OPTICS AND PRESCRIPTIONS How Much Refraction Takes Place

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 Conjunctiva Cornea Acqueous humor Lens Viterous humor 1 -2 diopters 3 -4 diopters 40 diopters 4 -5 diopters 5 -8 diopters 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 • High index materials • Photochromic

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.

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 unmaintained • LP = Light perception • NLP = no light perception And my very favorite • Unable to test

WHEN GLASSES WON’T HELP. . .

That is your job- • That is when you are vital SO WHAT DO YOU DO • You Assess • You Plan – based on the data • You Intervene – implement you plan with all involved • Student • Parents/family • Teachers

And more • You modify and adapt the curriculum to give access • You assess again – How is your intervention going/working- is the student being successful – has you work made a positive impact • You inform • You train the student • To understand their abilites • To advocate for their needs • To raise their expections – challnege them! • You OBSERVE, LISTEN, AND LEARN