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¨OPTICS AND PRESCRIPTIONS ¨How Much Refraction Takes Place in the Normal Eye? ¨Normal eye generates approximately 60 diopters. ¨Each of the clear surfaces of the eye contribute at least some refraction. ¨Amount of Refraction Contributed by Each Structure Tears 1-2 diopters Conjunctiva 3-4 diopters Cornea 40 diopters Acqueous humor 4-5 diopters Lens 5-8 diopters Viterous humor 5 diopters ¨Conditions Which Cause Refractive Problems ¨Myopia (nearsightedness) ¨Hyperopia (farsightedness) ¨Astigmatism (everything’s blurry) ¨Can Refractive Errors be Corrected? Yes!!! Through the use of concave and convex lenses. ¨Correction of Refractive Errors ¨The myopic eye has too much refraction (bending power): ¤Ex: Normal = 60 and Myopic = 70 ¨The hyperopic eye has too little refraction: ¤Ex: Normal = 60 and Hyperopic = 50 ¨History of Optical Correction ¨1000 AD – reading stone that was laid on reading material to magnify it. ¨1284 Italy -- Salvino D'Armate invented first pair of wearable glasses. ¨Eyeglasses from around 1400 ¨A reproduction of early wearable eyeglasses. ¨Early Representations in Art ¨The earliest representation of spectacles in artwork came from Tommaso da Modena. ¨Two brothers copying manuscripts – one with glasses, one with a magnifier. ¨ Read More About It Go back to the Notes Index for our web site to go to a full article about the history of optics and prescriptions. ¨Types of Lenses ¨Single vision ¨Bifocal ¨Progressive ¨Reading glasses ¨Types of Lens Material ¨Glass- hardest, most scratch resistant, and heaviest ¨Plastic and Polycarbonate- lighter and thiner than glass but often scratch easily. Lower in cost ¨High index materials- Thinner, lighter. Index refers to a increased ability to refract light ¨Photochromic – these darken as they are exposed to increasing levels of UV rays ¨Right Eye and Left Eye ¨OD = right eye ¨OS = left eye ¨OU = both eyes together ¨The Numbers and What They Mean – minus (-) ¨A minus (-) indicates taking away diopters of refraction. ¨People with a minus correction have myopia (nearsightedness). ¨The higher the number after the minus, the higher the degree of myopia. ¨Plus (+) ¨A plus (+) indicates adding diopters of refraction. ¨People with a plus correction have hyperopia (farsightedness). ¨The higher the number after the plus, the higher the degree of hyperopia. ¨Astigmatic correction (no. X no.) ¨Two numbers separated by an X or the word “Axis” on a prescription indicates that the client has an astigmatism. ¨Remember that an astigmatism is some sort of “wave” in the shape of the cornea. ¨The first number of the two will have a plus or (more typically) a minus in front of it. It represents the amount of refraction needed by the “wave.” ¨The second number represents the direction (from 180 to 360 degrees) that the “wave” takes. ¨Add ¨Add means that a bifocal is needed and states the power that it will be. ¨Typically, these range from +0.75 to +3.00. ¨Prisms ¨If the basic prescription is followed by a small number with a superscript (1^) it indicates prism correction. ¨There may be more than one set of prism numbers for each eye. ¨Somewhat rare, usually expensive, and often require special manufacture ¨Sample prescription ¨Sample prescription ¨Non-standard acuity notations ¨HM = hand motion ¨CF = count fingers at X feet ¨CSM = central steady and maintained ¨CSUM = central steady and unmaintained ¨LP = light perception ¨NLP (sometimes “nil”)= no light perception ¨Unable to test ¨WHEN GLASSES WON’T HELP. . . ¨That is your job ¨Assess ¨Plan and Intervene (and assess again) ¨Modify and adapt ¨Inform ¨Train and Advocate Observe, Listen, and Learn
