optical dispensing. frames materials: –cellulose acetate or zylate is the most commonly used...

OPTICAL DISPENSING

FRAMES

MATERIALS:

– Cellulose acetate or zylate is the most commonly used material for plastic frames.

• Monel is a corrosion resistant alloy, and is the most prevalent material used for metal frames.

PLASTIC MATERIALS

Cellulose acetateCellulose propionateCarbon fiber graphite PolycarbonatePolyamideOptylNylon

Cellulose acetate

Cellulose is mixture of cottonseed fibers, wood flakes, stabilizers and plasticizers.

Zyl is east to adjust and has the unique ability to slightly reduce in size to accommodate a lens that is edged a bit small or to stretch to house a lens that is edged to large.

Cellulose propionate

Cellulose propionate is another plastic material used to produce injection molded frames. Because it is lightweight and very strong it lends itself well to the production of ultra thin and over sized frame styles.

Carbon fiber graphite

CFG is a light weight materials (about one forth the weight of zyl and metal) that consists of a carbon compound and a textiles fiber called ceramic whisker.

Polycarbonate

It is used in the manufacturing of bullet proof glass and crash helmets. In eye care it is used for sports and safety purposes.

Polyamide

Polyamide is a type of nylon that is very strong and light weight in nature. It is easily tinted and is available in a wide range of colors.

Nylon

It is a virtually unbreakable, hypoallergenic frame materials that in today's market, is mostly used for injection molded sun glasses as well as men’s frame styles.

Optyl

It is a plastic frame materials that is hypoallergenic, light weight, and keeps its finish over time. It is a lasting durable material known for returning to its original shape when thoroughly heated.

METAL FRAME MATERIALS

Monel Nickel Nickel –Silver Phosphorous bronze Stainless steel Titanium Aluminum Beryllium Cobalt

Monel &Nickel

Monel is a combination of nickel and copper. It is a strong stable material that also lends itself to making nose pad arms, bridges and end pieces.

Nickel is a strong and generally bends without breaking to making nose pad arms. Patients are sometimes allergic to this products.

Nickel-silver & phosphorous

NS is a strong rigid material that is suitable for hinges, end pieces, bridges and decorative trims. This is brittle material.

Also called phosphor-bronze is an alloy comprised mostly of copper. Adjustments can be a problem because of the “springy” characteristics of the material.

Stainless-steel & Titanium

It is very popular because this material is strong even in thin streamlined applications. This metal is alloy comprised of manganese, nickel, iron and chromium.

Titanium is a naturally occurring element that is highly corrosion-resistant and is incredibly lightweight. If the wearers allergic to other metals and is purchasing a titanium frame to avoid allergic skin reactions.

Aluminum, beryllium & cobalt

Aluminum is very popular . This make it even lighter than titanium, it is rigid material that is difficult to adjust.

Beryllium is used in the production of temples by combining with other metals. It is very expense.

Cobalt offers a highly polished finished and is often used in thin frame designs. It is also expensive.

Types of frame

Full frameCombination frameSemi-rimless Full rimless (or) Drill mountHalf eye

Frames

Frame parts

Frame front

The frame front has either a sculpted bridge or a bridge device that is attached to the frame. The bridge is an important part of the frame because it connects the two eye wires and it supports most of the weight of the spectacles on the patients nose.

Frame part

Bridge type

Plastics:– Saddle, modified saddle, keyhole, adjustable

bridge .

Metal :• Adjustable nose pad, uni – fit bridge,

saddle bridge

Nose pad

Temples

There are five temple design used in frame manufacturing

• Skull temples • Library temples• Convertible temples• Comfort cable temples• Riding bow temples

Temples

Frame selection

The best frame for a patient complements his or her facial structure, requires minimal adjustments, and will securely hold the lenses in place.

Frame styling

The size and the shape of the frame greatly affect the overall cosmetic appearance of the finished prescription lenses. The best way to control the finished look is to first imagine the thickness and curves of the lenses.

Determining facial wrap

There are seven facial shapes:

– Oval– Triangle– Round– Long– Square– Inverted triangle– Diamond

Frame selection

Frame types vs. facial proportions

Oval shape faces - any frame shape Round face - angular frames Square face - round or oval shape Long face - deep vertical frame Triangle } Inverted triangle } oval or rounded

. diamond face } designs.

LENSES

Abbe value

The abbe value (first describe by Ernest k. abbe a German optical physicist) indicates the ability of a lens material to purely refract white light without chromatic aberration.

Abbe value of common lens materials.

MATERIAL

Glass , crown

CR 39

Spectralite

High index 1.56 (resin)



Polycarbonate

High index glass

INDEX

– 59

– 58

– 47

– 39

– 37

– 32

– 31

– 25

Lens types

Lenses are classified as spheres, cylinder and prisms.

Lens material

CR-39GlassTransitionsHigh index lensesPolycarbonate

Lens designs

Single vision lenses Bifocals Trifocals Occupational segments Progressive Corrective curve lenses Aspherics Lenticular bowl Blended myodisc Safety lenses Slab off prism

Bifocals

Single vision lenses

Single vision lenses correct vision for one focal length. (focal length is the distance at which the lens focuses an object that is 1 meter away from the lens). They could be prescribed for distance vision only or for near vision only.

Bifocals

Bifocal lenses correct vision at two distances, usually with a prescription for distance vision at the top of the lens and a segment at the bottom of the lens for close work.

Bifocal segments are available in many designs and sizes. There are round segments called kryptok bifocals as well as flat top.

Round segments are available in 22 – 24mm sizes and flat top bifocals are made in 25,28 or 35 mm sizes.

Trifocals

Trifocal lenses have three viewing distances or segments. A conventional trifocal lens has a distance portion and intermediate segment and a bottom segment to correct vision at 33 cms.

Trifocal lenses can be prescribed to correct vision at varying distance.

Trifocals

Progressive addition lenses (PAL)

PAL consists of distance, intermediate and near zones. They cause less of an image jump than lined segments because the power differences between the zones are achieved thorough slight, gradual changes in power, unlike that of conventionally lined bifocals or trifocal. PAL are sometimes called bifocals but in actuality perform most like trifocals because they offer an intermediate area.

PAL lens

Corrective curve lenses

A lens which could produce the same quality of vision through the periphery as through the optic center of the lens would need have a radius that corresponded with the radius of the moving eyeball.

Corrective curve lens

Aspherics

Aspheric lenses improves the peripheral optics and the cosmetic appearance of the lenses. The curvature of an aspheric design change in the outer portion of the lens. This is especially true with mid-to high-powered lenses.

Aspheric lens

Aphakic lenses

Cataract lenses are aspheric lenses that are available as lenticular design. This means a minus lenticular carrier is used to house the high powered plus prescription. They should be fit as a close to the eye as possible in order to provide a wide field of vision for the patient.

Aphakic lens

Blended myodisc

A myodisc or blended myodisc lens is used for patients who have very high myopia. It is a lenticular lens with a carrier, and produce a clear central area for vision with a significantly thinner lens edge. It is available from -12.0 D

Another lens for high myopes is the biconcave lens. This lens is concave and ground on both the front and back surface, resulting in an overall thinner and lighter weight lens.

Myodisc

Safety lenses

– Special purposes lenses must also have an “S” marked on the lenses to signify that the lenses are for special purpose. An example of special purpose occupational lenses would be those that are needed by welders. Productive lenses for someone in this occupation must have a filter that guards the welder from damaging optical radiations.

Safety lenses

Slab off prism

This is given for anisometropic patients. If one eye having a plus correction and the other eye having a minus correction often needed glasses with a specially ground lens treatment called slab off.

Slab of prism