Basic Optics

1. Lynn Lawrence, CPOT, ABOC Basic Optics

2. Disclaimer • Please prepare for certification testing with materials from the organization in which you want your certification granted i.e.: • AOA • JCAHPO • ABO • NCLE • OT

3. Lacrimal gland Superior punctum Superior canaliculus Lacrimal sac Excretory ducts Inferior punctum Nasal cavity Inferior canaliculus Nasolacrimal duct Adnexa: Lacrimal System

4. Outline • The Visual System • Physiology • Ametropias • Ophthalmic Lenses • Properties of Light • UV, Visible, and Infrared Spectrums • Reflection, Refraction, & Absorption • Aberrations • Lens Designs • Fitting • Basic Optical Formulas

5. Abbreviations - the following is a listing of accepted abbreviations: • O.D. = right eye • O.S. = left eye • O.U. = both eyes • + = convex, plus • - = concave, minus

6. The Visual System Eye Movement or ocular motility The eye is connected to the orbit by several muscles which control movement... Orbit

7. The Visual System There are two main refractive bodies in the human eye... Cornea Crystalline Lens

8. Vitreous Chamber • Functions: • Refraction of light • Internal support • Holds retina in place • Spots in vision may be floaters in the vitreous Post vitreous detachment How many chambers are inside the eye?

9. The Visual System Cornea The cornea is the primary refractive element in the eye... ... with a power of around +42-44 diopters

10. The Visual System Cornea The tear film maintains both the health and optics of the cornea...

11. Tear Film Layers oil aqueous snot Where does a contact lens rest?

12. The Visual System Crystalline Lens The crystalline lens has a power of around +12-18 diopters... ...it is primarily responsible for changing the eye’s focal point…a term referred to as accommodation

13. The Visual System The retina is the “film” or sensory body... Retina

14. The Visual System Retina Light is converted to electrical impulses which are sent through the optic nerve... Fovea ...the “blind spot” is the point at which the optic nerve connects Optic Disc Macula

15. Retina – 10 layers Outside of eye • Pigment epithelium • Rods • Cones • Outer plexiform layer • Horizontal cells • Bipolar cells • Amacrine cells • Inner plexiform layer • Ganglion cells • Nerve fiber layer Vitreous (inside of eye)

16. Anatomy / Physiology of the Eyeball 3 Layers • Fibrous Layer *Cornea *Sclera • Vascular Layer *Choroid *Ciliary body *Iris • Nerve Layer *Retina *Macula *Optic nerve What function does each layer have?

17. Visual Anomalies Ametropias In a “normal” eye, parallel light is brought to a focus on the retina... ...an eye free of refractive error is called “emmetropic”

18. Visual Anomalies Ametropias An eye with excessive focal power for its length focuses light in front of the retina... ...this refractive error is known as “myopia”

19. Visual Anomalies Ametropias An eye with insufficient focal power for its length focuses light in front of the retina... ...this refractive error is known as “hyperopia”

20. Visual Anomalies Ametropias Another refractive error can occur if every axis is not refracted evenly... ...this refractive error is known as “astigmatism”

21. Visual Anomalies Ametropias As the eye ages, the crystalline lens loses flexibility... ...this results in a condition known as “presbyopia”

22. Visual Anomalies Presbyopia The inability to focus on near objects becomes noticeable around age 40 and steadily worsens thereafter...

23. Vision & Ametropias ...this plus lens may stand alone (NVO) or may work with distance correction (ADD) E E Distance Rx ADD

24. Refractive Errors • Myopia • Hyperopia • Astigmatism • Presbyopia • Amblyopia

25. Emmetropia vs. Ametropia • Emmetropia • No refractive error • Rays of light focus on the retina • Ametropia • An optical error • Corrected by glasses, contact lens or refractive surgery

26. Emmetropic Eye Emma is a perfect woman

27. Myopia • Also called “Nearsighted” • Axial myopia • Eye is too long • Rays of light fall in front of retina • Index myopia • Diabetes/cataracts • Corrected by a concave, or minus lens

28. Myopic Eye A lens without power is referred to as ____________?

29. Myopia • A refractive condition where parallel light rays focus in front of the retina when the eye is at rest • Termed nearsightedness • Patient may have 20/20 vision at near, but distance vision will be reduced • Corrected with minus lenses

30. Hyperopia • Also called “Farsighted” • Axial length of the eye is too short • Rays of light fall virtually behind the retina • Affected by accommodation • Corrected by a convex, or plus lens

31. Hyperopic Eye The type of lens that corrects for the farsighted condition is called ______?

32. Hyperopia • A refractive condition where parallel light rays focus behind the retina when the eye is at rest • Termed farsightedness • Patient may have 20/20 vision at distance and near • Corrected with plus lenses

33. Astigmatism • Corneal Astigmatism • 2 different points of focus • Cornea is “football-shaped” • Corrected by cylinder at a specific axis • Lenticular Astigmatism • Crystalline lens • Irregular Astigmatism • Cannot be corrected by a lens • Keratoconus • Corneal trauma

34. Astigmatism A lens that corrects for sphere and cylinder is called _________?

35. Astigmatism

36. Astigmatism • A refractive condition where different meridians of the eye have different powers • Corrected by lenses which incorporate cylinder power • Usually due to different curvatures of the cornea A lens that corrects for cylinder only ____?

37. Presbyopia • Natural aging of the crystalline lens • Affects accommodation • Corrected by additional plus power at near • Bifocal • Trifocal • Progressive • Reading glasses

38. Presbyopia • A condition in which lost elasticity of the lens leads to the inability to accommodate • Age related condition What age does presbyopia normally begin?

39. W h i t e L i g h t Ophthalmic Lenses Properties of Light Refraction - Dispersion All prisms break white light into its component colors... Dispersed Light ...this is called dispersion and results in chromatic aberration

40. Ophthalmic Lenses Properties of Light Refraction - Dispersion Blue waves are more compact than red waves... ...therefore, they are refracted to a greater degree

41. Ophthalmic Lenses Properties of Light Refraction - Dispersion Blue waves are more compact than red waves... ...therefore, they are refracted to a greater degree

42. Ophthalmic Lenses Properties of Light Absorption A dark lens absorbs light...

43. Ophthalmic Lenses Properties of Light • Power Error • Distortion • Marginal Astigmatism • Chromatic Aberration • Unwanted Prism* Aberrations The most common aberrations found in ophthalmic lenses are:

44. Ophthalmic Lenses Properties of Light • Refractive power • Off-axis viewing of objects • lens tilt • peripheral objects • Vertex distance • Lens material Aberrations Aberrations occur due to various factors:

45. Ophthalmic Lenses Properties of Light Aberrations – Power Error Spherical lenses are stronger in the periphery...

46. Ophthalmic Lenses Properties of Light Aberrations – Distortion The result is barrel distortion... This is created by a minus lens… ...the periphery of an object will be minimized to a greater degree than the center

47. Ophthalmic Lenses Properties of Light Aberrations – Distortion Plus lenses create the opposite effect...pincushion effect Aspheric lenses reduce distortion ...the periphery of an object will be magnified to a greater degree than the center

48. Ophthalmic Lenses Properties of Light Aberrations – Distortion Compare a spherical lens to an aspheric lens of equal power... ...notice the central curve & thickness

49. Ophthalmic Lenses Properties of Light Prism Although prism is not technically an aberration, unwanted prism does affect quality of vision... ...the optical center of a lens usually has no prism

50. Ophthalmic Lenses Properties of Light Prism The eye does not always view objects through the optical center... ...what will the eye perceive?