¨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
Conjunctiva3-4 diopters
Cornea40 diopters
Acqueous humor4-5 diopters
Lens5-8 diopters
Viterous humor5 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