Ophthalmic lenses Flashcards
What is a semi - finished lens?
Have the base curve (F1) completed but will require the power curves (F2) to be cut into the rear of the blank.
Surface blanks.
Thicker and normally packaged in boxes.
What is a finished lens?
Have both the front (F1) and the back (F2) surfaces complete.
Thinner and packaged in envelopes.
What are some main lens characteristics?
Style
Design
Material
What are other characteristics that are not considered main characteristics of lenses?
Coatings
Treatments
Tints
What are some physical characteristics of lenses?
Size Thickness Front and back curves Powers Add
What are some determining factors for a semi- finished lens package?
Design Style Material Coating Thickness Size Base curve Add
Using the packaged image, determine the following for a semi- finished lens:
Design Style Material Coating Thickness Size Base curve Add
Design: BF Style:D-35 (FT-35) Material: unknown Coating: none Thickness: unknown Size: 70mm Base curve: +8.25D (True Curve: 8.38D or Sag of 5.15 rad) Add: +1.75D
What are some determining factors for a finished lens package?
Style Design Material Coatings Size CT Power
Using the packaged image, determine the following for a finished lens:
Style Design Material Coating Size Power
Style: SV Design: SV Aspheric Material: 1.60 Hi Index Coating: SRC (SuperShield) Size: 75mm Power: +1.50 Sphere
What are the 6 categories of lens materials?
Glass Cr-39 Polycarbonate Trivex Mid-Index Hi-Index
What are the characteristics of lens materials?
Shatter resistance Scratch resistance Optical clarity Weight Thickness Tint ability
What are the characteristics of glass?
Shatter resistance: most fragile
Scratch resistance: more resistance than plastic
Optical clarity: ABBE value of 59, superior clarity
Weight: heavy, almost twice of plastics
Thickness: thicker than most
Tint ability: cannot absorb tint, must be colored during original manufacturing of glass mixture
What are the characteristics of CR-39?
Shatter resistance: most shatter resistance
Scratch resistance: most resistant
Optical clarity: other than Crown glass, is highest ABBE value of all.
Weight: heavier finished lens
Thickness: most results are thicker than other plastics because lower index of refraction.
Tint ability: great to tint , easy to remove tint.
What are the characteristics of polycarbonate?
Shatter resistance: most popular for safety and sports eyewear.
Scratch resistance: very soft and must have SCR applied after surfacing.
Optical clarity: good, but has one of the lowest ABBE value
Weight: very lightweight
Thickness: can produce one the thinnest finished lens including a CR down to 1.0mm
Tint ability: will not tint, will need a tintable SRC applied to lens rear to hold tint.
What are characteristics of Trivex?
Shatter resistance: may be equal to poly
Scratch resistance: soft and needs SRC
Optical clarity: very good, has lower aberrations than higher index materials.
Weight: lowest of all
Thickness: similar to mid-index. Thinner than CR-39, thicker than a hi-index lens.
Tint ability: tints well at very low temp. Must have SRC afterwards.
