Lecture 7-Decision making in optometry

Things to consider when dispensing:

Myopia,hypermyope,astigmat

High or low rx

Presbope

Occupation- how they’re using the glasses

Hobbies

The aesthetics

Considerations in a high prescriptions include?

The thickness and weight of the lens- comfort

Power rings not aesthetically pleasing

Magnification and minification of the eye (Mag on + rx, and min on - rx)

Spherical and transverse aberrations.

Additional measurements needed (back vertex, when rx is more than 5D)

Ways of minimising lens thickness of the lens?

Want a frame with minimum decentration, patients pupil its at box centre of the frame

No more than 3mm decentration per eye

Where is the lens the thickest in a myopic and hypermyopic lens?

Myopic lenses are thickest at edges and hypermetropic lenses are thickest in the middle

Frame shape plays a role into the thickness

Oval shape frames r ideal for hypermetropic lenses.

What is the refractive index?

A ratio of how light travels through air and how it travels through a medium

N=velocity of light in air/velocity of light in material.

How we use refractive index in corresponse to lenses?

High refractive index slows down light more and it refracts more, so lens curvature and thickness can be reduced.

What are the advantages of a high refractive index?

. Thinner lens

.Lighter lens

What are the disadvantages of high refractive

index?

More reflection (anti reflection coating)

More chromatic aberration, the light is split (v value)the lower the v value the worst. 30-60, this causes blur.

What else to consider when looking at lens material?

Impact, chemical and scratch resistant.

Specific. Gravity which is the ratio of density of material and density of water. The heavier the material the heavier the lens.

What are aspheric lenses?

Has a flatter curved edge than typical lens

How to remove power rings?

It’s caused by internal reflection at the lenses edge.

Anti reflective coating and darker frame rims will help.

What about magnification and minifcation?

Myopic lenses make the world look smaller to patient and makes their eyes look smaller to the world

Hypermetropic lenses cause magnification of world and their eyes

Lenses like aspherics can reduce this look,but its largely unavoidable.

Lenses to correct presbyopia

Single vision lenses for different distances , bi focals (d segments)

What are the three types of bifocals?

D seg bifocals, E seg bifocals and R-seg bifocals

What are the 4 coatings?

Anti reflective

Hard coating

Tints - make sure you ask of ocupation

Blue light filter

What are the three frame types?

Full rim

Rimless

Supra

What are the advantages of having a plastic frame?

More likely to be hypoallergenic than metal (no allergies)

Resistant to permanent deformation when dropped impacted or dented

Easy to mould and shape into interesting forms during manufacture

What are some disadvantages of plastic frames?

Tend to have fixed bridge rather than pads-need to select correct bridge style and side length for patient

May be more breakable than metal

Require more frame than metal tend to be heavier.

What is cellulose acetate frames?

A type of plastic frames Which are relatively easy to manufacture

What are the pros of cellulose acetate frames?

Inexpensive

Have reinforced edges

Can be laminated or dyed

Only Need a moderate temperature to adjust

What are the cons of cellulose acetate frames?

Can discolour with age and react with skin to form white deposits

What is optyl?

A different type of plastic which frames are made of It is light and tends to cause any allergies known as memory plastic.

What is SPX?

ANOTHER type of plastic frame, which requires high temperatures to mold and sides are reinforced. Are robust and lightweight, are also flexible

Facts about nickel silver metal frames:

Inexpensive frame,

colour is either electroplated or lacquered, however skin reacts to the nickel, the green transfers onto skin.

Main advantage is that it is cheap and easily adjusted

What are nickel titanium glasses?

Memory metal, returns to its original shape when heated =, much lighter than nickel silver.

What are pure titanium frames?

Very light, upto 50% lighter the nickel titanium glasses, are corrosion resistant but hard to repair and very expensive