Diopteric power= What is Diopter ? A unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length in meters. F ∞ 10 cm (f) in meter 1 0.1 1 = 10 D
- 16. Cylindrical lenses area cut from a cylinder. The outer surface of the cylinder gives the lens plus power, while the inner surface gives minus power. CYLINDRICAL LENS The cylindrical lens has an axis and a meridian. The axis of the lens is the axis of original cylinder and the meridian is at right angles to the axis. The cylindrical lens has no power along the axis. The power is in the meridian.
- 17. CYLINDRICAL LENS Concave cylinder Convexcylinder Cylinder
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- 20. How to IdentifyLenses? lenses can be identified by : Their physical properties . Lensometer
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- 25. 6M EMMATROPIA Parallel rays oflight are brought to pinpoint focus on the retina, when accommodation at rest
- 26. Normal axial length EMMATROPIAREQUIRMENTS Normal refractive power Of cornea Normal refractive power Of lens 23.5 -24.00 mm 42 Diopter 18+- Diopter Total Power of the eye 60D
- 27. AMMATROPIA are a groupof refractive disorders of the eye where the parallel rays are not brought to pinpoint focus on the retina when accommodation is at rest. Etiology Abnormal axial length of the eyeball. Change in curvature of the ocular media. Alteration in refractive index of ocular media: • Lens:(e.g. Cataract ) – Absent. (e.g. Aphakia) • Cornea: Increased.
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- 29. Myopia is thaterror of refraction where parallel rays are brought to focus in front of the retina when accommodation is at rest . Myopia
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- 31. MYOPIA (Near sightedness) Axialmyopia Most common type
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- 33. MYOPIA (Near sightedness) Refractivemyopia Increase refractive power of cornea or lens Less common
- 34. Myopic fundus (Pathologicalmyopia) • Progressive retinal pigment epithelial (RPE) thinning A tessellated appearance ( Tigroid fundus ) . • Peri-papillary atrophy. • Oval appearance of optic disc, The tilted appearance myopic crescent ( temporal crescent) • Lacquer cracks • Fuchs spots (also referred to as Forster-Fuchs spots) • Staphyloma development,
- 35. Myopic fundus (Pathologicalmyopia) Normal fundus x
- 36. Myopic fundus (Pathologicalmyopia)
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- 42. MYOPIA (Near sightedness) Concaveor diverging lenses Minus lenses
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- 45. Hypermetropia is thatametropia where parallel rays are brought to focus behind the photosensitive layer of the retina Accommodation can partially or completely eliminate hypermetropia . Hypermetropia
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- 47. Hypermetropia (Far sightedness) Axialhypermetropia
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- 49. Hypermetropia (Far sightedness) Refractivehypermetropia Decrease refractive power of cornea or lens
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- 51. Hypermetropia (Far sightedness) Convexor converging lenses Plus lens
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- 54. Astigmatism is thaterror of refraction where all parallel rays are not brought to focus at a point may be in front or behind the photosensitive layer of the retina Astigmatism above 2D cylinder is considered to be high astigmatism, Astigmatism has strong hereditary tendency. Astigmatism
- 55. Astigmatism Image focused inretina as line instead of point Corneal or lenticular Most commonly corneal in origin .
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- 58. How to correctastigmatism ? +1.75 DC
- 59. How to correctastigmatism ? +1.75 DC
- 60. How to correctastigmatism ? +1.75 DC
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- 64. Presbyopia 25 cm Normally imagefocused on retina by action of accommodation reflex Normally accommodation reflex preserved until age 45 years
- 65. Accommodation reflex Contraction inciliary muscle Relaxation in zonules Increase in A/P Diameter of lens Increase in lens power
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- 69. Causes of Accommodationreflex loss By age >> 45 years . When crystalline lens removed ( Cataract surgery ) Occur early in hypermetropia and late in myopia
- 70. How to correctpresbyopia By PLUS Lenses ( convex ) .
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- 72. Anisometropia is thebinocular state where refractive power of the two eyes is not equal. Difference > 2.5D Antimetropia is a term that denotes refraction in two eyes of different types, i.e. one is myopic and the other is hypermetropic. To have a binocular single vision, both eyes should have isokonic images. Anisometropia
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- 74. Anisometropia Significant anisometropia andaphakia best corrected with : CL To avoid aniseikonia And to preserve BSV CL = Contact lense ---- BSV = Binocular single vision ---- Aniseikonia = Different in retinal image size
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- 80. Refractive error symptoms VisualSYMPTOMS Non visual Decrease Distant vision Decrease both Decrease Near vision ASTHENOPIA SQUINT BLEPHARITIS RECURRENT STYE
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